Flash Flooding and Debris Flows in West Virginia, May 27 to 30, 2023

Area Forecast Discussion
National Weather Service Blacksburg VA
941 PM EDT Sat May 27 2023

.SYNOPSIS...
Low pressure off the South Carolina coast will move slowly north
tonight through Sunday night bringing widespread rain and below
normal temperatures to the region. Tuesday and Wednesday the
probability of rain decreases, but dry and warmer weather does
not arrive until the end of next week.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 930 PM EDT Saturday...

Light rain continues to overspread the region with the greatest
concentration generally in areas near and west of I-77. Coverage
gradually decreases the farther the away from this location with
only very patchy light rain across the southern Alleghany
Highlands. Meso-scale models over a small break in the activity
across the southwest portion of the region a little past
midnight, but with another resurgence of cover as we head into
the pre-dawn hours of Sunday.

Have made minor tweaks to hourly temperatures and dew points
based upon the latest observations and expected trends over the
next several hours.

As of 705 PM EDT Saturday...

     Widespread light rainfall becomes heavier tomorrow...

As of this evening stacked low pressure was spinning off the
coast near Charleston, SC. A plume of moisture stretched from it
NW towards Knoxville and into the Ohio Valley. Additional
forcing NE of the low was supporting an area of thunderstorms
over the NC coast. We were getting some of the lighter moisture
being drawn in from the ENE north of these areas. The result was
light but persistent rain across northern NC and parts of SW VA
and even into SE WV. Rainfall amounts were light so far with
just a few hundredths falling every hour, and a sharp cutoff .
We will continue to skirt the deeper moisture through tonight,
and expect most to see several periods of light rain off and on.

Isentropic lift increases towards daybreak. As the surface low
lifts north along the coast, some of the deeper moisture will
work in along the southern Appalachians. This will result in
periods of heavier rainfall Sunday. Overall looking gloomy and
cool.

Adjusted PoPs and temperatures/dew points slightly for this
update.

As of 120 PM EDT Saturday...

     Confidence high for rain and wind tonight...

Two closed upper lows, one over the Tennessee Valley and the
other off the South Carolina coast will merge tonight, lower
500MB heights over the Carolinas. At the surface low pressure
will track from the South Carolina coast into North Carolina by
Sunday.

Starting with a large surface temperature/dewpoint spread this
afternoon with dew points in the upper 30s to mid 40s. The air
mass will saturate from the top down and as has been the case
for the past few runs, will slow down the northern edge of the
rain with the system. Will use the timing off the HRRR and HREF
which gets the rain in to Roanoke and Lynchburg around 22Z/6PM
and not up to Lewisburg and Hot Springs until 03Z/11PM.

Surface and low level winds veer to the east and southeast
tonight and remain easterly on Sunday. As the winds become
east, the low level jet increases into the 45 to 50 knot range
leading to low level convergence and slightly better upslope
lift. Isentropic lift is still decent too, especially tonight.

Even with all the clouds and mixing this evening, temperatures
will lower and dew points will rise as low levels moisten.
Little change in temperature is expected once the humidity is
near 100 percent. Clouds and rain will also keep temperatures
unseasonably cold on Sunday. Forecast high temperature are close
to records for coldest maximum. See the climate section of this
discussion.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
As of 1220 PM EDT Saturday...

     Continued cool and rainy conditions...

The upper closed low and stacked sfc low is progged to meander
slowly eastward through the period allowing for continued slugs
of enhanced Atlantic moisture advecting across the area along
the north and eventually west of the center. Despite some
warming temps compared to the weekend, there doesn't look to be
much instability available unless some breaks in cloud cover and
daytime heating during the afternoon could locally enhance sfc
based parcels. Just hard to see anymore than a slight chance of
thunder given this setup and northeast to east fetch. Tuesday
even looks to be possibly more stable with stronger wedging
combining into the setup.

For QPF, Sunday night through Monday looks to have most of the
area with the heavier amounts generally in the 1-1.5 inch
range for storm totals, then an additional quarter to half inch
shifted to the eastern CWA for Tuesday. While these totals are
not very impressive, any localized flood threats may depend on
antecedent conditions and what precip amounts are realized from
the weekend rounds.

Forecast confidence is medium to high.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 1220 PM EDT Saturday...

   Shower and storm chances for Wednesday then some slight
   chances Thursday and Friday. Temps moderating warmer...

For Wednesday, as the aforementioned low dampens to the east of
the area, we still stay in a regime of some residual enhanced
moisture but with little discernible forcing mechanism present.
This with limited progged instability mainly warrants a day of
general chance pops and slight thunder mention.

For Thursday into Friday, some weak ridging could win over and
allow for a pocket of drier airmass pushing in from the north.
Guidance solutions are indicating we may be able to lessen pops
for these days. For now will keep some parts with just a slight
chance of precip.

