Wednesday 9 a.m.
Today's video shows how a storm developing in the Plains can bring a large swath of snow from there to the western Great Lakes. We also see how Chicago should experience rain, then a sudden cold wave with a change to snow and tricky travel prospects. The I95 corridor will have rain followed by cold, gusty winds for the weekend. Then, in contrast to what the GFS showed yesterday, a low pressure area is shown approaching the Northeast on Christmas. Stay with us as we determine the likely outcome.
During the past week, the polar vortex (large low pressure area) at the 10mb level (where pressure is only 1% of the atmospheric pressure at sea level) has migrated across the pole (see map below). The arrow on the map shows how the center has moved. Warming (see label on map) has taken place over northern North America. This is not the classic change that has been linked to subsequent extreme cold outbreaks in the central and eastern U.S. However, the same kind of change we have now (but farther north and west than this change) preceded a shift to very cold weather in Alaska earlier in the month. IF this signals a cold air buildup in central Canada, cold air could much more easily venture farther south and east than we have seen so far.
One important point: say we are seeing a signal that points to the increased chance of cold and snow in the Middle and North Atlantic states. However, keep in mind we are looking at a change that covers a pretty large area. We cannot then logically apply that to the details in a much smaller area. In other words, saying there is a greater chance of snow in the Middle Atlantic region does not tell us where the snow/rain line is in any particular storm. It cannot tell us whether Philadelphia and New York City get rain or snow while areas 50-100 miles to the northwest get all snow. It is a real stretch to claim that an overall change that affects an entire region to be able to predict specific changes over a much smaller area.
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Coastal Southeast no warmer today than some of coastal Northeast