... High pressure will cover the Ohio Valley and Mid Atlantic region through Saturday night along with dry weather. Sunday night through Tuesday night a deep low pressure system will track from the Gulf Coast into southeast Canada. This will bring rain and wind to the area Sunday night and Monday followed by very windy and much colder weather on Monday night through Tuesday night, along with mountain snow showers.
NEAR TERM /THROUGH TODAY/... As of 620 PM EST Friday...
A healthy deck of mid/high clouds continues to push over the region from the southwest. Expect the clouds will be thick enough to slow radiational cooling and lessen fog potential overnight. Also expect some low clouds to push in from the west late associated with a very weak frontal boundary, leaving the hilltops obscured in upslope clouds and possibly some patchy drizzle/sprinkles.
Two pieces of short wave energy within a long wave trough in the northern stream cross southeast Canada and the northeast United States tonight and Saturday.
For the Mid Atlantic region and central Appalachians,500MB heights fall slightly a the trough axis will be offshore by the end of the day Saturday.
Models were showing a strip of 30 to 40 knot northwest low level winds along the southern Blue Ridge late tonight into Saturday morning. Will be increasing wind speeds and gusts along the ridge line south of Roanoke into northwest North Carolina.
The clouds over the Middle and Lower Mississippi valley will expand into the area late this evening. Most of these clouds will clear the foothills and piedmont on Saturday so plenty of sunshine and another day with above normal temperatures. Stratocumulus will remain over the mountains through the morning, but even western slopes will clear out for the afternoon. Enough cloud cover early in the day to keep maximum temperatures close to normal.
SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/... As of 115 PM EST Friday...
Surface high pressure will jog across the region Saturday night into Sunday. The center of this ridge will move off the NC/VA coast Sunday night, leaving the western edge over the area. Overrunning moisture and rain from a southern stream complex across the southern states will then create and enhance an insitu wedge over the area Sunday night into part of the day Monday.
The southern stream complex will consist of an upper level low moving over the Red River Valley Saturday night, the Tennessee Valley Sunday and then into the Ohio Valley Sunday night into Monday. The surface low forms along the Texas coast then joins the upper level low when it is in the Tennessee Valley. This system becomes occluded over the Ohio Valley Sunday night into Monday. A northern stream upper level low over the Great Lakes will phase with the southern stream system on Monday to create a new colder closed lower over the Ohio Valley. This system will slowly move to the northeast Monday night into Tuesday.
This Sunday night into Tuesday system is not only complex but brings a multi-faceted range of weather features along with it.
1) Strong Dynamics and a negative-tilted trough will interact with an eroding wedge to possibly bring rotating storms and heavy rain to the area Sunday night into Monday morning. Models current have a triple point tracking in the vicinity of Southside VA which supports a strong convection case. Rainfall amounts could average 1-2 inches along and east of the Blue Ridge, under an inch along western slopes. On the other side of the coin, models have a habit of eroding the wedge to quick in our neck of the woods. If a line of convection across the southeastern states is strong enough, it may rob moisture coming into the area. If this does happen, heavy rain chances will be lower and the wedge may hang around a little longer.
2) A dry slot is expected over the area Monday afternoon. By this time the wedge should be gone with temperatures jumping into the 50s and 60s. These temperatures seem cool, but are warmer than normal for the end of November.
3) Phasing/Merging of the northern and southern stream lows will combine Gulf moisture with very cold air to have rain changing over to snow across the mountains Monday night. 850H temperatures drop below 0C through the afternoon. However 1000-850 MB thickness remains above 1300m into the early evening. This suggest the change- over to snow will start in the higher elevations first. Lower elevations may see snow starting to fall, but will melt on contact through most of the evening, some of that is due to a warm ground.
4) The closed low over the Ohio Valley will slowly move to the northeast Monday night into Tuesday night. With temperatures remain at or below freezing, accumulating snow across the mountains will occur through the period. Being under the deformation zone and upslope longer than anyone else, western Greenbrier should see the highest snowfall totals for Blacksburg CWA.
5) A 40kt low level westerly jet could bring gusty conditions to the area Monday night into Tuesday. However, extensive cloud cover should keep these gusts above 3000 ft. The stronger winds will occur Tuesday night as pressure rises behind the departing low. Models are also advertising a 50kt cross-barrier jet along the Blue Ridge.
LONG TERM /TUESDAY THROUGH FRIDAY/... As of 145 PM EST Friday...
The upper level low will be moving to the northeast Tuesday night into Wednesday. Snow showers and windy conditions will eventually give way to sunshine and warming temperatures Thursday. However, rain returns to the region on Friday as warm air overruns another surface wedge.
The coldest time in the period will be Wednesday morning with lows in the 20s, wind chills values in the teens. The wind will subside some on Wednesday but remain cold with highs in the 30s west of the Blue Ridge to the 40s east. Temperatures moderate a few degrees each day but remain colder than normal Thursday and Friday.