-- Discussion containing changed information from previous version are highlighted. --
686
FXUS61 KRNK 260908
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
508 AM EDT Sun May 26 2024

.SYNOPSIS...
A series of disturbances will pass across the lower Mid-Atlantic
through Monday, triggering rounds of shower and thunderstorm
activity ahead of an approaching cold front. The front will
pass across the central Appalachians Monday evening, ushering in
drier and slightly cooler weather for much of the coming week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 240 AM EDT Sunday...

Key Messages:

1. Mostly sunny and warm today, so keep plenty of cool non-
alcoholic beverages and sunscreen handy if remaining outdoors
for extended periods of time.

2. A line of showers and thunderstorms will arrive from the
west this evening, a few of which are likely to become severe.

3. Another line of showers and thunderstorms may arrive early
on Memorial Day, though timing and intensity are less certain.

Starting the morning off with mostly clear skies and light
winds, making for the perfect setup for the development of
patchy fog. IR satellite imagery already depicts fog filling in
the mountain river valleys, a trend that will continue over the
next few hours.

With mostly clear skies in place after sunrise, temperatures
will spike upward, allowing fog to burn off quickly after 8 am.
Temperatures will max out in the upper 70s to the mid 80s by
mid-afternoon. Will be keeping an eye on the potential for a
line of showers and thunderstorms arriving from the west and
reaching the Interstate 77 corridor during the 5 pm to 7 pm
timeframe. The storms will then race quickly to the east,
reaching the Highway 29 corridor in the Piedmont during the 7 pm
to 9 pm timeframe.

With a day of strong heating expected, believe there will be
enough energy in the atmosphere to allow a few storms to
intensify to severe levels, more so across the mountains as the
storms arrive just after maximum daytime heating. The main
threat will be damaging winds, though large hail and even an
isolated tornado cannot be ruled out. There is also the chance
of heavy downpours that may lead to localized flooding, though
these storms will be moving fast enough that prolonged heavy
rain will remain a remote possibility.

By 10 pm, the severe threat will temporarily diminish as the
line passes out of our area to the east, bringing a brief lull
in the organized activity, with only residual showers to contend
with. However, decent agreement exists in the rapid update
weather forecast models that another line of storms will
approach from the west during the predawn hours of Monday. Not
as confident on the timing of this next round of activity or its
intensity given that it would be entering an environment
drained of instability by the earlier round of storms.

Expect early morning lows to start Memorial Day to range from
the low to mid 60s.

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/...
-- Changed Discussion --
As of 200 PM EDT Saturday...

Key Messages:

1). Greatest threat for severe thunderstorms expected on Monday.

2). Unseasonably cool with mainly mountain rain showers Tuesday
and Wednesday.

Monday will be an active weather day for most of the CWA as a
cold front, deepening upper trough over the Great Lakes, and an
associated vigorous short wave impact the weather across the
region. The day is expected to start out with a diminishing
overnight OH/TN Valley MCS arriving on our western border just
before or near daybreak. This system will play a crucial role in
determining the amount of severe weather that occurs or does
not occur later in the day. The threat for severe weather with
this first round of showers/thunderstorms should be low given
that it should be in a greatly diminished state. However, strong
wind gusts associated with the associated advancing cold pool
will still be possible, especially for areas west of the I-77
corridor around daybreak. This is part of the reason that there
is a "slight"risk for severe thunderstorms generally west of
I-77 tonight/early Monday.

