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Monday, Monday…

The blogpost title sounds like the beginning of song lyrics…but we’ll leave it at that.  The weather conditions will slide downhill as today progresses, culminating in rainfall reaching the Fredericksburg vicinity sometime early afternoon.  In fact a quick peek at radar shows a rain shield from the south already along the I-64 corridor with Richmond airport reporting light rain at this hour.  The timing of the wet introduction to the ‘Burg is not pinned down precisely since the first precipitation to arrive will have to moisten a fairly dry airmass (dew points are near the 50 degree (F) mark) before rain actually reaches the ground.

The surface low pressure system that is approaching from the south is evolving into a complex one that will traverse northeastward across the Ohio Valley and West Virginia mountains.  That will provide the following setup by 8:00 a.m. Tuesday morning:

As can be seen there are a lot of colorful parts to this map.  The actual low pressure center (red “L”) is shown over Kentucky and trails a purple line (an occluded front) that splits into a red line (warm front) and a blue line (cold front).  This setup – described here – will have a profound effect on our weather over the next 3 days. (The brown  lines are minor surface troughs that may also influence our weather while the green lines are areas of rain.)

The surface winds west of the warm front will be from the east and northeast and will keep a wedge of shallow and cool surface air over the ‘Burg Monday and Tuesday.   The less dense air east and south of the warm front will struggle to bulldoze the denser “cold air damming” wedge northward.  The forecast models usually have trouble depicting this so the wedge – with its low overcast and dismal conditions – typically hangs around longer than anyone wants it to.  Meanwhile the main body of moisture looks to stay west over the mountains, soaking them with over an inch of rain while Fredericksburg will see only a quarter-inch between now and Wednesday morning.  Then one of those surface troughs may trigger some showers and thunderstorms Wednesday afternoon and bring a bit more rain to the area.

Once all this mess clears the area sometime Wednesday afternoon the sun will return.  Until then the high temperature will wind up in the upper 60′s Monday, the upper 70′s Tuesday (if the warm front can push the cool air wedge out of the area early enough), and perhaps near 80 on Wednesday.  Then our beautiful autumn weather will make a grand reappearance for the latter half of the week!

Permalink: http://news.fredericksburg.com/weather/2012/10/01/monday-monday/

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