Friday, January 14, 2011
The storm system arriving Monday night will be mostly rain for central Virginia, but there continues to be a decent signal for some freezing rain (glaze of ice) in areas just north and west of Richmond. High pressure will keep a cold and dry airmass in place across the Mid-Atlantic due to cold air damming, or a "wedge" effect. Cold, dry air is dense and hugs close to the surface. When high pressure is situated over New England, the counter-clockwise flow around the high funnels this air down the east side of the Appalachians, and in some cases, as far southwest as Alabama. Moisture from the approaching storm system will ride up and over this cold air, creating a favorable environment for freezing rain. Models don't handle low-level cold air very well, so I am undercutting their guidance temperatures a good bit. The freezing rain will change over to all rain Tuesday morning as strong warm air advection boosts temperatures in the lower atmosphere well above freezing.
Meteorologist Carrie Rose explained on Friday's edition of Virginia This Morning some of the weather and climate patterns that can and are influencing our Winter of 2010-2011 so far. December 2010 for Richmond was the 7th coldest on record, and average temperatures so far in January 2011 have been running about 2 degrees colder than normal, which isn't as drastic as December, but certainly continues the cooler-than-normal temperature pattern. We also already have recorded 10" of snow at Richmond International Airport, when an average entire snowfall season will produce about a foot of snow (11.7" average 1971-2000, or 13.0" average 1897-Present Day). You can watch the video of Carrie explaining this by clicking here. Here's a hint: this graphic explains the dominant atmospheric pattern influencing our weather much of December and January.