WEBVTT 00:01.600 --> 00:03.000 RONALD SMITH: We're finishing up a section 00:03.000 --> 00:10.870 on storms here, and we've talked about convective 00:10.867 --> 00:16.867 storms. That is, air mass thunderstorms, severe 00:16.867 --> 00:17.697 thunderstorms-- 00:17.700 --> 00:20.370 oh, by the way, I've been calling these things severe 00:20.367 --> 00:23.267 thunderstorms. When you're reading the book, notice they 00:23.267 --> 00:27.827 have subdivided that category into three or four smaller 00:27.833 --> 00:29.033 categories. 00:29.033 --> 00:31.673 You've got your squall lines and your mesoscale convective 00:31.667 --> 00:32.467 systems, and so on. 00:32.467 --> 00:35.097 So just remember, again, they're going into this in 00:35.100 --> 00:38.330 somewhat more detail than I did in class. 00:38.333 --> 00:41.233 And then the third category we had was hurricanes. 00:41.233 --> 00:44.973 And we finished that up last time. 00:44.967 --> 00:48.527 But if there are any questions on these convective storms, 00:48.533 --> 00:54.633 this would be a time to bring other points out. 00:54.633 --> 00:56.633 Any questions about hurricanes that you've thought about 00:56.633 --> 00:57.903 since last time? 01:00.867 --> 01:01.427 No? 01:01.433 --> 01:02.703 OK. 01:04.467 --> 01:06.897 Well then, the last category that we'll be 01:06.900 --> 01:08.670 doing is quite different. 01:08.667 --> 01:11.397 It's the mid-latitude frontal cyclone. 01:11.400 --> 01:15.200 And as I mentioned in the beginning of the section, this 01:15.200 --> 01:17.770 gets its energy source from a different place. 01:17.767 --> 01:20.767 All the convective storms get their energy from the release 01:20.767 --> 01:23.027 of latent heat as water vapor condenses to 01:23.033 --> 01:24.603 form liquid or ice. 01:24.600 --> 01:25.930 But not these. 01:25.933 --> 01:29.173 These come from horizontal temperature gradients. 01:29.167 --> 01:33.967 The point is that, if you've got cold air next to warm air, 01:33.967 --> 01:35.627 there is potential energy there. 01:35.633 --> 01:39.333 Because the warm air wants to rise, and the cold air wants 01:39.333 --> 01:43.033 to sink and spread underneath the warm air. 01:43.033 --> 01:47.233 So if I were to release-- 01:47.233 --> 01:49.903 if I had a wall, for example, separating the warm air and 01:49.900 --> 01:53.400 the cold air, and I suddenly remove that wall, things would 01:53.400 --> 01:55.430 start to change. 01:55.433 --> 01:56.633 The warm air would rise up. 01:56.633 --> 01:58.733 The cold air would slump and slide under. 01:58.733 --> 02:03.303 So there is energy available when you've got these lateral 02:03.300 --> 02:04.270 temperature gradients. 02:04.267 --> 02:08.997 And that is the source of energy for frontal cyclones. 02:09.000 --> 02:13.130 So this name is a long one, but mid-latitude tells us 02:13.133 --> 02:15.373 where these things form. 02:15.367 --> 02:17.727 Frontal-- a front is a boundary between 02:17.733 --> 02:20.073 cold and warm air. 02:20.067 --> 02:22.227 And, of course, this is a little bit redundant, because 02:22.233 --> 02:25.933 mid-latitudes is the region where you get the strongest 02:25.933 --> 02:28.833 contrast between cold air to the north and 02:28.833 --> 02:30.003 warm air to the south. 02:30.000 --> 02:32.500 So there's a little bit of redundancy here. 02:32.500 --> 02:34.200 But then it's a cyclone. 02:34.200 --> 02:38.070 It ends up being a counterclockwise circulation 02:38.067 --> 02:41.727 in the northern hemisphere, just like a hurricane. 02:41.733 --> 02:44.133 But the dynamics and the details are really quite 02:44.133 --> 02:47.803 different, even though they end up with a circulation 02:47.800 --> 02:52.630 around a low pressure center, just like a hurricane. 02:52.633 --> 02:54.973 They grow from a disturbance along the polar front. 02:54.967 --> 02:58.897 The polar front is this boundary that goes around the 02:58.900 --> 03:02.000 earth in mid-latitudes, separating cold from warm air. 03:02.000 --> 03:04.730 And when a little kink develops in that boundary, as 03:04.733 --> 03:07.533 I'll show you, it then grows and 03:07.533 --> 03:10.373 develops a frontal cyclone. 03:10.367 --> 03:15.267 Because they occur in the belt of westerlies, as they evolve 03:15.267 --> 03:18.467 and grow they move from west to east-- 03:18.467 --> 03:22.727 not always directly from west to east, maybe at some angle. 03:22.733 --> 03:25.633 But generally they move from west to east. I've never-- 03:25.633 --> 03:28.833 I don't think I've ever seen a frontal cyclone that went 03:28.833 --> 03:31.673 backwards, that moved towards the west as it developed. 03:31.667 --> 03:35.867 They all move east in some way. 03:35.867 --> 03:38.367 And eventually-- so these storms do have a life cycle. 03:38.367 --> 03:40.697 They don't last forever. 03:40.700 --> 03:43.070 They start from a little kink in the polar front. 03:43.067 --> 03:44.167 They grow. 03:44.167 --> 03:48.767 And as I will show, once the warm air has all been lifted 03:48.767 --> 03:52.527 upwards, then the energy source is gone, and these 03:52.533 --> 03:54.533 storms will begin to die. 03:54.533 --> 03:56.503 So they do have a natural life cycle. 03:56.500 --> 03:58.500 Typically, they last-- 03:58.500 --> 04:02.900 I don't know-- five to seven days as they move across the 04:02.900 --> 04:06.500 landscape from west to east. 04:06.500 --> 04:11.800 So here's a simple picture of one. 04:11.800 --> 04:16.670 It's got the classic features of the low pressure center, 04:16.667 --> 04:19.527 the cold front, and the warm front. 04:19.533 --> 04:22.973 And also scattered around the diagram are some of the 04:22.967 --> 04:25.697 indications of some of the types of local 04:25.700 --> 04:28.470 weather that you get. 04:28.467 --> 04:30.727 So I'll come back to define these fronts in just a minute, 04:30.733 --> 04:35.033 but first of all you've got some rain showers along the 04:35.033 --> 04:36.273 cold front. 04:38.133 --> 04:40.573 In this case you've got some freezing rain up here. 04:40.567 --> 04:41.867 Remember what causes that. 04:41.867 --> 04:47.127 That's that cold aloft warm and then cold near the surface 04:47.133 --> 04:50.203 that can supercool those raindrops before 04:50.200 --> 04:51.800 they hit the surface. 04:51.800 --> 04:55.730 And you've got the light snow here, heavy snow 04:55.733 --> 04:57.673 back in the cold air. 04:57.667 --> 05:02.167 So a lot of local types of weather are going along with 05:02.167 --> 05:03.697 this large scale storm. 05:03.700 --> 05:07.630 Now in order to make any sense of frontal cyclones, you have 05:07.633 --> 05:11.303 to know the different definitions of the fronts. 05:11.300 --> 05:14.530 The word front by itself simply means a boundary 05:14.533 --> 05:17.533 between warm and cold air. 05:17.533 --> 05:24.703 A cold front, indicated by the filled triangles, is when the 05:24.700 --> 05:26.000 cold air is advancing. 