Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 161813

Area Forecast Discussion
National Weather Service Blacksburg VA
113 PM EST Sat Feb 16 2019

Two low pressure systems will track from the Tennessee Valley
across the Carolinas, the first today and the next on Sunday
night. Tuesday high pressure will cover much of the eastern
United States, then on Wednesday and Thursday another low and
cold front cross through the Mid Atlantic region.


As of 100 PM EST Saturday...

Our forecast update for this afternoon will reflect a rapid
ending of the widespread precipitation across the eastern half
of the area. Only patchy light rain or snow is expected for a
few more hours across the eastern areas. The forecast will also
reflect a more rapid clearing of clouds from northwest to
southeast across the area, with the clearing line reaching near
a Bluefield to Roanoke to Lynchburg line by sunset. Have also
tweaked the hour temperatures, dew points, and winds to better
match the current observations and expected trends through the
afternoon hours.

As of 235 AM EST Saturday...

No changes planned to Winter Weather Advisory.

Precipitation covered much of the Tennessee Valley early this
morning. This was associated with a short wave that extended from
southern Illinois into eastern Tennessee. Latest RAP, HiResNMM,
HiResArw and NamNest all had similar timing and placement of this
short wave, moving it east today and offshore tonight.

At the surface a cold front trailed from southeast Virginia to a low
in eastern Tennessee then into the lower Mississippi Valley. The low
will move east along the front as the front moves south today.
Models have high pressure and more stable air moving into the Mid
Atlantic region behind the low for tonight. Surface and low level
winds will turn to the northeast as the low crosses North Carolina
then to the southeast as the high wedges south.

Guidance still supports a band of 0.25 to 0.50 inches of rain from
southern Kentucky across southern Virginia. Lighter amounts on the
north side of that strip and a sharp northern edge to the
precipitation, possible from near Lewisburg across the Alleghany
Highlands. Expect a majority of the precipitation to be east of
Lynchburg and Danville by 21Z/4PM but enough low level moisture
remains to keep clouds in the area overnight. As winds become
southeast tonight, stratus and fog will fill in over the southern
Blue Ridge and foothills. Will trim back probability of
precipitation before 12Z/7AM Sunday.

After temperatures drop behind the front early this morning, little
to no recovery for the rest of the day.


As of 353 AM EST Saturday...

A warm front aloft will overrun a cool air surface wedge Sunday
morning. Increasing isentropic lift along with warm moist air will
produce light precipitation through early afternoon. The last few
days, model forecast soundings suggested precipitation would be a
mixture of snow/sleet changing to rain. Models are now bringing a
pretty significant warm nose over the area with some valley
temperatures remain below freezing through mid morning and adiabatic
cooling along eastern slopes of the Blue Ridge through early
afternoon, giving a chance for light icing from freezing

During the afternoon and evening hours, a wave is expected to
develop along the southern edge of the wedge and track across the
Carolinas Sunday night. This wave and with increasing jet dynamics
over the area will bring more widespread rainfall to the region
overnight, exiting the piedmont Monday morning. Convection is
possible across the Carolinas and may rob moisture heading north to
limit rainfall amounts to a couple of tenths north of Highway 460 to
a third to half of an inch south. This rainfall should not result in
any flooding but will bring rises along creeks and streams into

A cold front will track over the region Monday morning removing the
wedge and rain. Modest pressure rises with a 35-40 kts low level jet
will bring breezy and gusty conditions to the area through the day
Monday. The time frame of the strongest winds will occur just behind
the front between 6AM and noon. Winds speeds and gusts will not be
close to advisory levels, therefore no headlines are expected. High
pressure builds over the area Monday night.

It is also worth noting that the 00Z GFS has some upslope snow
showers behind the front. Trajectories from the Great Lakes do not
look desirable for accumulations, but can not rule out some snow
falling along western slopes from convective showers with heating
under cold pool over the Ohio Valley.

Precipitation falling in to the wedge Sunday along with an easterly
wind will keep temperatures cooler than normal Sunday. As the wedge
erodes Sunday night, temperatures will warm a few degrees.
Temperatures Sunday into Sunday night will likely hover between the
upper 30s to lower 40s. On Monday before the cold air arrives,
temperatures should warm into the mid to upper 40s west of the Blue
Ridge to the mid to upper 50s east. Under cool high pressure Monday
night, temperatures drop back into the upper 20s to mid 30s.


As of 350 PM EST Friday...

This period will continue to see more wet and unsettled weather with
no real good chance of seeing sunshine for the duration of the week.
The low that developed in the gulf will move northeast toward the
Great Lakes Wednesday into Thursday providing a continuous source of
moist air. While this southerly flow will more or less eliminate the
threat for winter type precip, the continuous onslaught of rain will
introduce the risk of flooding. WPC days 1-7 precip outlook
currently highlights areas exceeding 4", mainly in western NC, but
at least 2-3" area wide. Current GFS and ECMWF peg the heaviest
precip occurring Wednesday through Thursday as the cold front
associated with the low passes, then lingers to the south of the
forecast area. Therefore, this will be the likely time frame to
focus on in future forecasts as the event approaches. Aforementioned
models begin to diverge greatly by Friday with the Euro bringing in
high pressure behind the front, while the GFS develops yet another
system to the southwest that begins to move even more precip into
the region. Have opted to lean toward the GFS solution for the time
being as am erring on the side of caution, but will need to monitor
future runs for consistency.


As of 1245 PM EST Saturday...

Precipitation is currently exiting the region to the east, but
sub-VFR conditions remain in its wake for much of the area. The
exception is areas along and north of a KLWB-KHSP line. This
region is VFR with limited cloud cover trending less. This
clearing line will make its way south to near a KBLF-KROA-KLYH
line by sunset with sub-VFR remaining across areas to the south.
Patchy flog will also start to develop around sunset.

Overnight, another system will approach the area from the west
and increase low level flow from the south. This will bring
light rain/drizzle into western sections through the night along
with lowering ceilings. Precipitation from this next system
will start spreading eastward across the area during the day
mainly in the form of rain, with those areas at or below
freezing experiencing freezing rain. Ceilings through the
morning hours will remain mainly VFR across eastern sections and
sub-VFR across the mountains.

Confidence in the above scenario is moderate.

Extended Aviation Discussion...

By Sunday afternoon the entire area is expected to have a good
chance of seeing rain or freezing rain with most areas sub-VFR.
These conditions will continue into at least the first part of
Sunday night. By late Sunday night into early Monday, northwest
winds on the backside of the departing system will help eastern
areas return to VFR with patches of sub-VFR across the mountains
thanks to upslope for across southeast West Virginia.

Monday into Tuesday we will have a brief break in the wet
weather with many locations experiencing VFR conditions. The
exception may be some late night or early morning patchy fog.

Wednesday into Thursday a frontal boundary stalls across the
area and allows for plenty of opportunities for precipitation
and sub-VFR conditions.




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