Monday 9:45 AM
A storm crossing the Gulf states dropped heavy rain over a wide area, and the moisture is moving northeastward. However, the upper air trough supporting the rain is shown to weaken slowly on the computer model (I use this term interchangeably with numerical forecasts) maps, and so places in the Northeast should not match the Gulf states in the rainfall amount department. One thing that is apparent is with a persistent flow from the Gulf states to New England, it will be warmer than average for this time of year.
Last week at this time, I showed a GFS forecast map for Oct. 10 that suggested it could snow in central and northern Pennsylvania. I suggested the model would change looks over time and, in fact, the very next run has a warmer look and no snow. On the other hand, a typhoon re-curved over the western Pacific, and this kind of event has often been followed by an upper air trough n the East about 10 days later. The most recent runs of GFS has trended toward this trough in the East scenario, and this suggests next week will be quite a bit cooler than this week (with the first push of cooler air arriving this weekend).
The numerical forecasts (I use this term interchangeably with computer models) for next week will certainly change in various ways before next week arrives, but there are hints that the higher terrain downwind from the Great Lakes could get their first snow showers of the season next week. This map for next Thursday shows a close call setup for this:
Meanwhile, my daily video shows what we can expect this week:
Looking at next week, the GFS ensemble spaghetti plot of upper air winds shows how much agreement there is among members of the ensemble (same model running multiple times using slightly different starting assumptions). The maps are from next Tuesday, Nov. 25, and Thanksgiving Day, Nov. 27. There is good agreement on the first map, but a lot of spread two days later.
The location of lake-effect snow bands is tightly controlled by geography, topography and wind. From this pressure analysis, we see why the wind favored heavy snow staying south of the hardest hit Buffalo snow belts earlier today.
If this timing works out, there would be good travel weather for the Northeast Corridor on Wednesday while snow showers cross the Great Lakes and reach the northern and central Appalachians.
This map from one of my tweets yesterday (accuElliot) showed the wind direction most favorable for heavy lake-effect snow in and near Buffalo. Just a minute change in direction greatly affects the location of the heaviest snow, almost as if you were operating a fire hose. The snow is so deep (more than 4 feet in spots and deepening) that officials were considering the use of high lift equipment to extract vehicles.
It suggests rain in the I-95 corridor and snow from the mountains of West Virginia and Pennsylvania to southwestern Maine. Other models and ensemble versions will be examined this weekend as we narrow down the uncertainties associated with this fast-moving storm. Whatever the form of precipitation, you can count on another shot of cold air behind it. Lake-effect snow will be common as well.
I can see how slippery spots can develop from Philadelphia's northern and western suburbs on northeastward. The highest amounts of snow may be from Boston's western and northern suburbs on through Portsmouth, Portland and Augusta. Some spots could get 3-4 inches. Be ready for a slow commute tomorrow morning. If these problems develop, they could occur rather suddenly.