Windblown Snow Spreads From Maryland to Maine

Tuesday morning

A storm centered in extreme southwestern Virginia at midmorning will be southeast of Cape Cod at sunrise tomorrow. With the storm adding moisture and a steady stream of ice cold air feeding in from eastern Canada, a substantial accumulation of dry, powdery snow will cover the I-95 corridor from northeastern Maryland to eastern Massachusetts with 6- to 12-inch blanket. Along the eastern New England coast, gale-force gusts will combine with the snow to create blizzard conditions. This map shows the pressure pattern across the Northeast at 10 a.m. ET.

This early-morning video shows how things should unfold during the next few days.

One tool I like to use in snow amount predicting sounds ridiculous. You look at a 200 mb map. At that high level, troughs are warm and ridges are cold, the opposite of the arrangement at 500 mb. I look for the warmest reading in a trough and the coldest temperature in the downstream ridge, then draw a line connecting them. I take the difference in readings and divide by two to get an accumulation estimate in inches. You can see why that seems ridiculous: how can a Celsius temperature calculation miles overhead give an estimate of snow accumulations in inches? I have found it helpful over the years. I won't use it for a specific accumulation forecast, but it is a guideline. Also, if we are thinking that a storm will bring a lot of snow, but the temperature spread from trough to ridge is small, it is a red flag suggesting we could go overboard on accumulations. Here is a map showing the arrangement this morning. Since we are making a forecast, I look at the downstream end of the line as being the area where this method may work best.

In this case, 7 inches is the predicted amount. Realize, of course, a tool like this cannot help with fine scale details within a storm, cannot handle changes in the flow pattern with time, cannot anticipate the effects of mountains and oceans, cannot help with the snow/rain line, etc., etc.