Tuesday, November 13, 2012

Weekly Forecasts (Valid Nov. 13 - Dec. 5)

November 13-November 20: Warm trend continues across much of the nation. Periodic disturbances hit the Northwest and North Plains. Stormy trend begins to develop in Southeast, Northeast.

November 21-November 28: Stormy trend envelops East Coast, but positive NAO keeps much of precipitation offshore. General warm trend persists through much of nation. Watch for unusually strong systen near end of the month. Plains see a few storms during this period.

November 29-December 5: Unusually strong storm system hits country. Exact effects unknown. Cooling trend develops. A second East Coast system is not out of the question. West Coast gets a couple of storm systems.

Confidence in these forecasts: 50% - 70%


Major Thanksgiving Storm Targets Plains

Preword: Yesterday's post concerning the storm being diverted offshore was NOT the energy I was originally watching. That said, please discount yesterday's post on this Thanksgiving storm.

(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!

These ensemble members valid for Thanksgiving morning from the 12z GFS Ensembles show that a strong storm system is predicted, in strict accordance with my LRC forecast. You can tell the presence of a storm system by seeing a depression in the lines, or by a circle of green with other little circles in it. Those circles show a cutoff low, or a regular low pressure system that has been pushed out of the jet stream, hence the name 'cut off'.

Several ensemble members show this cutoff low hitting the Midwest, Plains and Ohio Valley before transitioning towards the Northeast through the next 24 hour forecast period. This means that the Plains may get the worst weather before Thanksgiving, the Midwest may bear the brunt on Turkey Day, and the Northeast may have to hunker down as Thanksgiving leftovers are slowly devoured the next couple of days.

TO CLARIFY: Yesterday's post on the Thanksgiving storm was for a different piece of energy unrelated to my LRC forecast. This storm system IS related to my forecast, and is the one I was originally calling for.

In summary:
•Major Thanksgiving storm possible for Plains-Midwest-Ohio Valley
•Snow is very possible, but the exact potential is unknown.
•I am very confident in this forecast.