January 31, 2011 - Brief Forecast Update

By: Mallory Brooke
By: Mallory Brooke

While the main areas of snow and ice stay to our north and west, we will still be impacted by this system. Read all about it on today's blog.

Morning everyone - was it me or was it ridiculously hard to get out of bed this morning. I tell ya, the sun sure is hiding from us lately!

So here's what we have going down over the next 48 hours. The models are doing a horrible job handling the cold air damming (CAD) as they usually do. Temperatures will continue to stay around the freezing mark, or just below, throughout much of the day Monday. Isolated areas of freezing drizzle and flurries are possible and overrunning continues.

What models agree on: Heaviest precipitation comes in early Wednesday morning and lasts through lunch time. The biggest threat areas for ice remain to our north, closer to the Mason-Dixon line.

What's uncertain: How long CAD holds on...

Temperatures stay rather stagnant through Monday, with sunshine not helping as much - true CAD setup. Overnight lows Monday into Tuesday drop to the mid 20's, therefore we're looking at freezing drizzle/flurries possible once again Tuesday as overrunning continues. Precipitation should be a tad more widespread than Monday but we won't be seeing an organized area of precipitation until Tuesday night/Wednesday morning.

This is when things get tricky. Models had CAD breaking down Tuesday afternoon as southerly winds come in, bringing temperatures to the mid to upper 30's. However, easterly winds return Tuesday night, reinforcing damming once again. The question is - can we get our temperatures back below freezing? How much influence will be brief break in damming affect us?

Keep in mind that there is still some snow pack in the Valley, and especially the higher elevations (was just on the Blue Ridge Parkway Sunday - at least 4-5" there). Snow pack and a frozen ground will influence temperatures, especially once winds subside (from southerly) and begin to switch back to easterly. Another phenomena we see in the Valley is "cold air drainage" from our mountainsides. Cold air is more dense and heavier than warm air, therefore if the mountainsides are cold, often times the cold air drains back into the Valley and the warm(er) air is displaced.

My current thoughts on the forecast through Wednesday: Temperatures stay at or below freezing through Tuesday lunch time. Isolated patches of freezing drizzle/flurries/sleet possible from today through this entire time period. I think temperatures break freezing and get into the mid to upper 30's as highs Tuesday afternoon- therefore any freezing drizzle/flurries that may have fallen would melt. Tuesday night temperatures fall back in the 30's as CAD tries to setup again. I think the southern Valley (Augusta) will hold at temperatures just above freezing (33º-35º), central Valley (Rockingham, Shenandoah, Page) with hold just at or blow freezing (30º-32º) and the northern Valley (Frederick, Clarke, Warren) will fall to the upper 20's. This being said, some areas will start out as ice as the main area of precipitation moves into the Valley early Wednesday morning. Slick spots are a definite possibility Monday, Tuesday, and Wednesday morning. Though actual ice accumulations will be minimal (<.10") if any, that's all we need to get roads slick. Any frozen precipitation will change over to rain from south to north Wednesday morning.

Of course in situations like this, forecasters will be doing a lot of "now-casting" with this storm system. Feel free to ask questions! I will update later as more model guidance comes in.

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