05:29.433 --> 05:33.403 A warm front, indicated by the filled half-circles, is when 05:33.400 --> 05:36.700 the warm air is advancing. 05:36.700 --> 05:40.100 So those little symbols are telling you how these fronts 05:40.100 --> 05:40.900 are moving. 05:40.900 --> 05:42.070 The cold air is back here. 05:42.067 --> 05:42.797 The warm air is there. 05:42.800 --> 05:45.530 So we know, because that's defined as a cold front, we 05:45.533 --> 05:47.473 know that it's moving in this direction. 05:47.467 --> 05:50.167 This one, the warm air is here, the cold air there. 05:50.167 --> 05:52.397 It's a warm front, so that means 05:52.400 --> 05:53.530 the warm air is advancing. 05:53.533 --> 05:54.873 It must be moving in that direction. 05:54.867 --> 05:57.927 So in a way, those are telling you a little bit about motion, 05:57.933 --> 06:00.973 how that front is moving with time. 06:04.800 --> 06:06.330 So thats a-- a few other definitions-- 06:06.333 --> 06:10.003 this little sector back here is called the warm sector. 06:10.000 --> 06:13.430 And of course it has warm air moving up, very 06:13.433 --> 06:14.703 often in New Haven. 06:14.700 --> 06:17.670 Very often that air is coming from the Caribbean. 06:17.667 --> 06:20.297 And behind it you've got cold air. 06:20.300 --> 06:22.770 And usually that's coming down from Canada. 06:22.767 --> 06:26.927 So you end up with a contrast here, across the cold front 06:26.933 --> 06:30.273 between air masses of different sources-- 06:30.267 --> 06:33.897 Caribbean area here, Canadian air here. 06:33.900 --> 06:39.100 Notice also, this meets the criteria that I laid out a day 06:39.100 --> 06:44.500 or two ago about needing to transport heat northwards. 06:44.500 --> 06:48.800 So here's northward-moving warm air, 06:48.800 --> 06:51.130 southward-moving cold air. 06:51.133 --> 06:55.533 Probably the same amount of air altogether is moving, but 06:55.533 --> 06:59.103 there's a net transport of heat. 06:59.100 --> 07:01.400 Because you're pushing warm air northward and cold air 07:01.400 --> 07:03.870 southward, there's a net amount of heat 07:03.867 --> 07:05.697 being carried northward. 07:05.700 --> 07:10.670 And that helps to balance the excess solar radiation near 07:10.667 --> 07:16.397 the equator, and the deficit of solar radiation and emitted 07:16.400 --> 07:18.530 radiation near the pole. 07:18.533 --> 07:21.673 So this plays a big role in the general 07:21.667 --> 07:23.727 circulation as well. 07:23.733 --> 07:28.533 Questions so far on frontal cyclone? 07:28.533 --> 07:32.403 So here, now, is the history of one. 07:32.400 --> 07:37.230 It starts as a little dimple in the polar front. 07:40.267 --> 07:44.197 And already you can see the characteristics. 07:44.200 --> 07:46.830 The cold air begins to advance, so we can label that 07:46.833 --> 07:48.503 as a cold front. 07:48.500 --> 07:51.600 The warm air begins to push northward, so it can be 07:51.600 --> 07:54.030 labeled as a warm front. 07:54.033 --> 07:56.073 But it's very weak. 07:56.067 --> 08:00.067 A day or two later it'll look more like this. 08:00.067 --> 08:08.967 This is a fully developed, mature cyclone-- 08:08.967 --> 08:13.327 low pressure center, cold front, warm front, warm 08:13.333 --> 08:17.173 sector, cold air from behind. 08:17.167 --> 08:19.967 Then it goes to this stage. 08:19.967 --> 08:24.167 This is called the early occlusion. 08:24.167 --> 08:29.897 And the word occlusion refers to the fact that now the cold 08:29.900 --> 08:32.500 fronts and the warm fronts, at least in the northern part-- 08:32.500 --> 08:34.100 not here but up here-- 08:34.100 --> 08:37.130 they're beginning to come together. 08:37.133 --> 08:41.173 I want to try to describe that to you. 08:41.167 --> 08:43.627 And the main thing you have to recognize-- 08:43.633 --> 08:46.473 I'll try to do it here on the table and hope you can see me. 08:46.467 --> 08:49.867 These fronts are drawn where they intersect the 08:49.867 --> 08:51.097 surface of the Earth. 08:51.100 --> 08:53.730 But they're not vertical boundaries in the atmosphere. 08:53.733 --> 08:58.333 They are tilted boundaries between cold and warm air. 08:58.333 --> 09:02.703 So for example, here's the cold front with cold air 09:02.700 --> 09:04.530 underneath the wedge. 09:04.533 --> 09:08.633 Here's the warm front with cold air underneath the wedge. 09:08.633 --> 09:12.533 And when they come together like this, now they're 09:12.533 --> 09:14.533 occluding, because they have touched at the 09:14.533 --> 09:15.733 surface of the Earth. 09:15.733 --> 09:17.773 I'll lift it up and pretend the surface of 09:17.767 --> 09:18.927 the Earth is here. 09:18.933 --> 09:22.003 When they come together like this, now they are occluding. 09:22.000 --> 09:24.730 And notice that the warm air, which was in the middle, has 09:24.733 --> 09:27.203 been pinched off the ground. 09:27.200 --> 09:30.500 Now the warm air is up, and you've got cold air and cold 09:30.500 --> 09:33.700 air that have touched each other at the 09:33.700 --> 09:34.430 surface of the Earth. 09:34.433 --> 09:38.573 So that's the meaning of the word occlusion. 09:38.567 --> 09:41.867 It's where the cold front and the warm front have come 09:41.867 --> 09:45.997 together, pinching the warm air upwards. 09:46.000 --> 09:47.770 And that is where it wants to be, right? 09:47.767 --> 09:48.727 Warm air is buoyant. 09:48.733 --> 09:49.473 It wants to be up. 09:49.467 --> 09:54.797 So as soon as the occlusion begins, then the energy source 09:54.800 --> 09:59.370 to keep this storm going begins to weaken. 09:59.367 --> 10:01.527 This is the early occlusion. 10:01.533 --> 10:04.173 And now we can say, cold front, warm front, and 10:04.167 --> 10:05.197 occluded front. 10:05.200 --> 10:07.030 Notice the symbols they're using. 10:07.033 --> 10:11.373 They put the warm front and the cold front together on the 10:11.367 --> 10:14.067 same side of the line, indicating that's now an 10:14.067 --> 10:15.427 occluded front. 10:15.433 --> 10:18.503 And here, it's occluded all the way down to there. 10:18.500 --> 10:21.800 And you've only got a little bit of the original cold and 10:21.800 --> 10:22.500 warm front. 10:22.500 --> 10:24.670 This one, they've labeled it late occlusion. 10:24.667 --> 10:27.227 This storm is dying at this point, it's weakening. 10:27.233 --> 10:30.003 Due to friction and so on, the energy source is gone. 10:30.000 --> 10:32.400 Friction is acting to decay it. 10:32.400 --> 10:36.370 Typically, it'll take five to seven days to go from this 10:36.367 --> 10:38.127 stage to that stage. 10:38.133 --> 10:40.933 And by that time, it's probably traveled 5,000 or 10:40.933 --> 10:45.003 10,000 kilometers from west to east. This storm may have 10:45.000 --> 10:47.730 begun to form east of the Rocky Mountains, and it may 10:47.733 --> 10:49.903 finally occlude as it's approaching 10:49.900 --> 10:51.930 Greenland, or even England. 