335
FXUS61 KRNK 161404
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
1004 AM EDT Fri Aug 16 2024

.SYNOPSIS...
High pressure slides off the coast this afternoon while a cold
front approaches the Appalachians this evening. This front will
be slow moving and will not exit our area until Sunday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1000 AM EDT Friday...

No changes for the morning update.

Key Message: Increasing chances for showers and storms this
afternoon into tonight, mainly across the mountains. Some of the
storms could bring torrential downpours.

On the weather map, we have high pressure situated from the
mid-Atlantic into the Carolinas. A warm front stretches from the
Midwest into KY, with a cold front from Wisconsin to the
southern Plains. Warm frontal showers are advancing across the
Ohio Valley and will become more numerous across our western CWA
this afternoon.

The forecast today is a blend of models as they all seem to be
in good agreement in bringing in showers/few storms to the
mountains as shortwave energy shifts across the upper TN
Valley. Upper flow become difluent to aid in lift and will be in
the warm sector with increasing pwats and humidity. This should
lead to any heavier storms to bring torrential downpours, so
cannot rule out some localized flooding in the mountains, with
less coverage into the Piedmont. As for severe storms, majority
of models are keeping higher instability along/west of the
Appalachians, so although a strong storm or two may occur, thing
severe threat is low. Also cloud cover may inhibit instability
this afternoon.

Upper low will shift toward the Great Lakes tonight and our area
remains in a difluent upper pattern, so appears showers/few
storms will linger into tonight with best coverage still over
the mountains.

With more clouds today, but with southerly flow, highs will run
close to normal with mid 80s east to mid 70s to lower 80s west.

Increasing dewpoints, with showers and clouds will bring low on
the muggy side about 5-10 degrees above normal tonight, with mid
60s to around 70 for most.

Forecast confidence is above average, except average on clouds
and pops.

&&

.SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/...
As of 130 AM EDT Friday...

Key Points:

1. Good coverage of showers/storms Saturday and Sunday, especially
areas west of the Blue Ridge.
2. Less coverage on Monday, still best coverage west of the Blue
Ridge.
3. Locally heavy rain possible Friday through Saturday night.
4. Above normal temperatures on Saturday with values trending
downward through Monday.

A look at the 15 Aug 12Z NCEP Ensemble Mean 500 mb Geopotential
heights shows a shortwave trough that moves from the western Great
Lakes into the Lower Ohio Valley Saturday into Sunday. Sunday into
Monday the trough amplifies as its trough axis becomes centered over
the region. By late Monday night, the trough axis is slightly east
of the region. At the surface, on Saturday morning, low pressure is
expected to be over Michigan with an associated cold front trailing
southwest into the mid-Mississippi Valley. By Sunday morning, the
low is expected to be over Lake Erie with the cold front extending
south into the eastern Kentucky and Tennessee. By Monday morning,
the low is expected to be over central Pennsylvania with its cold
front extending south to central or eastern Virginia/North Carolina.
By late Monday night, the low is expected to be over New England
with front just off the coast of the mid-Atlantic region of the US.
Concurrently, high pressure will be centered over the Upper
Mississippi Valley by late Monday night.

Output from the 15 Aug 12Z Ensemble Situational Awareness Table
shows 850mb temperatures across the region averaging +18C to +20C on
Saturday, +15C to +17C on Sunday, and +13C to +15C on Monday. The
low end of range of temperatures on Monday correspond to the 2.5 to
10 percentile of the 30-year climatology. Precipitable Water values
on Saturday are expected to range from 1.50 to 1.75 inches, 1.25 to
1.50 inches on Sunday and Monday.

The above weather scenario continues to offer a Saturday with
increasing chances of showers and storms from west to east as the
day progresses. Coverage wanes only slightly Saturday night with the
best coverage remaining over western sections. On Sunday, a cold
front crosses the region. The timing of the front across the region
does not look to coincide with peak heating of the day. However, its
presence will still act as a focus for shower/storm development.
Additional coverage is expected during peak heating of the day in
association with the approach and arrival of the parent upper
trough. Coverage will be best across western sections. By Monday,
the axis of the upper trough is expected to be over, or just east of
the region. This will place the region within a northwest flow
regime.  Precipitation chances will be greatest over Southeast West
Virginia, south into the Northern Mountains of North Carolina where
the effects of upslope northwest flow will be the greatest paired
with heating of the day. Daytime coverage should wane through the
evening hours of Monday. Temperatures will be highest on
Saturday and trend lower through the period.

Confidence in the above weather scenario is moderate to high.

&&

.LONG TERM /TUESDAY THROUGH THURSDAY/...
As of 130 AM EDT Friday...

Key Points:

1. Little to no precipitation.
2. Below normal temperatures.

A look at the 15 Aug 12Z NCEP Ensemble Mean 500 mb Geopotential
heights shows a trough just to our east Tuesday morning. Through
Thursday, this feature is expected to decrease in amplification as
is it retrogrades to back over the Lower Ohio Valley. At the
surface, on Tuesday morning low pressure is expected to be over New
England with front just off the coast of the mid-Atlantic region of
the US while high pressure will be centered over the Upper
Mississippi Valley. As we progress into Thursday, the front near the
coast loses its depiction within the ensemble mean. However, high
pressure shifts east and is centered over the central Appalachians
by Thursday morning.

Output from the 15 Aug 12z Ensemble Situational Awareness Table
shows 850mb temperatures are expected to range from +12C to +14C on
Tuesday. For many locations, especially northern parts of the
region, the low end of this range corresponds to the 2.5 to 10
percentile of the 30-year climatology. For Wednesday, values are
only slightly milder in the +13C to +15C range. On Thursday, values
of +14C to +16C are forecast. Precipitable Water values are expected
to range from 0.75 to 1.00 inch on Tuesday. The low end of this
range across far Southwest Virginia and Northwest North Carolina
will fall into the 2.5 to 10 percentile of the 30-year climatology.
Values slowly increase through Thursday when values are expected to
average 1.00 to 1.25 inches across the area.

The above weather scenario offers primarily dry conditions through
the period with below normal temperatures.

Confidence in the above weather situation is moderate to high.

&&

.AVIATION /14Z FRIDAY THROUGH TUESDAY/...
As of 635 AM EDT Thursday...

Overall forecast through the afternoon will be VFR but
showers/storms could bring sub-VFR to the mountains.

Less coverage in the Piedmont so keeping storms out of tafs for
now at LYH/DAN.

Ceilings are likely drop Friday night at all sites to MVFR east
to IFR or lower in the mountains.

Confidence is slightly above average except on storms
impact/timing on individual airports.


.EXTENDED AVIATION OUTLOOK...

Slow moving front will keep scattered-numerous showers/storms
around into the weekend with sub-VFR at times. Upper trough
advances overhead by Monday so despite front being east,
showers/few storms will likely occur in the heating of the day
so anticipate some sub-VFR condition, but generally Sat-Mon
outside of storms will be VFR and any late night fog.

Confidence higher for dry and VFR Tuesday as high pressure
builds in.

&&

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

&&

$$

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