Area Forecast Discussion
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FXUS61 KRNK 281056
Area Forecast Discussion
National Weather Service Blacksburg VA
656 AM EDT Wed Sep 28 2016
A weak frontal boundary will continue to meander east of the Blue
Ridge through late week. A strong upper level area of low pressure
will also drop south into the Tennessee Valley Thursday into
Friday before lifting back north by Saturday. The combination of
these features will lead to rounds of showers and storms through
the rest of the week before drier weather arrives this weekend.
.NEAR TERM /THROUGH TONIGHT/...
As of 250 AM EDT Wednesday...
Bands of deep convection continue across southern sections early this
morning to the east of the stalled surface front and under the tail of
a passing jet max to the north. Latest short term guidance shifts this
area of weak instability/convergence east by sunrise as a weak surface
wave passes. This may bring a brief lull in coverage early this morning
with low clouds likely to persist back to the Blue Ridge in the wake of
this early shra/tsra per weak easterly flow.
Strong upper low to the north should continue to dig south into
the Ohio Valley later today causing sharpening of the backing southwest
flow aloft across the region. This should act to spill moisture
back westward by afternoon ahead of perhaps another weak surface
wave sliding up the residual surface front to the south. Guidance
suggests this will allow for a highly diffluent scenario to take
shape aloft this afternoon with good shear including decent
low/mid level flow of 30-40 kts espcly eastern third later on. In
addition, arrival of cooling aloft should help overcome potential
lack of good instability given low clouds lingering out east. Most
solutions including the latest Cams tend to focus best coverage
along/east of Highway 29 per high PWATS, then gradually fill in
back into the Blue Ridge. Will also have a leading band of showers
ahead of the upper low approaching the west late, but still
appears will be a break between the two over the far
west/southwest sections where drier air will remain nosed in.
Therefore running with a gradient of likely/categorical pops east to
likelys eastern slopes of the Blue Ridge to low/slight pops far west.
Appears the east also has the best shot at isolated pulse/training
storms given chilly temps aloft while QPF of 1-2 inches possible
in spots but not widespread enough at this point for a watch
today. Highs mostly in the 70s pending clouds/showers, but could
get close to 80 southeast if convection is less or later to
Complex interaction of the residual front and bands of showers around
the upper low will persist into the overnight with added potential for
stronger storms north/east at least this evening per 00z ECMWF. Could
eventually work into a dry slot aloft espcly western half later tonight
as suggested by the latest HiRes-ARW but that remains iffy as
features likely slower to exit than progged. Otherwise given
expected good lift and continued deep moisture off models eastern
half, will continue likely pops through around midnight and then
slowly taper to mostly chance most sections late. With lots of
clouds lingering and the front stuck across the region, expect
lows to be warmer than earlier expected with mostly 50s mountains,
while the east likely remains in the low/mid 60s overall.
.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 400 AM EDT Wednesday...
A closed upper low is expected to stall across the Ohio River Basin
during the day Thursday, while a series of disturbances, including
an encroaching cold front from the west, will begin to interact with
the deep atlantic moisture and pulse along the mid Atlantic Seaboard
through the period. As a result, ongoing showers and thunderstorms
are expected to continue across the eastern Piedmont counties of
Virginia and North Carolina during the morning hours Thursday.
Showers and storms will likely increase in coverage and intensity by
mid afternoon, continuing the spread with the flow of moisture
around the low and along the boundary. Some of the thunderstorms
could be strong with hail, gusty winds, and heavy downpours.
Impressive low level lapse rates coupled with unseasonably low
freezing levels could aid in ultimate hail potential. Thunderstorm
activity is expected to diminish in large part due to the loss of
daytime heating and the subsequent instability axis overnight
Thursday. Continuing light to moderate shower coverage will maintain
through much of the overnight hours, with uncertainty remaining in
just how much precipitation will fall. The NAM/ECMWF models continue
to indicate very wet conditions while the GFS continues to keep the
heaviest precipitation a bit north of the forecast area. Have tended
to split the difference between the two model camps when it comes to
Temperatures during the period continue to trend cooler for highs
and warmer for lows. Expect daytime highs struggling to breach 70
degrees THU/FRI thanks to cloudcover. Low temps will remain cool,
but trending a bit warmer than guidance due to abundant
cloudcover and continued Warm Air Advection East of the Blue Ridge
prior to the low pulling back North. Sub 50s to the west will be
remain possible Overnight Thursday and especially overnight
.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 300 PM EDT Tuesday...
Closed upper low continues to lift northward through the Ohio Valley
into the weekend. The low center continues to push into the Great
Lakes by Sunday evening and New England by Monday. The low will
move into the Atlantic ocean on Tuesday. Meanwhile, the potential
for tropical low development across the Caribbean may lead to a
threat for the southeast early next week. This is being monitored
by the NHC and WPC.
Temperatures will start cooler for Saturday with continued
improvement as precip/cloudcover comes to an end, then
temperatures begin to moderate Sunday into Tuesday.
.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
As of 640 AM EDT Wednesday...
Convection has continued to weaken and pass to the east of the TAF
sites early this morning leaving a swath of low clouds across the
east and patchy fog to the west. Expecting at least MVFR cigs with
ocnl IFR to hang in along/east of the Blue Ridge this morning and
perhaps into this afternoon. Things will also become more
unstable east of the Blue Ridge with scattered showers, some
thunderstorms and mainly sub-VFR cigs where any convection does
develop. To the west, appears more in the way of VFR cigs likely
once early fog/stratus erodes although isolated convection also
possible across the west later in the day. Therefore keeping lower
cigs longer across eastern locations while including more
vicinity mention of shra/tsra in all except the KLWB/KBLF
corridor, and prevailing lower conditions from KLYH-KDAN where
storms are more likely.
Showers and storms likely to linger into the overnight with best
coverage again along/east of the Blue Ridge with periodic MVFR to
IFR possible mainly KROA and points north/east. Some patchy fog
also could occur to the west, mainly in the valleys but appears
could be too much cloudiness to allow radiative processes to
produce dense fog. Therefore only including mention for brief MVFR
level vsbys in fog at KLWB/KBCB later tonight. Few showers also
possible mountains with the upper low but too iffy to include
More widespread sub-VFR appears possible Thursday with the upper
low just west of the mountains and deeper moisture in place along
the residual surface front in the east. This may lead to periods
of showers and storms Thursday into Thursday night including
rounds of heavier rainfall espcly affecting sites along/east of
the Blue Ridge.
Extended aviation discussion...
A deep upper low will remain over the Ohio and Tennessee Valleys
through Friday night. This will keep variable clouds, MVFR cigs,
and periods of -SHRA across the region through much of the period.
Should finally see VFR return during Saturday and continue Sunday as
the upper low lifts north and weak high pressure builds in.