As much as it's fun to learn about meteorology through real weather events, please be careful and I hope everyone stays safe through this serious storm.
It seems like just yesterday we were scoffing at the wild divergence in weather models for the approaching snow and now we're facing yet another historic weather event. Where the heck did this come from and why has it been so hard to predict?
First off, let's review what we know about nor'easters. We know it's warm, moist air from the south running into cold air from Canada. Right?
What else we know is that the Jet Stream is what's driving both the cold and warm. Specifically, the Polar Jet for the cold and the Subtropical Jet for the warm. Wikipedia gives us some handy aids for visualizing those particular forces
From my colleague Alastair I learned that the cold ingredient is an Alberta Clipper. That means warm, moist air started from the Pacific and headed across Canadian mountain ranges all the way to where the Rockies reach into the south of Alberta (ahem... that's the second province from the left). The air dumps its moisture on the way up the mountains and warms on its way down the east side. As it comes off the Rockies (see also, Chinooks winds) it hits the cold air that's been sitting in the Canadian prarie and a storm forms that heads across the U.S.
(I know from my past weather posts that many of you are well versed in weather phenomena, so hopefully you can help me understand the role of Arctic Oscillation in this whole concoction. It looks like we're in a generally negative trend so does that explain the trajectory of the Clipper running into the U.S. instead of keeping a more northerly bearing?)
Ok, that's enough theory, let's see if we can go back and watch the birth of Nemo.
First, I want to take a look at the Jet Stream model here. This is going to update over time, so I've taken a couple of images of what happened earlier in the week before they disappear from the model's time range.
Let's start with Monday. If you're struggling with the orientation, the perspective is looking down at the North Pole. The U.S. is in the lower right. We see the Jet Stream making a dip from the South Pacific and running right up to British Columbia. I don't know for sure how quickly this weather travels across the continent, but if I had to guess when the warm, moist Pacific air that began this storm first made its way to Alberta, that's what I'd pick.
Moving ahead to Tuesday, we get a good look at that Subtropical Jet in the Gulf of Mexico that's going to give Nemo its warm, moist ingredient.
I'm assembling these images in the wee hours of February 8, so the two storms, the Alberta Clipper and the rain storm coming up the coast from the Gulf, are still distinct. By the time I publish this later today that may not be the case.
Here's a pretty look at the two from around 3 a.m. The low on the Atlantic Coast is actually in the southern portion of all that rain. As all the meteorologists are explaining this morning, the storm is spinning water in off the ocean. The low in the Midwest is way up at the top of that front line, like somewhere between Toledo and Cleveland. That's already giving some snow to the folks there.
What's going to happen is that the two lows are going to crash into each other and make a super low. ("Super low" is a term I just made up. If you know what the actual term is, let me know. Is it a bomb?) The cold is what's going to make the snow, but the pressure drop is what's going to make the extreme wind.
Presumably at some point a weather site or TV guy will give us a cool animation of these two moving on a collision course. One place we can see it briefly in advance of it actually happening is in the forecast models.
Before we go on, let me point out that if you're into these weather maps, you'll have a really great time exploring this page where NOAA keeps the model animations.
For the purposes of watching these storms collide, I chose the first box of the Global Forecast System and then selected the Atlantic view. From there I chose the first box again, but that doesn't produce a permalink I can share, so you're on your own.
Again, these models are constantly updating, so it may be that by the time you click these links the days leading up to Nemo are no longer stored. That's why I've saved these individual frames. I should also make clear, these images are from a forecast model, not from the actual weather. They're just so we can get a sense of the storm's motion and formation and appreciate why it's tricky to figure out the paths of intersection.
In the image below we see them starting to merge. Notice also how the number of rings around the storm increase and are closely packed together. They increase because the barometric pressure is dropping in the center. When they're close together like that, it means the pressure changes rapidly over a short distance, and that means strong winds.
And out to sea...
As ever, I appreciate any insights or expertise that you can offer to help make this a more thorough and accurate item.
Leave a Comment:
Wow! I'm not a meteorologist or even a scientist, but I actually understood that!
Thanks,
It's Feb 8th, a winter storm is heading to the NorthEast.
Stop the presses, notify the president, release the hounds.....
I just can't wait until July, then we can hear how hot it is in the NorthEast..
I grew up in southern NE and both extremes are true. Heavy snows are not that uncommon. Let me say first, that southern NE (except the western parts) tends to be damp because nothing is that far from the sea. Systems collect moisture from the ocean as they move up the eastern seaboard. In winter, if there is no cold system moving in from the west (NE itself is actually fairly far north) they get rain. But if there is a cold front moving in from the west and it hits the warmer moist system moving up the coast, they get snow, sometimes enormous amounts of snow. Alberta Clippers tend to produce lesser amounts of snow because they have moved so far over land already and have lost a lot of their moisture; but they tend to be very cold because they come out of Canada. The Alberta Clipper moving east that will meet the moisture coming up from the south in this storm passed through WI yesterday and dumped about 7 inches on my lawn...not considered that much by New Englanders. It is colliding with the warmer moist air coming up coast. Now you have cold from Canada hitting tons of moisture from the south the result is very heavy snowfall. In the 1978 blizzard, central CT got 30" but where my family lives in NE RI they got 60" from that storm. Have you ever seen 60 inches from one rather quick storm. It is mind boggling!
