Saturday, November 10, 2012

Major Thanksgiving Storm Likely For Midwest, Great Lakes

I am making the call for a major Thanksgiving storm system (likely with snow) to hit the Midwest, Great Lakes, and possibly the Plains and Northeast. Let's take a look at why I am now making this call.

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!

I think it's time we turn to the models to see what they're saying. This is the morning forecast from the GFS model for Thanksgiving. This image shows precipitation over a 12 hour period, as well as MSLP lines. The pink line is the rain/snow line. Any precipitation above that line would be snow, and precip. below the line is likely to be rain. The GFS is forecasting a pretty strong storm system to be present across the Midwest/Great Lakes on the morning of Turkey Day. While the GFS has been juggling the position of this storm system, it has been forecasting a strong storm system in the general East US on Thanksgiving.

As you can see in the above forecast, there is a lot of color above the pink line. Yes, this would mean snow. However, because all I am confident in is the presence of a storm in the mentioned regions, I don't think now is the appropriate time to make calls on precipitation. However, if there is to be precipitation, it will most likely focus in on the Upper Midwest and Great Lakes.

This is likely to be the most accurate forecast for this system if we rely on the LRC, but any East US forecast with a strong storm system could verify if we use only the East Asian theory. Personally, I think it's a good idea to combine the two and use the GFS forecast above (which will definitely change in coming days).

Let's sum this all up:
•I am making a call for a storm system on Thanksgiving Day.
•This system will hit the Midwest, Great Lakes, and Northeast.
•Snow is likely, possibly heavy in some areas.
•Cold weather will follow the system.


ENSO Update: El Nino Lurking Beneath The Waters

The ENSO state as of now remains troubled, with a large expanse of warm waters below the surface, but very little amounts of warm water are actually reaching the surface, where it matters.

The image above shows the latest observed underwater temperature anomalies. Above normal temperature waters are shown in yellows and oranges, while cooler waters appear in blues. At about the 100-200 meter zone, there is a big body of above normal water to the east of the 180 longitude line. That puts this warm body of water roughly in the Nino 3.4 - Nino 3 regions, known as the area most used for identifying the ENSO state. While this body of water may look pretty strong, observe the cool body of water just developing between 50-300 meters below the surface to the west of the 180 line. This cooling trend has just started developing, and based on an animation of underwater temperature anomalies, this cooling trend should continue. That would eat away at the warm body of water, especially in the Nino 3.4 region.

There is a second warm body of water between the surface-150 meter mark, which is more compact and appears more likely to move to the surface. However, just as the aforementioned body of water is having trouble, this second above-normal body of water is also struggling. If you see the upper-right corner of the picture, you can see a small pocket of much below-normal temperature anomalies. That is just off the coast of South America on the Equator. This pocket of cold water is also eating away at the warm waters, but I have more confidence that this body of warmth will propagate to the surface rather than sit underwater and be slowly eaten away by the cool waters, like what is happening near the 180 longitude line.

Observed sea surface temperatures as of Halloween show pretty much what I was diagnosing in the underwater section below. We can see a warm body of water on the surface to the west of the 180 longitude line, while there is a general mess of above and below normal anomalies to the east of the 180 longitude line. In other words, the areas to the east of this line are undetermined as far as the ENSO state goes.

I expect a warming trend on the surface, focused between the 140-100 W longitude lines as the warm body of water tries to move towards the surface. Cooling is likely just off the immediate S. American coast on the Equator, as the cold pocket I explained above could very well bump up to the surface.

Seeing as the CPC cancelled their El Nino watch (as was widely expected), and the first days of November bring about an undetermined ENSO state, I expect this unknown state to continue through the month of November, possibly in to December. This possibility for December will ride on what the big body of water I mentioned first does.