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.


Coastal Storm Will Not Affect Northeast Next Week

Models have been showing that a strong storm system may develop on the East Coast at the beginning of next week, and some agencies have been putting out warnings on how this system will strike the Northeast. I believe that this storm system will keep itself offshore, just as the above ECMWF model forecast is indicating.

This is the North Atlantic Oscillation forecast for the next couple of weeks from the ESRL/PSD agency on the left, and the NCEP agency on the right. I prefer the ESRL/PSD forecast, because all the NCEP forecast is is the GFS and its ensembles, while the ESRL/PSD has its own individual ensembles, apparently not relied on by any given model.

For those new to the NAO, here's a quick breakdown of the effects the NAO has: 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. If these storms would have gone north along the East Coast, they are known as  Nor'easters (commonly seen in a negative NAO).

If we use those rules of thumb on the NAO and apply them to the above forecast, we see that the NAO will be neutral/going negative around the 21st, when this storm would supposedly be the strongest while still maintaining a fair distance from land. However, what many do not know is that there is a 4 day lag between the NAO's change and the effects the NAO then has. If we apply that rule to this situation, we then see that the NAO would begin to show signs of its negative phase around the 25th-27th, well after this storm system is out of the region.

In conclusion:
•A coastal storm may develop along the Southeast in coming days.
•This storm system will be diverted out to sea, not affecting land.