Area Forecast Discussion
Issued by NWS Blacksburg, VA

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242
FXUS61 KRNK 270615
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
215 AM EDT Thu Apr 27 2017

.SYNOPSIS...
High pressure will build across the southeastern United States
resulting in a considerable boost to the temperature with above
seasonal warmth expected by the weekend. An increase in southwesterly
wind flow will bring enough moisture back into the area by late
Thursday to promote widely scattered afternoon and evening showers and
thundershowers over the mountains.

&&

.NEAR TERM /THROUGH TODAY/...
As of 710 PM EDT Wednesday...

With low pressure off the middle Atlantic coast pulling away and some
ridging aloft, expect quiet weather to prevail through tonight. Believe
there is enough ground moisture from recent rainfall to help moisten
the boundary layer and generate some patchy valley fog toward
daybreak. For Thursday, despite most energy guidance is becoming
a bit more enthusiastic and faster with the cold front
approaching from the west tomorrow. Precipitation will hold off
until the afternoon and there looks to be enough instability and
some shear to support some stronger storms/clusters. Have
bumped POPs up to high chance/likely to reflect this thinking.

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/...
As of 410 PM EDT Wednesday...

Unseasonably warm, summerlike weather expected with the potential
for showers and thunderstorms especially along and west of the Blue
Ridge Mountains heading into the latter part of the week.

Showers and thunderstorms will move east across the region Thursday
afternoon into Thursday evening. Partly cloudy conditions will
prevail Thursday night into Friday morning. Low temperatures
Thursday night will range from the mid 50s in the mountains to the
60s in the Piedmont.

Friday and Saturday feature the re-establishment of an amplified mid-
level ridge across a large part of the Southeastern CONUS.
Meanwhile, a mid-level trough will dig and deepen over the Four
Corners Region. The closed low will slowly edge northeast towards
the plains this weekend. A surface low develops in Texas Friday and
travels northeast into Saturday night. A warm front extends eastward
from the low center in the Ohio Valley, followed by cold front
trailing south. The frontal boundaries will serve as a trigger for
showers and thunderstorms.

On Friday, the air mass in low-levels is relatively capped, progged
instability aloft is around -2 to -4 Showalter indices and MUCAPES
in excess of 1000 J/kg. This supports isolated showers and
thunderstorms Friday afternoon into Friday evening mainly from the
Blue Ridge west. High temperatures on Friday will climb into the mid
70s in the mountains to the mid 80s in the Piedmont. Any convection
will taper off quickly Friday night. It will be a mild night with
readings from mid 50s in the mountains to the mid 60s in the
Piedmont.

As the low center lifts northward Saturday, the combination of
heating and an unstable airmass will create a few showers and
thunderstorms along and west of the Blue Ridge. High temperatures
Saturday will moderate to around 80 degrees in the mountains to
around 90 degrees in Piedmont. It will be mild Saturday night with
lows generally from around 60 in the west to the upper 60s in the
east.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 410 PM EDT Wednesday...

Very warm and humid conditions continue Sunday with the chance for
showers and thunderstorms, especially along the Blue Ridge. By
Monday, the vertically stacked upper closed low over the Midwest
will move into the Great Lakes region. This will push a vigorous
cold front into the area from the west with a good chance of showers
and thunderstorms through Monday afternoon into Monday night. High
pressure will then build on for Tuesday with cooler weather and
windy conditions. Moisture increases on Wednesday, with better
chances of rain Wednesday night into Thursday.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
As of 210 AM EDT Thursday...

Clear skies will promote good radiational cooling early this
morning with ambient ground moisture from recent rainfall
leading to some patchy valley (MVFR) fog, otherwise expecting
widespread VFR conditions all sites through 18z/2PM Thursday
before frontal showers and a few storms arrive along the western
slopes of the Appalachians. Increasing clouds/showers are the
result of an approaching cold front. Ongoing line of deep
convection over the TN valley is forecast to weaken this morning
before redeveloping along the outflow boundary as it moves into
the western Appalachians this afternoon. Storm coverage the
afternoon is expected to be scattered in nature...thunderstorm
clusters as opposed to a solid line. Southerly winds will become
a bit gusty from mid morning on per 35 to 40 knot LLJ ahead of
the approaching front.

Showers/Storms are forecast to linger until loss of daytime
heating. The actual surface front is expected to wash out and
dissipate as it crosses the mountains, so in spite of a wind
shift as it crosses the mountains this evening, very little if
any wind shift is expected over the piedmont east of the
mountains where the winds will remain predominantly out of the
south or southwest.

Extended Aviation Discussion...

Mainly VFR flying weather is expected for Friday and into the
weekend as high pressure builds over the southeast states
promoting temperatures which will be much above normal. Warming
surface temperatures also means increasing atmospheric
instability. As such, potential will exist for cloud build-ups
and the risk for isolated to scattered thunderstorms along the
spine of the Appalachians during the peak heating hours each
afternoon.

&&

.HYDROLOGY...
As of 525 PM EDT Wednesday...

Flood warnings continues for the Dan and Roanoke Rivers

The Dan River has crested and is falling at Danville, and has
crested at Paces. At South Boston the river is slowly rising and
should crest after midnight tonight.

The Roanoke River at Randolph has crested and will begin falling
this evening.

&&

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

&&

$$
SYNOPSIS...PM
NEAR TERM...MBS/RCS
SHORT TERM...KK
LONG TERM...KK
AVIATION...PM
HYDROLOGY...



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