-- Discussion containing changed information from previous version are highlighted. --
443
FXUS61 KRNK 301043
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
643 AM EDT Tue Apr 30 2024

.SYNOPSIS...
A cold front moves through the region today with showers and
isolated thunderstorms. Dry, high pressure follows for late
Wednesday into Thursday with continued above normal
temperatures. Another cold front brings wet weather to the
region for Friday and the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 300 AM EDT Tuesday...

Key message:

 - Showers and isolated thunderstorms this afternoon

Band of precipitation along a cold front extended from Michigan
to central Arkansas. This band of precipitation was moving
slowly east as a short wave over western Tennessee was resulting
in a wave of low pressure along the surface front. Cloud cover
increases from the west this morning followed by showers and
isolated thunderstorms in the afternoon. Hi-Res models had some
differences in the timing of the precipitation, but the 3KM NAM
lined up well with the location at 06Z/2AM. This models showed
the leading edge of precipitation out to the Blue Ridge around
noon, then crossing the foothills and piedmont in the afternoon
before dissipating after sunset.

Not seeing a particularly supportive environment for thunderstorms
today. Will keep thunderstorm probability below 25 percent. Any
thunderstorms could have heavy rain, but overall flooding threat is
isolated.

Upslope flow behind the front was not very strong but the wind
direction does briefly turn to the west and northwest. Still enough
upslope component and low-level moisture to produce low clouds on
the western slopes of the central Appalachians tonight.

High temperatures in the mountains will be cooler than on Tuesday
due to the incoming cloud cover. East of the Blue Ridge where there
will more sunshine this morning, highs will warm back into the 80s.
Will stay close to NBM guidance for lows tonight.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/...
As of 155 AM EDT Tuesday...

Key Points:

1. Above normal temperatures with Thursday the warmest day.
2. A few showers and storms Wednesday.
3. Dry Thursday.
4. Showers and storms increase in coverage and from west to east
Friday afternoon and night.

A look at the 29 April 00Z NCEP Ensemble Mean 500 mb Geopotential
heights shows A building shortwave ridge over the Lower Ohio and
Tennessee Valleys on Wednesday with a shortwave trough centered just
off the cost of the Delmarva Peninsula. By Thursday, the ridge has
strengthened and is centered from the Great Lakes region southeast
across the Southern Appalachians. A trough is expected to deepen
over the Northern Plains states south into the Rockies. On Friday,
the axis of the ridge becomes more n-s oriented, but still centered
over our region. The Central US trough moves eastward slightly. At
the surface, low pressure is located near the Texas Panhandle on
Wednesday with high pressure centered off the coast of the
Carolinas. By Thursday, the low and associated cold front are
situated over the Plains States with perhaps one low over Iowa and
another over Texas. High pressure mains situated off the US East
Coast. By Friday, low pressure moves into the western Great Lakes
region, while a high pressure ridge remains centered off the East
Coast. A weak front may extend southeast from the low into our area
on Friday.

Output from the 29 Apr 12Z Ensemble Situational Awareness Table
shows 850mb temperatures around +12C to +13C over the area on
Wednesday, +14C to +16C on Thursday and Friday. The high end of this
range of numbers reaches the 90 to 97.5 percentile of the thirty-
year climatology. Precipitable Water values will be around 0.75 to
1.00 inch on Wednesday, 0.75 inch on Thursday, and  1.00 inch on
Friday.

The above scenario will keep a small chance of showers across our
area on Wednesday as clockwise flow around the offshore high advects
moisture upslope into the region. The building upper ridge will help
limit coverage. Thursday dry and warmer conditions are expected. By
Friday, some isolated to scattered showers/storms will enter the
forecast across the mountains with the approach of a front and
increase moisture pooling across the region. Temperatures will
average above normal conditions through the period with Thursday
being the warmest of the three days.

Confidence in the above weather patterns is moderate to high.

&&

.LONG TERM /SATURDAY THROUGH MONDAY/...
As of 130 AM EDT Tuesday...

Key Points:

1. Slightly cooler temperatures but still a bit above normal
2. Chance of showers and storms each day with Saturday having the
greatest probability.

A look at the 29 April 00Z NCEP Ensemble Mean 500 mb Geopotential
heights shows the East Coast ridge flattening a bit on Saturday as a
shortwave trough moves into the Upper Mississippi Valley. By Sunday,
the ridge has shifted east of our region and the shortwave trough is
expected to over the eastern Great Lakes/Lower Ohio Valley. By
Monday, the shortwave trough crosses New England and flow over our
region trends zonal. At the surface, on Saturday, low pressure moves
into Ontario with a front extending south into the Upper Mississippi
River Valley. By Sunday, this front is expected to be over our
region with the parent low near the Ontario/Quebec border. For
Monday, there is a lot of averaging being done among the various
ensemble members which is washing out any notable details. This
suggests decreased confidence in just how much progress the front
moves east of the area on Monday.

Output from the 29 Apr 12Z Ensemble Situational Awareness Table
shows 850mb temperatures around +12C Saturday through Monday.
Precipitable Water values will be around 1.25 inch on Saturday, 1.00
to 1.25 inch on Sunday, and 1.00 inch for Monday.

The above scenario favors decent coverage of showers and storms
Saturday into Sunday. Monday is a bit of a question mark given the
decreased confidence specific placement of the front. Small chances
of at least showers are warranted for Monday because of this.
Temperatures will trend cooler than they had been mid-week, but
still average above normal for this time of year, especially the low
temperatures.

Confidence in the above scenario is low to moderate.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --
As of 640 AM EDT Tuesday...

VFR and light winds are expected through today.

Band of precipitation along a cold front extended from central
Ohio to central Tennessee. This band of precipitation was
moving slowly east as a short wave over western Tennessee was
resulting in a wave of low pressure along the surface front.

Ceilings lower from west to east today, followed by showers and
isolated thunderstorms. Hi-Res models had some differences in
the timing of the precipitation, but the 3KM NAM showed the
leading edge of precipitation out to the Blue Ridge around noon,
then crossing the foothills and piedmont in the afternoon
before dissipating after sunset. Ceilings lower to IFR in the
mountains after 00Z/8PM but locations east of the Blue Ridge
will remain VFR.

Not seeing a particularly supportive environment for thunderstorms
today. Any thunderstorms could have heavy rain, leading to MVFR
visibility. Probability of showers is high enough to include in
the body of the TAF but probability of a thunderstorm at
individual airports was too low to include anything but VCTS.
Bufkit forecast soundings from the FV3 and 3KM NAM suggest KLYH
and KDAN may not moisten up enough for any precipitation until
after 21Z/5PM.

Upslope flow behind the front was not very strong but the wind
direction does briefly turn to the west and northwest. Still enough
upslope component and low-level moisture to produce MVFR to IFR clouds
on the western slopes of the central Appalachians tonight.

Average confidence in ceiling, visibility, wind, and the timing
of showers and thunderstorms.

Extended Aviation Outlook...

Widely scattered will still be possible Wednesday as the front
exits the area.

Thursday is forecast to be VFR and dry.

The next cold front and probability of precipitation arrive in
the area on Friday. This brings the potential for showers and
thunderstorms with MVFR ceilings and visibilities through the
weekend.
-- End Changed Discussion --

&&

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

&&

$$

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