FXUS61 KRNK 190831

Area Forecast Discussion
National Weather Service Blacksburg VA
431 AM EDT Mon Mar 19 2018

Low pressure over the central U.S. will move east today
resulting in increasing cloud cover. This system will initially
bring rain to the mid Atlantic Region beginning later today and
lasting into Tuesday, but wintry precipitation will be possible
Tuesday night into Wednesday as cold air wraps into the system
from the north and west. Brief clearing is expected for the end
of the work week with yet another storm system effecting the
region for the weekend.


As of 400 AM EDT Monday...

Clouds will be on the increase today as storm system over the
central U.S. approaches our region. Models generate very little
rain during the daylight hours, due to the lingering effects
from yesterdays dry airmass. However, can't rule out a brief
period of light rain until isentropic lift finally overcomes
dry layers permitting widespread rain tonight.

Low pressure to our west will track east and into our region for
tonight...models suggesting a widespread wetting with between a
half inch /0.50/ and one inch /1.00/ of rain. During this time
frame (now through daybreak Tuesday), temperatures remain warm
enough for all of the precipitation to fall as rain. Temperatures
today are forecast to climb back into the 50s, then drift back
into the 40s this evening with onset of the steadier rain.


As of 400 AM EDT Monday...

Progressive upper flow with an active southern stream will keep
a steady stream of weather systems tracking across the region
during the period with the threat of notable rainfall, perhaps a
few thunderstorms, and then winter precipitation in the form of
accumulating snowfall.

A Miller B type scenario will evolve Tue-Wed as a southern
stream low tracks from the TN Valley into the central and
southern Appalachians, then migrates toward the SC/NC coast
before moving offshore and intensifying into a potential
significant noreaster later Wed into Thu.

As the surface low tracks into the eastern TN valley Tuesday,
widespread rainfall is expected with total liquid QPF of 1 to
1.5 inch by Tue afternoon/evening. As the surface translates
first to our southeast, colder air will begin to filter in both
from the west around the upper trough and also down through the
Shenandoah Valley in a wedge fashion. The column will cool
enough for precipitation to change from rain to snow in a top
down fashion, mainly I-64 corridor and western mountains/higher
elevations first, then working its way toward the Piedmont and
east of the Blue Ridge after sunset Tue. With the March sun,
warm ground, and initially above 0C 850mb temps until Tue
afternoon from the north to south, feel that accumulations will
be hard to come by until after the sun sets and the surface low
moves to our east/northeast Tue night, again in a top down
fashion. Higher elevations and further north have the best
chance of seeing 1 inch or more of snow.

Snow accumulations are quite problematic. First, ground
temperatures are warm and will not be below freezing at the
beginning of the event, and really only for a brief period Tue
night/early Wed in most areas. Second, March sun will render
accumulations difficult until after sunset Tue evening. Most of
the snow accumulation will come as the upper low sags southward
across the area and a deformation zone lingers over the area Wed
from the slowly northward moving coastal system.

Model snow accumulations are mainly in the 1-3 inch range, with
the exception of the GFS, which just like last weeks snowstorm
is double the other models, largely because it is double the QPF
as well. WPC has cut snow amounts roughly in half and shifted a
bit further west from earlier outlooks. Discussed the
possibility of a watch and/or advisory with neighboring offices.
While initially on board with a Watch for I-64 corridor and
through the western mountains of the CWA down into northwest NC,
latest WPC and most model guidance suggests warning criteria
snow will not be met with this event, with amounts at advisory
levels or less in most areas. This would be a 4th and 5th period
advisory, so that decision will be deferred to the day shift. We
feel quite certain that this event will net an advisory for a
number of counties along/west of the Blue Ridge, but confidence
in reaching Watch/Warning level criteria is too low to issue a
4th period Watch at this time. Will continue to highlight
potential in the HWO/eHWO and DSS mediums until confidence
increases. An advisory may well come out later today.

Another concern as the coastal system/noreaster gins up will be
strong northwest winds. This is evident Wed into Thu, much like
the system of last week.

Temperatures will be near normal Tuesday, but as the upper
trough moves to our south and the coastal low develops, will
drop to well below normal levels. 850mb temps in the core of the
upper low will drop toward -6C in the Wed-Thu time frame. This
will yield low temperatures in the 20s west to 30s east and
highs in the 30s west to 40s east, about 15-20 degrees below


As of 400 AM EDT Monday...

Active weather pattern is expected to continue with continued
mostly below normal temperatures. Progressive upper flow will
result in another fast moving/vigorous mid-latitude low pressure
area reaching the CWA as quickly as Friday night/early Saturday.
Once again, may be dealing with at least some threat of winter
precipitation with this event with a lingering wedge of cool air
in the wake of the preceding system and a warm front with good
isentropic lift, lifting northward into the region Saturday.
Most models are suggesting at least some period of snow/sleet
mountains and northern I-64 corridor areas until temperatures
warm into the 40s Saturday afternoon. The threat for winter
precipitation may return again Sunday morning in the
north/mountains. Temperatures will remain well below normal
during this period once again. Lows mainly in the 20s west to
30s east with highs in the 30s and 40s west to the lower 50s


As of 400 AM EDT Monday...

Mainly VFR under light and variable winds through first half of
today. Models indicate gradual development of MVFR Cigs along
spine of Appalachian Mountains by this afternoon. Approaching
mid CONUS storm system will result in increasing threat for rain
and lowering visibilities with MVFR vsbys developing toward
sunset then lowering to IFR during the overnight also associated
with development of IFR cigs and ocnl light to moderate rain.

Extended Aviation Discussion...

Low pressure will move ovhd Tuesday with continuation of
rain/low cigs/vsbys. As the low pressure system heads offshore
Tuesday night, precipitation wrapping along the western
periphery of this system is expected to change to snow. This
will result in lingering MVFR/IFR conditions, and gusty north
to northwest winds on Wednesday. Drier air should finally result
in improving conditions Thursday as high pressure builds from
the northwest.


As of 340 AM EDT Monday...

The Mount Jefferson NWR remains off the air and will likely be
sometime this week before it is operational again.




Back to Main Forecast Discussion Page