433
FXUS61 KRNK 171837
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
237 PM EDT Wed Jul 17 2024

.SYNOPSIS...
A front will cross the region tonight, bringing thunderstorms
this evening. This front shifts south of the area by Friday
allowing for cooler temperatures, but the proximity of the front
will keep showers and thunderstorms in the forecast through the
weekend.

&&

.NEAR TERM /THROUGH THURSDAY/...
As of 235 AM EDT Wednesday...

Key Messages:

1) Scattered thunderstorms this afternoon/evening

2) More thunderstorms on Thursday

Thunderstorms are will continue to develop this afternoon and storms
will be capable of strong winds gusts and very heavy rainfall.
Convective allowing models still indicate an more organized line
evolving as the storms cross east of the Blue Ridge and tracks
through the piedmont, mainly between 20Z/4PM and 00Z/8PM.

Showers and thunderstorms will diminish in coverage after
sunset but never completely erode. A cold front will cross
through the area overnight turning the wind from the southwest
to the northwest. This will also bring clouds into the mountains
after midnight. Expect patchy fog to develop after sunset,
especially in locations that have rain in the afternoon and
evening.

Best probability of thunderstorms Thursday afternoon and evening
will be in southern Virginia and northern North Carolina.

Lows tonight will be mild, limited by the surface dew points in
the mid 60s to lower 70s. Stayed close to NBM for highs on
Thursday.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
As of 1245 PM EDT Wednesday...

Key Points:

1. Near normal temperatures.
2. Showers/Storms limited to mainly southern sections Thursday night
through Friday night.
3. Better coverage of showers/storms on Saturday.

A look at the 17 July 00Z NCEP Ensemble Mean 500 mb Geopotential
heights shows a general area of troughiness extending from central
Quebec southwest into the Lower Ohio Valley. Within this general
region of troughiness, some ensemble averaged shortwave trough are
expected to head along roughly the US/Canadian border. This pattern
places our region within southwest flow aloft. At the surface
Thursday night into Friday, high pressure will be centered over the
Ohio Valley with a frontal boundary oriented w-e over the Deep
South. By Saturday into Saturday night, there may be a bit of
buckling northward of this front. Ensemble averaging offers only
small hint at this while some deterministic guidance and WPC
forecast frontal positions offer stronger support of this trend.

Output from the 17 July 00Z Ensemble Situational Awareness Table
shows 850mb temperatures averaging about +13C to +15C across the
area Thursday night into Friday. By Saturday into Saturday night,
temperatures moderate a bit to around +17C across the region.
Precipitable Water (PW) values Thursday into Thursday night will be
on a tight nw-se gradient across the region with values around 0.75
over Southeast WV to around 1.50 inches over Southside Virginia. As
we progress into Saturday/Saturday night, values increase to a nw-se
gradient of around 1.50 inches to 1.75 inches.

The above weather scenario suggest that Friday may be the driest day
of this portion of the forecast with the front farther south, and
high pressure building into the Ohio Valley. As the front shifts a
bit farther north on Saturday, we may see better daytime coverage of
diurnal afternoon/evening activity before it dissipates after sunset.

Temperatures are expected to be near normal values for this time of
year.

Confidence in this section of the forecast is moderate.

&&

.LONG TERM /SUNDAY THROUGH TUESDAY/...
As of 1245 PM EDT Wednesday...

Key Points:

1. Temperature trending to values above normal.
2. Shower/Storm chances trending higher.
3. Locally heavy rain possible by Tuesday/Wednesday.

A look at the 17 July 00Z NCEP Ensemble Mean 500 mb Geopotential
heights shows the persistent trough to our northwest remaining in
place through Wednesday. However, on gradual change is expected to
be a weakening of this trough as an equally persistent ridge over
the Southeast US strengthens. This pattern still keeps us within a
southwest flow aloft, but with better ridging closed to overhead, we
may be more capped to surface based convection and see higher
temperatures. At the surface, the center of surface high pressure
heads north into Canada from the Ohio Valley, and a frontal boundary
tracks north to closer to the Ohio Valley. This would place our
region on the warm side of the front. Additionally, a ridge of
surface high pressure builds into the Southeast US.

Output from the 17 July 00z Ensemble Situational Awareness Table
shows 850mb temperatures average about +17C to +18C across the
region each day. PW values gradually increase through the period. By
Wednesday, values of 1.75 to 2.00 inches will be common across the
region. Those areas at or above the 2.00 inch mark will be within
the 90 to 97.5 percentile of the 30-year climatology.

The above weather scenario offers moderating temperatures with
values a little above average through the period. Precipitation will
be on the increase as a front lifts north of the region. Once the
front is north of the region, the region will be in a more unstable
regime with above normal afternoon temperatures and higher humidity
values. By Tuesday/Wednesday, locally heavy rain will be possible
given above normal PW values.

Confidence in the above weather scenarios is low to moderate.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
As of 145 PM EDT Wednesday...

Thunderstorms are will continue to develop this afternoon and storms
will be capable of strong winds gusts and very heavy rainfall.

Visibility will be MVFR to IFR with the heavy rainfall,
otherwise VFR away from the storms.

Showers and thunderstorms will diminish in coverage after sunset
but never completely erode. A cold front will cross through the
area overnight turning the wind from the southwest to the
northwest. This will also bring IFR/MVFR ceilings into the
mountains after midnight. Expect ceilings to remain MVFR at KLWB
and KBLF through the 18Z end of the TAF forecast period.

Expect patchy MVFR fog to develop after sunset, especially in
locations that have rain in the afternoon and evening.

Average confidence in ceiling, visibility, and wind.

AVIATION OUTLOOK...

Front will be slow to exit the region, or be positioned just
south of the area into the weekend. Additional showers
and thunderstorms are expected in KDAN afternoon and evening on
Thursday and across the area on Friday through Monday. Expect
sub-VFR conditions with any of these storms.

Late night fog with result in IFR to MVFR visibility, otherwise
VFR.

&&

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

&&

$$

SYNOPSIS...AMS
NEAR TERM...AMS
SHORT TERM...DS
LONG TERM...DS
AVIATION...AMS