Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 261850

Area Forecast Discussion
National Weather Service Blacksburg VA
250 PM EDT Tue Jul 26 2016

Lingering strong high pressure aloft over the Carolinas will
result in hot and humid weather into at least mid week. A weak
frontal boundary just north of the area should also continue to
oscillate across the Mid-Atlantic region through the end of the
week. Weak impulses riding along the front will combine with deep
moisture to produce periodic rounds of showers and thunderstorms
each day.


As of 249 EDT Tuesday...

Heat advisory remains in effect until 8 pm for South Central
Piedmont of Virginia.

The strong upper ridge is weakening and slide southeast
tonight into Wednesday. A shortwave passing to the north this
evening into tonight, will push the frontal boundary further south
into higher pwat air around 2 inches including high surface based
instability. This feature combine with differential heating,
orographics, residual outflow and low level convergence will
generate scattered showers and thunderstorms into tonight. On the
Day One Convective Outlook, our forecast area remains in a marginal
threat for severe storms with primary concern damaging winds. Given
weak steering but some unidirectional westerly component aloft,
looks like storms will be slow moving with locally heavy rains
possible. The best severe chances will come from downbursts within a
highly unstable water loaded type environment. Will mention isolated
severe in HWO.

Weak mid level wave along the front to the north should exit this
evening into tonight allowing the boundary to sag south. How far
south remains a question for debate. Outside of isolated convection,
expect another very warm and muggy overnight with moisture and
debris clouds. Low temperatures tonight will range from the mid 60s
in the mountains to the mid 70s in the Piedmont.

A weak surface front will stall across our region on Wednesday.
Scattered showers and thunderstorms are expected Wednesday
afternoon into Wednesday evening. SPC Day Two convection Outlook
places eastern portions of forecast area in Marginal threat. The
Shear is still not very impressive so the probability for widespread
severe remains low. The main threat being pulse storms and any
clusters that can organize due to outflow boundary interactions.
High temperatures on Wednesday will range from around 80 degrees in
the northwest mountains to the mid 90s in the Piedmont. Heat index
may climb to near the century mark in eastern Piedmont, just
short of heat advisory levels.


As of 243 PM EDT Tuesday...

Will start to see the strong upper ridge over the southeast break
down this period as stronger upper wave moves across the Great
Lakes. Models also overall in agreement in a stronger vort moving
from the Mid Mississippi Valley Wednesday night into the eastern
Ohio Valley by Thursday evening. This signal suggests an increased
likelihood of storms with greatest coverage over the mountains
Thursday. Therefore increase pops to likely along and west of the
Blue Ridge for Thursday. There is good upper support with jet
dynamics such that severe storms is possible if we get enough
heating. However timing of complex may bring more clouds to the area
Thursday morning limiting solar insolation.

This wave shears to the mid Atlantic by Friday with 5h heights
falling. Should maintain at least threat of storms Friday as frontal
boundary starts to linger over the mid Atlantic. Question will be
how far south this front makes it.

We should start to see temperatures settle toward seasonal lat July
norms by Friday but will remain sticky/humid. Highs Thursday will
range from the lower to mid 80s west to lower 90s east.

By Friday highs will be in the upper 70s to lower 80s west to around
90 east.


As of 130 PM EDT Tuesday...

Overall pattern situation favors storminess every day but especially
in the afternoon/evening. A frontal boundary situated from the Ohio
Valley over to the Central Plains will slowly shift southeast into
the Virginias and North Carolina over the weekend. Airmass will
remain unstable and moist. Some issue with how far this front makes
it as 5h ridge may be hard to break, but still looks like belt of
westerlies will shift at least into our northern forecast area over
the weekend.

Highs will be seasonal with lows slightly above normal through most
of the period. Highs will range from the lower to mid 80s mountains,
to upper 80s to around 90 east. Lows will be in the lower to mid 60s
mountains, to upper 60s to around 70 east.


As of 138 PM EDT Tuesday...

SCT to BKN VFR ceilings with pockets of MVFR/IFR convection
expected this afternoon into tonight. Given strong instability
would expect greater coverage of storms this afternoon compared to
the widely scattered activity Monday. However, models continue to
vary on expanse and locations of coverage as ridging aloft appears
stronger than earlier forecast, while focus on residual
outflow...southeast lee trough and the upstream pre-frontal zone
could lend to multiple clusters in spots later this afternoon.

Mention VCTS in most taf locations for this afternoon into this
evening. Believe the taf site with the best chance of a
thunderstorm is KROA. Widely scattered clusters of shra/tsra may
linger into tonight before again fading to patchy fog/stratus
overnight. KLWB is the taf site with the best chance for low
clouds and fog late tonight into Wednesday morning.

Scattered MVFR showers and thunderstorms are expected
Wednesday especially during the afternoon and evening hours.

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

Extended aviation discussion...

The upper ridge will remain just south of the area and a residual
front nearby through Saturday. This should allow for periodic
daily convective coverage through much of the period until the
boundary either fades or sinks farther south. Appears more
widespread sub- VFR possible in convection later Thursday per a
stronger wave along the front with perhaps some decrease in
coverage by the weekend as this feature passes. However given
uncertainty appears at least diurnal MVFR/IFR possible each
afternoon/evening through Saturday for now. Late night and early
morning fog will likely occur at the usual valley locations, and
those chances increase across the entire region if any rain occurs
during the afternoon or evening at any site.


Record high temperatures for Tuesday (7/26)

Roanoke.....101 in 1930
Lynchburg...104 in 1934
Danville.....99 in 2012
Blacksburg...94 in 1987
Bluefield....91 in 1993

Record high temperatures for Wednesday (7/27)

Roanoke.....103 in 1936
Lynchburg...103 in 1936
Danville....102 in 1952
Blacksburg...94 in 1993
Bluefield....89 in 1966


VA...Heat Advisory until 8 PM EDT this evening for VAZ046-047-058-


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