10:51.933 --> 10:55.733 So these things travel a long distance while they are going 10:55.733 --> 11:00.533 through this kind of a life cycle. 11:00.533 --> 11:01.803 Questions on that? 11:05.400 --> 11:11.030 So this is another cartoon. 11:11.033 --> 11:13.703 But this one shows a little bit of that tilted structure. 11:13.700 --> 11:15.870 So here's the map view-- 11:15.867 --> 11:19.327 north, south, east, west. There's the cold front, the 11:19.333 --> 11:21.703 warm front, the warm sector. 11:21.700 --> 11:26.930 Now if I do a vertical slice of the atmosphere here, it's 11:26.933 --> 11:28.133 drawn at the bottom. 11:30.533 --> 11:32.303 There's the sloping cold front. 11:32.300 --> 11:33.870 And where it hits the ground is where it's 11:33.867 --> 11:35.867 marked on this map. 11:35.867 --> 11:38.367 There's the sloping warm front. 11:38.367 --> 11:41.397 And where it hits the ground is marked on the map there. 11:41.400 --> 11:44.530 And there are some characteristic cloud patterns 11:44.533 --> 11:45.933 that are connected with these fronts. 11:45.933 --> 11:46.803 Here-- 11:46.800 --> 11:51.570 cirrus, cirrostratus, altostratus, nimbostratus. 11:54.833 --> 11:58.573 Nimbo means rain, and you see it's raining there. 11:58.567 --> 12:01.967 And these are generally stratus clouds out ahead of 12:01.967 --> 12:03.297 the warm front. 12:03.300 --> 12:06.170 The cold front-- because you're lifting warmer air with 12:06.167 --> 12:09.267 more moisture in it, air that's in the warm sector, 12:09.267 --> 12:11.697 possibly air that's come up from the Caribbean-- 12:11.700 --> 12:15.000 you tend to get more instability. 12:15.000 --> 12:18.230 That's a little cumulonimbus cloud there. 12:18.233 --> 12:20.773 Or maybe in some cases it's stratus-- 12:20.767 --> 12:22.867 nimbostratus and altocumulus. 12:22.867 --> 12:26.727 But these tend to be more unstable near the position of 12:26.733 --> 12:29.503 the cold front. 12:29.500 --> 12:34.600 And then cold air back here, warm and cold again here. 12:34.600 --> 12:36.900 But remember, because this is a cold front-- not labeled 12:36.900 --> 12:38.330 here-- but this is a cold front, it's 12:38.333 --> 12:39.633 moving in that direction. 12:39.633 --> 12:41.903 This is a warm front, which means it's moving in that 12:41.900 --> 12:46.700 direction also, towards the right in that diagram. 12:46.700 --> 12:50.000 So if we back out now and look at a larger piece of the 12:50.000 --> 12:55.100 Northern Hemisphere on a typical day, anytime between 12:55.100 --> 13:00.600 now and next April, when you're getting strong 13:00.600 --> 13:03.630 temperature gradients north to south, this is typically what 13:03.633 --> 13:04.203 it looks like. 13:04.200 --> 13:07.800 So, generally, you've got the polar front wrapping all the 13:07.800 --> 13:12.030 way around the globe in mid-latitudes, with a fairly 13:12.033 --> 13:14.233 strong temperature gradient across it. 13:14.233 --> 13:16.503 And then, at different places it'll be 13:16.500 --> 13:17.300 doing different things. 13:17.300 --> 13:20.900 So on this little diagram you've got an occluded frontal 13:20.900 --> 13:22.670 cyclone here. 13:22.667 --> 13:26.367 You've got a mature one here and one that's just starting 13:26.367 --> 13:29.327 out here, for example. 13:29.333 --> 13:33.073 And the fronts are labeled accordingly, cold front, warm 13:33.067 --> 13:38.127 front, stationary front, warm front, cold front-- 13:40.933 --> 13:43.473 cold front, warm front, cold front, warm 13:43.467 --> 13:45.167 front, occluded front. 13:45.167 --> 13:50.527 So all the types of fronts are shown in this little cartoon. 13:50.533 --> 13:50.933 Question? 13:50.933 --> 13:52.603 STUDENT: Is there a difference between an occluded and a 13:52.600 --> 13:52.700 stationary front? 13:52.700 --> 13:55.570 PROFESSOR: Yeah, a stationary front is a 13:55.567 --> 14:01.597 definite cold-warm contrast, but it's not moving. 14:01.600 --> 14:04.700 Whereas an occluded front is a cold front and a warm front 14:04.700 --> 14:06.200 that have come together. 14:06.200 --> 14:09.900 Therefore, you've got cold air on both sides. 14:09.900 --> 14:12.200 And the warm air has been lifted aloft. 14:12.200 --> 14:13.700 So there is a big difference. 14:13.700 --> 14:15.300 Notice that they are drawn differently. 14:15.300 --> 14:19.000 This has the symbols on opposite sides, where here the 14:19.000 --> 14:20.670 symbols are on the same side. 14:20.667 --> 14:21.797 So think about that. 14:21.800 --> 14:26.500 Maybe put a sketch in your notebook for these four types 14:26.500 --> 14:27.170 of fronts-- 14:27.167 --> 14:29.097 cold front warm front, stationary front, 14:29.100 --> 14:29.970 and occluded front. 14:29.967 --> 14:33.967 This is kind of the language by which we describe 14:33.967 --> 14:36.867 mid-latitude frontal cyclones. 14:36.867 --> 14:42.367 So this is the big weather producer throughout the fall, 14:42.367 --> 14:44.897 winter, and spring months in mid-latitudes. 14:44.900 --> 14:49.930 These things just come at us, one after the other. 14:49.933 --> 14:52.703 Generally they control the cycle of weather in 14:52.700 --> 14:53.900 mid-latitudes. 14:53.900 --> 14:56.500 You'll have a couple days of warm air 14:56.500 --> 14:58.830 blowing from the South. 14:58.833 --> 15:00.673 Some precipitation will follow. 15:00.667 --> 15:03.127 Then you'll have a couple days with cold air coming 15:03.133 --> 15:05.473 down from the North. 15:05.467 --> 15:09.267 So imagine this whole thing moving west to east while you 15:09.267 --> 15:10.297 are stationary. 15:10.300 --> 15:12.270 It's almost as if you are moving in the other 15:12.267 --> 15:13.197 direction-- 15:13.200 --> 15:16.530 experiencing this, and then this, and then this-- 15:16.533 --> 15:18.203 as these things move over you. 15:18.200 --> 15:20.900 Unfortunately they're not periodic. 15:20.900 --> 15:22.830 They don't happen with great periodicity. 15:22.833 --> 15:25.503 So it becomes rather difficult to predict the weather. 15:25.500 --> 15:28.270 But as you get into the cycle-- if you begin to watch 15:28.267 --> 15:31.567 the weather every day, and occasionally take a peek at a 15:31.567 --> 15:34.597 weather map, you'll begin to understand this cycle of 15:34.600 --> 15:37.670 events that is coming at you day after day, week after 15:37.667 --> 15:42.827 week, throughout the cool season of the year. 15:45.767 --> 15:46.197 Yes? 15:46.200 --> 15:50.100 STUDENT: How can you tell by looking at it whether it's 15:50.100 --> 15:51.300 mature or in the early stages? 15:51.300 --> 15:52.930 PROFESSOR: Well, it's a little 15:52.933 --> 15:55.103 bit deeper, I guess. 15:55.100 --> 15:56.630 They've drawn that-- 15:56.633 --> 15:59.103 I must admit that was kind of a judgment call. 15:59.100 --> 16:01.070 These two don't look so very different. 