Friday, November 18, 2011

18z GFS Keeps Potential Northeast Thanksgiving Storm Offshore

Today's 18z GFS has kept the storm system to the south, more south than the 12z GFS. In this solution, precipitation would be kept to a minimum and snow accumulations would be lighter. We just checked individual GFS Ensemble members and found that only 2 of 12 members forecast snow in the region. Check stats below.

Ensemble members forecasting snow (out of 12 members)
0z GFS- 9/12 (75%)
6z GFS- 11/12 (92%)
12z GFS- 5/12 (42%)
18z GFS- 2/12 (17%)

We are not buying the idea of a snowstorm, but if enough cold air can be in place, I would expect MAXIMUM totals of 4 inches. This, of course, is subject to change as we are over 5 days out from the possible storm.

Long Range Forecast- 8 Days Out

Temperature Anomalies over next 8 days
Temperature Anomalies over the next 10 days are looking warmer than usual across the heavy majority of the country. This is not surprising at all, as teleconnections remain in horrible positions to provide some colder air for the country. The Northwest and portions of the Rockies may experience some cooler than normal temperatures. As systems move across the US, it is expected that warm air will rush up north out ahead of the storms, and with no intervention of colder air, I do expect the above image to verify.

Precipitation Anomalies over next 8 days
Precipitation anomalies over the country will be mainly below normal for the flatlands of the US (areas not mountainous, where precipitation can fall without provocation by a weather system). The Plains and Midwest will be in the midst of a dry spell, with this image indicating that the percent-of-normal anomalies will be at 25% or below for the Plains and Midwest. A storm system dragging Gulf moisture with it will create a wet situation in the nation's midsection and South Plains, with the system eventually affecting the Northeast. This system will keep anomalies steady, even above normal. Florida will be below average.

System Projected to Produce North Plains Moving Onshore

500 millibar heights indicate the system forecast to produce accumulating snow over the North Plains is moving onshore. This system will move over the North Rockies, weaken, and swiftly move across the North Plains to produce accumulating snow. Tonight's 0z Models should provide the 'final' and most accurate estimates for accumulating snow.
As for right now, today's 12z GFS shows lower amounts than our previous post where the GFS was estimating over a foot of snow possible for extreme SW South Dakota. Below is the 12z maximum snow depth forecast.
The extreme SW South Dakota will still have a very isolated spot of a foot or possibly more, while the rest of South Dakota will range from 1 inch to 5 inches. Minnesota and Wisconsin will get less snow than is currently forecast, but it will depend on how strong the system is when it crosses the Rockies.

ECMWF Prints Heavy Lake Effect Snow for Thanksgiving

The ECMWF model is forecasting some heavy snow to fall over the Northeast the day before and going into Thanksgiving. We are hesitant to believe this, especially as the teleconnections will be unfavorable for any cold weather, and the GFS is forecasting an inch at best. However, the ECMWF and GFS both predicted the Halloween Snowstorm in the long range, so at this point it's more in depth than the teleconnections. We will have a briefing this afternoon on the unfolding situation.