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143
FXUS61 KRNK 090129
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
929 PM EDT Wed May 8 2024

.SYNOPSIS...
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Chances of showers and thunderstorms will continue through
Thursday when a cold front crosses the Mid Atlantic. Cooler
conditions will arrive for the weekend with the potential for
mountain showers. Warmer air should return during next week.
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&&

.NEAR TERM /NOW THROUGH THURSDAY/...
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Issued at 929 PM EDT Wed May 8 2024

There`s a break in the action across the forecast area -- well,
at least for the time being. With the latest subjective analysis
indicating a surface front hanging out near the I-66 corridor,
our region remains in the warm sector. This evening`s sounding
shows a "healthy" amount of dry air in the lowest 15 kft. of the
atmosphere (give-or-take), likely due, at least in part, to a
deep westerly flow in the atmosphere. Given this, I admittedly
have some concern about our shower/thunderstorm probabilities
through the rest of the night.

Right now, we`re watching the ongoing convection that`s
occurring to our west. That`s still expected to head into our
area closer to midnight, although given the westerly flow in
place, the amount of convective coverage could be debated. I
made some adjustment to timing and convective coverage for
(primarily) the overnight hours earlier this evening. This was
based on fairly consistent runs of high-resolution CAMs and
predicated on a slight backing of the flow aloft. (In other
words, the current westerly flow becomes a slightly more
favorable southwesterly flow.)

Both thermodynamically and kinematically, the most favorable
environment for any strong or severe thunderstorms should remain
south of the Virginia/North Carolina border overnight. In this
area, effective bulk shear values greater than 35 kts., along
with CAPE values (surface-based and mixed-layer) greater than
500 J/kg may be seen.

In short, additional updates will likely be needed as we see how
the atmosphere evolves this evening.

As of 125 PM EDT Wednesday...

Key Messages:

1) The severe threat is decreasing overall. Showers and
thunderstorms are possible later this evening into Thursday.

2) A cold front will cross the Mid Atlantic on Thursday.

Cloud debris from earlier showers and thunderstorms is crossing
over the Appalachian Mountains in association with an outflow
boundary. The 12Z RNK sounding this morning revealed a notable
amount of westerly flow and drier air just above the surface.
Based on the latest high-resolution models, the severe threat
has shifted further south to North Carolina and Tennessee. As a
result, the threat in Virginia and West Virginia has decreased.

Scattered showers and thunderstorms may occur in northwest
North Carolina during the afternoon, but the best chances may
not take place until late this evening into tonight as the
outflow boundary is buckled back northward as a warm front due
to an approaching low pressure system in the Plains. Showers and
thunderstorms could reach the mountains but fade before
completely crossing the Blue Ridge overnight. The antecedent
conditions remain rather dry, so any flood threat is marginal.

The cold front from the aforementioned low pressure system will
cross the Mid Atlantic on Thursday. However, the central area of
low pressure should pass to the north over Pennsylvania. Some of
the models indicate the showers and thunderstorms possibly
splitting Virginia and West Virginia during Thursday afternoon,
but the chances will remain in the forecast due to the
dynamical and orographical lift possible along with the warm and
humid air. The wind could also turn breezy from the west during
Thursday as the cold front passes.
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&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
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As of 130 PM EDT Wednesday...

Key Messages:

1. Cooler temperatures for the weekend.

2. Showers and thunderstorm possible late Saturday.

A broad mid level trough will swing through the Great Lakes and
Mid Atlantic, its axis to the east of the area by late Friday,
and northwesterly flow aloft over the central Appalachians. A
cold front crosses the region Thursday, and will be to the east
of the forecast area by the start of this forecast period, with
overall shower and storm activity decreasing into Friday,
although some upslope showers in the west may linger through the
day as a shortwave rounds the base of the trough. Chances for
storms are greatest over the NC Piedmont, where there will be
greater instability. A cooler and drier airmass comes in behind
the front, bringing below normal temperatures for the weekend.
Cold air advection and pressure rises behind the front will lead
to gusty winds for Friday, mainly in the west and higher
elevations.

Subsidence in the wake of the departing wave will keep Saturday
dry to start the day. Another trough digs southward towards
the area by late Saturday, its associated surface low tracking
across the Great Lakes into the upper Mid Atlantic by Sunday.
The cold front crosses through the area late Saturday into
Sunday, increasing precipitation chances through that time
frame. However, thinking coverage of showers and storms will be
limited by the drier airmass overhead.

Temperatures will drop to below normal Friday and through the
weekend behind the frontal passage on Thursday. At this time,
probabilities for low temperatures below 40 degrees are highest,
around 50% to 70%, in the typical cold spots, like Burkes
Garden and Mount Rogers and western Greenbrier County WV,
Saturday morning.
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&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 130 PM EDT Wednesday...

Key Messages:

1. Gradual warming trend through the period.

2. Chances for showers and thunderstorms increase towards
midweek.

Mid and upper level ridging builds in to the west of the area
behind the trough, and surface high pressure expands eastward
into the Mid Atlantic for the start of the long term forecast
period. This will bring an end to the precipitation and keep
Sunday and Monday mostly dry. With high pressure overhead, and
increasing 500mb heights from the ridging, expecting clearer
skies and a warming trend in temperatures. An upper trough
develops in the lee of the Rockies during the first half of the
work week, and deepens as it tracks into the south central US,
and then across the Gulf Coast states, tapping into plentiful
moisture from the Gulf. As the surface high shifts east and into
the Atlantic, precipitation chances increase as the southerly
flow from the high brings some of this moisture into the area.
After Tuesday and further into the middle of the week, long term
models diverge on the placement and timing of the heaviest
precipitation from this system, which lowers forecast confidence
this late in the forecast period. That being said, most of
Tuesday and Wednesday have the greatest chances for showers and
possibly storms.

&&

.AVIATION /01Z THURSDAY THROUGH MONDAY/...
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Issued at 929 PM EDT Wed May 08 2024

VFR flight categories across the forecast area this evening will
reduce overnight, as additional SHRA/TSRA move into the region
from the W. Precipitation could impact W/SW terminals as early
as 09/0300 UTC, with much of the forecast area, especially S of
KLWB-KLYH seeing some -SHRA/TSRA through the overnight hours.
Reduced CIGs/VSBYs due to precipitation will allow widespread
reductions into MVFR territory to be seen, with some IFR CIGs
possible. The greatest odds of this happening are across my SE
WV terminals, where BR could be seen (in addition to the
SHRA/TSRA) toward 09/1200 UTC.

Expect improvement in flight categories after 09/1200 UTC, with
a return to VFR anticipated between 09/1500-1800 UTC. W-SW winds
are expected to increase ahead of an approaching cold front
Thursday, with additional SHRA/TSRA anticipated to develop
during the afternoon.

Extended Aviation Outlook...

Lingering upslope flow could provide showers and MVFR ceilings
for BLF and LWB on Friday, while the Piedmont remains VFR due to
downslope flow. Cooler weather will arrive for the weekend. Some
upslope mountain showers may occur during late Saturday into
early Sunday. VFR conditions should persist through Monday as
high pressure takes control of the Mid Atlantic.
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&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...None.
NC...None.
WV...None.

&&

$$

SYNOPSIS...PW
NEAR TERM...DB/PW
SHORT TERM...AS
LONG TERM...AS
AVIATION...DB