257
FXUS61 KRNK 140550
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
150 AM EDT Wed Aug 14 2024

.SYNOPSIS...
High pressure will keep our weather mainly dry through
Thursday. The next widespread chance for rain arrives toward the
end of the week and the weekend as a low pressure system
approaches from the Ohio River Valley.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 105 AM EDT Wednesday...

Key Messages:

1) Patchy to areas of fog in the mountain valleys and across
southern VA into NC this morning

2) Mainly dry but isolated showers possible across the Blue
Ridge this afternoon.

High pressure centered across the Great Lakes shifts east to the
Mid Atlantic this afternoon, which is going to keep a majority
of us with mainly clear skies and dry weather today. Some
differential heating along with a passing shortwave could spark
a shower or thunderstorm along the Blue Ridge south of Roanoke
and more-so across the High Country of NC this afternoon but
suspect limited coverage so kept pops mainly 20 percent or
lower.

Prior to this, fog appears likely across our NC counties into
southern VA this morning but should not be too dense, with river
fog into mountains also. Will monitor obs/trends to see if any
statements need to be issued since schools are back in session
for some.

Any showers should fade this evening with mostly clear skies
tonight.

Highs today close to normal with mid 80s east to mid 70s to
lower 80s west. Lows tonight to also run close to normal with
lower to mid 60s east to upper 50s west.

Forecast confidence is above average except average on shower
coverage.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/...
As of 145 AM EDT Wednesday...

Key Points:

1. Still dry for Thursday.
2. Good coverage of showers and storms Friday through Saturday
night, especially across western sections during afternoon/evening
hours.
3. Cold front crosses the area late Saturday night.

A look at the 13 Aug 12Z NCEP Ensemble Mean 500 mb Geopotential
heights shows a shortwave ridge over the region Thursday into
Friday. Friday Through Saturday night a shortwave trough will
progress eastward across the Great Lakes region and amplify,
reaching the spine of the central and southern Appalachians by late
Saturday night. At the surface, high pressure will be over the
region on Thursday while low pressure will be over the Upper
Mississippi Valley. As time progresses, the high will head east into
the western Atlantic while low pressure progresses into and eastward
across the Great Lakes region. A cold front will cross our area late
Saturday night.

Output from the 13 Aug 12Z Ensemble Situational Awareness Table
shows 850mb temperatures between +15C and +17C on Thursday. The
range inches slightly higher on Friday to +16C to +18C. By Saturday,
numbers are slightly higher as well within the +17C to +19C range.
Precipitable Water values on Thursday will range from 1.00 to 1.25
inch across the region. Values progressively increase Thursday night
into Friday, reaching around 1.75 inch by Friday afternoon. On
Saturday, numbers fall to around 1.25 to 1.75 inch from west to east
across the region.

The above weather scenario offers mainly dry conditions still for
Thursday. However, by Friday, with the exiting of high pressure, and
the approach of a cold front, low level southerly moisture flow is
expected. With daytime heating an increased upper level dynamics,
look for good coverage of afternoon showers and storms, especially
over the mountains. Prior to the afternoon, isolate to scattered
showers are possible across western sections as early as late
Thursday night. Friday night through Saturday night, the chance of
showers and storms will continue with the approach of a cold front.
The front is expected to reach the region late Saturday night into
early Sunday morning.

Expect temperatures to average around normal for this time of year.

Confidence in the above weather situation is moderate to high.

&&

.LONG TERM /SUNDAY THROUGH TUESDAY/...
As of 145 AM EDT Wednesday...

Key Points:

1. Continued, but lower, chances of showers/storms into early next
week.
2. Temperatures slightly above normal.

A look at the 13 Aug 12Z NCEP Ensemble Mean 500 mb Geopotential
heights shows a shortwave trough over the spine of central and
southern Appalachians Sunday morning. This feature is expected to
experience very little, if any, progress eastward through Tuesday.
At the surface, a cold front will move southeast of the region
Sunday into Monday. By Tuesday, high pressure will start to work its
way into western parts of the area.

Output from the 13 Aug 12z Ensemble Situational Awareness Table
shows 850mb temperatures are expected to be +16C to +18C on Sunday,
+16C to +17C on Monday and Tuesday. Precipitable Water values are
expected to range from 1.25 to 1.50 inch on Sunday, 1.00 inch to a
little over 1.25 inch on Monday and Tuesday.

While the cold front will be exiting the region, the axis of the
parent upper trough will be slow to depart. This feature with an
expected cold pool aloft will help keep mid-level lapse rates on the
steep side. While coverage will be less than what is expected for
Friday and Saturday, peak heating isolated to scattered
showers/storms are expected Sunday, Monday, and perhaps even Tuesday.

Temperatures are expected to average a few degrees above normal.

Confidence in this portion of the forecast is moderate.

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
As 105 AM EDT Wednesday...

VFR conditions are expected at all terminals through most of
the taf period. The only exception will be the potential for
patchy fog to develop this morning. Confidence in fog is
highest at KLWB but some patchy fog may impact KBCB and KDAN.

Any patchy fog should vanish by 13z, Winds will remain light
from the east to northeast on Wednesday.

EXTENDED AVIATION OUTLOOK...

Thursday should remain dry with VFR conditions across the Mid
Atlantic as high pressure maintains control. However,
as high pressure moves offshore on Thursday night, clouds will
increase from the west due to an approaching cold front. This
front should bring a good chance of showers and thunderstorms
along with potential MVFR/IFR ceilings during Friday and
Saturday. Thunder chances may lower by Sunday as more stable air
arrives behind the cold front.

&&

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

&&

$$

SYNOPSIS...PM/PW/WP
NEAR TERM...WP
SHORT TERM...DS
LONG TERM...DS
AVIATION...PW/WP