Wednesday, November 14, 2012

Significant Storm System Could Round Out November

A significant storm system will likely round out the month of November for the country, as my long range indicators are showing at this time. Let's jump right into this potential, and why I'm pretty confident.

Many of you have heard me talk about East Asia. Lo and behold, here she is again. This is the GFS Ensemble mean forecast anomaly for the 500mb level- the best atmospheric level to find areas of high and low pressure. While there appears to be quite a jumble of activity ongoing here at home, we're going to go across the pond to East Asia, in the upper left hand corner of this image.

If we look in the upper left-hand corner, we see a deep shade of blue encompassing a portion of East Asia. This forecast is valid for November 18. If I put the 6-12 day gap between East Asia and weather on the East Coast into this forecasted system in East Asia, we end up with a potential East US storm system hitting between November 24 - November 30. Personally, I like to err on the side of 8-10 days, to roughly November 26 - 28.

So we have now established the potential for a system to hit somewhere in the East US, but we don't know where. Let's turn to the North Atlantic Oscillation, or NAO. The forecast ensembles for the NAO take it through this current positive phase before crashing down back into negative territory in the final days of November. The ensembles are surprisingly in good agreement on this solution, which only means good things for this forecast.

For those not as educated on the technical stuff of the weather, the North Atlantic Oscillation has two phases: positive and negative. In the positive phase, warm weather commonly prevails over the East US, and storm systems are deflected out to sea, away from the East Coast. In a negative NAO, the jet stream buckles south into the Northeast, leading to cold in that region and an enhanced potential for storm systems to shoot up the coast and bring about a Nor'easter.

So now, we have established two key points: There is potential for a storm system to strike the East US, and this system (if it happens) would likely hit at a time when the NAO is negative. However, we have one more big component that you will want to see concerning this forecast.

This is the observed surface conditions in the North Pacific at the time of publishing (November 13). As you can see, there is a very strong storm system raging in the region just to the west of the Gulf of Alaska. It is a known fact that when there is a strong storm system in the Bering Sea/Gulf of Alaska (GOA) region, a storm system has been known to form in the East US about 18-21 days later.

The strength of this East US storm depends on the strength of the GOA storm, but no correlation has been established between those two factors. If we go 17-21 days out from November 13, we find ourselves between November 30 - December 4. This timeframe is a little bit away from the East Asia correlation we established. My thinking is that these two storms will end up being one storm, as model forecasts have been showing a very strong storm system in the East US during this end-of-November timeframe.

In conclusion:
•I am seeing potential for a significant storm system to hit the East US near the end of November.
•A negative NAO could make this a Nor'easter.
•The East Asia rule and Bering Sea rule apply to this situation.

It will be interesting to see how this plays out and what these two rules do for this timeframe. I will update this situation soon, probably in a couple of days unless something big comes up.



Anonymous said...


I don't think that you should move your long range forecasts to a new blog. Part of why I enjoy coming to your site is for the variety of topics. But I do think it would be great if you continue updating your Analog Directory.

Anonymous said...

Would this be rain or snow for the northeast?

Josh Herman said...

Andrew, I am curious how the EA ULL will merge with the GOA ULL when each has a different ETA in the EC. Perhaps I am digesting your words incorrectly, but it seems each correlation you mention is it's own entity, OR are they actually the same ULL just shown in different model time frames. Can you explain more?

More information on the EA or BS/GOA correlations Andrew discusses exist the AccuWX Forums. These correlations are discussed in full magnitude there.


Anonymous said...

Andrew, Is this storm for the end of november would it hit southern minnesota before the east coast?
Thanks Amy

bweather said...

I was looking at the same thing yesterday!!