16:01.067 --> 16:03.197 This one was occluded, though, so I could see that this is in 16:03.200 --> 16:03.830 the final-- 16:03.833 --> 16:06.673 These, maybe it was a judgment call as to whether this is 16:06.667 --> 16:07.567 more mature. 16:07.567 --> 16:08.967 It just looked like they'd drawn it a little 16:08.967 --> 16:10.327 bit deeper, to me. 16:14.933 --> 16:19.833 And as I've discussed when we were talking about clouds, 16:19.833 --> 16:23.003 from space these storms look like giant commas. 16:26.200 --> 16:29.230 Then, once you see the comma, you can try to figure out 16:29.233 --> 16:30.833 where those fronts are. 16:30.833 --> 16:33.073 The cold front is probably down here. 16:35.733 --> 16:37.473 The center of the low pressure is somewhere in here. 16:37.467 --> 16:39.997 It almost has an eye in this case. 16:40.000 --> 16:41.700 Winds are going around this direction. 16:41.700 --> 16:44.730 The cold air from Canada is coming down in here. 16:44.733 --> 16:46.233 Warm air is blowing up there. 16:46.233 --> 16:51.733 The warm front might be back in here without much of an 16:51.733 --> 16:52.403 occluded front. 16:52.400 --> 16:53.730 Or it might actually be this-- 16:53.733 --> 16:56.933 I'm sorry, it might actually be this, in which case this 16:56.933 --> 16:58.503 would be occluded all the way up there. 16:58.500 --> 17:02.230 So I can't tell for sure from that diagram where the warm 17:02.233 --> 17:03.433 front and the occluded front is. 17:03.433 --> 17:04.673 But it might be-- 17:04.667 --> 17:05.967 I'm sure that's a cold front. 17:05.967 --> 17:09.167 But where the occlusion takes place I'm not exactly sure. 17:09.167 --> 17:10.697 And the same thing over here. 17:10.700 --> 17:12.770 This is a different case altogether, but notice how 17:12.767 --> 17:14.897 similar they are-- 17:14.900 --> 17:19.070 low pressure center, probably an occluded front 17:19.067 --> 17:19.867 through here somewhere. 17:19.867 --> 17:21.667 And then these fronts will split apart. 17:21.667 --> 17:25.327 You'll have the warm front and the cold front. 17:25.333 --> 17:28.003 The cold air, when it comes down from Canada-- 17:28.000 --> 17:29.670 notice how clear the sky is-- 17:29.667 --> 17:33.467 when it comes over the ocean, that will be cold air over 17:33.467 --> 17:34.497 warm ocean. 17:34.500 --> 17:37.930 And you'll get this cumulus clouds 17:37.933 --> 17:39.073 building up over the ocean. 17:39.067 --> 17:42.067 Because you've suddenly heated that air from below, 17:42.067 --> 17:45.697 destabilizing the lapse rate, causing convection, and 17:45.700 --> 17:48.600 causing cumulus clouds to form. 17:48.600 --> 17:50.300 These aren't precipitating. 17:50.300 --> 17:51.200 These are precipitating. 17:51.200 --> 17:54.400 These are just cumulus clouds out over the ocean. 17:57.467 --> 17:58.697 Questions? 18:00.600 --> 18:05.670 So these are storms, and we need to know what they do. 18:05.667 --> 18:08.127 To a large extent they are beneficial because they bring 18:08.133 --> 18:09.973 us the rain that we need. 18:09.967 --> 18:12.667 And the snow up in the mountains that will then melt 18:12.667 --> 18:17.527 in the spring and summer and give us water in the rivers. 18:17.533 --> 18:22.933 But, on the other hand, they can also bring damaging winds. 18:22.933 --> 18:25.203 Especially on the-- 18:25.200 --> 18:28.130 I'll tell you where the strong winds usually occur. 18:28.133 --> 18:30.503 Sometimes you get strong winds in the warm sector, but 18:30.500 --> 18:34.100 usually the strongest winds are back here, behind the 18:34.100 --> 18:41.300 cyclone, coming down from the Northwest. And of course the 18:41.300 --> 18:44.770 rain, while it's needed, can sometimes be very heavy. 18:44.767 --> 18:48.627 Or the snow can be very heavy, which can cause flooding or 18:48.633 --> 18:52.903 deep, impenetrable snow drifts. 18:52.900 --> 18:57.570 Because these storms do bring cold air down from the north, 18:57.567 --> 19:01.667 often they can cause very severe wind chill episodes, 19:01.667 --> 19:06.327 with strong wind, sub-zero temperatures, and quite 19:06.333 --> 19:11.073 dangerous to be out in, in this kind of a storm. 19:11.067 --> 19:16.967 And then over the ocean, those strong winds mentioned here, 19:16.967 --> 19:20.527 winds passing over the ocean generate ocean waves. 19:20.533 --> 19:23.473 The stronger the winds, the bigger the waves. 19:23.467 --> 19:28.067 And they can be quite damaging to ships at sea. 19:28.067 --> 19:34.797 So these things have benefits but also dangers. 19:34.800 --> 19:38.600 I'll talk about a few of the famous ones in just a minute. 19:38.600 --> 19:41.000 Meteorologists like to put names on things. 19:41.000 --> 19:45.170 I think every field likes to put names on things. 19:45.167 --> 19:50.997 These are four typical storm tracks, directions where 19:51.000 --> 19:53.800 mid-latitude frontal cyclones tend to move fairly 19:53.800 --> 19:55.600 frequently. 19:55.600 --> 19:59.330 Ones that come in off the west coast that were generated in 19:59.333 --> 20:02.373 the vicinity of Hawaii are sometimes referred to 20:02.367 --> 20:05.867 meteorologists as the Pineapple Express. 20:05.867 --> 20:08.727 Fun to use terms like that. 20:08.733 --> 20:12.233 Ones that come down from Canada are generated up in 20:12.233 --> 20:14.803 here and then come down towards the Midwest are often 20:14.800 --> 20:16.600 referred to as Alberta Clippers. 20:19.833 --> 20:24.403 We get a lot of storms in the west that were generated just 20:24.400 --> 20:26.100 east of the Rocky Mountains. 20:26.100 --> 20:28.130 We call those Rocky Mountain Storms because 20:28.133 --> 20:29.973 of where they generated. 20:29.967 --> 20:33.497 But the most famous one from New England that you may have 20:33.500 --> 20:35.630 heard about is the Nor'easter. 20:35.633 --> 20:37.303 How many have heard that term Nor'easter? 20:37.300 --> 20:37.730 All of you. 20:37.733 --> 20:42.533 So this is just another mid-latitude cyclone-- 20:42.533 --> 20:43.373 frontal cyclone-- 20:43.367 --> 20:45.927 but it's called a Nor'easter. 20:45.933 --> 20:50.133 And its characteristic is that it's normally generated in the 20:50.133 --> 20:55.533 northern part of the Gulf of Mexico, or more typically here 20:55.533 --> 20:58.333 along the coast, the East Coast of the United States. 20:58.333 --> 21:04.703 And then it moves up to New England from the South. 21:04.700 --> 21:06.170 Anybody know why they're called Nor'easters? 21:10.367 --> 21:10.927 STUDENT: They travel northeast? 21:10.933 --> 21:11.203 PROFESSOR: Well, okay. 21:11.200 --> 21:14.200 One answer is that they're traveling northeast. But 21:14.200 --> 21:16.070 remember, this is a traditional term. 21:16.067 --> 21:20.727 This term goes back 200 or 300 years before the motion of 21:20.733 --> 21:23.303 these storms was understood by anybody. 21:23.300 --> 21:24.800 Right? 