Wednesday 10 a.m.
Yes, the headline could be interpreted as a misspelled way of writing how a New Englander might say bad karma, but there is a comma-shaped feature on the weather map, and when it passed through western Virginia, it dumped such heavy snow that more than 250,000 people lost power. As the eastern part of this swirling cloud mass reached Richmond, Va., this morning, there were thunderstorms followed by snow. This video gives the overall forecast idea for the Northeast, then I will come back to the "bad comma."
The cloud pattern in the East roughly resembles a comma, and a circular comma head is where the heaviest snow was occurring. The picture at the start of my video (above) shows where the comma was at 6 a.m. You can see that it moved a good distance between then and 9:32 a.m. when this picture was made.
I think the main forecast issue for later today, tonight and into tomorrow, is where the comma head migrates. It looks likely to graze the Philadelphia area later this afternoon (most of it passing to the southeast), passing southeast of New York City (suggesting not much snow there), then heading toward eastern New England. The Boston, Providence and New Bedford area could get some accumulation late tonight and tomorrow. The overall storm will likely change size and shape in time, so other factors will come into play. This means the storm should continue to cause wide variations over short distances. The forecast models have shown that the back edge of the precipitation will move more slowly tomorrow over eastern New England than it did farther south today.
Once the storm leaves, milder air will spread eastward from the Midwest. In Boston, the temperature may return to the 40s on Sunday and 50s Monday and Tuesday. The warmup will reach D.C. to Philadelphia during the weekend. Sunday will be the shortest day of the year because the change to daylight time means the day has only 23 hours. We might think of it is a benchmark of spring when you can take a walk after dinner with daylight for the first time since before Halloween.
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.