Friday, January 14, 2011

Light Icing Possible Monday Night

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.

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