In summer, that warm moisture still comes up from the South and raises the humidity everywhere within 30-50 miles from the sea. There is no real cool air coming from the west, so the hot air from the south stays hot. So it is not uncommon to end up with temperatures of 90-100 degrees and a humidty of 70%. Now I lived a long time all over Southern New England and now I live in WI where it can be pretty hot or very cold, but usually it is dry. Living in New England during a heat wave is like living in a Sauna, you sweat like crazy and it doesn't evaporate to cool your body because the air is already saturated. In the winter, temps can drop below zero, but the air is still bone chilling damp. It is not an easy climate, but it is a gorgeous part of the world. If it did not adversely affect my health, I would still live there. While I love WI, and the dryer air keeps me healthier, I will always love New England.
a "Bomb" as referred to in weather, is a synoptic-scale storm that has its central pressure drop by 24 hPa (Hectopascals, used to be known as millibars) or more within a 24 hour period. and this storm is well on the way to hitting that technical classification, bombing out quite nicely (meteorologically speaking).
but winds being generated are more from the pressure difference between the low that's bombing out (the higher the difference between the two the higher the winds), and the area of high pressure in Quebec and the Maritimes acting as a dam. That cold air in eastern Canada is what is causing the rain to be changed over to snow in eastern PA, eastern NY, and New England (with the same process that gives the northeast "back door cold fronts" that people like in the middle of summer): cold air damming (http://en.wikipedia.org/wiki/Cold_air_damming). Without that Cold Air "Dam", you would not have the same system. This cold-air damming, depending on where the high pressure sets up and how long it sits there and spins, can even bring snow and ice all the way down into Georgia and the Carolinas with any onshore flow of moisture.
otherwise, everything else looks good.
.
THIS IS THE MAP (link to Radar Weather Gov national map) I look at first thing every morning. You may wish to bookmark this map, it can be a bit difficult to locate this map which is without embedded links and resizes to fit your browser window.
THIS link takes you to the National Mosaic.
At THIS LINK (radar.weather.gov) you can click on your own local dot to get local java script radar. Pretty cool, with a well defined squall line I can guess within a few minutes when we'll get hit.
.
Love the word, "super-low". But I think two lows coming together may be called a mid-latitude cyclone? Which is a lot scarier.
Here is a link to the "EURO Model" Notice the tightness of the isobars as the storm collides with the US east coast (Rhode Island to Maine) area. This suggests very strong winds. also look at the intensity of the green that his in the middle of the narrow isobars.
Pretty amazing storm so far. I hope nobody loses power, especially us. In terms of your pronouncement of a Super Low, and since it is a winter storm, can we just refer to this as a Shovel-Ready Low pressure system? As alerts go anyway! Keep smiling, and keep watching!
Sorry wrong EURO Model map. This EURO Model shows whats happening now better from the predictive standpoint of two days ago. www.ecmwf.int/products/forecasts/d/charts/medium/deterministic/msl_uv850_z500!Wind%20850%20and%20mslp!72!North%20America!pop!od!oper!public_plots!2013020612!!/
Cool, er, that's so chill.
I watch the Pacific ocean satellite somewhat frequently. As an 8th generation native (yes, someone got here and displaced the indigenous but I digress) if it rained every day that would be fine.
That keeps the fire danger down and allows the creeks and streams, even rivers in southern California to harbor all manner of flora and fauna that persist, even during years of drought like conditions.
Especially so for the Mojave and Great Basin deserts (Death Valley National Park) Arizona, and so on.
Once I heard a guy say "Anyone who doesn't like the desert has a character flaw.
Sorry you folks will be shoveling snow though, a great explanation about the phenomena.
I love that this is what you are up to in the wee hours. Thanks for this, I'll be watching from out here in the Northwest. Bundle up and stay safe over there!
To all in the Northeast under this weather pattern take care, keep warm and safe.
Ah, weather events. Why is it that every big storm is "historic" of "extreme"...just for comparison, in my lifetime, we have had huge snow events in the north east the following years that I can remember: 73, 77, 78, 92, 93, 96, 97, and 06. (hey, what do you know, a roughly 10 year cycle)
Not all of these affected the DC, NY, Boston corridor, but 2 feet of snow in a single big storm is not rare at all in the greater northeast (NY, NJ, PA, and north).
I think what could make this storm historic in terms of effects is the very high winds. I am a former New Englander and I think you missed a few, but I could be wrong. :)
I'm sure I did. True, high winds across large areas is somewhat more rare, at least in winter storm. But having spent 12 years in NJ, and 18 in upstate NY, I can remember a few with 60-70 mph winds.
I live in AL now...can't say I miss the snow and cold. On the other hand, no tornado season in NY.
Excellent. And, yeah, everyone in the affected area, please take care.
However, please don't call this "Nemo". That is literally only a Weather Channel marketing gimmick. The NWS and NOAA do not name winter storms. If you see it on Weather Underground and think, "Wow, I guess Nemo [or whatever, for future storms] IS the official name," no, it's not -- Wunderground was purchased by The Weather Channel.
Sorry, I'm just really annoyed at the need for TWC to gussy this up. If NWS starts naming 'em, that's one thing.
Rachel, you are my Hero of Truth and Integrity! Well, that was in response to the episode I watched about the militarization issue, and the Hagel and Brennan nominations. As to the weather, you mirror my interest in science and knowledge and always have something to say that increases my own store of information. Thank you! Thank you!
I have to admit that by the time I finally got re-connected so I could leave a comment, I've forgotten the exact thought I wanted to express about the show. I did, after all, just turn 76 years of age. While I can grasp the large concepts of nanotechnology (my latest interest), I often forget those niggling little items of memory. So, I may be back later when the thought pops back into the foreground. Thank you, again. You are a bright and shining beacon!
Good information about the state of the US National Weather Service at http://cliffmass.blogspot.com/2013/01/fixing-national-weather-services.html
Mother nature doing her thing. Winter weather make you appreciate other seasons. Also, this is normal just less frequent. Folks just need to stock up and bless those without fireplaces and wood stoves.