Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 211256

Area Forecast Discussion
National Weather Service Blacksburg VA
856 AM EDT Sat Apr 21 2018

High pressure will be over the area through the weekend. Low
pressure will approach from the southwest Monday and slowly
track northeast to the Virginia coast by Wednesday. This will
bring widespread rain and below normal temperatures to the Mid
Atlantic region the first half of next week.


As of 855 AM EDT Friday...

Forecast updated to let freeze warning expire. Going forecast of
sunny skies and highs in the 60s looks on track.

Previous discussion from early morning...

Freeze warning remains in effect for the southern Shenandoah
Valley this morning. Temperatures will jump above freezing by
9 AM.

Surface high pressure centered along the Virginia coast, will
weaken some today, but still keep the area very dry. Morning dew
points are in the upper teens to upper 20s and with a light
southeast wind, they will increase into the upper 20s to lower
30s this afternoon. Also helping to increase humidities will be
an inverted surface trough emerging west of the Appalachains.
This trough may develop some fair weather cumulus clouds this
afternoon. Under mostly sunny skies and very dry air,
temperatures this afternoon will warm into the upper 50s to mid
60s areawide, coolest in the higher ridges.

A back-door front will stall across northern Virginia tonight.
This front will bring increasing cloudiness mainly to areas
north of highway 460. These clouds will help keep overnight
temperatures mild in the upper 30s to lower 40s.


As of 210 AM EDT Saturday...

Models still resolving the speed and track of the upper low
coming out of the Southern Plains. Expect ridging over the Ohio
Valley and Mid Atlantic region will lead to a slow eastward
progression of the upper low. Deep moisture reaches the central
Appalachians by Monday. GFS and NAM similar holding off arrival
of the precipitation until after 12Z/8AM Monday.

Best lift and upper diffluence will be Monday night. Upslope
will also be very strong Monday night and Tuesday. Butfkit
showed southeast winds from the surface through at least 5000
feet. This will bring precipitable water values of 1.0 to 1.5
inches into the foothills and mountains.

In-situ wedge develops on Monday and strengthens Monday night.
Wedge will remain in place until primary surface low advances to
the Virginia coast and winds become northwest. The wedge and
precipitation will hold maximum temperatures on Monday and
Tuesday 10 to 15 degrees below normal.


As of 300 PM EDT Friday...

For Tuesday night, the question of the timing and track of the
upper low continues. However, with the NAM not a player in the
solutions, the resultant consensus between the GFS, Canadian and
European solutions are more in line. Our rain will continue
over the area Tuesday night with Wednesday looking like the
point where we get on the backside of the system with the
precipitation transitioning to steep lapse rate showers as the
center of the low passes overhead, or close to the region.

On the heels of the Monday/Tuesday system will be a fast moving
northern stream system. Again guidance varies with this system
as well. Solutions differ as to whether or not this system is a
closed low, the GFS, an open low, Canadian, or relatively weak
trough, European. Either solutions brings its associated upper
system across our region Wednesday night through Thursday night,
thus keeping showers to some degree in the forecast. Details to
the extent can be worked on closer to the time of passage next

Our progressive pattern doesn`t end on Thursday. Yet a third
system is progged to cross the region within the northern stream
jet. This one currently is expected to be more potent than the
Wednesday/Thursday system.

Temperatures during this portion of the forecast will again be
challenging, but there is expected to be general trend toward
milder conditions comparing Wednesday through Thursday, with
slightly cooler conditions on Friday as compared to Thursday.
All days are expected to average a little below normal for this
time of year.


As of 710 AM EDT Saturday...

High pressure will control our weather through Sunday. Great
flying weather expected with high confidence for VFR conditions
and light winds.

Extended Aviation Discussion...

Clouds will begin to creep back into the area late Sunday in
advance of an approaching low in the Lower Mississippi River
Valley. However, cloud bases should remain VFR until deeper
moisture arrives Monday. SCT MVFR showers are possible in
southern Virginia and northern North Carolina Sunday night with
rain becoming widespread across the Mid Atlantic region on
Monday. MVFR/IFR ceilings and visibilities are expected Monday
night and Tuesday due to widespread rain and an upslope southeast
wind. SCT MVFR showers will continue into Wednesday.




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