Area Forecast Discussion
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FXUS61 KRNK 210546
Area Forecast Discussion
National Weather Service Blacksburg VA
146 AM EDT Tue Mar 21 2017
Weak low pressure will push east across the Appalachians
overnight, triggering showers and isolated thunderstorms as a
warm front lifts across the mid Atlantic states. As the low
progresses east, a cold front will push south across the area
Tuesday as high pressure builds in from the upper Midwest for
the middle of the week.
.NEAR TERM /THROUGH TODAY/...
As of 845 PM EDT Monday...
MCV driven complex of showers and storms along the nose of the
850 mb theta-e axis continues to approach from the northwest
this evening and expect the initial band to cross the mountains
in the next hour or two. Appears main batch of more organized
coverage will clip the northwest as well through midnight with a
trailing line feature perhaps reaching the far southwest zones
as well before fading. Just how widespread/strong the
showers/storms will be remains iffy as evening soundings show
support for elevated convection above the dry near surface
inversion while surface instability remains about nil. Latest
HRRR tends to fade coverage crossing the ridges but doesn`t have
much of a handle on the trailing band to the southwest. Since
more of a dynamic system would expect shra/tsra to go further
than model guidance despite loss of heating. Thus upped pops a
bit sooner to categorical northwest while extending the likelys
farther south over the next few hours. Also appears feature will
exit sooner after midnight with showers fading out east with
possibly a few bands redeveloping far southwest where kept
higher pops while trimming eastern half shortly after midnight.
Some upward adjusts to temps overnight given moistening
dewpoints with lows mostly in the 40s to around 50.
Previous discussion as of 345 PM EDT Monday...
Currently keeping an eye on a complex of showers and
thunderstorms over central Indiana which are associated with a
low pressure system that is advancing up the Ohio River Valley
this afternoon. Weather forecast models are in good agreement
that this low will pass across the central Appalachians
overnight, with the associated showers and possibly isolated
thunderstorms advancing to the Interstate 64 corridor shortly
before midnight. Believe this convection will begin to diminish
as it drifts southward toward the North Carolina/Virginia state
line as winds in the wake of the cold front dragging behind the
low shift increasingly westerly and downslope. Despite frontal
passage, cold air does not yet truly enter the area, and
overnight low temperatures will hold in the 40s nearly
Through late Tuesday morning, expect residual rain shower
activity to linger along the ridges of southeast West Virginia
through the highlands of North Carolina, as well as in the
vicinity of the passing cold front south of Highway 460 across
the Piedmont. Latest forecast model solutions have become a
little faster with the passage of the front, indicating less
instability than previously called for along the southern end of
the forecast area during the afternoon where temperatures are
expected to rise into the 70s. Still, cannot rule out a slight
chance of thunderstorms from late morning through mid afternoon
across the south, though instability will be minimal. Scattering
of clouds during the afternoon will promote high temperatures
in the low/mid 70s across the Piedmont, while areas along and
west of the Blue Ridge will hold in the 60s.
.SHORT TERM /TONIGHT THROUGH THURSDAY/...
As of 300 PM EDT Monday...
Models are trending faster and further to the south with a
west-to- east oriented frontal passage Tuesday night. Even
though models have most of the area dry by midnight, we decided
to cut PoPs by half going from 60 percent to 30 percent. The
highest PoPs remain along the VA/NC border south. The dew point
front lags behind with the colder, drier air not entering the
northern portion of the CWA (Lewisburg Wv-Lynchburg VA) until
around sunrise Wednesday morning. Therefore, leaned toward the
warmer MET guidance Tuesday night with most areas staying above
freezing with the exception of higher ridges across Greenbrier
County to the Alleghany Highlands. Moisture should be gone by
the time cold air filters into the area Wednesday to limit
accumulating snow to these ridges.
High pressure will build in from the north Wednesday. The
coldest air should not sink south until Wednesday evening as the
center of the high wedges south across the piedmont. Wednesday
temperatures will range from the upper 40s to lower 50s west to
upper 50s-lower 60s east Wednesday. Cold air Wednesday night
will send temperatures down into the mid to upper 20s across the
forecast area. We will see uniform temperatures Thursday in the
upper 40s to lower 50s as dry cool wedge engulfs the region.
.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
As of 300 PM EDT Monday...
Cool wedge of high pressure will begin to move off the VA/NC
coast Thursday night. As the center of the wedge tracks east, a
warm front will push moisture over the mountains which should
only result in an increase in cloud cover Friday and Friday
night. However, a bubble high will likely remain east of the
Blue Ridge and over the foothills and piedmont counties into
Friday night. This bubble of cool air and easterly flow will
keep high temperatures east of the Blue Ridge close to 60F while
the mountains warm into the lower to mid 60s. The wedge should
be completely erode out of the region by Saturday afternoon with
temperatures warming into the mid 60s to lower 70s across the
An area of low pressure is expected to track from the Midwest
Saturday night towards the Ohio Valley Sunday. This system has
the potential to bring severe weather to the region Sunday and
Sunday night. The track of the system and timing of prefrontal
convection into the region will be the biggest influence on how
widespread severe potential may become.
.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
As of 135 AM EDT Tuesday...
Radar showed a band of rain moving east, away from KDAN and
KLYH. Another cluster of showers was approaching from West
Virginia. SPC-HRRR has this precipitation weakening but moving
across KLWB then KLYH by 09Z/5AM before dissipating.
Boundary from southern Missouri into the southern Appalachians
will be the focus for showers and thunderstorms today. Storms
that develop over Tennessee will move east into North Carolina
this afternoon and evening. Both front will continue to move
south overnight and will be well into central and southern North
Carolina by Wednesday morning.
Northwest wind will combine with low level moisture to generate
upslope MVFR/IFR low clouds mainly west of the Blue Ridge early this
morning. The lower ceilings will hang in for most of the day
over the mountains, while sites east of the Blue Ridge should
become VFR this morning and remain as such through Tuesday.
Extended Aviation Discussion...
High pressure builds in for Wednesday which should improve
ceilings back to VFR.
By Thursday the high will wedge in from the northeast, so will
remain mainly VFR. It is possible that residual lower ceilings
may get trapped especially along and east of the Blue Ridge
Wednesday night into Thursday, resulting in possible MVFR
ceilings. Dry and warmer weather is expected on Friday.