-- Discussion containing changed information from previous version are highlighted. --
799
FXUS61 KRNK 231040
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
640 AM EDT Thu May 23 2024

.SYNOPSIS...
A front will stall across the Ohio Valley today and Friday,
resulting in multiple days with showers and thunderstorms over
the area. Then a low pressure system crossing the Great Lakes
will push a cold front through the Mid Atlantic region early
Tuesday. This will lead in drier and cooler weather for the
middle of next week.

&&

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

Key messages:

   - Confidence high on timing of thunderstorms today
   - Confidence lower on the location of storms

Band of showers and isolated thunderstorms over the mountains
had moved northeast and dissipated, leaving mid and high clouds,
mainly over the mountains early this morning. These clouds may
partially limit heating in the morning, but still enough
sunshine to result in an unstable air mass by afternoon. With
the stalled front well to the north of the region, lifting will
not be especially organized but more dependent on outflow
boundaries and topographic forcing.

Convective allowing models have reasonably good agreement with the
timing of the thunderstorms today, showing the bulk of the storms in
the 19Z/3PM to 23Z/7PM time frame. However storms may develop as
early as noon in the northwest north Carolina mountains and last
until midnight in the North Carolina piedmont. In general expected
CAPES to reach 1500-2000 J/kg by this afternoon with the largest
values across southern Virginia and northern North Carolina. SPC
SREF and the DESI Grand Ensemble were suggesting low, less than 25
percent, probability of CAPES exceeding 2000 J/kg today. Location of
thunderstorm development today is more questionable.

WPC probabilistic rainfall forecast showed at least a 60 to 70
percent of 0.25 inches of rain throughout southwest Virginia,
northwest North Carolina and southeast West Virginia before Friday
morning. Plan to increases Probability of Precipitation along the
VA/NC border for the late afternoon and early evening. 3 hr Flash
Flood guidance in general is only 1.5 to 2.0 inches, and with heavy
rainfall rates in the thunderstorms, localized flooding remains a
threat.

Starting out with mild temperatures in the lower 60s to lower 70s.
Will not take much heating for most locations to reach the mid 70s
to mid 80s. Maximum temperatures at any particular spot will depend
on the amount of cloud cover this morning and the timing of the rain
this afternoon. A combination of persistence and NBM guidance will
be used for minimum temperatures tonight.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/...
As of 230 AM EDT Thursday...

Key Points:

1. Continued locally heavy rain concerns for Friday/Friday night.
2. Additional showers and storms through the weekend.
3. Well above normal temperatures.

A look at the 22 May 00Z NCEP Ensemble Mean 500 mb Geopotential
heights shows a shortwave trough cross the Ohio Valley on Friday. A
deeper trough is expected to be developing over CA/NV. By Saturday,
the shortwave trough is expected to be centered near NJ, with
another shortwave trough over the Great Lakes region. The longer wave
trough over western CONUS is expected to shift into near a ID
to AZ line. By Sunday, the western CONUS trough will now be a
central CONUS longwave trough, with southwest flow aloft over
our region. At the surface, for Friday, low pressure is expected
to be situated over the western Great Lakes region with an
associated cold front extending south into the mid-Mississippi
River Valley. The associated warm front is expected to be draped
southeast across our region. By Saturday, the low will be near
the Ontario/Quebec border with its a cold front extending south
along the spine of the Appalachians by the early evening. For
Sunday, Another low pressure will be deepening across central
CONUS. Its associated warm front is expected to extend eastward
into the Ohio Valley.

Output from the 22 May 12Z Ensemble Situational Awareness Table
shows 850mb temperatures across the region will average +16C for
Friday, and +17C for Saturday and Sunday. The values on the weekend
are forecast to be within the 90 to 97.5 percentile of the 30-year
climatology. Precipitable Water values are expected to average 1.25
to 1.50 inches on Friday, 1.00 to 1.25 inches Saturday, then back to
1.25 to 1.50 inches Sunday.

The above scenario offers a forecast whereby precipitation chances
will remain elevated on Friday with a stationary or warm front over
or near our region. We will have a continued good coverage of
showers and some storms. A locally heavy rain threat will continue
as activity focus along the front and/or showers/storms training
over the same location. Saturday, the system`s cold front moves
through the area, with a continued convective potential. Late
Saturday into early Sunday we may get a little break in the
activity, but the next system`s warm front arrives by the afternoon
and evening. Temperatures will continue to be well above normal for
this time of year.

Confidence in the above weather pattern is moderate to high.

&&

.LONG TERM /MONDAY THROUGH WEDNESDAY/...
As of 230 AM EDT Thursday...

Key Points:

1. Good coverage of showers and storms continue through Saturday.
2. Primarily mountain showers and storms Wednesday.
3. Warm Monday and Tuesday but cooler Wednesday.

A look at the 22 May 00Z NCEP Ensemble Mean 500 mb Geopotential
heights shows a longwave trough making gradual progress from the
Mississippi Valley on Monday to over the Tennessee Valley by
Wednesday. During this process, this trough is expected to become
more amplified. At the surface, by Monday evening, low pressure will
be centered over or near Lake Erie. An associated cold front will
extend southwest into the Lower Mississippi Valley. For Tuesday, the
low shifts east to southern Quebec/NY with it cold front extending
south over our region. By Wednesday, ensemble averaging still
maintains general troughiness from Quebec south to the coast of the
Carolinas. High pressure builds over the Mississippi Valley.

Output from the 22 May 12Z Ensemble Situational Awareness Table
shows 850mb temperatures will average +16C to +17C across the area on
Monday, +12C to +14C on Tuesday, and around +10C for Wednesday.
Precipitable Water values are expected to average 1.25 inches on
Monday, 1.00 inch Tuesday, and a little over 0.75 inch for Wednesday.

The above weather scenario offers a forecast whereby showers and
storm chance will remain probable up through the passage of a cold
front on Saturday. While Wednesday will not be a dry day, activity
will be confined primarily to the mountains as an upslope northwest
flow pattern develops. Temperatures will still be well above normal
on Monday, but trend slightly cooler Tuesday, but notably cooler by
Wednesday.

Confidence in the above weather pattern is moderate.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
-- Changed Discussion --
As of 640 AM EDT Thursday...

Mid and high clouds from upstream convective complexes over the
area this morning. These clouds will gradually erode this
morning, enough to result in an unstable air mass by afternoon.

Convective allowing models have reasonably good agreement with
the timing of the thunderstorms today, showing the bulk of the
storms in the 19Z/3PM to 23Z/7PM time frame. Have used this
timing in the local TAFs. However storms may develop as early as
noon in the northwest north Carolina mountains and last until
midnight in the North Carolina piedmont. Location of
thunderstorm development today is more questionable.

Any of the strong to severe thunderstorms with produce MVFR
visibility due to heavy rain and strong to damaging wind.
Otherwise, the wind will be less than 10 knots from the west to
southwest.

Average confidence for ceiling, wind, and visibility

EXTENDED AVIATION OUTLOOK...

Periods of showers and thunderstorms, especially each afternoon
and evening will continue through Monday. MVFR remain likely
with any of the thunderstorms.
-- 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/NF