Area Forecast Discussion
Issued by NWS Blacksburg, VA

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487
FXUS61 KRNK 150800
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
400 AM EDT Tue Aug 15 2017

.SYNOPSIS...
Upper disturbances move over the area today, with a stalled
frontal boundary in place. This front shift southeast tonight,
with high pressure shifting over the Mid-Atlantic Wednesday. A
cold front moves from the Midwest Thursday into the Appalachians
Friday.


&&

.NEAR TERM /THROUGH TONIGHT/...
As of 330 AM EDT Tuesday...

Scattered to numerous showers early this morning from WV/SW VA east
to the piedmont. This is occurring along sfc boundary with wave of
low pressure over KY/TN, interacting with pwats over 2", as well as
a couple of vorts from TN to western NC.

Will see greatest concentration of showers over the piedmont of VA
and from the Mountain Empire north toward Greenbrier this morning.

Overall high-res solutions painting a wet morning for most of the
forecast area. Once main axis of upper level energy shifts east of
the mountains this afternoon, should see decreasing threat over the
mountains, then this evening in the east, though some of the high-
res models pushing batch of showers east of the WV mountains/far SW
VA by 12z this morning. Given radar trends, should be close.
Nonetheless 50 pops to 80 pops warranted with highest along/east of
the Blue Ridge. Again, hedging on whether we get sun this afternoon
or not, and high-res models showing some breaks, so instability
should increase with help of upper vort to allow thunderstorms to be
isolated to scattered, or embedded in the main area of showers.

Should see skies clearing tonight from the northwest as deeper
moisture shifts to the east/southeast, though how far given
Hurricane Gert further east slowing thing movement of the front
down. Gert should be pushing back out toward the northeast late
tonight allowing this to happen. Another shortwave skims across the
TN/NC tonight which may keep showers isolated along/south of the
NC/VA border.

With clearing skies, light winds, and moist ground look for more fog
late tonight into Wed morning.

Highs today a few degrees warmer than Monday since wedge erodes, but
still a few degrees below normal, with mid 70s to around 80
mountains, to lower to mid 80s east.

PWATS are expected to drop off some late tonight, and should see
lows still held up some, with lower to mid 60s mountains, to upper
60s to around 70 east of the Blue Ridge.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
As of 245 AM EDT Tuesday...

Another surface high will drift over the northern Mid Atlantic
Wednesday and wedge south into the Carolinas Wednesday night.
Upslope flow across North Carolina High Country may be enough to
spark some storms late in the afternoon. Weak steering flow will
have any storms drifting east over the foothills in the evening,
then fading by sunset. Storms are also possible along the SW VA Blue
Ridge in the afternoon. However, mid level cap is lower, therefore
storms will have a tough time developing or be short-lived. The
wedge boundary should not advance into the area until the evening,
therefore temperatures Wednesday will warm to or a few degrees above
normal. Shallow wedge comes sliding across the region Wednesday
night. Easterly flow will bring some low deck clouds into the
region, but models look to dry and stable for any precipitation
overnight.

A cold front is expected to move from the Midwest Thursday to the
Appalachains Friday. Pressure falls Thursday will erode the wedge by
the afternoon. Prefrontal short waves will then bring the first
round of storms into the region Thursday afternoon and evening. The
next round will be with the passing of the cold front Friday.
Thursday looks to be the better of the two day for strong to severe
storms to pass over the area. If Thursday`s activity is lack luster,
then Friday may be busy. Temperatures Thursday will warm above
normal with mid to upper 80s west of the Blue Ridge to the lower 90s
east. Similar temperatures expect Friday but could be cooler
depending on timing of the frontal passage.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
As of 312 PM EDT Monday...

Cold front finally moves across the forecast area Friday night. A
considerable amount of variance exists in the 12z GFS and ECMWF
solutions for the weekend, particularly on if the front makes a full
clear across VA or if it hangs around/stalls and picks up tropical
moisture keeping our eastern and southern counties wet. Adding to
this uncertainty is the timing of a mid-level disturbance in the
northern stream across the Great Lakes region. Therefore, kept at
least 15-30% PoPs east of the Blue Ridge for the weekend until less
variability in guidance becomes apparent. Stayed close to a blend of
guidance for highs and lows which keep temperatures near typical mid-
August levels. A potentially warmer period is indicated by the GFS
and ECMWF early next week as a broad heat ridge dominates much of
the Plains and into the Ohio Valley.

&&

.AVIATION /08Z TUESDAY THROUGH SATURDAY/...
As of 130 AM EDT Tuesday...

Poor flying conditions expected across the entire region this
morning with periods of showers heavy at times, especially in
the Danville area. When showers occur vsbys could drop to IFR
1-3sm, with cigs around 1-3kft. With lighter showers or none,
expect some vsbys to sink below 1sm, and confidence not high
enough to go this direction except perhaps LWB/BCB/BLF. Cigs
will also drop below 1kft. Overall sub MVFR with LIFR thru at
least 12-14z, then should start to see cigs/vsbys edge up to
MVFR at all sites in the 14z-17z time frame, then VFR
afterwards, except lingering MVFR through mid afternoon at
LYH/LWB/BCB.

Greatest rainfall threat looks to occur through 15z today, then
afternoon coverage looks less in the mountains, with better
coverage in the piedmont. For now kept VCSH this afternoon east
of the mountains, however, thunder is possible.

Extended Aviation Discussion...

Widespread fog is again expected late Tuesday night as we clear
out some,with dense fog possible. Wednesday into Thursday the
frontal boundary to our south will meander north and south for a
bit until such time the departure of Hurricane Gert allows the
front to be shunted to the southeast. While the front is in our
proximity, daily scattered precipitation and rounds of sub-VFR
conditions are probable. Late night/early morning mountain and
river valley sub-VFR fog will be possible.

Friday into Saturday, we look to our northwest for our next
approaching upper level system. This one will bring a cold
front into and through the area Friday night. Look for an
increase in precipitation on Friday with storms possible during
the afternoon and evening. Sub-VFR conditions will accompany
the heavier showers and storms, and also persist in the form of
late night and early morning fog heading into Saturday morning.

&&

.EQUIPMENT...
As of 755 PM EDT Saturday Aug 12th...

KFCX doppler radar will continue to be down for the rest of the
month due to a failing bull gear. It will only be operational
during this time frame for brief periods if an imminent
significant widespread severe weather and/or hydrologic event
occurs. Operating the system for any amount of time until the
bull gear is replaced risks a catastrophic failure that would
further extend system downtime. From the 17th through the 27th
the radar will most likely be down completely as the repairs
are expected to be made during this period.

&&

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

&&

$$
SYNOPSIS...DS/WP
NEAR TERM...WP
SHORT TERM...RCS
LONG TERM...AL
AVIATION...AMS/DS/WP
EQUIPMENT...RAB/WERT



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