Monday 10 a.m.
A loosely organized storm in the Plains will move east and transform into well-organized, gale-producing storm off the East coast. That's the easy part. The challenge is assessing how far north the heavy snow extend. The reason that is so important is that, within a distance of about 150 miles, accumulations can range from a covering to well over a foot.
With many situations, we see a track curving to the northeast as the main storm strengthens offshore. This happens because the upper-air trough helping to support and steer the storm gets deeper, and the flow ahead of it becomes more southerly. Last night's GFS predicted exactly that, and if taken literally, suggests 18 inches of snow for Boston Wednesday night and Thursday after dumping more than 6 inches on New York City.
However, there is a blocking pattern in place over northern New England and eastern Canada. If the block holds, the storm will detour out to sea instead of turning up the coast. That's exactly what the European model predicted last night and why it projects less than inch of snow for both New York City and Boston. Meanwhile, both models predict at least 6 inches of snow for Chicago. Here's my morning video.
This map is a working draft of our snow accumulation predictions. Please check our latest videos and stories to learn more about this developing situation.
Street flooding in some of the heavier rain
Such is the stuff that generates rumors, worries or snowstorm dreams that later turn out to be unfounded.
As we close out November and start December this week, the Northeast will have two rounds of rain and a warmup.