Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 260842 CCA
AFDRNK

Area Forecast Discussion...CORRECTED
National Weather Service Blacksburg VA
442 AM EDT Fri Apr 26 2019

.SYNOPSIS...
A strong cold front will cross the region from the west today
before exiting offshore this evening. High pressure will build
in behind this system through the start of the weekend. A weak
cold front may bring isolated showers to western parts of the
area Saturday night into Sunday, but overall, high pressure will
continue to dominate our weather pattern through at least
Tuesday of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 340 AM EDT Friday...

Strong upper trough will dig southeast across the region today
helping propel a cold front over the mountains this morning and
through eastern sections by mid afternoon. Ahead of the front will
see bands/swaths of more warm advection/shallow based convection
early this morning with the heaviest rain over the west closer
to the front.

Main initial concern with potential to see deeper convection
develop espcly along the Blue Ridge by late morning, and then
organize heading east into the Piedmont before exiting toward
late afternoon if not sooner. Models continue to show uncertainty
with how things evolve with the overall trend being faster/weaker
with convection given the expansive cloud cover early on, and
best instability out along the eastern perimeter of the CWA.
Most CAM solutions do show one main broken line emerging east of
the mountains early this afternoon ahead of the main shortwave
trough, but really not developing until east of the area where
better theta- e ridging and forcing will exist over more
instability. This has supported shifting the Day1 slight risk
outlook just east of the area this morning for now. However
still looking at strong shear/diffluence aloft that will support
some risk of severe storms mainly eastern third and higher pops
even if deeper convection is more embedded. Expect rainfall to
quickly taper behind the front by mid to late afternoon with
perhaps some added heavier showers lingering west as the 850 mb
boundary crosses. Highs tricky with readings likely to
steady/fall far west this morning with some rises near the Blue
Ridge, and moreso east where some 70s still likely.

Otherwise as the front crosses, will see a surge in west/northwest
winds from west to east this afternoon given a quick increase in
pressure rises and abrupt cooling aloft. Appears a rather high
inversion level may keep the higher speeds aloft, but looks like a 1-
3 hour burst of advisory level speeds across the region, and possibly
higher mountains espcly if any showers are leftover. Thus added
another row of counties along the eastern slopes of the Blue Ridge
to cover the foothills, while leaving out points east since thinking
will be a short duration event that would better fit a SPS.

Upper trough boots east overnight allowing high pressure to build in
from the west through daybreak. Pressure gradient will remain in
place as low pressure departs to the north and deeper cold advection
ensues, so should remain quite windy espcly mountains overnight
given a lingering 45-50 kt jet at 850 mb. Expect some upslope showers
across the northwest during the evening before the column dries
out with little pop remaining late and clearing elsewhere espcly
east. Chilly lows under the strong cool advection with some 30s
likely mountains and perhaps upper 30s/low 40s east where winds
may decouple a bit late.

&&

.SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/...
As of 415 AM EDT Friday...

Saturday will start out rather breezy and cool with the Wind
Advisory/High Wind Warning continuing until noon. It will be
quite chilly Saturday with morning temperatures starting out in
the 30s west to the 40s east and wind chills in the 20s. There
may be a few spots at the highest elevations near freezing with
850mb temperatures possibly as low as -4C in the northwest early
Saturday. However, not expecting any frost because it will be
quite dry and there will be entirely too much wind.

While Saturday will start out mostly clear and dry, a fast
moving Alberta Clipper like system will be racing east-southeast
during the day tracking across the Midwest into OH by evening.
Moisture is quite limited, but dynamics are strong enough to
support solid cloud cover and perhaps even a few showers late
day/evening. Gusty downslope westerly winds will allow
temperatures to warm to seasonal levels east of the Blue Ridge
Saturday, but with these same winds and increasing cloud cover
it will remain a bit on the cool side across the western parts
of the CWA Saturday.

The disturbance in OH will continue to move east toward PA
Sunday and the associated frontal system will move into NC and
then stall as a subtropical ridge begins to amplify across the
southeast U.S. This ridge will be one of the primary weather
focuses for next week as it builds into the Mid-Atlantic region.
Showers and a few thunderstorms will be possible along/near the
boundary Sunday afternoon, say near the VA/NC border and
southward suggested by increasing CAPE and limited moisture
convergence.

