153
FXUS61 KRNK 121831
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
231 PM EDT Mon Aug 12 2024

.SYNOPSIS...
An upper level disturbance will cross the area Tuesday resulting
in clouds and isolated showers, otherwise a large area of high
pressure centered over the northern Mid-Atlantic will keep the
weather mainly dry. The next widespread chance for rain arrives
toward the end of the week as a low pressure system approaches
from the Ohio Valley.

&&

.NEAR TERM /THROUGH TUESDAY/...
As of 230 PM EDT Monday...

Key Message: Mainly dry weather tonight with clouds and a few
showers Tuesday. Primary threat for showers is along and south
of the VA/NC border.

Weather pattern is relatively benign. High pressure is centered
to our north and is expected to maintain mainly dry conditions.
The only fly in the ointment is an upper level disturbance, or
short wave trough, that will pass across the area from west to
east Tuesday. Feature does not look that impressive but still
anticipating passage of mid/upper level moisture that may
generate virga or light showers Tuesday morning, followed by
a chance for thunderstorms generally south of the VA/NC border
Tuesday afternoon where somewhat better instability will exist
over the Carolinas.

Due to the increasing cloud cover tonight, did not advertise
any fog...temperatures ranging from 55 to 60 in the mountains
to the lower 60s piedmont. The clouds should hold temperatures
down a few degrees Tuesday (compared to Monday) with highs
generally in the 70s.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/...
As of 115 AM EDT Monday...

Key Points:

1. Near normal temperatures.
2. Isolated/Scattered showers/storms on Tuesday.
3. Mainly dry Wednesday.
4. Isolated/Scattered showers/storms Thursday and Thursday night.

A look at the 11 Aug 12Z NCEP Ensemble Mean 500 mb Geopotential
heights shows a long wave trough moving east of the region Tuesday
into Wednesday as an upper ridge builds over the Upper Mississippi
River Valley. Wednesday into Thursday, an upper trough remains
positioned over the western Atlantic, while ridging shifts east to
over the Ohio Valley. A weak shortwave trough deepens over the Upper
Mississippi Valley Thursday night. At the surface, a high pressure
center is depicted strengthening over the Great Lakes/Ohio Valley
region Tuesday through Thursday, but each day progress slowly
eastward in position.

Output from the 11 Aug 12Z Ensemble Situational Awareness Table
shows 850mb temperatures will average +14C to +16C across the region
Wednesday and Thursday. Precipitable Water values will average 1.00
to 1.25 inches across the region during this portion of the forecast.

The above weather pattern should allow for some isolate to scattered
showers/storms on Tuesday as daytime heating interacts with the
passage of the trough axis. Wednesday should be dry for most of the
region with the trough axis to our east, and high pressure build
into the Ohio Valley. Thursday still should be primarily dry.
However, as the ridge axis shifts east, and an upper level trough
approaches from the west, expect the low level flow to take on more
a southerly component. This may allow for a bit more more moisture
into the region. Combined with daytime heating, isolated/scattered
afternoon showers/storms will be possible. Rather than dying out at
sunset, with the continued approach of the shortwave trough Thursday
night, the activity is expected to continue into and through the
overnight hours.

Confidence in the above weather scenario is moderate to high.

&&

.LONG TERM /FRIDAY THROUGH SUNDAY/...
As of 115 AM EDT Monday...

Key Points:

1. Near or slightly cooler than normal temperatures.
2. Daily chances of showers/storms with best chance west.

A look at the 11 Aug 12Z NCEP Ensemble Mean 500 mb Geopotential
heights shows the weak shortwave trough over the Ohio Valley
remaining nearly stationary, but increasing in amplitude Friday
through Sunday. At the surface, through Sunday, the center of high
pressure shifts east into the western Atlantic while low pressure
develops over the Lower Ohio Valley.

Output from the 11 Aug 12z Ensemble Situational Awareness Table
shows 850mb temperatures inch upward slightly to an average of +16C
across the area by the weekend. Precipitable Water values will trend
higher over the weekend with numbers closer to the 1.25 to 1.50 inch
range.

A slow eastwardly moving upper trough over the Great Lakes/Ohio
Valley will keep our region within a moist, mild, and unstable
airmass heading into and through the weekend. Each day shower/storm
coverage should be greatest over western sections. For temperatures,
lows should trend slightly milder as dew point values increase.
However, a greater abundance of cloud cover and better chances of
precipitation may mean high temperatures slightly cooler than those
expected mid-week.

Confidence in the above weather scenario is moderate.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
As of 230 AM EDT Monday...

Mainly VFR expected through the 24 hour valid TAF. Increasing
mid/upper level moisture tonight should prevent river fog
formation. Clouds may generate some virga or light showers
Tuesday morning. Weak instability may lead to widely scattered
thunderstorms across the piedmont of NC Tuesday afternoon.

Winds generally 5kt or less from the north.


AVIATION OUTLOOK...

Mainly dry weather expected Wednesday and Thursday.

An organized area of low pressure will approach the area by
Friday bringing the potential for precipitation and widespread
sub-VFR flight conditions.

&&

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

&&

$$

SYNOPSIS...PM
NEAR TERM...PM
SHORT TERM...RAB
LONG TERM...RAB
AVIATION...PM