997
FXUS61 KRNK 311736
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
136 PM EDT Thu Jul 31 2025

.SYNOPSIS...
High pressure will gradually weaken as a cold front enters the
area tonight from the north. Expect widespread showers and
thunderstorms this afternoon and evening, with some
redevelopment of showers and thunderstorms for Friday as the
front slows down to our south. This activity will bring very
heavy rainfall at times. Temperatures begin to cool down Friday
into the weekend with a few mostly dry days into early next week.

&&

.NEAR TERM /THROUGH FRIDAY/...
As of 100 PM EDT Thursday...

Key Messages:

1) Heavy rainfall will be the main threat today, potentially
resulting in areas of flash flooding.

2) A front will continue to move south, and another round of
heavy rain will be possible on Friday.

A surface front is currently situated over the Ohio Valley and
extends east across Maryland. This front will continue to drop
south through tonight. High ambient moisture has pooled in front
of the southward moving front and widely scattered thunderstorms
are expected to continue through late this evening and into
tonight.

Areas of biggest concern for slow moving storms will be areas
north of US 460 closer to the actual front. Enough confidence
here to issue a Flood Watch for flash flooding, which will be in
effect through the early morning hours on Friday. Strong surface
heating, coupled with a very moist boundary layer has resulted
in SBCAPE values already exceeding 3000 J/kg across the area.
Deep convection will only enhance rainfall rates today and with
already several days of heavy rain, some locations are
certainly susceptible to flash flooding through tonight. Should
see intensity of storms decrease after sunset, but likely to see
convection continue through at least midnight and possibly even
into early Friday morning.

The front will continue to slowly move south during the day on
Friday, but not quick enough to completely clear the area before
the afternoon. Another round of afternoon and evening
thunderstorms are expected along the front, this time better
coverage will be centered along and south of US 460, especially
in the vicinity of the NC/VA border. Once again, very slow
moving storms with highly efficient rainfall rates will result
in an increased flash flood potential into Friday evening.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
As of 130 PM EDT Thursday...

Key Points:

1. Additional rounds of showers/storms Friday evening with locally
heavy rain possible, especially across the southern portions of the
area.
2. Temperatures will average a few degrees below normal.

A look at the 31 Jul 00Z NCEP Ensemble Mean 500mb Geopotential
Heights shows the axis of a longwave trough pattern center over the
region Friday evening. Concurrently, expansive ridging is
anticipated over much of central, western, and southeastern CONUS. A
closed low is expected to be over the Gulf of Alaska. For
Saturday/Saturday night, a general shift eastward is expected for
longwave trough, with it centered over the St. Lawrence Seaway on
Saturday evening. Looking upstream, a shortwave through is expected
to be heading southeast on the west side of the longwave feature
over James Bay. Little chance is expected for the position of the
ridging across much of CONUS and the low south of Alaska. For
Sunday/Sunday night, the ensemble averaging offers a bit of an
expansion of the overall coverage area of the aforementioned
longwave trough. There will be either be an expansion westward of
the overall width of this trough and/or positive interference from
the shortwave trough moving southeast on the longwave`s western
extent to offer this expansion in size to over portions of the Great
Lake/Ohio River Valley region. Ridging holds fast over western
CONUS and a low remains over the Gulf of Alaska.

At the surface on Friday evening, a cold front will be across
eastern NC/SC/GA. A broad region of high pressure is expected to be
centered over the western Great Lakes region. For Saturday/Saturday
night, the center of the high shift to over the Lower Ohio River
Valley. The eastern extent of the associated ridge of the high will
start to nose south along the lee of the Appalachians. A cold front
will be oriented w-e along the Gulf Coast States. An associated
inverted trough is expected to extend north from this front over
eastern KY/TN. For Sunday/Sunday night, the center of the high
shifts east to over the area of PA/NY/NJ, with its associated ridge
axis extending southwest along the lee of the Appalachians. Little
movement is expected for the Gulf Coast front and associated
inverted trough.

A look at the 31 Jul 00Z NAEFS Ensemble Situational Awareness data
shows 850mb temperatures on Friday evening ranging from around +14C
to +17C, n-s across the area. As we progress through Friday night
and the day Saturday, values are expected to fall to a range of
around +12C to +14C, ne-sw. Values Saturday night drop a couple more
degrees C across the area before returning on Sunday afternoon to
values similar to Saturday afternoon. Conditions from late Friday
night through Saturday, and Saturday night, will correspond to a
range within the 2.5 to 10 percentile of the 30-year CFSR
climatology.

