Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 191942

Area Forecast Discussion
National Weather Service Blacksburg VA
342 PM EDT Mon Mar 19 2018

Low pressure over the central Plains will cross east over the
Tennessee Valley and central Appalachians on Tuesday. The low
will then deepen off the coast and track northeast Wednesday and
Thursday. High pressure will cover much of the eastern United
States on Friday.


As of 210 PM EST Monday...

Vorticity advection, isentropic lift and upslope forcing will
all contribute to widespread rain across southwest Virginia,
southeast West Virginia and northwest North Carolina tonight.
Water vapor loop shows a short wave over the Tennessee Valley
which will cross the central Appalachians tonight. Will be
leaning toward the heavier side of the guidance for rainfall
amounts. Clouds and warm air advection will limit temperature
drop tonight. Will use a non diurnal temperature trend for

Models continue to indicate the beginning of cooler temperatures
advancing down the eastern slopes of the appalachians late Tuesday.
Otherwise there may a be sleet or snow mixed in with the rain north
of I-64 Tuesday. BUFKIT forecast soundings keep Hot Springs rain
until afternoon with a slow transition to snow in the afternoon.
Surface temperatures may not drop below freezing during the day
so any accumulation before dark will be minimal.


As of 330 PM EDT Monday...

Guidance seems to have come into general agreement with the complex
synoptic evolution of our midweek weather system. Several surges of
short wave energy will carve out a broad, deep trof which culminates
in a closed low moving across the Appalachians and central mid
Atlantic region on Wednesday. The short wave energy rotating around
the trof will drive development of low pressure that will move up
the Atlantic coast Tuesday night and Wednesday as a surface
reflection of the upper low lingers back to the west over the
mountains, all while a wedge of high pressure lingers east of the

As the initial wave Monday night departs to the east early Tuesday,
expect some light lingering precipitation through early Tuesday
afternoon. By Tuesday afternoon expect convection to develop on the
western/southern periphery of the wedge as the upper trof begins to
push over the region from the west. Convective elements will then
ride up over the wedge as the complex structure of surface low
pressure begins to develop. During this time also expect
synoptically induced dynamic cooling to aid thermodynamic cooling
and allow for a transition from rain to snow from north to south and
from high to low elevations, with the possible exception of
locations deeper into the NC piedmont. Snow will then continue
through Wednesday with primary forcing from the closed upper low.
Ptype will become complicated by diurnal effects of heating
especially east of the Blue Ridge and at lower elevations and wet
snow conditions may not be very efficient at accumulating. The event
will gradually taper off as the upper low slowly pulls off to the
east Wednesday afternoon/night and lingering upslope snow showers
diminish by Thursday morning.

The end result will be several inches of wet snow across the region
Tuesday night through Wednesday with greater amounts west of the
Blue Ridge and at higher elevations, and lower amounts further to the
south and east. Currently leaning toward thermal profiles which would
more favor sleet as a mixed ptype than freezing rain during the
transition Tuesday night mainly north of Interstate 64 but this is a
fine line and will be monitored closely. While confidence remains low
in specifics, there is enough certainty in potentially impactful winter
weather to warrant the issuance of a winter storm watch for locations
along and west of the Blue Ridge from Tuesday night through Wednesday.
This watch may be adjusted in timing and/or coverage, and some
locations may eventually transition to a warning or advisory.


As of 330 PM EDT Monday...

A large ridge being undercut by southern stream energy and moisture
will move across the eastern US into the first part of next week.
This will keep our weather active through Monday.

After a brief break of fair weather on Friday, a warm front
extending from low pressure in the midwest will begin to push
precipitation back into the region Saturday. Temperature profiles
point to the possibility of wintry precipitation especially from the
Blue Ridge west through Saturday night. Solutions then start to
diverge with the possibility of the frontal boundary and wedge
lingering over the region with precipitation through the weekend, or
possibly a brief break on Sunday before the next wave brings
precipitation back for Monday. Will blend solutions to find a
compromise, but the main point is to expect unsettled conditions
into the first part of next week with temperatures generally below


As of 145 PM EDT Monday...

Mainly VFR this afternoon in southwest Virginia, northwest
North Carolina and southeast West Virginia with a few spots of
MVFR and light rain along the Virginia/North Carolina border.
Widespread moderate rain will spread across the region from the
southwest with MVFR to IFR ceilings. High confidence of IFR to
LIFR conditions between 03Z/11PM to 09Z/5AM when lift and
upslope is maximized.

Primary batch of rain moves northeast of the area Tuesday
morning. Moderate confidence that ceilings and visibility will
improve to VFR after the rain ends on Tuesday. Next round of
rain will move after the 18Z end of the TAF period.

Extended Aviation Discussion...

As a 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
MVFR/IFR conditions, and gusty north to northwest winds Tuesday
night and Wednesday. Drier air should finally result in
improving conditions Thursday as high pressure builds from the
northwest. Another low pressure system will bring rain and the
associated MVFR or lower conditions for Friday and Saturday.


As of 335 PM EDT Monday...

The Mount Jefferson NWR remains off the air. The radio unit
needed to repair the system is expected to arrive on Wednesday.
The earliest this system will again be operational will be
Wednesday afternoon.


VA...Winter Storm Watch from late Tuesday night through Wednesday
     evening for VAZ007-009>020-022>024.
NC...Winter Storm Watch from late Tuesday night through Wednesday
     evening for NCZ001-002-018.
WV...Winter Storm Watch from late Tuesday night through Wednesday
     evening for WVZ042>044-507-508.


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