Temps look to have a welcomed snap back to reality and moderate
even up to above climo norms by the end of the work week.
Friday forecast highs should generally range from mid 70s to low
80s in the mountains and some low to mid 80s for the piedmont.

Forecast confidence is medium.

&&

.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
As of 215 PM EDT Saturday...

Two closed upper lows, one over the Tennessee Valley and the
other off the South Carolina coast will merge tonight, lower
500MB heights over the Carolinas. At the surface low pressure
will track from the South Carolina coast into North Carolina by
Sunday.

Starting with a large surface temperature/dewpoint spread this
afternoon with dew points in the upper 30s to mid 40s. The air
mass will saturate from the top down and ceilings were already
lowering. Have KDAN reaching MVFR around midnight/04Z, KBCB
around 06Z/2AM, KBLF/KLYH around 09Z/5AM, KLWB/KROA by 11Z/7AM.
Ceilings will continue to drop throughout the day Sunday
reaching IFR at all local TAFS except for KLWB by 14Z/10AM.

Widepspread MVFR rain and fog will fill in across southwest
Virginia, northwest North Carolina and southeast West Virginia
around the same time as the ceilings drop to MVFR. Rain and fog
will continue past the 18Z/2PM end of the TAF forecast period.

Surface and low level winds veer to the east and southeast
tonight and remain easterly on Sunday. As the winds become
east, the low level jet increases into the 45 to 50 knots. Wind
gusts overnight will remain in the 15 to 25 knot range.

EXTENDED AVIATION OUTLOOK...

Poor flying conditions will persist into Monday night.

Gradual improvement should take place during Tuesday as low
pressure starts to move east. The probability of precipitation
will lower but the chance of showers with afternoon
thunderstorms will continue into Wednesday.

VFR ceilings and visibilities will return for Wednesday and
Thursday.

&&

.CLIMATE...
As of 215 PM EDT Saturday...

Listed below are the record cold maximum temperatures for May
28th

Bluefield WV...51 in 1992
Danville VA....61 in 1968
Lynchburg VA.. 57 in 1992
Roanoke Va.....56 in 1992
Blacksburg VA..54 in 1997

&&

.EQUIPMENT...
As of 645 PM EDT Saturday...

The temperature reading at Roanoke (ROA) has been erroneous
since a hardware failure this morning. Electronics technichians
were evaluating the problem. Use this data with caution. Parts
of the preliminary 5PM climate report have been sent as
missing.

&&

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

&&

SYNOPSIS...AMS
NEAR TERM...AMS/DS/SH
SHORT TERM...AB
LONG TERM...AB
AVIATION...AMS
CLIMATE...AMS
EQUIPMENT...AMS

Hazardous Weather Outlook
National Weather Service Blacksburg VA
300 PM EDT Sat May 27 2023

NCZ005-006-VAZ007-019-020-024-035-044>047-058-059-WVZ042>044-507-508-
281900-
Rockingham-Caswell-Tazewell-Alleghany VA-Bath-Rockbridge-Amherst-
Pittsylvania-Campbell-Appomattox-Buckingham-Halifax-Charlotte-Mercer-
Summers-Monroe-Eastern Greenbrier-Western Greenbrier-
300 PM EDT Sat May 27 2023

This Hazardous Weather Outlook is for north central North Carolina,
central Virginia, south central Virginia, southwest Virginia, west
central Virginia and southeast West Virginia.

.DAY ONE...This afternoon and tonight.

No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

NCZ001>004-018>020-VAZ009>018-022-023-032>034-043-281900-
Ashe-Alleghany NC-Surry-Stokes-Watauga-Wilkes-Yadkin-Smyth-Bland-
Giles-Wythe-Pulaski-Montgomery-Grayson-Carroll-Floyd-Craig-Roanoke-
Botetourt-Patrick-Franklin-Bedford-Henry-
300 PM EDT Sat May 27 2023

This Hazardous Weather Outlook is for north central North Carolina,
northwest North Carolina, south central Virginia, southwest
Virginia and west central Virginia.

.DAY ONE...This afternoon and tonight.

The probability for widespread hazardous weather is low.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

A prolonged period of light to moderate rainfall with periods of
locally heavy rainfall is expected along the Blue Ridge. Localized
flooding will be possible. General rainfall amounts of 1-3 inches
are expected across this region for the period Sunday through
Tuesday, with local amounts of 4-5 inches possible.

.SPOTTER INFORMATION STATEMENT...

Spotters, CoCoRahs observers, and the public are encouraged to send
reports of significant rainfall as well as any observed flooding to
the National Weather Service in Blacksburg, VA. Reports can be
submitted via phone by calling 1-866-215-4324, through our social
media platforms, by email at rnk.skywarn@noaa.gov, or online at
www.weather.gov/rnk.