583
FXUS61 KRNK 111900
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
300 PM EDT Sun Aug 11 2024

.SYNOPSIS...
High pressure will cover the Northeast and Mid Atlantic states
tonight through Wednesday. This will result in dry weather and near
normal temperatures. The next chance of showers and thunderstorms
arrives toward the end of the week as a low pressure system
approaches from the Ohio Valley.

&&

.NEAR TERM /THROUGH MONDAY/...
As of 215 PM EDT Sunday...

Key message:

    - No significant weather hazards

12Z RNK sounding showed a cap just above 850MB, so limited
stratocumulus development this afternoon. Otherwise occasional
batches of mid and high clouds cross the area through Monday.
Depending on the timing of the clouds overnight, there will be
patchy fog in the river valleys west of the Blue Ridge.

Lowered NBM guidance for tonight in typical cool spots. Otherwise
stayed close to guidance for minimum and maximum temperatures.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/...
As of 240 PM EDT Sunday...

Key Messages:

1). Shower/thunderstorm chances increase across the mountains,
but no significant hazards expected through this period.

2). Temperatures remaining a bit below normal.

Zonal flow will generally prevail across the northern tier of
states and down to near the VA/NC line and points westward near
the same latitude. Troughing will be evident across the Great
Lakes and northeast. A weak frontal boundary will linger just to
our south through the period, but appears to remain just enough
to the south to preclude any widespread rain or thunderstorms in
our area. Precipitation during the Tue/Wed period should be
largely confined to the western mountains and mostly diurnal in
nature, with the best chances in northwest NC and into Grayson
county VA closer to the moisture, instability, and frontal
boundary.

By Wednesday, the trough will deepen further and help to push a
the frontal boundary further south Wed-Thu. Drier air will again
confine the best chance for any afternoon/evening
showers/thunderstorms to the far southwest part of VA and
adjacent areas of northwest NC. Much of the CWA east of I-77
will remain dry through this time frame.

Temperatures will be slightly below normal for mid-August
through the time frame as a pocket of colder air aloft lingers
over the region in association with the persistent trough to our
north. In fact, looking at the U.S. as a whole, the coolest air
at 850mb resides over the Mid-Atlantic and central/northern
Appalachians, so August for our area is beginning to feel more
like fall while the rest of the U.S. bakes with 850mb
temperatures well above +20C in many areas! For us, this means
highs in the 70s west to lower/mid 80s east with no 90s! Low
temperatures will be in the 50s to lower/mid 60s at night.

/Confidence Levels in Forecast Parameters/
- Moderate to High Confidence in Temperatures,
- Moderate Confidence in Precipitation Probabilities,
- Moderate Confidence in Wind Direction and Speed,
- Low to Moderate Confidence in Thunderstorm Potential.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 245 AM EDT Sunday...

Key Messages:

1). Increasing chances for showers and thunderstorms during the
later half of the week,

2). Temperatures remaining near to slightly below normal through
the period.

Differences are evident among the long range models as to how an
upper low across the OH Valley/IL/IN region evolves. The GFS
shows it sagging southward into the upper Midwest and lingering
into the weekend and early next week. The ECMWF essentially cuts
off the low, but further north over the Great Lakes and tries to
keep more of an open trough. At any rate, the consensus is that
it will impact our weather one way or another with abundant
cloud cover, below normal temperatures, and above normal
precipitation chances.

Of greatest interest during the period is the initial
trough/frontal passage in the Fri-Sat time frame. GFS depicts a
negatively tilted trough an associated line of convection
rotating through the region somewhere in the 00Z Saturday to
18Z Saturday time frame. Timing of this feature will be crucial
as to whether or not there will be a severe threat. Beyond that,
there are indications that with the upper low to our west and a
tropical system moving northward through the western Atlantic an
easterly flow/wedge like pattern may set up resulting in below
normal temperatures and potentially several days of
cloudy/damp/unusually cool temperatures for mid-August. At any
rate the extended periods look wet and with below normal
temperatures.

/Confidence Levels in Forecast Parameters/
- Moderate Confidence in Temperatures,
- Moderate to High Confidence in Precipitation Probabilities,
- Moderate Confidence in Wind Direction and Speed,
- Moderate Confidence in Thunderstorm Potential.

&&

.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
As of 225 PM EDT Sunday...

Mainly VFR conditions expected tonight and Monday.

12Z RNK sounding showed a cap just above 850MB, so limited
stratocumulus development this afternoon. Bufkit forecast
soundings showed stratocumulus at 2500-4500 Feet. Otherwise
occasional batches of mid and high clouds cross the area through
Monday.

Depending on the timing of the clouds overnight, there will be
patchy fog in the river valleys west of the Blue Ridge. Expect
enough radiational cooling for for to form around 09-10Z/5-6AM
along the rivers. Kept MVFR in for KLWB for a few hours.

Any fog will dissipate and conditions will return to VFR once
the shallow inversion breaks and mixing begins in the morning,
around 13Z/9AM.

Above average confidence for ceiling, visibility, and wind.


AVIATION OUTLOOK...

Scattered showers and thunderstorms may occur during Tuesday
afternoon, mainly along the southern Blue Ridge. Chances of
afternoon convection could continue into Wednesday and Thursday.

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

&&

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

&&

$$

SYNOPSIS...AMS
NEAR TERM...AMS
SHORT TERM...RAB
LONG TERM...RAB
AVIATION...AMS/BMG