491
FXUS61 KRNK 260205
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
1005 PM EDT Wed Sep 25 2024

.SYNOPSIS...
Rounds of scattered showers and thunderstorms will continue
across the area tonight and Thursday with the rainfall
resulting in increasingly saturated soils. Then Thursday night
and Friday moderate to heavy rain around Hurricane Helene will
greatly enhance the threat of flooding in the mountains and
foothills. Over the weekend the remnants of the tropical system
will be trapped over the Tennessee Valley with a lower
probability and coverage of showers.

&&

.NEAR TERM /THROUGH THURSDAY/...
As of 955 PM EDT Wednesday...

Key Messages:

1) Tornado threat is non-zero overnight, with plenty of
vorticity available in the lower atmosphere to support quick
spin-ups.

2) Most will just see periods of moderate rain, fog, and
drizzle towards morning.

2) Less coverage of rain tomorrow mid morning until the first
bands of Helene arrive.

Convection continues across the area, although there has been
some weakening in the last 15 to 30 minutes from a severe
standpoint. With a tropical airmass in place, a stationary
boundary snaked across the region was able to provide additional
storm relative streamwise vorticity than what was in the
environment otherwise. This enhanced storm relative helicity and
helped support rotation and prompted multiple tornado warnings
tonight.

Expect rain, drizzle, and occasional thunderstorms tonight.
Stratus will lower to 500 ft or less overnight into Thursday.
There should be a break in convection for some generally 9 to 10
am and lasting until the afternoon, when the first rain bands
from Helene approach from the south.


As of 300 PM EDT Wednesday...

Key message:

    - Marginal threat of severe thunderstorms in the mountains this
      afternoon and evening

    - No change to the Flood Watch at this time

Very slow improvement in the retreat of the stratus today, resulting
in the best instability from Greenbrier County WV to Tazewell
County VA and across southern Virginia into northern into northern
North Carolina. Hi-Res and convective allowing models show isolated
to scattered thunderstorms, mainly after 5PM ahead of the persistent
line of storms southern West Virginia into eastern Tennessee. a
second cluster of showers and thunderstorms will develop and move
across the mountains and foothills overnight. More showers and
thunderstorms are expected on Thursday. No change to the Flood Watch
is planned at this time.

With the moist airmass and surface dew points in the 60s,
temperatures will stay mild overnight. Highs on Thursday will be
held in check due to the clouds and precipitation.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
As of 220 PM EDT Tuesday...

Key Messages:

1: Outer bands of Hurricane Helene will cause showers as early as
Thursday

2: Heaviest rainfall will be Friday morning


On Thursday night we will be well within the reach of Helene`s outer
bands, as she is a storm with a large radius. Friday morning will be
when Helene`s center makes its closest pass to southwest VA. Friday
morning will be the time period in which the heaviest rain falls,
though parts of the Blue Ridge and High Country of NC may have
already received upwards of 1-2" from Thursday and during the
overnight period. This will pre-saturate the ground before the
highest intensity rainfall rates. This situation is a clear set up
for flash flooding, and it will have to be a closely monitored
event. Additionally, winds will be their strongest Friday morning as
well with winds gusting around 50 MPH along ridges in the High
Country and southwest VA, 35-45 MPH in other parts of the mountain
region. The Piedmont will be less impacted, gusting up to 25 MPH.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 230 AM EDT Wednesday...

Key Messages:

1) Tropical airmass remains through Saturday.

2) Cooler weather arrives Sunday behind a cold front.

3) Low rain chances are possible each day through the middle of
next week.

As Tropical Storm Helene begins to dissipate over the
Appalachian mountains early on Saturday, remnant moisture and
breezy conditions will remain across the area. Rain chances
decrease significantly on Saturday but remain possible. High
temperatures will be in the 70s, with eastern piedmont locations
around 80. For Sunday, surface high pressure over New England
will begin to wedge back into the RNK CWA, pushing drier and
cooler air southward. Residual moisture from Helene will
continue to ride over top of this wedge, leading to light
showers and cloudy conditions continuing into early next week.

Due to the cloud cover and high pressure wedge, temperatures
are expected to remain below normal beginning on Sunday. Highs
will be in the 60s and 70s, with lows in the 50s to around 60
degrees through midweek. Winds also remain slightly elevated due
to the wedge. There is some model disagreement with where the
remnant low and associated moisture will go early next week. The
Ensemble Situational Awareness Table continues to keep
precipitable water values around 1.5 inches for early next week.
Due to this, PoPs are kept modest through the forecast period,
with showers possible each day.

&&

.AVIATION /02Z THURSDAY THROUGH MONDAY/...
As of 1000 PM EDT Wednesday...

Areas of showers and thunderstorms were bringing varying
conditions to the area...anywhere from IFR to MVFR. Expect this
to continue overnight, however ceilings will become LIFR/IFR
everywhere as dew point depressions lessen/temperatures drop
towards the dew point. Drizzle and low stratus along with patchy
fog will be common in the AM. Not expecting much improvement
however throughout the day, with low levels becoming saturated
ahead of Helene and her rainbands. May see a lower chance for
rain from about 15Z to 21Z, before the first rainband arrives.

Average confidence in ceiling, visibility, and wind.


EXTENDED AVIATION OUTLOOK...

Widespread moderate to heavy showers and isolated thunderstorms
will cover the mountains and foothills with light rainfall
amounts in the piedmont on Thursday night and Friday. Wind
speeds will increase in the mountains. Gusts of 25 to 45 kts are
likely at the higher elevations. Wind gusts at local TAF sites
will remain at or below 40 knots.

Moderate  in flight conditions and diminishing winds are
expected Saturday through Monday. A chance of light showers will
continue around the remnants of Helene.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...Flood Watch through Thursday evening for VAZ007-009-015.
NC...Flood Watch through Thursday evening for NCZ001-002-018-019.
WV...None.

&&

$$

SYNOPSIS...AMS
NEAR TERM...AMS/SH
SHORT TERM...VFJ
LONG TERM...RCS
AVIATION...AMS/SH