Archive for January 9, 2011


Yesterday’s snow squalls were quite impressive. The snow fell heavily for brief periods. The snow bursts were caused by a very cold air aloft causing extreme instability in the atmosphere and literally squeezed out the existing moisture that was in the atmosphere Saturday afternoon. Cold air cannot hold as much water vapor as warm air, so the water vapor precipitates out into snow. This phenomenon is more common up to our north and west. These upper level disturbances were moving around a large polar vortex over New England. Sunday should be sunnier but it will still be a bit breezy. The winds should relax on Monday.

As I stated in my previous post, a major winter storm seems likely for the Mid and North Atlantic States on Tuesday. However, the exact details of where the heaviest snow will be and what areas will see rain mixed in (or possibly all rain) need to be worked out. This storm is really going to be a major forecast challenge as there are so many factors that have to be considered with this system. Here’s what forecasters think is going to happen. A low pressure area is going to develop in the Northern Gulf of Mexico on Monday. This cyclogenesis will be caused by an upper level disturbance moving eastward across the deep south. The low will move northeast towards the Carolina coastline. This low pressure system will be quite complex as upper-level energy may cause another low to develop further inland. That will complicate an already complex situation. This system will spread a wintry mix of precipitation across the Tennessee Valley on Monday. The exact track of this system will determine what type of precipitation Hampton Roads receives. If the low tracks further east, snow will be more likely but if it tracks too far offshore, then dry air could reduce precipitation amounts, especially to our north and west. If the low tracks further west, then warmer air will be drawn into the system causing rain instead of snow. Also, with the other low pressure system forming further inland, it could pull in warmer air aloft changing the snow to rain on Tuesday. (See my Weather Fact on why snow is so hard to predict here in Hampton Roads). The low pressure systems are expected to consolidate off the coast of Long Island and really blast Southern New England with a blizzard or near blizzard conditions. NYC may be under the gun again for heavy wind driven snow, just what they really need.

Please monitor your local media and the National Weather Service (NWS) for updates, advisories and warnings that may be issued for the period Monday night through Tuesday night.

 Thanks for reading.

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