21:24.800 --> 21:27.470 Wind from the northeast. So if you are a New England 21:27.467 --> 21:29.767 fishermen or a farmer-- 21:29.767 --> 21:31.127 especially a fisherman-- 21:31.133 --> 21:34.073 and you're fishing offshore here, and the wind begins to 21:34.067 --> 21:38.427 pick up from the northeast, that is a sign 21:38.433 --> 21:39.933 that a storm is coming. 21:39.933 --> 21:44.203 And you would quickly head back to a sheltered cove or 21:44.200 --> 21:48.430 back to land to get your ship out of the storm. 21:48.433 --> 21:51.173 So a Nor'easter is named Nor'easter because the first 21:51.167 --> 21:55.097 sign of it in New England is the development of a 21:55.100 --> 21:58.530 northeasterly wind, an incoming-- wind coming in from 21:58.533 --> 22:01.803 the northeast. Now why is that unusual? 22:01.800 --> 22:02.670 Why would you notice that? 22:02.667 --> 22:06.167 Well, you're in the belt of westerlies here. 22:06.167 --> 22:08.697 So the winds are normally coming from west to east. So 22:08.700 --> 22:11.700 when a wind begins to go from the northeast, well that's a 22:11.700 --> 22:12.300 little bit different. 22:12.300 --> 22:15.300 And why is that a sign of a storm to come? 22:15.300 --> 22:19.570 Well, if a cyclone is coming at you from the South-- 22:19.567 --> 22:22.527 remember the winds are coming around it this way-- 22:22.533 --> 22:26.003 and so the first sign of it you will feel as it moves 22:26.000 --> 22:28.270 towards you is that easterly wind. 22:28.267 --> 22:30.797 You add a little bit of friction into that, and it's 22:30.800 --> 22:33.030 going to be a northeasterly wind. 22:33.033 --> 22:37.333 So the term Nor'easter comes from the wind direction that 22:37.333 --> 22:43.603 is the first indication that this storm is approaching you. 22:43.600 --> 22:44.830 Is that clear? 22:49.633 --> 22:51.333 OK, Nor'easter-- 22:51.333 --> 22:53.473 frontal cyclone approaching New England from the South, 22:53.467 --> 22:55.067 first sign is the strengthening wind from the 22:55.067 --> 22:58.127 northeast. There've been a lot of famous ones. 22:58.133 --> 22:59.903 I've just listed a few. 22:59.900 --> 23:03.170 There was a big blizzard in New England in 1888 that was 23:03.167 --> 23:06.297 the Storm of the Century type thing that you can Google and 23:06.300 --> 23:07.500 find out about it. 23:07.500 --> 23:10.330 Soon after I moved to New Haven in 1978 23:10.333 --> 23:12.673 there was a big blizzard. 23:12.667 --> 23:14.827 I remember we slept in our offices because we couldn't 23:14.833 --> 23:15.603 get home that night. 23:15.600 --> 23:18.430 There were drifting snow. 23:18.433 --> 23:21.203 And then recently there've been some, not quite as strong 23:21.200 --> 23:22.000 or as famous. 23:22.000 --> 23:24.030 But there's been some other Nor'easters. 23:24.033 --> 23:27.933 And here's a typical satellite image. 23:27.933 --> 23:29.503 And Florida is covered here. 23:29.500 --> 23:31.700 But generally this is the East Coast of the United States. 23:31.700 --> 23:35.230 And there's a big cyclone with a cold front, the occluded 23:35.233 --> 23:37.373 front, the warm front back into here. 23:37.367 --> 23:41.197 And that storm is moving up the coast from south to north 23:41.200 --> 23:43.770 bringing all those different types of damages-- 23:43.767 --> 23:46.727 the winds, the heavy rains-- 23:46.733 --> 23:51.933 further up north, heavy snow, maybe even some freezing rain 23:51.933 --> 23:55.533 up in the Northeast. So all these different local things 23:55.533 --> 23:56.033 can happen. 23:56.033 --> 23:56.333 Yes? 23:56.333 --> 24:01.103 STUDENT: How do the winds come from the northeast if the 24:01.100 --> 24:03.000 frontal-- if the front is coming from the South? 24:03.000 --> 24:04.400 PROFESSOR: OK, lights on for a second here. 24:13.800 --> 24:18.530 If I've got-- here's Florida, Cape Hatteras, Cape Cod, Long 24:18.533 --> 24:20.833 Island, New Haven. 24:20.833 --> 24:25.973 So there's a low pressure center here, let's say. 24:25.967 --> 24:29.767 Above the boundary layer where there's no friction, the 24:29.767 --> 24:32.327 isobars are going to be like this. 24:32.333 --> 24:35.733 And the winds are going to be traveling right around like 24:35.733 --> 24:39.503 that, paralleling the isobars. 24:39.500 --> 24:42.500 Down in the frictional boundary layer, where the 24:42.500 --> 24:44.970 winds aren't quite geostrophic, there's a little 24:44.967 --> 24:45.797 bit of a turning. 24:45.800 --> 24:49.030 They tend to move in, still generally going parallel to 24:49.033 --> 24:50.973 the isobars but with a little bit of 24:50.967 --> 24:54.727 cross-isobar flow as well. 24:54.733 --> 24:57.203 So here you've got some northeasterly winds. 24:59.767 --> 25:03.527 Now as this storm moves up in this direction, this pattern 25:03.533 --> 25:05.073 just translates. 25:05.067 --> 25:08.497 And so the first thing a fisherman up here feels is the 25:08.500 --> 25:11.070 wind blowing from the northeast, which is a sign 25:11.067 --> 25:11.727 that that's-- 25:11.733 --> 25:13.433 so it's not the fronts that I'm talking about. 25:13.433 --> 25:18.233 It's the winds around that low pressure center that gives 25:18.233 --> 25:21.003 rise to the northeasterly winds as the first sign that 25:21.000 --> 25:23.230 this thing is approaching, as it moves up the 25:23.233 --> 25:24.503 coast. Does that help? 25:28.133 --> 25:29.373 Other questions on this? 25:34.633 --> 25:40.273 So, a lot of famous storms. The wreck of the Edmund 25:40.267 --> 25:45.797 Fitzgerald was a big tanker ship in the Great Lakes. 25:45.800 --> 25:48.070 And along came a frontal cyclone-- 25:48.067 --> 25:49.467 you see it drawn here-- 25:49.467 --> 25:53.827 back in 1975, developed waves so great on the Great Lakes 25:53.833 --> 25:58.303 that this ship broke apart and sank. 25:58.300 --> 26:01.930 Quite a thing at the time. 26:01.933 --> 26:03.903 Has anybody ever heard the song about 26:03.900 --> 26:06.670 that by Gordon Lightfoot? 26:06.667 --> 26:07.767 Google it. 26:07.767 --> 26:08.467 Listen to that song. 26:08.467 --> 26:09.127 It's a great song. 26:09.133 --> 26:14.873 It coincided with kind of the folk music era as well. 26:14.867 --> 26:18.397 And so this song became quite well known, describing this 26:18.400 --> 26:22.930 disaster but also fitting into the genre of folk 26:22.933 --> 26:23.933 music at the time. 26:23.933 --> 26:27.103 So very strong frontal cyclone generating waves 26:27.100 --> 26:29.870 on the Great Lakes. 26:29.867 --> 26:31.397 The blizzard of 1978-- 26:31.400 --> 26:33.870 the one I mentioned, here in New Haven-- 26:33.867 --> 26:35.867 here's a satellite image of it. 26:35.867 --> 26:39.427 Now what you're seeing here, remember, are just the cumulus 26:39.433 --> 26:42.403 clouds as the cold air behind the cyclone comes 26:42.400 --> 26:43.230 out over the ocean. 