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FXUS61 KRNK 260739

Area Forecast Discussion
National Weather Service Blacksburg VA
339 AM EDT Sun Mar 26 2017

A series of low pressure systems will bring unsettled weather
with a good chance for showers and thunderstorms, mainly west 
of the Blue Ridge, through Tuesday. Temperatures will remain 
well above normal with a gradual warming trend bringing high 
temperatures well into the 70s through the first part of next 


As of 315 AM EDT Sunday...

Satellite imagery and surface obs indicate mostly mid/high
clouds over the region. However, radar shows precipitation
associated with an approaching low pressure system is not far
off to our west. This stacked low will move from the 
Mississippi valley into the Great Lakes region and push a 
frontal system into the area from the west. The aforementioned
precipitation will spread across locations west of the Blue
Ridge this morning with just a chance of showers spreading east
of the Ridge by later this afternoon. Instability is largely 
absent but modestly steep mid/upper lapse rates may be able to 
support some rumbles of thunder.

As the closed low opens and slides by to our northwest we will
get into some shallow upper ridging that will lessen any dynamic
forcing to support widespread showers. However fairly deep
moisture will remain across the region and allow orographic
affects in the southerly flow to continue a chance of showers 
mainly along and west of the Ridge through Sunday night.

Highs today will be a good 5 to 10 degrees above normal with
lower 70s in the east to upper 50s/middle 60s in the west.


As of 315 AM EDT Sunday...

Both the 00z GFS/ECMWF seem to be in fairly good agreement with the 
5h pattern with some minor differences with the surface and precip 

Monday still looks like to be cloudier with some low level 
convergence working across the mountains, so will still see some 
showers and isolated thunderstorms developing namely in the 
mountains. Temperatures despite the cloud cover rise to the mid to 
upper 60s mountains to lower to mid 70s foothills/piedmont.

Surface front and upper shortwave enter the mountains by 12z Tuesday 
so increasing threat of showers and some thunderstorms late Monday 
night in the mountains, with coverage increasing along and east of 
the Blue Ridge after 8am Tuesday. Some forecast differences shaping 
up Tuesday afternoon, since both 00z models showing a faster drying 
solution starting to move in from the southwest. Will leave high 
chance to low likely pops mainly along and north of a Bluefield-
Pulaski-Chatham line, but will see less coverage over the NC 
mountains/foothills/piedmont after 2-4pm.

Sfc low somewhat weak, but as the low moves across, the 8h jet of 30-
35kts with some westerly flow along/behind the front should bring 
some gust to 20-25 mph. High temperatures dependent on sunshine and 
showers, thinking the piedmont will see potential for some sunshine 
more than the mountains, with even better chance of more sun 
arriving in the NC foothills in the afternoon. Warm temperatures 
overall with highs in the mid to upper 70s east of the Blue Ridge, 
with upper 60s to around 70 in the mountains.

Brief period of residual showers across the Appalachians Tuesday 
night with drying elsewhere. Frontal boundary will shifts to the 
coast by 12z Wednesday, but extends west into the Gulf Coast States. 
Meanwhile, high pressure over Ontario will build southward into the 
TN valley. This high shifts east Wednesday into Wednesday night, 
with a battle between drier/cooler air north and more moist air 
south. Will start to see lower dewpoints work in Wednesday afternoon 
on a north to northeast wind. Not out of the question  to keep some 
clouds around, especially across the NC mountains/foothills with 
sprinkles possible. Wednesday night, the flow in the low levels 
should turn more southeast, and cannot rule out the chance for 
showers to develop along the southern Blue Ridge and adjacent 
foothills from Floyd to Boone.

High temps Wednesday will mild, though if there is more clouds we 
could be cooler. For now going with lower to mid 60s mountains, to 
lower to mid 70s foothills/piedmont.


As of 400 PM EDT Saturday...

Mainly dry Thursday outside some showers over the southern Blue
Ridge in the morning, with some increasing moisture after 00z
Friday in the southwest Virginia area.

By Friday, the next, and fairly potent, upper low tracks toward
the area. However, there is considerable discrepancy between 
the GFS and the ECMWF in the configuration and timing of this 
system into the eastern U.S. The GFS depicts more of an open 
wave reaching the CWA as early as Thursday night moving east of 
the area by Friday afternoon. Meanwhile, the ECMWF is much 
slower, deeper, and further south with a cutoff upper low 
lifting it slowly north-northeast into the Ohio Valley by late 
Friday. The difference between the two models can be accounted 
for in noting the strength and blocking of an upstream ridge 
across the Atlantic. This upstream ridge is much stronger per 
ECMWF, which also depicts a notable wedge down the east side of 
the Appalachians as the closed low lifts north into the Ohio 
Valley. The ECMWF would result in a much wetter and stormier 
pattern for the CWA, although it would not arrive until Friday 
as opposed to Thu night per GFS. For now, have generally broad 
brushed the area with high chance to likely pops beginning Thu 
night and continuing into Friday. In addition to the differences
noted above, there are also massive differences between the two
models regarding instability and the potential for severe, with
the ECMWF much more noteworthy in this category. For now, have 
included a chance for thunder without any further details. It 
will likely take several runs for the models to resolve their 
differences on this system. Another system is slated to follow 
by the end of the weekend or the beginning of the next week, so 
the active pattern is expected to continue into the next week.

Temperatures will be closer to normal Wed-Thu, then begin to
trend back to above normal levels Fri-Sat.


As of 235 AM EDT Sunday...

A slow moving stacked low pressure system will move from the 
Mississippi valley into the Great Lakes region and push a 
frontal system into the area from the west. This will allow us 
to start Sunday with VFR at TAF sites, followed by precipitation
spreading westward across the area and a trend for lowering 
cigs to MVFR by the afternoon along and west of the Blue Ridge. 
The downward trend will continue as we head into Sunday evening 
with MVFR spreading east of the Ridge and IFR setting in to the 
west, but any significant obvis looks to hold off until after
this TAF period. Instability is largely absent but modestly 
steep mid/upper lapse rates may be able to support some rumbles 
of thunder. However, believe the expected chances and coverage 
of thunder is quite low so will not include any mention in the 
TAFs. The low level wind field will be amplifying west of the 
Blue Ridge as the low approaches and this will create some gusty
conditions but wind speeds do not appear as if they will pose 
any significant issues for aircraft.

Extended Aviation Discussion... 

An active weather period with a series of vigorous upper-level
low pressure areas tracking from west to east across the U.S.
during the week. Monday the area will be between systems, but a
moist/unstable air mass will remain in place and widely 
scattered showers and isolated thunderstorms are possible. Areas
of sub-VFR cigs/vsbys are also possible, especially during the 
morning hours, in low clouds and fog. The next upper-level low 
will arrive Tuesday with another chance for showers and 
thunderstorms along with periods of sub-VFR conditions. 
Wednesday-Thursday may bring a period of improved aviation 
conditions as a weak cold front temporarily pushes the deeper 
moisture south of the area. However, by Friday the next in the 
series of upper-level systems arrives with another chance for 
showers, thunderstorms, and sub-VFR conditions.





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