As we progress into Monday, as noted above, the subtropical
ridge to our south will become one of the main weather players
for the week. 500mb heights rise to 588dm or better by Tuesday.
The weak frontal boundary will drift back to the north and
linger through at least midweek near the MD/PA/WV border area.
Monday will mark the beginning of a several day period that
trends a lot more like June/July than late April/early May. Look
for diurnally driven convection Monday afternoon in the far
north near the front and across the western mountains due to
differential heating.

/Confidence in Forecast Parameters/
Temperatures - Moderate,
Precipitation Probabilities - Moderate,
Winds - Moderate to High,
Thunderstorm Threat - Low to Moderate.

&&

.LONG TERM /TUESDAY THROUGH THURSDAY/...
As of 430 AM EDT Friday...

An warm and increasingly unsettled period expected as a frontal
boundary/baroclinic zone meanders and lingers about the region,
mostly to our north after Monday. Meanwhile, a strong subtropical
ridge will amplify across the southeast U.S. and into the Mid-
Atlantic through at least Midweek. Overall, the baroclinic zone
will reside to our north through this period. 500mb heights over
the region increase to 588dm or better through midweek with
850mb temperatures rising from near 0C over the weekend to
around +15C by midweek. The atmosphere will be increasingly
capped and convection will thus be largely diurnal and driven by
differential heating, favoring the far north near the front and
the western mountains. It appear that the pattern will change
little until late week when a stronger short wave emanating in
the southwest U.S. finally begins to break down the eastern U.S.
ridge. Will keep pops in the slight chance/chance range and mostly
diurnal/afternoon and evening variety, typical of a summer
environment.

Temperatures will rise to well above normal levels by midweek
with highs in the 80s areawide, except 70s higher elevations of
the mountains. Low temperatures will be mostly in the 50s west
to the 60s east.

/Confidence in Forecast Parameters/
Temperatures - Moderate to High,
Precipitation Probabilities - Moderate,
Winds - Low to Moderate,
Thunderstorm Threat - Moderate.

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
As of 105 AM EDT Friday...

Cloud cover and spotty rain showers are expected into the
overnight. However, conditions are expected to remain VFR
through roughly 09Z/5AM. After this time, flight conditions will
gradually deteriorate with the advance of a generous area of
showers and storms ahead of an approaching cold front. By
daybreak Friday, the vast majority of the area will see MVFR
ceilings and MVFR to low-end VFR visibilities.

Winds will be on the increase from the south starting tonight,
and ramp up significantly from the west following the passing of
the front Friday afternoon. By that time, surface gusts across
the higher ridges of the mountains will be near 25 to 40 kts
with the mountain valleys and piedmont region more in the range
of gusts of 15 to 25kts.

Flight categories will improve rapidly as drier air is ushered
into the area in the wake of the cold front Friday night. The
hold out will be parts of southeast West Virginia where lower
ceilings and lingering precipitation will remain into Saturday
morning, thanks to the strong upslope component there. Winds are
expected to remain gusty across the foothills and mountain
counties into Saturday morning.


EXTENDED AVIATION DISCUSSION...

VFR conditions are expected into the start of the weekend as
high pressure builds into the region. Winds will remain very
gusty Friday night into the start of Saturday morning thanks to
the tight pressure gradient between this approaching high and
the departing low.

A weak cold front may bring some isolated showers to western
sections on Sunday, along with gusty winds to area along and
west of the crest of the Blue Ridge. Brief, isolated sub-VFR
conditions are possible across southeast West Virginia.

Sunday through Tuesday generally VFR conditions are forecast.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...Wind Advisory from noon today to noon EDT Saturday for VAZ007-
     009>014-016>020-022>024-032>035.
     High Wind Warning from noon today to noon EDT Saturday for
     VAZ015.
NC...Wind Advisory from noon today to noon EDT Saturday for NCZ003-
     019.
     High Wind Warning from noon today to noon EDT Saturday for
     NCZ001-002-018.
WV...Wind Advisory from noon today to noon EDT Saturday for
     WVZ042>044-507-508.

&&

$$
SYNOPSIS...DS/JH
NEAR TERM...JH
SHORT TERM...RAB
LONG TERM...KK/RAB
AVIATION...DS/JH/RCS


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