26:43.233 --> 26:45.703 But these are the fronts back here. 26:45.700 --> 26:48.200 And very strong winds connected with that, and a lot 26:48.200 --> 26:49.730 of snowfall. 26:49.733 --> 26:54.503 And this is what the highways look like the next morning 26:54.500 --> 26:57.730 after the blizzard passed away. 26:57.733 --> 27:03.303 And then, have you heard of The Perfect Storm? 27:03.300 --> 27:07.270 This book by Sebastian Junger became quite a best seller 27:07.267 --> 27:11.297 describing a storm that hit the Grand Banks and sank a 27:11.300 --> 27:14.270 fisher boat, the Andrea Gail. 27:14.267 --> 27:15.667 And here's a picture of that storm. 27:15.667 --> 27:16.927 And notice it looks like the others. 27:16.933 --> 27:19.303 You've got the cold front, the warm front, the occluded 27:19.300 --> 27:22.300 front, the cyclone, strong winds, and so on, producing 27:22.300 --> 27:24.870 big waves and sunk that little-- 27:24.867 --> 27:30.127 So you can read about that in Junger's book. 27:30.133 --> 27:31.473 Now you get the same thing in the 27:31.467 --> 27:33.727 Southern Hemisphere, remember. 27:33.733 --> 27:38.103 In Southern Hemisphere winter you get a big north-south 27:38.100 --> 27:39.600 temperature gradient. 27:39.600 --> 27:43.670 And you get the mid-latitude frontal cyclones. 27:43.667 --> 27:45.227 They rotate in the opposite direction. 27:45.233 --> 27:49.933 Just like hurricanes rotate oppositely in the Southern 27:49.933 --> 27:54.533 Hemisphere, so do mid-latitude frontal cyclones. 27:54.533 --> 28:00.703 They are-- the winds spin clockwise around frontal 28:00.700 --> 28:03.370 cyclones in the Southern Hemisphere. 28:03.367 --> 28:06.427 And they are very strong down there, perhaps even stronger 28:06.433 --> 28:09.133 than in the Northern Hemisphere, which has given 28:09.133 --> 28:14.173 rise to these amusing terms for these latitude belts, 28:14.167 --> 28:15.467 which you may have heard-- 28:15.467 --> 28:18.667 the Roaring Forties, the Furious Fifties. 28:18.667 --> 28:23.597 And even I've heard the term Screaming Sixties used, 28:23.600 --> 28:26.800 referring to these latitude belts where you get very 28:26.800 --> 28:31.200 intense and frequent mid-latitude frontal cyclones. 28:31.200 --> 28:36.800 And if you're sailing on a clipper ship 150 years ago, 28:36.800 --> 28:39.130 out of England, trying to reach somewhere-- 28:39.133 --> 28:43.733 First of all, remember that the way you would do that-- 28:43.733 --> 28:47.003 the winds down here are westerlies, just as they are 28:47.000 --> 28:48.930 in the Northern Hemisphere mid-latitudes. 28:48.933 --> 28:52.803 So if you wanted to go to Australia you'd come down here 28:52.800 --> 28:57.500 and then go east. And then if you wanted to return to 28:57.500 --> 29:00.530 England you wouldn't try to go back against these. 29:00.533 --> 29:03.433 You'd go further east. And you'd come this way and then 29:03.433 --> 29:04.473 come back around. 29:04.467 --> 29:08.627 So here we have to go around the Cape of Good Hope. 29:08.633 --> 29:10.273 Here you've got to go around Cape Horn. 29:10.267 --> 29:14.897 And especially Cape Horn is famous for all the shipwrecks 29:14.900 --> 29:17.630 that have occurred as ships have tried to go around or 29:17.633 --> 29:22.473 through this belt of very intense and frequent 29:22.467 --> 29:24.397 mid-latitude frontal cyclones. 29:24.400 --> 29:28.200 So it's a very dangerous part of the world ocean in which to 29:28.200 --> 29:31.000 travel unless you've got a big ship. 29:31.000 --> 29:32.900 I've crossed that passage a couple times. 29:32.900 --> 29:36.800 And once or twice it's been fairly calm, and other times 29:36.800 --> 29:38.030 it's been anything but. 29:41.967 --> 29:44.867 Well, that's what I was going to say about frontal cyclones. 29:44.867 --> 29:47.097 Again, it's not as detailed as what the book goes into. 29:47.100 --> 29:48.670 But are there any questions at this 29:48.667 --> 29:50.567 point on frontal cyclones? 29:56.500 --> 29:57.930 Weather forecasting-- 29:57.933 --> 29:59.903 This is not a course in weather forecasting. 29:59.900 --> 30:03.900 You could take a whole course in this. 30:03.900 --> 30:06.900 But I want to say a few words about how one forecasts all 30:06.900 --> 30:09.800 these different types of storms, especially the 30:09.800 --> 30:12.930 mid-latitude frontal cyclones. 30:12.933 --> 30:18.103 It's pretty simple but it's a big enterprise. 30:18.100 --> 30:20.500 The way you do it is first describe the initial state of 30:20.500 --> 30:21.200 the atmosphere-- 30:21.200 --> 30:23.670 that is, temperature, pressure, wind, humidity-- 30:26.367 --> 30:32.327 everywhere, globally and vertically, at one time. 30:32.333 --> 30:35.873 You use weather balloons for that, surface stations, and 30:35.867 --> 30:40.927 satellites to get that state of the atmosphere described. 30:40.933 --> 30:44.833 Then you can use that as the initial condition on a giant 30:44.833 --> 30:48.133 integration of the equations of motion. 30:48.133 --> 30:51.303 These complicated equations, which you have seen simplified 30:51.300 --> 30:53.270 versions of in this course-- 30:53.267 --> 30:58.227 like the perfect gas law, the hydrostatic equation, cloud 30:58.233 --> 31:00.273 processes, and so on-- are all 31:00.267 --> 31:01.827 programmed into these equations. 31:01.833 --> 31:03.503 And then they're integrated forward. 31:03.500 --> 31:07.130 This is a huge job and usually the largest supercomputers 31:07.133 --> 31:11.633 that exist in the world are dedicated to this problem. 31:11.633 --> 31:14.803 There are a few other defense applications that also have 31:14.800 --> 31:16.530 some of the world's biggest supercomputers. 31:16.533 --> 31:19.473 But for the most part, meteorology has led the way in 31:19.467 --> 31:22.197 the use of the biggest computer you could get, 31:22.200 --> 31:26.930 because it's a giant problem to compute forward in time the 31:26.933 --> 31:29.203 weather processes all around the globe. 31:29.200 --> 31:32.770 It all has to be done simultaneously. 31:32.767 --> 31:34.927 In this country it's the National Weather Service that 31:34.933 --> 31:36.233 does all of that-- 31:36.233 --> 31:38.833 collects the data and puts them into the equation and 31:38.833 --> 31:42.303 runs-- puts them into the computer and integrates those 31:42.300 --> 31:43.800 equations forward. 31:43.800 --> 31:46.230 And you get your forecasts directly from the Weather 31:46.233 --> 31:49.173 Service if you want, but then there's a big private-sector 31:49.167 --> 31:53.027 industry that lies on top of that. 31:53.033 --> 31:59.233 They get the raw results from the computer output and then 31:59.233 --> 32:03.403 process it to make it useful for the consumer. 32:03.400 --> 32:06.770 They make pretty graphics, nice maps, predictions of 32:06.767 --> 32:10.267 what's going to happen hour by hour, build nice websites. 