Special Weather Statement, NWS Blacksburg, VA

Area Forecast Discussion
National Weather Service Blacksburg VA
303 PM EDT Wed Jun 14 2017

.SYNOPSIS...
High pressure offshore will maintain a warm and humid airmass
across the region through late week. A weak backdoor front may
dip south into the region tonight into Thursday, enhancing the
threat for showers and storms, before lifting back north by
Friday. Another weak cold front will approach the area from the
west this weekend with added showers and storms likely.

&&

.NEAR TERM /THROUGH THURSDAY/...
As of 303 PM EDT Wednesday...

High pressure located just off the Southeast coast will continue to
advect warm unstable air into our region this afternoon into
tonight. A weak backdoor cold front will drop south tonight into
Thursday. SPC Mesoanalysis at 18z showed CAPEs from 1000 to 2500
j/kg across our forecast area. Values of CAPES are just a little
lower then the modified rnk sounding indicated, perhaps trimmed by
morning cloudiness. First round of convection this afternoon
developing across the northwest mountains as seen on WSR-88d images.
Scattered diurnal showers and thunderstorms will continue to develop
this afternoon into tonight along residual outflows, differential
heating zones, and local terrain circulations. The day one
convective outlook has place our forecast area in marginal risk.
with a similar weather pattern to that seen yesterday, still expect
the potential for strong to severe storms. Moderate buoyancy and
weak vertical shear suggest that the primary threat will be isolated
strong/damaging gusts with downbursts. There is the potential for
hail also with freezing level about 12k similar to yesterday with
stronger updrafts. With higher pwats around 1.5 inches, slower
moving and training convection could result in flooding issue.

Convection may better organize as the shortwave aloft arrives later
this afternoon, then eventually jumping to the eastern lee trough
this evening per weak westerly flow.  in other words, cells will
move east into the Foothills and Piedmont. Shortwave should again
exit overnight taking leftover lift to the east/southeast after
midnight. Another piece of energy to the northwest along with the
backdoor front near the Blue Ridge could cause showers to redevelop
north and west overnight. With low level moisture and light winds
expect areas of fog to formed tonight into Thursday morning. It will
be another warm and humid overnight with lows from the upper 50s in
the mountains to near 70 degrees in the piedmont.

Backdoor cold front dropping southward will lose steam or push
Thursday, and should stall somewhere in the east near a line
stretching generally from Lexington to South Boston Virginia. This
will result in another day of strong heating on the warm side of the
boundary. Scattered showers and thunderstorms are expected with CAPE
values again in excess of 1000 J/kg, increased low level convergence
associated with the front, pwats around 1.5 inches and weak upper
level winds. A few of the thunderstorms could be strong to severe
during the afternoon and evening. SPC Day two has place western
portions of our forecast area in a marginal risk for Thursday with
the potential for wind and hail. Naturally, more stable conditions
are anticipated behind the front which should significantly limit
the amount of convection. High temperatures on Thursday will range
from the mid 70s in the mountains to the mid 80s in the Piedmont.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
As of 303 PM EST Wednesday...

Frontal boundary will be draped over the region on Thursday with some
wedging in the east. This looks to serve as a focus for convective
development with ample instability, but lack of shear will continue to
be a limiting factor for severe weather. The boundary eventually
dissolves as wedge erodes through Friday as the upper pattern settles
into some sympathetic ridging ahead of a vigorous trof moving through
the upper midwest. This will leave us in moist/unstable weakly forced
environment by Saturday. Severe threat will continue to be limited by a
lack of shear, though after several days of convection local hydro
issues may arise if downpours repeatedly affect the same areas.

Temperatures will remain around seasonal levels with low/mid 80s east
of the Blue Ridge and upper 70s/low 80s to the west.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 303 PM EST Wednesday...

Deep southwesterly flow will keep warm/moist/unstable conditions with
little shear over the region into the first part of next week. This
will keep a chance for showers/thunderstorms with downpours and a low
probability for severe convection through Sunday. By Monday, an upper
low will move through the Great Lakes region and push a trof into the
eastern US. This looks to provide enough momentum to push a cold front
through the region on Monday with a good chance for thunderstorms,
along with a better low level wind field that may bring us a better
chance for severe weather. The front will not get very far and will be
lingering close enough to keep a chance for some scattered
showers/storms especially east of the Blue Ridge for Tuesday and
Wednesday.

Temperatures will trend down just a bit behind the front, then start to
rebound by midweek. Expect highs generally in the mid/upper 80s east of
the Ridge with upper 70s/lower 80s west.

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
As of 135 PM EDT Wednesday...

Scattered MVFR/IFR showers and thunderstorms will develop in the
warm unstable air this afternoon into tonight. The combination
of low level boundaries,heating and a backdoor cold front will
enhance the coverage later this afternoon into tonight. The
front will drop south this afternoon into tonight. Appears best
organization of storms will be along the Blue Ridge by
early/mid afternoon before sliding east toward KLYH/KDAN late in
the day. Therefore keeping VCTS in for all sites this afternoon
while including a TEMPO for lower conditions in TSRA.

Some of the storms may linger past sunset in the east with a
return to mainly VFR cigs once convection fades later this
evening. Patchy fog is again possible but again dependent on
the amount of debris mid deck late tonight and possible
redevelopment of showers over the north and west late. A weak
backdoor front could also allow more fog and IFR cigs to advect
into KLYH toward daybreak Thursday. Morning low clouds should
lift, then scattered MVFR convection will develop during the
afternoon.

Medium confidence in ceilings, visibilities and winds during
the taf period.

Extended Aviation Discussion...

Very moist conditions will linger through late in the week. A
backdoor front will oscillate across eastern sections
Thursday evening before retreating back to the north. A
stronger cold front and upper- level disturbance will arrive
from the west late in the week. Therefore, expect scattered to
numerous convective activity, mainly during the afternoon and
evenings, throughout the week and into the weekend. This will
allow for extended periods of sub- VFR ceilings and
visibilities. In addition, radiational late night/early morning
fog will be on the increase.

&&

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

&&

SYNOPSIS...JH/KK
NEAR TERM...KK
SHORT TERM...MBS
LONG TERM...MBS
AVIATION...JH/KK

Hazardous Weather Outlook
National Weather Service Blacksburg VA
311 PM EDT Wed Jun 14 2017

NCZ001>006-018>020-VAZ007-009>020-022>024-032>035-043>047-058-059-
WVZ042>044-507-508-150900-
Ashe-Alleghany NC-Surry-Stokes-Rockingham-Caswell-Watauga-Wilkes-
Yadkin-Tazewell-Smyth-Bland-Giles-Wythe-Pulaski-Montgomery-Grayson-
Carroll-Floyd-Craig-Alleghany VA-Bath-Roanoke-Botetourt-Rockbridge-
Patrick-Franklin-Bedford-Amherst-Henry-Pittsylvania-Campbell-
Appomattox-Buckingham-Halifax-Charlotte-Mercer-Summers-Monroe-
Eastern Greenbrier-Western Greenbrier-
311 PM EDT Wed Jun 14 2017

This Hazardous Weather Outlook is for north central North Carolina,
northwest North Carolina, central Virginia, south central Virginia,
southwest Virginia, west central Virginia and southeast West
Virginia.

.DAY ONE...This Afternoon and Tonight.

Scattered strong to isolated severe thunderstorms will be possible
through this evening with damaging winds the primary threat. In
addition, slow moving storms could produce very heavy rainfall that
may result in localized flooding.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

Additional rounds of strong to isolated severe thunderstorms will
occur from Thursday into the weekend with the more widespread
coverage of stronger storms west of the Blue Ridge.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

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