-- Discussion containing changed information from previous version are highlighted. --
049
FXUS61 KRNK 251132
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
732 AM EDT Sat May 25 2024

.SYNOPSIS...
A series of low pressure systems will cross the Great Lakes and
northeast United States today through Monday, before pushing a cold
front through the Mid Atlantic region by early Tuesday. While there
will be daily afternoon and evening thunderstorms, the highest
probability of precipitation will be Sunday night and Monday. The
front will lead in drier and cooler weather for the middle of next
week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 245 AM EDT Saturday...

Key message:

   - Typical summer thunderstorms this afternoon and evening

Patchy fog will continue to develop early this morning. Visibility
will occasionally be less than one mile in locations along rivers
and lakes, and in the Virginia and North Carolina piedmont where
there is less cloud cover impeding fog formation. Fog will dissipate
rapidly after sunrise.

Isolated thunderstorms in eastern Kentucky will move into western
Virginia this morning, as they weaken, then dissipate. The air mass
will heat up the rest of the morning, with CAPES topping out in the
1200-1500 J/kg range by the time thunderstorms begin to develop.
Convective-allowing models and Bufkit forecast soundings have storms
developing generally in the mountains, and more specifically along
the southern Blue Ridge in the noon to 1PM time range. There will be
an overall eastward movement of the isolated and multi-storm
clusters. Expect a majority of the thunderstorms to dissipate
quickly after 8PM. No particular forcing or enhancement to produce
severe wind or large hail today, but for any outdoor activities,
take one last look at the sky before launching the boat or striking
out on that trail. Be weather aware and follow lightning safety
rules. "When Thunder Roars, Go Indoors!"

Aside from far southwest Virginia, and the Mountain Empire into
northwest North Carolina which will have some remnant cloud cover as
the overnight thunderstorms dissipate, expecting plenty of sunshine
today. Will lean toward warmer guidance for maximum temperatures
today. Little change planned to overnight lows.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/...
As of 430 AM EDT Saturday...

Key Messages:

1).  Concerns for severe thunderstorms Monday.

2).  Unseasonably cool conditions begin to take hold Tuesday.

A potent mid-level disturbance, that will help to trigger a
major severe weather outbreak in the Midwest/Central/Southern
Plains today will move eastward Sunday through Monday helping to
suppress a broad upper ridge over the southeastern U.S. While
the system will not deliver the punch to our region that it will
to the mid part of the U.S. it nonetheless has a good chance of
bringing strong to severe thunderstorms to our area, especially
Monday.

For Sunday, the forecast region will be far enough in advance of
the upper-level disturbance to experience a fairly summerlike
day with scattered mainly afternoon showers and thunderstorms.
Coverage and intensity should favor the western parts of the CWA
where dynamics will be better. With warm temperatures mostly in
the 70s mountains to the 80s elsewhere and dewpoints in the 60s
instability will be more than sufficient for scattered
thunderstorms. Dynamics will also become increasingly favorable
by evening, especially in the west. Isolated strong to severe
thunderstorms will be possible Sunday afternoon/evening with the
threat diminishing by midnight. Locally heavy rainfall is
possible, but widespread heavy rainfall is not expected as the
convection is expected to be unorganized. Therefore, the broad
brushed approach with respect to the marginal WPD risk of
excessive rainfall is largely thought to cover the random nature
of the convection.

Monday is the main day for severe weather. However, early
morning convection will play a major role in determining the
degree and intensity of convection. Thus, confidence in a
significant severe weather outbreak across our region is low at
this time. Based on current model trends, it appears a
diminishing area of convection will reach the western CWA late
Sunday night/early Monday morning. Severe thunderstorms are
unlikely with this activity, although some strong winds with a
dying MCS or similar convective structure would be possible
early Monday morning mainly along/west of the I-77 corridor.
This is highlighted with the western part of the CWA being in a
"marginal" risk Sunday night/Monday, ending 12Z Monday morning.

Redevelopment of convection would then be expected along/east
of the Blue Ridge during the afternoon, which is where the main
severe weather threat would exist. If the scenario unfolds in
this manner, morning convection will leave cloud cover and a
mesohigh in place, which would greatly limit the severe weather
potential depending on how long such lingers. However, if the
organized convection from the overnight activity arrives sooner
or later, the severe weather threat would increase and also
encompass areas further west. SPC has now included most of the
CWA Monday in a "slight" risk for severe thunderstorms, with
even supercells possible. Again, timing of morning convection
will be the key. Hopefully, we will be able to pinpoint down
this timing problem better tomorrow.

By Tuesday, an upper low across the Great Lakes deepens and
helps to push an unseasonably cool air mass down into the
region. With an almost winter like pattern, cyclonic flow will
contribute to considerable upslope and cold advection cloud
cover across the mountain with scattered rain showers.
Temperatures will trend downward to around 10 degrees below
normal on Tuesday.

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

&&

.LONG TERM /WEDNESDAY THROUGH FRIDAY/...
As of 515 AM EDT Saturday...

Key Messages:

1). Deep upper low across the Great Lakes dominates the weather
through the period.

2). Below normal temperatures, variable cloud cover, scattered mainly
mountain rain showers.

A deep upper low sagging southward from the eastern Great Lakes
will dominate the weather across the region through the period.
850mb temperatures will fall from +18C on Monday to around +5C
by Wednesday/Thursday. The cyclonic flow and cold advection
along with upslope northwest flow will keep abundant cloud cover
across the mountains with scattered largely diurnal rain
showers. An isolated thunderstorm cannot be ruled out during the
afternoon/evening given cold air aloft and fairly steep lapse
rates given the late May insolation.

Maximum temperatures will fall into the 60s mountains/west and
70s Piedmont with lows dipping into the chilly 40s west and 50s
east through much of the period. These temperatures are around
8-10 degrees below normal for late May.

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

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
As of 725 AM EDT Saturday...

Visibility will be IFR to LIFR in locations along rivers and
lakes, and in the Virginia and North Carolina piedmont at the
start of the TAF forecast period including at KLWB, KLYH, and
KDAN. The shallow fog will dissipate by 13Z/9AM.

The air mass will heat up the rest of the morning, with CAPES
topping out in the 1200-1500 J/kg range by the time
thunderstorms begin to develop. Convective-allowing models and
Bufkit forecast soundings have storms developing generally in
the mountains, and more specifically along the southern Blue
Ridge in the noon/16Z to 1PM/17Z time range. There will be an
overall eastward movement of the isolated and multi-storm
clusters. For now have VCTS in all of the local TAFs. Expect a
majority of the thunderstorms to dissipate quickly after
8PM/00Z.

Fog will develop in the favored river valleys and in locations
that have rain in the afternoon and evening. Have added MVFR fog
in for KLYH, KBCB and KDAN, and LIFR fog in at KLWB late
tonight.

Average confidence for ceiling, wind, and visibility

EXTENDED AVIATION OUTLOOK...

Periods of showers and thunderstorms, mainly in the afternoons
and evenings, will continue through Monday. MVFR conditions
remain likely with any thunderstorms. The highest probability of
precipitation and associated MVFR conditions will be Sunday
night and Monday.

A front will cross through the area sometime Tuesday, turning
winds to the northwest and eventually bringing drier air to much
of the area. A low chance for showers and thunderstorms will be
possible across WV Tuesday and Wednesday, otherwise VFR.

Patchy fog with periods of MVFR/LIFR will be possible in the
mornings near mountain and river valleys.
-- End Changed Discussion --

&&

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

&&

$$

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