Monday, November 12, 2012

Major Thanksgiving Storm Will Be Diverted Offshore


The major Thanksgiving storm that I made the call for a couple days ago will still happen- however, now the storm system will be forced offshore thanks to a positive NAO.

(Originally published November 10)This is a 500mb height anomaly forecast, valid a few days out. As you can see, there isn't much going on in the United States, so why am I showing you this? Well, we have to go to East Asia for that answer. If you look in the top left corner of the image, you will see a strong trough present in East Asia. It has been shown that there is a 6-10 day gap between what happens in East Asia and what happens in the East US. So, if we use this forecast (valid November 13) and apply the 6-10 day gap to it, we end up at November 22, or a day or two from Turkey Day.

We can also use the Lezak Recurring Cycle (LRC), which is, in the simplest of simple explanations, a repeating pattern that forms every fall and cycles through the winter. This pattern first forms in September-October. A strong storm system hit the Plains, Midwest and Great Lakes on October 2. If we use the expected 51 day gap between each cycle and add on a day or two to give the forecast a little wiggle room, we find this strong storm system hitting the Midwest/Great Lakes on November 21-23, which falls right on Thanksgiving!

However, this storm system will miss the United States. You see, while East Asia will be correct in a major storm hitting the East Coast, a positive NAO will get in the way of this system actually getting close to land. When you have the North Atlantic Oscillation (NAO) in a positive state, the jet stream is diverted east out to sea for storms that ride the Gulf Coast and are known as Nor'easters when the actually go up the East Coast (commonly seen in a negative NAO).

Despite this East Coast miss, the Plains may still find some precipitation in the forecast for Thanksgiving. This Hour 252 forecast of the GFS Ensembles on the evening of Thanksgiving depicts may individual ensemble members showing big depressions in the lines, which are storm systems. The lower the depressions, the stronger the storm system. Some members are even forecasting a big green circle. This means a cut-off low is present, which is a regular low pressure system that is no longer influenced by the jet stream.

In conclusion:
•The Major Thanksgiving storm will still verify- but it will be directed offshore.
•The Plains may get in on some wintry fun, however.
•Warmth expected for the South.



Anonymous said...

Is snow still possible in the Great Lakes?If is winter storm warning possible?

Aran Jacobs said...

Thank you!! I see snow is in forecast a week after Thanksgiving.That forecast has been there a while.

Anonymous said...

When you say plains, could that include the Front Range and plains of Colorado?

Owen12789 said...

What about Springfield, IL? Are we in the path? :)

Anonymous said...

wont be any snow with this system anyways

Anonymous said...

LOL! Latest 11/13 12z Euro blows up storm east half of country again Tksgivng wknd as Alberta clipper phases in! Not offshore. That's what happens when you try to take these models per-vatum DAILY and so far out. Now ya see you don't. I've watched these models for nearly 40 yrs... general patterns projections; YES...actual wx two weeks out and same day? Extremely rare. You'll learn because you are extremely smart! Great Blog for the science knowledge; now be more realistic on forecast projections and timing.

Andrew said...

Anonymous at 2:21: I find it interesting that you support this argument with a single model run. You yourself said that you shouldn't take a single model run and go with it. Also, with your 40 years of experience, would it not make sense to you that the pretty strong +NAO defies this proposed phasing?

WeatherHistorian_SeMI said...
This comment has been removed by the author.
Anonymous said...

You proved my point, you now assume the projection of the NAO+ was right but now it is NAO-.

So which is correct? I see now you are saying your error on storm through wrong "piece of energy". But that far out; that piece of energy is developed on initial conditions which are 1- not always the best and 2-missing a lot of data NOT sampled. 3-Subject to the models errors and preference and 4-Get amplified as time go on in the run. I worked with NOAA for several decades have seen numerous models come and go. Where do you work?

Andrew said...

Anonymous: Believe it or not, I used to lean on the models full-time. Since the beginning of this year, I have began phasing out my reliance on models. This forecast is made entirely on other rules I have found over time. And yes, I did see the wrong piece of energy. That's because I was looking in the wrong part of the nation, not because of a model.