470
FXUS61 KRNK 050109
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
909 PM EDT Fri Oct 4 2024

.SYNOPSIS...
A cold front crosses the region tonight with scattered showers
and isolated thunderstorms, and followed by high pressure. A
Stronger cold front pushes through the region on Sunday night,
leading in cooler and drier air. Dry weather and high pressure
are expected well into next week.

&&

.NEAR TERM /THROUGH SATURDAY/...
As of 900 PM EDT Friday...

Key Messages:

1) Valley fog and patchy fog across the Piedmont look possible tonight
as lingering surface moisture and clear skies in place allowing
for efficient radiative cooling tonight.

The forecast continues to remain on track this evening. All
showers and thunderstorms have dissipated across the region,
leaving mostly clear skies in their wake as the front finally
clears the region. This will allow for efficient radiative
cooling tonight, with valley and patchy fog possible tonight
across portions of the region. Westerly and northwesterly winds
tonight will transition to northeasterly Saturday afternoon
leading to a relatively pleasant sunny day, with highs reaching
the upper 70s and low 80s, and dewpoints remaining in the upper
50s.


Previous discussion...
As of 215 PM EDT Friday...

Key Messages:

 -Scattered showers and isolated thunderstorms until sunset
 -More fog Saturday morning.

Despite multiple layers of clouds for much of the day, still
enough heating for the atmosphere to become unstable. Low level
convergence along a pre-frontal trough and west upslope flow
have generated scattered showers and isolated thunderstorms
mainly over the mountains. The axis of showers and thunderstorms
will drift east this afternoon and evening. Hi-Res and
convection allowing models have a cluster of showers lingering
north of Lexington and just east of the Blue Ridge until the
late evening.

Synoptic scale models now have the cold front crossing the Mid
Atlantic region between 00Z/8PM and 12Z/8AM which will bring the
wind around to the northwest and north tonight, then northeast
on Saturday. wind speeds will diminish overnight and patchy fog
will develop after midnight.

Any fog and low clouds will dissipate shortly after sunrise.
There is little change in air mass with the frontal passage so
lows tonight and highs on Saturday will still be above normal.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
As of 1245 PM EDT Friday...

Key Points:

1. Warm and dry Saturday night and Sunday.
2. Scattered showers Sunday night, especially western sections.
3. Drier and cooler Monday and Monday night.

A look at the 4 Oct 00Z NCEP Ensemble Mean 500 mb Geopotential
heights shows a shortwave ridge centered over the Upper Ohio Valley
Saturday night. Additionally, a shortwave trough was centered over
Manitoba with its axis extending southeast into the Upper
Mississippi River Valley. By Sunday night, the shortwave ridge
shifts east to over the Canadian Maritimes. The shortwave trough
heads into the Eastern Great Lakes region and trends negatively
tilted. By Monday night, the trough`s eastward advancement slows,
with its axis situated over, or just east of our region. At the
surface, on Saturday night, high pressure will be centered over
Quebec, with its ridge axis extending southwest along the spine of
the Appalachians. Concurrently, low pressure will be over southern
Manitoba with a cold front heading south into the Upper Mississippi
River Valley. By Sunday night, the low will have shifted east, and
its associated cold front will be passing into and then across our
region. By Monday night, the front will be in the western Atlantic,
with high pressure building behind it over Midwest.

Output from the 4 Oct 00Z Ensemble Situational Awareness Table shows
850mb temperatures over the region Saturday night into Sunday
ranging from +12C to +14C. The upper end of this range brushes the
90 to 97.5 percentile of the 30-year CFSR climatology. Sunday night,
850mb temperatures head downward in the wake of the cold front. By
Monday afternoon, values of +8C to +11C are expected across the
region. Values trend slightly lower Monday night into the +6C to +9C
range.

The above weather pattern offers a warmer than normal and dry period
for Saturday night into Sunday. Sunday night, with the cold frontal
passage, we are still expected scattered showers across the area,
especially across western sections. Monday into Monday night, drier
and cooler air will be entering the region.

Confidence in the above weather scenario is high.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 130 PM EDT Friday...

- High pressure system brings in drier and cooler air.

As the northern upper level low travels east, a surface high
pressure system will move into the Mid-Atlantic by mid week.
Winds will be light and continue to be from the northwest. The
atmosphere will be stable as the surface high settles in. Most
of the stronger cold air advection will have already passed
but addition CAA is possible depending on the alignment of the
surface high. Even without additional CAA, the new air mass
will be much drier, cooler, and closer to seasonal autumn
conditions. The surface high is expected to linger for the rest
of the forecast period and bring back the sun for the
foreseeable future.

&&

.AVIATION /01Z SATURDAY THROUGH WEDNESDAY/...
As of 700 PM EDT Friday...

The progression of the cold front has quickly exited all of the
terminals this evening. Visible satellite shows clearing in the
shower and thunderstorms wake this evening, which looks to
continue through the remainder of the overnight hours. Surface
winds over the next 3-6 hours should start to swing around to
the north/northwest before becoming northeasterly at around 5-10
knots sometime between 16 and 18 UTC Saturday.

Model trends keep most sites at VFR or MVFR through the early
morning hours on Saturday, with typical valley fog likely with
clearing conditions through the overnight hours. This means that
KLWB will likely drop down to LIFR conditions once again
briefly in the early morning hours as visibilities drop. Any fog
and low clouds that do develop during the overnight hours
should quickly dissipate after sunrise on Saturday as dry air in
the boundary layer starts mixing to the surface. Overall, expect
VFR conditions to prevail at all terminals beyond the early
morning hours.

Average confidence for the extent of fog and visibilities
overnight.

EXTENDED AVIATION OUTLOOK...

Gusty winds are possible behind a cold front Sunday night and
Monday in the mountains. BLF and LWB may see -SHRA from that
same front during that time.

Monday and Tuesday look VFR, with patchy morning fog possible
in the favored mountain and river valleys.

&&

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

&&

$$

SYNOPSIS...AMS
NEAR TERM...AMS/EB
SHORT TERM...DS
LONG TERM...CG
AVIATION...AMS/EB