The above weather patterns offers the following forecast. There will
still be good coverage of showers/storms Friday evening as the axis
of the upper trough crosses the region. Coverage, and the potential
for locally heavy rain, will be greatest across southern portions of
the area. By Saturday into Sunday, any additional showers/storms are
expected closest to the inverted trough over eastern KY/TN with vast
majority of the region precipitation-free. Temperatures will average
a few degrees below normal for this time of year through the period.

Confidence in the above weather scenario is moderate to high.

&&

.LONG TERM /MONDAY THROUGH WEDNESDAY/...
As of 130 PM EDT Thursday...

Key Points:

1. Gradual erosion of a cold air damming pattern is expected.
2. Increasing coverage of showers/storms heading into mid-week.
3. Gradually increasing temperatures to values near normal by
Thursday.

A look a the 31 Jul 00Z NCEP Ensemble Mean 500mb Geopotential
Heights shows for Monday/Monday night two shortwave troughs within a
longerwave pattern over portions of the Upper Mississippi River
Valley to the Ohio Valley. Ridging over western CONUS get shunted
eastward a bit in response to the low over the Gulf of Alaska
opening up into a wave and approaching the Pacific Northwest. For
Tuesday/Tuesday night, the shortwave trough(s) over the Mid-West
weaken and lift north closer to the Canada/US border over WI/MI. A
shortwave trough moves onshore the Pacific Northwest, and ridging
across much of the southern half of CONUS strengthens. For
Wednesday/Wednesday night, the WI/MI shortwave trough heads east and
is expected to be near NY/PA/OH Wednesday evening. A trough holds
fast over the Pacific Northwest and broad ridging continues over
most of the the southern two-thirds of CONUS. On Thursday, the
shortwave trough moving towards New England/mid-Atlantic is expected
to amplify slightly and become a bit more broad. Elsewhere across
CONUS, conditions are status quo.

At the surface, for Monday/Monday night, a ridge of high pressure
remains situated over the lee of the Appalachians. A stalled w-e
oriented front remains stationary along the Gulf Coast states. Low
pressure is expected to develop and deepen over west TX. For
Tuesday/Tuesday night, the lee side ridge continues. However, there
are indications of a strengthening baroclinic zone over the mid to
lower Mississippi Valley as the Gulf Coast states stalled front
buckles northward. For Wednesday/Wednesday night, we may start to
see some erosion of the lee side ridge as a front approaches from
the southwest. By Thursday, ensemble averaging suggest no lee side
ridge with south or southwest flow increasing to the east of a
deepening low pressure system over central CONUS.

A look at the 31 Jul 00Z NAEFS Ensemble Situational Awareness data
shows 850mb temperatures Sunday into Sunday night within the 2.5 to
10 percentile of the 30-year CFSR climatology. On Monday, values
start to inch upward, with afternoon readings around +14C to +15C.
By Tuesday, a little higher at +15C to +16C. The same trend is
expected Wednesday with late afternoon values of +16C to +17C.
Finally, by Thursday afternoon, values closer to +17C to +18C are
expected.

The above weather patterns offers the following forecast. The cold
air damming pattern will be established across the region over the
weekend will hold fast into at least Monday. Passed Monday, this
feature will start to gradually erode as the center of the primary
high shifts into the western Atlantic, and south to southwest flow,
and an associated front, approach the area. Look for progressive
more daytime coverage of showers and storms as we head into mid-
week. Temperatures will start this period averaging a few degrees
below normal, but trend to values around normal by Thursday.

Confidence in the above weather scenario is moderate.


&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
As of 130 PM EDT Thursday...

Widespread VFR at the moment, but expecting more MVFR to IFR as
the evening progresses. Thunderstorms will continue to develop
and heavy rainfall will be the main threat, thus brief
reductions to vsby are likely at any given terminal through at
least 00z/8PM. A few storms will also be capable of wet
microbursts as well. Coverage of storms should decrease
overnight, but areas of fog will begin to fill in and some LIFR
will be possible, especially in locations that receive rain this
afternoon/evening. Slow to clear in the morning and some MVFR
clouds could linger into late morning. Hints of VFR may briefly
return midday Friday.


.EXTENDED AVIATION OUTLOOK...

A deepening trough overhead and the proximity of the front and
plenty of moisture will trigger more showers and storms for
Friday afternoon and Friday night. Some morning fog will
continue to be a daily threat, but lessening moisture may help
inhibit widespread fog development. May see a few isolated
afternoon storms over the southern Blue Ridge through Sunday,
but otherwise VFR expected into early next week.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...Flood Watch from 8 PM EDT this evening through late tonight
     for VAZ023-024-034-035-045>047.
NC...None.
WV...None.

&&

$$

SYNOPSIS...BMG
NEAR TERM...BMG
SHORT TERM...DS
LONG TERM...DS
AVIATION...BMG