32:10.267 --> 32:12.367 You know some of the companies that do this. 32:12.367 --> 32:14.367 The Weather Channel is such a company. 32:14.367 --> 32:16.927 There's a company called AccuWeather that does this 32:16.933 --> 32:17.803 sort of thing. 32:17.800 --> 32:20.500 There's a half a dozen others. 32:20.500 --> 32:23.100 They don't do any of this work themselves. 32:23.100 --> 32:25.600 So, actually, it's a pretty sweet deal for these companies 32:25.600 --> 32:28.270 because the government does all the hard work. 32:28.267 --> 32:31.767 And all they do is kind of pretty up the forecast, make 32:31.767 --> 32:35.127 it more useful for you and I, and then sell it to a 32:35.133 --> 32:36.073 television station. 32:36.067 --> 32:39.627 Or sell it to us, or whatever, in a nice useful form. 32:39.633 --> 32:41.473 And then that whole process is repeated 32:41.467 --> 32:43.067 every 12 hours, right? 32:43.067 --> 32:45.627 That's why those balloons go up every 12 hours. 32:45.633 --> 32:49.303 That's the start of the next forecast cycle. 32:49.300 --> 32:53.600 So that's basically the way the forecast system works. 32:56.700 --> 32:59.430 People are always complaining about the-- 32:59.433 --> 33:02.403 that's one of the burdens of being an atmospheric 33:02.400 --> 33:04.070 scientist. You sit down to somebody-- 33:04.067 --> 33:06.297 pick somebody on a bus and, before you know it, they're 33:06.300 --> 33:08.530 complaining about how bad the weather forecasts are. 33:08.533 --> 33:11.533 You get a little bit tired of hearing that, because they're 33:11.533 --> 33:13.403 actually-- for some purposes, they're not that bad. 33:13.400 --> 33:15.530 They're pretty good. 33:15.533 --> 33:21.373 Now here's a diagram put out by the National Weather 33:21.367 --> 33:23.667 Service, so it may be a little bit biased. 33:23.667 --> 33:26.697 But, no, it's very statistical. 33:26.700 --> 33:29.230 They define a skill score. 33:29.233 --> 33:32.473 I don't have the mathematical form of that to give you, but 33:32.467 --> 33:35.267 it's some kind of a measure of the quality of the forecast-- 33:35.267 --> 33:37.827 how accurate the forecast was, compared to 33:37.833 --> 33:40.903 what actually happened. 33:40.900 --> 33:44.700 And it's plotted on a scale from 0 to 80. 33:44.700 --> 33:47.800 But 100 would be a perfect forecast, 33:47.800 --> 33:49.670 perfect in all respects. 33:49.667 --> 33:56.827 This happens to be a forecast for the 500 millibar level. 33:56.833 --> 33:58.903 So it's not every aspect of the weather that's being 33:58.900 --> 34:03.700 presented here, just the shape of the isobaric patterns at 34:03.700 --> 34:05.100 500 millibars. 34:05.100 --> 34:10.130 And starts in 1955 when weather forecasting first 34:10.133 --> 34:13.733 began, using computers, and goes up to 34:13.733 --> 34:17.103 almost the present day. 34:17.100 --> 34:20.670 Let's follow the blue curve, which is a 36-hour forecast. 34:20.667 --> 34:23.767 So this is the skill of predicting the weather a day 34:23.767 --> 34:26.967 and a half in advance-- 34:26.967 --> 34:28.967 telling the future, if you like. 34:28.967 --> 34:32.197 What's the weather going to be 36 hours ahead? 34:32.200 --> 34:35.270 The skill score was, like, 24 when I first started, and 34:35.267 --> 34:39.297 today it's something like 78. 34:39.300 --> 34:41.700 Again, I haven't giving you the formula by which that 34:41.700 --> 34:43.400 statistical measure is derived. 34:43.400 --> 34:45.870 But that's a pretty good improvement over the time. 34:45.867 --> 34:48.667 It's caused by two things, improvements in the numerical 34:48.667 --> 34:54.167 models and improvements in measuring that initial state. 34:54.167 --> 34:55.467 Both things are very important. 34:55.467 --> 34:57.697 You've got to measure the initial state better, and 34:57.700 --> 35:00.070 you've got to have a more accurate model with higher 35:00.067 --> 35:03.567 spatial resolution, too. 35:03.567 --> 35:07.967 Now if you try to do a 72-hour forecast-- 35:07.967 --> 35:10.067 a three-day forecast-- 35:10.067 --> 35:13.267 of course, your skill is going to be lower. 35:13.267 --> 35:15.727 The further out you go in the forecast the worse is going to 35:15.733 --> 35:18.133 be the quality of your forecast. But that, too, has 35:18.133 --> 35:19.373 been improving. 35:19.367 --> 35:24.897 So today the 72-hour forecast is about as good as a 36-hour 35:24.900 --> 35:28.430 forecast was in the early '80s. 35:28.433 --> 35:30.073 So we're definitely making progress on this. 35:30.067 --> 35:33.027 And of course, people are trying to compute out still 35:33.033 --> 35:34.603 further in time. 35:34.600 --> 35:36.770 If you go into the Weather Channel you'll find forecasts 35:36.767 --> 35:39.927 out seven, eight, even nine days in advance. 35:39.933 --> 35:41.803 I don't usually trust those. 35:41.800 --> 35:46.470 But they're fun to look at and speculate about what might be. 35:46.467 --> 35:47.697 Questions on this? 35:50.267 --> 35:52.667 So for example, I've shown you some of these. 35:52.667 --> 35:57.127 This is a 500 millibar map from a couple days ago. 35:57.133 --> 36:00.833 It's this that they're basing that skill score on. 36:00.833 --> 36:02.973 Now that's a problem, because you or I might be more 36:02.967 --> 36:06.367 interested in whether it's going to rain or not. 36:06.367 --> 36:08.767 But that's not what that particular skill score-- there 36:08.767 --> 36:09.767 are others that measure that. 36:09.767 --> 36:13.127 But that particular skill score was just whether the 36:13.133 --> 36:15.973 correct prediction was made for the shape of those 36:15.967 --> 36:19.267 isobaric disturbances at 500 millibars. 36:19.267 --> 36:23.127 So I don't mean to claim that that measure of skill is 36:23.133 --> 36:24.103 all-encompassing. 36:24.100 --> 36:29.300 It just measures one aspect of weather forecasting. 36:29.300 --> 36:35.530 So here's my off-the-cuff summary about how well we're 36:35.533 --> 36:39.103 doing with various types of storms. With severe 36:39.100 --> 36:42.670 thunderstorms we predict the probability pretty well. 36:42.667 --> 36:45.667 In other words, you'll hear a forecast saying something like 36:45.667 --> 36:50.227 80% chance of thunderstorms tomorrow afternoon. 36:50.233 --> 36:52.603 We do that pretty well. 36:52.600 --> 36:56.100 But in terms of predicting when and where an individual 36:56.100 --> 37:00.230 storm is going to occur, we have almost no skill at that. 37:00.233 --> 37:02.573 We don't know whether it's going to occur over Hartford 37:02.567 --> 37:06.797 or Stamford. 37:06.800 --> 37:09.500 We just can't do that kind of local forecasting with this 37:09.500 --> 37:12.430 kind of storm because they're too chaotic, they're too 37:12.433 --> 37:14.373 random, in what triggers them. 37:17.100 --> 37:18.730 Hurricanes-- oh and the tornadoes which come out of 37:18.733 --> 37:22.203 those, we're very poor at predicting when and where a 37:22.200 --> 37:23.770 tornado will arise. 