Area Forecast Discussion
Issued by NWS Blacksburg, VA

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184
FXUS61 KRNK 261523
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
1123 AM EDT Sun Mar 26 2017

.SYNOPSIS...
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
week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1100 AM EDT Sunday...

Radar indicated a 30 mile wide band of rain showers propagating
east across the western CWA. As of 11AM the leading edge was
along the I-77 corridor. Movement was to the east at 20 mph.

Rain band was associated with a front aloft, extending N-S from
Low pressure moving through the western OH Valley and into the
Great Lakes. The actual surface front was over western KY/TN, so
this initial rain band has outrun any surface instability and
has been weakening with time. Rainfall amounts have been
averaging about a quarter of an inch, but think as this band of
showers moves east, the overall qpf will diminish with amounts
of a tenth of an inch. Timing suggests these showers will reach
Highway 220 corridor...Clifton Forge, Roanoke, Martinsville,
Reidsville between 2-3PM.

Once the initial front aloft passes and the showers come to an
end then clouds will thin with instability driven showers
increasing across the KY/TN ahead of the actual surface front.
These showers and potential for thunderstorms will approach from
the TN valley late in the afternoon with primary impact to areas
west of I-77 after 5PM.

As the main upper level low slides by to our northwest tonight,
dynamic support will decrease. The actual surface front is
forecast to wash out before crossing the mountains so this will
maintain a persistent southerly flow across the forecast area
overnight. As such, there will be a continued chance of showers
mainly along and west of the Blue Ridge overnight, although
nothing severe per waning instability.

Temperatures this afternoon will be warm with highs 5 to 10
degrees above normal with lower 70s in the east to upper
50s/middle 60s in the west. Temperatures tonight will also well
above normal with lows mainly in the 50s.

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/...
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
output.

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.

&&

.LONG TERM /THURSDAY THROUGH SATURDAY/...
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.

&&

.AVIATION /15Z SUNDAY THROUGH THURSDAY/...
As of 725 AM EDT Sunday...

Should see VFR cigs/vsbys for most taf sites this morning, with
some period of MVFR cigs near BCB/BLF.

A slow moving stacked low pressure system will move into the
Great Lakes region and push a frontal system into the area from
the west. This will increase our shower threat, mainly
along/west of the Blue Ridge from late morning into this
evening. As such will start seeing cigs lowering toward low end
VFR into MVFR by early afternoon BLF/LWB/BCB, and into ROA after
00z. For now, not expecting LYH/DAN to drop to MVFR or lower.

Overall should see VFR vsbys with lighter showers, though some
MVFR is likely in BLF/LWB and BCB at times this afternoon.

Cannot rule out some thunder in BLF/LWB but overall threat is
too low to have in TAFS.

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.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...None.
NC...None.
WV...None.

&&

$$
SYNOPSIS...MBS
NEAR TERM...PM
SHORT TERM...WP
LONG TERM...PM/RAB
AVIATION...MBS/WP



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