-- Discussion containing changed information from previous version are highlighted. --
165
FXUS61 KRNK 220614
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
214 AM EDT Sun Sep 22 2024

.SYNOPSIS...
Ongoing showers and thunderstorms across the Piedmont this
evening has lead to increased PoPs. There is a signal that some
isolated to scattered showers may develop along the NC/VA border
on the NC side in Rockingham and Caswell counties over the next
couple of hours; therefore, PoPs have been increased in these
areas as well. Temperatures were also adjusted as convection
this evening has caused some cooler pockets across the Piedmont
than what was previously forecast.

&&

.NEAR TERM /THROUGH TODAY/...
As of 140 PM EDT Saturday...

Key Messages:

1) A few strong to severe storms possible over S. Shenandoah Valley,
parts of the central/northern Blue Ridge, and the VA/NC piedmont
this afternoon and evening. Main concerns are localized damaging
winds and urban flooding.

2) Other areas may see showers/storms but likely not anything
strong. Heavy rain/isolated flooding still possible.

3) Fog and stratus possible overnight; stratus may linger over
the east through noon tomorrow under high pressure wedge.

The region remains in between broad upper level troughing over
the NE states and ridging centered over TX. At the surface, a
frontal system was approaching from the west. Farther north over
the eastern Great Lakes, the system was in the process of
occluding. IR imagery shows plenty of dry air aloft, with weak
mid level capping in place. This capping will continue to erode,
especially over the southern Shenandoah Valley and piedmont
areas by this afternoon.

PW values were around 1.2" this morning at KRNK, and will
increase  to about 1.4" or so through this afternoon in the
Shenandoah Valley, parts of the central/northern Blue Ridge, and
the piedmont ahead of the frontal system. Southerly winds will
increase convergence along the terrain, so convection will also
form along the Blue Ridge before drifting south. An upper level
left front jet streak and passing short wave energy will also
help support convection areawide. Instability and shear amounts
will be low to moderate over our area, but better to the NE and
E. We should still have enough ingredients to support a few
strong to isolated severe storms, again mainly over the S.
Shenandoah Valley, parts of the central/northern Blue Ridge and
the piedmont. Most of the activity will be multicell
clusters/lines and should be sub-severe, but may still contain
heavy rain. These main ideas are supported by SPC`s Day 1
Outlook, SREF ensembles, machine learning and CAMs.

The main concerns for the above mentioned areas will be isolated
damaging downdraft winds, as well as moderate to heavy rain
leading to isolated urban, small stream, and possibly flash
flooding.

Overnight we will be in the warm sector briefly before a
backdoor front moves through, allowing PW values to drop to
0.7 inches or less over the mountains by morning. This will
support moderate radiational cooling where skies clear, leading
to temperatures in the 50s to low 60s. Stratus will develop/move
over the foothills and also the eastern piedmont in association
with the passage of the backdoor front. Models are indicating
this stratus will hang around our eastern counties for much of
the day. Where skies clear overnight, and especially where it
rains, expect localized dense fog.

For Sunday, the upper level energy will be lacking for much of
the area, but there will be a stripe of PVA crossing over the
piedmont. At the surface, much drier air and high pressure
wedging in from the NE will likely smother most convection that
tries to form, but a stray shower will be possible later in the
day. Otherwise, expect mostly to partly sunny skies (outside of
where the stratus lingers) with highs in the upper 70s to mid
80s.

Confidence in the near term is moderate.

&&

.SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/...
As of 200 PM EDT Saturday...

Key Messages:

1: Monday should see the return of showers and storms, and
continuing into Tuesday


After a dry Sunday under some ridging and northeasterly flow, an
approaching front out of the plains will turn our flow back to the
south/southwest. With a stationary/warm front in the vicinity,
showers are likely to form on Monday afternoon, with the highest
probability in the mountains west of the Blue Ridge. Some of these
showers could produce lightning, but there is a low probability that
these storms will grow in strength such that they grow in strength
to become severe and potentially cause wind damage.

Tuesday the cold front will continue its march to the east, while
the warm front slowly lifts north in response to the approaching
attendant low associated with the cold front. Tuesday will see even
higher chances of showers and storms, with even more widespread
coverage in the entirety of the CWA. Temperatures will nudge a bit
cooler in this timeframe due to the increased cloud cover and rain
showers. Highs will remain in the mid to low 70s, and overnight dip
into the low 60s/upper 50s.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 230 PM EDT Saturday...

Key Messages:

1) High uncertainty remains in the long term period.

2) Chance of rain lingers through much of the week.

Quite a bit of variance among guidance this morning for the
period beyond Wednesday. This does not lead to much confidence
in the long term forecast, however ensemble guidance continues
to paint a rather stagnant pattern featuring daily chance of
rain and perhaps thunderstorms through mid to late week.

With rain potential and cloud cover, temperatures remain
slightly on the cooler side, generally in the 70s during the day
and 50s/60s overnight.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --
As of 200 AM EDT Sunday...

Radar indicates that rainfall has exited the area, with none
expected for the remainder of the night. Skies are mostly clear
per latest IR satellite imagery. Also beginning to see patchy
fog develop in spots, particularly in the mountain river valleys
as well as across the Piedmont where heavy rain fell earlier
this evening.

Patchy fog will burn off quickly after 13Z/9am. A backdoor cold
front will advance southward across the Piedmont during late
morning into the afternoon, making for a north to northeasterly
wind shift. May see scattered MVFR ceilings in the vicinity of
LYH during the afternoon, but not confident enough on that to
make mention in the TAFs, and believe most of the service area
will remain VFR through the day. Rapid update weather models
are hinting a few shower developing during the afternoon across
the mountains and foothills but, again, low confidence on how or
if these will develop.

During the 00Z to 04Z timeframe for Monday, high confidence
that widespread IFR stratus will develop and persist through
well after 12Z as marine air filters in behind the cold front.
Will not be surprised to see pockets of drizzle with this
activity as well.


EXTENDED AVIATION OUTLOOK...

Daily chance of showers, thunderstorms, and lingering sub-VFR
conditions continue Monday afternoon through at least midweek
as a slow-moving cold front approaches from the west.
-- End Changed Discussion --

&&

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

&&

$$

SYNOPSIS...NF/SH
NEAR TERM...SH
SHORT TERM...VFJ
LONG TERM...BMG
AVIATION...EB/NF