37:23.767 --> 37:25.667 So we use what's called nowcasting. 37:25.667 --> 37:29.467 It's a funny term, almost a metaphor for failure. 37:29.467 --> 37:33.397 But nowcasting means-- 37:33.400 --> 37:36.400 as I showed you in the film the other day-- nowcasting is 37:36.400 --> 37:42.970 seeing the thing and then saying, watch out, it's there. 37:42.967 --> 37:44.797 And also-- it's not quite that bad, because you could see it 37:44.800 --> 37:46.800 and see what direction it's moving. 37:46.800 --> 37:50.130 So you could give a few minutes' warning to a 37:50.133 --> 37:52.733 community where that tornado was approaching. 37:52.733 --> 37:55.933 But in terms of being able to predict something like that 37:55.933 --> 37:57.933 from a numerical model, no. 37:57.933 --> 38:00.503 We have no skill at being able to predict from first 38:00.500 --> 38:05.670 principles when and where a tornado will occur. 38:05.667 --> 38:11.197 Moving onto hurricanes, genesis means when you first 38:11.200 --> 38:12.400 create the hurricane. 38:12.400 --> 38:15.200 We're very poor at that. 38:15.200 --> 38:18.600 Once the hurricane is formed, we're quite good at predicting 38:18.600 --> 38:22.270 where its track is going to be. 38:22.267 --> 38:24.227 For example, Hurricane Irene was a good example of that. 38:24.233 --> 38:26.673 They really had that track nailed, even out three or four 38:26.667 --> 38:27.827 days in advance. 38:27.833 --> 38:32.973 They had a very good track forecast. As it changes its 38:32.967 --> 38:34.997 strength however as it moves along its track it may weaken 38:35.000 --> 38:36.270 or strengthen. 38:36.267 --> 38:38.767 We're not very good at that. 38:38.767 --> 38:40.197 So certain things we do well. 38:40.200 --> 38:41.730 Frontal cyclones we're pretty good at. 38:41.733 --> 38:44.403 These wintertime storms we often have good 38:44.400 --> 38:46.770 skill out to five days. 38:46.767 --> 38:50.727 Occasionally we have a real bust. The weather service will 38:50.733 --> 38:55.433 fail to predict the big storm genesis event or will forecast 38:55.433 --> 38:56.703 one that didn't occur. 38:56.700 --> 39:00.770 But those busts are increasingly rare. 39:00.767 --> 39:04.727 And I'm amazed sometimes at how skillful the prediction of 39:04.733 --> 39:07.973 these storms can be, out even several days in advance. 39:10.600 --> 39:11.870 Questions there? 39:14.100 --> 39:20.300 Now we won't finish this today, but I want you to start 39:20.300 --> 39:21.670 being aware of forecasts. 39:24.500 --> 39:26.900 I usually go to this page. 39:26.900 --> 39:28.300 You can click to it on my website. 39:28.300 --> 39:30.570 It's the NCAR real-time weather data. 39:30.567 --> 39:36.267 And for example, right now you could-- 39:36.267 --> 39:42.227 well let's look at the upper air data from 500 millibar 39:42.233 --> 39:45.073 sounding for this morning. 39:45.067 --> 39:47.567 This is the 12Z Friday sounding. 39:47.567 --> 39:50.427 You see the date and time up there. 39:50.433 --> 39:51.473 This is what the weather's doing 39:51.467 --> 39:53.067 right now at 500 millibars. 39:53.067 --> 39:58.527 There's a big trough in the west coast, a big ridge on the 39:58.533 --> 40:01.903 east coast, and then another cyclone moving away to the 40:01.900 --> 40:06.630 east. This would be the starting point for 40:06.633 --> 40:10.303 integrations forward in time. 40:10.300 --> 40:12.900 And then if we go back, we can see what the 40:12.900 --> 40:14.670 forecast is going to be. 40:14.667 --> 40:16.597 I'll click on the forecast tab up here. 40:19.667 --> 40:23.867 First of all, we could look-- here's the 12-hour forecast. 40:23.867 --> 40:32.067 So this is valid, yeah, 18 UTC Friday. 40:32.067 --> 40:39.027 So that's going to be valid in about three hours from now. 40:39.033 --> 40:43.773 And there's a nicely developed mid-latitude frontal cyclone 40:43.767 --> 40:50.367 down here, cold front, stationary front. 40:53.533 --> 40:54.773 Let's go forward in time. 41:01.767 --> 41:04.697 Let's go 36 hours in advance. 41:04.700 --> 41:08.030 This is valid 12Z Saturday, so this is tomorrow 41:08.033 --> 41:11.203 morning at 8:00 AM. 41:11.200 --> 41:12.500 You see what they're forecasting. 41:12.500 --> 41:14.970 The green gives you moisture and precipitation. 41:14.967 --> 41:17.897 The lows and the fronts are all there. 41:17.900 --> 41:22.600 So what about your New Haven weekend? 41:22.600 --> 41:25.830 It's not my job to give you an indication of the forecast. 41:25.833 --> 41:27.873 But anyway, it's going to be a nice weekend, right? 41:27.867 --> 41:30.567 We've got a high pressure center over us. 41:30.567 --> 41:33.467 High pressure centers have descending air, 41:33.467 --> 41:35.297 cleans out the clouds. 41:35.300 --> 41:38.230 Should be very nice for the weekend. 41:38.233 --> 41:40.033 And let's think about what's going to 41:40.033 --> 41:41.733 happen after that, however. 41:41.733 --> 41:44.333 For now I'm going to go to an animation. 41:44.333 --> 41:46.573 I think I want to animate this. 41:46.567 --> 41:48.427 Loop all times. 41:48.433 --> 41:54.003 We'll go to something like the 500 millibar winds, and we'll 41:54.000 --> 41:55.970 see if that's going to loop. 41:55.967 --> 41:58.667 Why isn't that looping? 41:58.667 --> 42:00.097 I didn't hit the loop there? 42:00.100 --> 42:03.200 Is that what I didn't do? 42:03.200 --> 42:07.730 OK, so these are the forecasts now, done from the recent 42:07.733 --> 42:10.233 balloon sounding as the initial condition. 42:10.233 --> 42:13.933 And you see that it's a very well developed 42:13.933 --> 42:15.973 trough ridge system. 42:15.967 --> 42:18.927 And generally the whole thing is creeping eastward. 42:18.933 --> 42:21.773 Now this doesn't go very far forward in time. 42:21.767 --> 42:23.727 In fact, I don't know why. 42:23.733 --> 42:26.373 Did I not click on the right thing here? 42:29.400 --> 42:31.070 Loop all times. 42:31.067 --> 42:34.427 Yeah, well it's only giving me a 12-hour forecast, which is 42:34.433 --> 42:35.203 not what I want. 42:35.200 --> 42:37.300 So let me try a different model. 42:37.300 --> 42:38.230 Yeah, OK. 42:38.233 --> 42:39.833 This one goes-- this will be a different model. 42:46.867 --> 42:51.297 Saturday, Sunday, still good weather over New Haven. 42:55.733 --> 42:58.473 So remember now, this is a computer integration. 42:58.467 --> 43:00.767 This takes the balloon sounding satellite data for 43:00.767 --> 43:04.527 last Friday, for today, and then integrates it forward in 43:04.533 --> 43:08.633 time to get the forecast. And it may not be accurate towards 43:08.633 --> 43:11.273 the end of the time period, but it's probably pretty good 43:11.267 --> 43:12.367 for the next couple days. 43:12.367 --> 43:13.027 We're out of time. 43:13.033 --> 43:14.773 We'll continue this on Monday.