Beyond this, current expectations are that thunderstorms will
redevelop along a cold front arriving behind the first round of
convective activity during the afternoon. Given modest
instability and shear, reasonably favorable conditions exist for
strong to severe thunderstorms during the afternoon. The
placement of the morning`s remnant outflow boundary, cold pool,
cloud cover, and mesohigh will play a key role in determine
where new thunderstorms develop and to what extent. The earlier
morning convective debris cloud cover clears and/or moves east
out of the area, the earlier and further west new thunderstorms
will develop and have an increased chance of becoming severe.
On the contrary, a later clearing or longer lingering of cloud
cover and cooler temperatures from morning convective remnants,
will reduce the severe weather threat, especially west of the
Blue Ridge. In either case, the main threat for severe weather
Monday, and that being during the afternoon, will be east of the
Blue Ridge. Brooks-Craven Severe Thunderstorm Parameter values
for Monday suggest a good chance of severe thunderstorms with
values among the highest I have seen in this area for a while,
namely 25,000 to 30,000 via some models. Nonetheless, various
other parameters and the aforementioned problematic timing
suggest the main threat for severe thunderstorms will be closer
to the I-85 corridor across eastern VA and northeast NC.

Temperatures Monday will remain on the warm side, but trend a
bit cooler west of the Blue Ridge because of the morning clouds
and precipitation.

Tuesday and Wednesday will be much quieter, although trending
breezy and unseasonably cool, more like April weather
conditions. This will take place as deep troughing develops
across the Great Lakes and sags southward into the northern
Appalachians and Mid-Atlantic region during the later half of
the week. High temperatures will only reach the 50s and 60s in
the mountains with lows dipping into the 40s at night. For the
bulk of the forecast area, high temperatures midweek will be
mainly in the 60s west to the 70s east with lows in the 40s west
and 50s east. Cyclonic flow and low-level cold along with
upslope flow across the western mountains will promote abundant
cloud cover and scattered rain showers. Given strong insolation
combined with cold air aloft, daytime lapse rates will become
rather steep which may trigger a few thunderstorms.

/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 to High Confidence in Thunderstorm Potential,
- Moderate Confidence in Severe Thunderstorm Potential.
-- End Changed Discussion --

&&

.LONG TERM /THURSDAY THROUGH SATURDAY/...
As of 230 PM EDT Tuesday...

Key Messages:

1: Largely quiet forecast with cooling temperatures

After Monday`s frontal passage, we will be positioned on the
western side of a mid-level trough, and the eastern side of a
surface high. For most of the week, this will force northerly or
northwesterly flow, and consequently, cold air advection.
Temperatures will be on the decline through Friday, when temps
will be around or a few degrees below normal. The mountains will
have scattered to broken cloud cover due to the flow, and some
isolated diurnal showers could form up Thursday. The surface
high will transition to directly overhead the Mid-Atlantic by
Friday, shutting off rain chances even further.

&&

.AVIATION /09Z SUNDAY THROUGH THURSDAY/...
As of 255 AM EDT Sunday...

Patchy fog this morning given mostly clear skies and light
winds. Fog particularly thick in the mountain river valleys,
including LWB and BCB. Expected to burn off quickly after 26/12Z
given sunshine and strong heating.

Expect winds from the south today at less than 10kts. VFR
conditions expected through most of the day until a line of
showers and thunderstorms arrives during late afternoon. This
line is expected to move rapidly from west to east, impacting
the mountains during the 26/21Z to 27/00Z timeframe, and the
Piedmont during the 26/23Z to 27/02Z timeframe. A few storms
across the mountains are likely to become severe, producing
damaging wind gusts, though large hail and an isolated tornado
cannot be ruled out also. Downpours and low ceilings will
accompany the storms, but are expected to remain temporary,
improving as the convection passes.

Lingering debris cloud cover tonight will limit fog formation,
though patches of fog may redevelop. Will be keeping an eye on
the potential for another line of storms during the predawn
hours of Monday, though uncertainty exits in both the timing
and intensity of this activity given that it may arrive late at
night when instability is diminished.

EXTENDED AVIATION OUTLOOK...

Periods of showers and thunderstorms will continue through the
daytime hours of Monday. MVFR conditions remain likely with any
thunderstorms. Thunderstorms developing Monday afternoon have a
chance of producing heavy rain, hail, damaging winds, and
frequent lightning.

A front will cross through the area late Monday into early
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.

&&

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

&&

$$

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