555
FXUS61 KRNK 240118
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
918 PM EDT Mon Sep 23 2024

.SYNOPSIS...
High pressure is situated across the Mid-Atlantic today, wedged
against the eastern face of the Appalachians. A slow-moving
cold front will meander along the Ohio River Valley over the
next several days, triggering rounds of showers and thunderstorm
activity that will persist through much of the workweek. PTC 9
lifting northward from the Gulf of Mexico toward the end of the
work week may bring more widespread rainfall to the region.

&&

.NEAR TERM /THROUGH TUESDAY/...
As of 915 PM EDT Monday...

Key Messages:

1) Additional rounds of showers and thunderstorms are expected
again on Tuesday, with a few bringing locally heavy rain and
damaging winds.

2) Cloudy conditions again tonight are expected with patchy fog
and additional showers and a few storms.

The only changes made to the forecast for tonight were
adjustments to the POPs. At 8 pm EDT, low level moisture was
pooling along a warm front located roughly along the eastern
slopes of the Blue Ridge. The 00Z/24 RNK sounding measured a
PWAT value of 1.56 inches which is above the 90th percentile for
this date. This anomalously high moisture combined with the low
level boundary and an approaching upper level disturbance will
likely spawn more showers and even a few storms with lingering
instability during the overnight hours, especially near the low
level boundary. Many of the CAMs, including the HRW NSSL which
has a fairly good grasp of the location of precipitation at 8 PM
EDT, reflect this as well. As a result, modified POPs to
account for showers/storms continuing through the overnight
hours.

No changes were made to the temperature or wind forecasts for
tonight.

A mid-level shortwave vorticity perturbation is expected to
push across the region late Tuesday afternoon and evening. This
coupled with a stalling cold front west of the Appalachian
mountains, and an upper level trough digging into the mid-
Mississippi valley will provide sufficient upper level
support/forcing for ascent for widespread shower and
thunderstorm developing Tuesday afternoon. A surface wedge
situated across the coastal plain will lead to southeasterly
flow across the VA/NC border during the afternoon and evening
hours on Tuesday. Current CAM guidance suggests that a warm
front will remain situated along or just north of the VA/NC
border tomorrow, which may provide a focus for severe weather,
and training thunderstorms. The biggest caveat will be the
placement of this boundary Tuesday afternoon, and the amount of
clearing south and west of this boundary to allow for
destabilization. WPC currently has an areawide marginal risk for
excessive rainfall on Tuesday as widespread rainfall totals of
1-2 inches are forecast. SPC similarly has a marginal risk for
severe thunderstorms for much of the western portion of the area
where destabilization is expected to be greatest. Overall,
expect highs in the upper 70s where clearing occurs across SW
Virginia and the VA/NC border, and low 70s to upper 60s where
low clouds hang around across interior Piedmont locations.


Confidence in the near term is moderate.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
As of 215 PM EDT Monday...

Key Messages:

1: Daily showers and storms

2: Potential for outer bands of PTC9 to bring further rain Thursday

A glacially slow cold front attendant to a low in the southern
Great Lakes will continue its march to the east in our
direction. The southerly flow will fetch plenty of Gulf moisture
to interact with a stationary front over the Mid-Atlantic,
leading to showers and storms for most of the day through
Wednesday evening. Wednesday there is a marginal risk of severe
storms west of the Blue Ridge, where orographic effects could
enhance the freely available moisture and moderate instability
into stronger convection. Main threat would be damaging
thunderstorm winds. Localized flooding may also be a concern, as
PWATs will be in the 1.5-1.75" range for most of the CWA, and
storms in this environment have been observed to be extremely
efficient rain producers. This problem could be exacerbated by
freshly fallen leaves as we are getting into the fall season,
which could be piled up from the aforementioned thunderstorm
winds. This can clog drains and sewer openings, preventing
runoff in streets and sidewalks.

By Thursday evening, we may be close enough to feel the impacts of
Potential Tropical Cyclone 9`s outer rain bands. PTC 9 is progged to
be quite a wide storm, so even though the center of the storm
(according to the current NHC track) will be near the panhandle of
Florida, the outer rain bands (and tropical moisture to interact
with the pre-frontal environment) could impact our NC counties as
early as Thursday evening.

Temperatures will be around normal, with little diurnal sway due to
high dewpoints and widespread thick cloud cover.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
As of 200 PM EDT Monday...

Key Messages:

1) Confidence is increasing that Potential Tropical Cyclone Nine
will affect the area Friday into the weekend, though exact impacts
remain uncertain.

2) Rainy, cloudy, and breezy conditions will persist and keep below
average high temperatures in place through the weekend.

High pressure over New England and the Great Lakes region will begin
to back out of the area on Friday, as PTC9 moves northward towards
our area. This high pressure, along with a cutoff upper-level low
over the Great Plains will steer PTC9 towards the northwest. Where
this turn occurs is still uncertain and will determine the magnitude
of impacts seen across the RNK CWA. Most model ensembles continue to
indicate the center of the low somewhere in the southern Appalachian
Mountains on Friday, but the past few model runs have not been
consistent with the track post-landfall, varying east to west.
Should the current forecast track continue with the storm moving
into far western North Carolina, heavy rainfall will be expected
across the CWA on Friday into Saturday as models are consistently
showing a band of rain spreading over the area.

Regardless of the exact track of the system, moisture is expected to
increase with showers possible each day through the period. PoPs
have been raised to reflect recent model runs and taking into
account that a tight gradient between the low pressure system to the
south and the high pressure system to the north will allow strong
easterly upslope flow to further enhance rainfall across the area.
This setup will continue into Saturday, though PTC9 will weaken as
dry air begins to overtake the system.

The aforementioned high pressure over New England will wedge back in
on Saturday, keeping cloudy and cool conditions in place, but
decreasing rain chances. Showers remain possible Sunday into Monday,
though Monday is trending drier. Highs throughout the period will
generally be in the 60s and low 70s, with breezy conditions
persisting. Low temperatures will remain mild, around 60 degrees
this weekend before lowering into the 50s next week.

&&

.AVIATION /01Z TUESDAY THROUGH SATURDAY/...
As of 736 PM EDT Monday...

Early this evening, MVFR to IFR CIGs were observed along and
east of the Blue Ridge and confidence is high that these
ceilings will fall tonight keeping poor flying conditions in
place well into Tuesday. For the mountain sites of KLWB, KBCB
and KBLF,while VFR conditions were observed this evening, a
moist airmass will allow CIGs to drop to IFR levels quickly
tonight.

These low cigs will continue well into Tuesday morning and
likely through Tuesday afternoon, with KDAN having the best
chance of seeing improving conditions. Confidence is low
regarding the timing of when/if CIGs improve to VFR category.

A nearly stationary front bisecting our area will allow periodic
showers to re-develop during the overnight hours, so kept VCSH
in for most locations tonight. A better chance for showers and
storms arrives tomorrow afternoon after 17-18Z.

EXTENDED AVIATION OUTLOOK...

MVFR/IFR stratus and fog are expected to occur in rounds through
at least the middle of the week, and increasingly likely to
persist through the end of the workweek. Rounds of showers and
thunderstorms will also continue to pass across the lower Mid-
Atlantic.

Low pressure lifting northward from the Gulf of Mexico toward
the end of the week may bring more widespread rainfall and sub-
VFR conditions to the region.

&&

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

&&

$$

SYNOPSIS...EB/NF
NEAR TERM...PH
SHORT TERM...VFJ
LONG TERM...JCB
AVIATION...PH