Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KRNK 180200
Area Forecast Discussion
National Weather Service Blacksburg VA
1000 PM EDT Fri Mar 17 2017
High pressure over the region will shift offshore this evening
ahead of a warm front approaching from the south. This front
will lift northeast through the area overnight before a trailing
cold front pushes across from the west during Saturday. High
pressure will follow the front on Monday, then another cold
front crosses the Mid Atlantic region Monday night.
.NEAR TERM /THROUGH SATURDAY/...
-- Changed Discussion --As of 940 PM EDT Friday...
Undergoing a transition of wintery wx in the Alleghanys to
thunderstorms over the New River Valley, though should see
limited cloud to ground strikes as instability east of the
Appalachians wanes. Also very dry air aloft in places with
colder thermal structure allow for graupel/sleet to occur. This
noted across the Lynchburg area as of 930pm. Radar showing
bright banding/melting level around 4000-4500 AGL over Bedford
Latest RAP13 showing area of moderate to heavier showers moving
out of the piedmont between 03-04z, with mix of sleet/snow
still possible until 1-2am EDT northeast of Lewisburg, WV to the
Alleghanys of Bath County. Handling with SPS for now, as only
getting minor accumulations. Temperatures running around
freezing at LWB/HSP.
Warm front situated from LEX-MWK this evening should head north
of us into the mid-Atlantic overnight allowing temps to
gradually warm above freezing.
Models still favoring overnight higher pops across the mountains
and south into the NC foothills and piedmont, as better jet
energy shifts southward toward 12z Saturday.
Previous discussion from mid afternoon...
Initial swath of precip along the leading edge of the deeper
warm advection aloft per latest model 850 mb temp gradient has
pushed across the northwest sections where saw a period of snow
where precip did reach the ground. Latest radar trends and HRRR
suggest a break in coverage to take shape once this initial
batch passes before deeper moisture ahead of the actual
warm/cold front combo arrives by early this evening. This may
bring another round of mix to far northwest sections before
temps aloft surge above freezing later this evening. However
some concern with dry air in that surface temps may still be
close to freezing around LWB/HSP. Thus keeping in a mix with
perhaps an inch or so of snow along the I-64 corridor but
without much freezing rain mention or advisory headline at this
Otherwise models suggest a decent slug of lift crossing the region
espcly this evening before deeper moisture axis slides to the south
late as the front folds southbound. Appears deep westerly flow could
limit eastward expanse of rainfall but given a favorable jet aloft and
lots of forecast diffluence expect momentum to carry rain farther east
than usual. Therefore beefed up pops to push likelys out just east of
the Blue Ridge tonight and high chances south/east. Even included some
elevated thunder mention across the southwest per steep lapses and
dynamics with QPF of up to one quarter inch east to three quarters
west. Dropped lows below mos most spots given a chilly start and more
evaporative cooling potential with lows close to freezing northwest and
upper 30s/low 40s elsewhere before perhaps rising some late.
Cold front crosses the region Saturday followed by increasing northwest
flow and gradual drying by mid to late afternoon outside of the upslope
northwest zones. However models suggest that a weak wave may form along
the boundary over southern sections in advance of the strong dynamic
shortwave trough that will arrive late. This may slow the exodus of the
showers espcly southeast sections so left in decent chance pops south
early on before switching to mostly upslope rain showers west during
the afternoon. Expect to see enough clearing and warming before
stronger cold advection arrives to help boost highs to around 50 far
west to 55-60 Blue Ridge to mid 60s east. Will also turn windy as the
850 mb jet increases to 40+ knots under the onset of the stronger cold
advection but below advisory levels per forecast high inversion levels
and only weak subsidence.
-- End Changed Discussion --
.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
As of 400 PM EDT Friday...
Upslope snow showers should pick up Saturday night along and west of
the Blue Ridge as an upper level trough pivots overhead. It appears
that up to a couple inches of snow seems likely for western
Greenbrier County tapering down to flurries in the New River Valley.
Good cold air advection warrants pushing lows on Sunday morning
below MOS guidance. Temperatures may struggle to increase initially
during Sunday due to cloud cover in the mountains, but high pressure
building from the north should allow skies to gradually clear by the
afternoon. By Sunday night, this high will move over the Appalachian
Mountains to allow another cold night with efficient radiational
The upper level pattern becomes more zonal by Monday, and
some ridging arrives from the southern Plains. Expect a good warm up
on Monday, but clouds will steadily increase during the afternoon
and evening from the northwest as a cold front approaches the Ohio
River Valley. The 12Z GFS pushes this cold front into the CWA a
little faster than the 00Z ECMWF during Monday night. There may be a
lag in moisture arriving at the onset due to recovery from a cold
and dry air mass from Sunday and Monday, so the slower ECMWF
solution was favored. However, some rain showers will probably reach
southeast West Virginia after midnight.
.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 400 PM EDT Friday...
The cold front should move from northwest to southeast over the CWA
on Tuesday. Meanwhile, another upper level trough will dig southward
from eastern Canada to bring colder air behind the frontal passage.
If the cold air arrives quickly enough, it could change the rain to
snow in the higher elevations of southeast West Virginia and the
northwest North Carolina mountains by Tuesday night. Cold air
advection will continue through Wednesday as a strong high pressure
area builds southeastward from the Great Lakes. Once overhead by
Wednesday night, expect another cold night with temperatures well
below freezing. This high should slide eastward toward the coast on
Thursday, and the numerical models hint that some wedging may occur
east of the Blue Ridge. A warm front will also approach from the
west due to a potent low pressure system over the northern Plains on
Friday, so the CWA should break free of the wedge with good
southwesterly flow and a building upper level ridge.
.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
As of 755 PM EDT Friday...
A warm front is generating significant isentropic lift over the
region and driving the development of showers mainly west of the
Blue Ridge as dry air to the east is generally preventing
precipitation from reaching the ground. Mid/upper lapse rates
are sufficient to support some convection as is evidenced by
lightning upstream. Additionally, cold temperatures are keeping
some mixed ptype across Greenbrier and Bath counties.
Believe the best chances for precipitation at TAF sites west of
the Ridge will be through about 06Z, with temperatures up north
will rise enough for an all rain scenario at KLWb by around 03Z.
The best chances for thunder look to be confines further south
and west so will not introduce thunder into the TAFs, though
this may have to be modified based on behavior of upstream
convection. Expect little in the way of appreciable
precipitation at eastern TAf sites.
A cold front then looks poised to move through the region
tomorrow. This will allow for a push of drier air to move in
from the southwest with improving flight conditions. However
westerly winds quickly become gusty, we will settle into an
upslope/downslope pattern by the afternoon with a return to MVFR
and some scattered showers in the west, but hold on to dry VFR
conditions in the east.
Extended Aviation Discussion...
Gusty post frontal northwest winds along with upslope western
mountain snow showers will develop Saturday night and continue
into part of Sunday. Best chances for sub-VFR with snow showers
at KBLF and perhaps KLWB will be Saturday night into Sunday
morning. High pressure building in on Monday should yield VFR
all terminals to start the week. However moisture ahead of
another cold front and associated weak low pressure may arrive
by Monday night, with sub- VFR possible later Monday night into
early Tuesday before improving conditions take shape into