Areal Flood Warning 21, NWS Blacksburg, VA

Area Forecast Discussion
National Weather Service Blacksburg VA
745 PM EDT Thu Aug 8 2024

.SYNOPSIS...
Moderate to heavy rainfall from Tropical Storm Debby will
continue through tonight, but then start to exit Friday.
This will result in a high risk of flooding, especially along
and east of the Blue Ridge. Debby pushes to the northeast by
Friday night, then cooler and drier air arrives by Saturday, and
will bring more tranquil weather for the weekend and start of
next week.

&&

.NEAR TERM /THROUGH FRIDAY/...
As of 730 PM EDT Thursday...

Key Messages:

   - High Risk of flooding tonight. Heavy rainfall may result
     in considerable to catastrophic flash flooding.

   - Tornado Watch extended through the overnight for the
     Piedmont mainly along/east of U.S. 29 in VA into Caswell
     County, NC

Per coordination with SPC we extended/expanded the Tornado Watch
til 7am for the Piedmont. However, trends in the models are
favoring the tornadic threat to exit in the midnight-3am time
frame. Will monitor trends. Leaned toward NBM and some high-res
models on tracking Debby and its rain. Looking like a drier
scenario further southeast per radar trends but the rain band
from the Shenandoah Valley into western NC will likely start to
edge back east overnight as Debby shifts north. Appears drier
air may end the rain sooner by Friday morning across our NC
counties. Will continue to monitor trends.

Previous discussion...

Band of moderate to heavy rain was along the southern Blue ridge
then into Buckingham County. This band will be lifting slowly
north as the tropical system moves slowly north. Due to the slow
motion of the tropical storm, expecting another 12 hours of
strong upslope easterly wind and rainfall rates average of 1 to
2 inches per hour. So some spots reaching 6 to 9 inches for
storm total still appears reasonable.

The wind forecast will be adjusted again around 5PM when the
next tropical bulletin is issued for Debby. Little change is
expected. Higher elevations will continue to have the potential
for 25 to 40 mph gusts through midnight.

As Debby move into northern Virginia, winds will turn to the
south and west, ending the upslope enhancement. Once the region
is on the south side of Debby, rain will end and wind speeds
diminish.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
As of 325 PM EDT Thursday...

Key Messages:

    - Lingering light showers possible through Friday night
    - Mostly dry weather expected for the weekend.

Little to no adjustments. Details will be refined once TS Debby
leaves the area

The remnants of what is currently Tropical Storm Debby will be into
the upper Mid Atlantic and New England by Friday night, as the
system gets lifted northward by an upper trough. Some lingering
showers in the area are possible overnight and into early Saturday
morning, as a surface front pushes into the region from the west.
Behind the front and tropical system, a cooler and drier airmass
will build into the area, and high pressure will become situated
overhead through Sunday. For the remainder of the weekend, weather
will be much drier, and only very limited chances of precipitation,
mainly in NC and southward, as the front stalls across the
southeastern states.

Temperatures will be cooler, near to a couple degrees below seasonal
normals, in the mid to upper 70s in the west, and mid 80s in the
east. Plentiful sunshine and lower dewpoints are expected through
Sunday.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 325 PM EDT Thursday...

Key Messages:

     - Quieter weather pattern for beginning of the week
     - Temperatures near normal

Little to no adjustments. Details will be refined once TS Debby
leaves the area

A much quieter weather pattern is expected for the beginning of the
work week, with surface high pressure settled over the Ohio Valley
and Mid Atlantic region, keeping precipitation chances limited. Some
isolated to scattered showers and thunderstorms are possible
Tuesday afternoon, mainly along and south of the VA/NC border, as a
front drifts northward into the Carolinas, but probabilities are low
at this time.

Temperatures will be near normal through the period, in mostly the
70s west of the Blue Ridge, and low to mid 80s east.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
As of 730 PM EDT Thursday...

Widespread IFR to MVFR ceilings expected through the overnight.
Looks like a good night to keep the planes grounded if possible
until Debby exits Friday. At times expect rain to be heavy at
all sites, with east-southeast winds gusting to 20-25kts. Vsbys
will drop to IFR. As we head into Friday morning, rain will
start to shift north and ending at most if not all sites by 18z,
with VFR expected as winds shift to the west/northwest.

Winds will be lighter on Friday.

Average confidence on visibility and wind.
Below average confidence on ceiling.

AVIATION OUTLOOK...

Remnants of Debby exit with VFR expected through the rest of the
period. Exceptions will be any fog/low clouds that form
especially Sat/Sun morning as ground moisture stays elevated.

&&

.HYDROLOGY...
As of 735 PM EDT Thursday...

Rainfall amounts have averaged 1-3 inches but some local 5"+
amounts have been observed. Still expecting rises to above flood
stage along portions of the Roanoke/Pigg and Dan River by
Friday, however, drier pocket of across NC this evening and lack
of deeper convection may lend to lowering. Still with PWATS
surging past 2.0" any rainfall will be moderate to heavy so no
changes to flood watches/warnings at this time. Appears the
remnants of Debby may exit sooner Friday.

Additional rainfall amounts tonight- Friday will average 1-3
inches along/north of US 460 in Virginia, with lower amounts to
the south and west. Locally higher amounts to 4-5" possible
along the Alleghanys/Blue Ridge north of Roanoke.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...Flood Watch through Friday evening for VAZ010>020-022>024-
     032>035-043>047-058-059.
NC...Flood Watch through Friday evening for NCZ001>006-018>020.
WV...Flood Watch through Friday evening for WVZ042>044-507-508.

&&

SYNOPSIS...AMS/AS/WP
NEAR TERM...AMS/WP
SHORT TERM...AMS
LONG TERM...AMS
AVIATION...AMS/BMG/WP
HYDROLOGY...BMG/WP

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