River Flood Warning 9, NWS Blacksburg, VA

Area Forecast Discussion
National Weather Service Blacksburg VA
321 PM EST Sat Feb 15 2025

.SYNOPSIS...
A large storm system Tracking from the Mississippi Valley tonight
through  the Ohio Valley on Sunday will spread rain and freezing
rain into the area on tonight. Rain and possibly thunderstorms will
continue into Sunday increasing the threat of flooding. Blustery and
much colder conditions arrive Sunday night and Monday as the low
tracks across New England.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 130 PM EST Saturday...

Key message:

     - Winter Weather Advisories continue
     - Areas of Fog tonight
     - Wind Advisory issued for Sunday into Monday

Temperatures along the Blue Ridge were rising slowly, but were still
from near 32 degrees as of 2PM. Deep moisture and strong
synoptic scale lift had returned to the Mid Atlantic region. The
southern edge of the warm front and isentropic lift advance
north of I-64 west of Lexington during the evening. South of the
warm front precipitation will stop or become much lighter.
However, with a light wind at the surface and abundant low level
moisture, fog will develop overnight. Dense fog, with
visibility at or below one half mile, is possible. Given the
amount of tree branches and power lines on roads in the area,
any fog will make it especially difficult to see these hazards.

The upper trough in the southern stream digs into the lower
Mississippi Valley tonight, then rounds the base of the long wave
trough and lifts northeast across to the Mid Atlantic coast on
Sunday, lowering 500 MB heights late tonight and Sunday.

Significant change in air mass and intense cold air advection starts
Sunday afternoon behind a cold front. Impressive upper diffluence
reaches the southern Blue Ridge by Sunday morning. Tonight through
the time the front crosses the area on Sunday 850MB temperatures
will be in the +6 to +10 range. By the end of the day Sunday 850 mb
temperatures crash to -4 to -8. Bufkit forecast soundings from the
3KM NAM showed a surge in wind immediately behind a cold front. The
boundary crosses the area between 8AM and 4PM. Models depict a 60
knot cross barrier low-level jet behind the front by Sunday evening.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
As of 130 PM EST Saturday...

Key Points:

1. Wind Advisory concerns Sunday night into early Monday
2. Low Wind Chills Sunday night into early Monday morning.
3. Dry and colder Tuesday.
4. Onset of potential winter storm late Tuesday night.

A look at the 15 Feb 00Z NCEP Ensemble Mean 500mb Geopotential
Heights show a double barrel closed low extending from Manitoba to
Quebec early Sunday night. Two associated trough axis extend from
this system. One will extend eastward over New England. The second
will extend south into the Ohio Valley. As we progress through
Monday and into Monday evening, the upper low will deepen and merge
into one low center, and shift east to over the Canadian Maritimes.
Nearly zonal flow is expected over our region. A trailing trough
associated with the upper low is expected to extend westward into
south central Canada. For Tuesday into Tuesday night, the trough over
south central Canada heads south into central CONUS and begins to
deepen. In response, flow over our region starts to back and heights
increase slightly.

At the surface, low pressure is expected to be located over New
England early Sunday evening with a tailing cold front along the mid-
Atlantic coast and eastern sections of the Carolinas. Concurrently,
an area of high pressure will extend from south central Canada, south
to Texas. By Monday into Monday night, the axis of the central US
ridge is expected to shift eastward to over the Southeast US. The
low over New England is expected to make gradual progress to over
the Canadian Maritimes. For Tuesday into Tuesday night, the axis of
the ridge shifts to over our region. Concurrently, an inverted
trough begins to develop from South Texas into the Lower Mississippi
Valley.

A look at the 15 Feb 00Z NAEFS Ensemble Situational Awareness data
shows 850mb temperatures Sunday Night falling behind a departing
cold front. By daybreak Monday, values are expected to range from
-14C to -10C, nw-se. These values correspond to the 2.5 to 10
percentile of the 30-year CFSR climatology. On Monday, these values
moderate a bit, reaching a range of -9C to -4C, n-s, by the early
evening. A slight warming trend continues Monday night with values
by daybreak Tuesday ranging from -8C to -2C, n-s. On Tuesday, values
remain about the same. Only a small increase is expected Tuesday
night, reaching -7C to -2C, n-s.

The above weather patterns offers a Sunday night where our region
will be on the back side of the exiting low pressure and the
building of high pressure to our west. The result will be a tight
pressure gradient between the two with very gusty conditions across
the region. The northwest flow will help maintain upslope snow
showers across the preferred regions of Southeast West Virginia,
south into the Northern Mountains of North Carolina. Snowfall amounts
should be minimal, with the highest totals over western Greenbrier
County.

Forecast 850mb winds are expected to range from about 40 to 50kts
across the region. The concern is the potential for Wind Advisory or
near Warning criteria winds. Combine the expected wind speeds with
both saturated soils and lingering damaged trees/limbs from the
recent freezing rain event, and the ingredients are there for trees
and power lines to be brought down.

As colder air surges into the area, the combination of the colder
temperatures and stronger winds will help to produce low wind
chills. The teens to lower 20s are expected for the Piedmont region.
Single digits will be common across the mountains with the single
digits below zero possible for western Greenbrier County and some of
the highest peaks of the Mountain Empire region of southwest
Virginia and the mountains of Northwest North Carolina

Winds decrease through the day on Monday and even more so Monday
night into Tuesday. Temperatures will be below normal for this time
of year.

For Tuesday night, we expect increasing cloud cover in advance of
our next approaching system. This system will be in association with
the developing inverted trough across the southern portion of the
US. Moisture will begin to stream into our area in advance of this
system. By daybreak Wednesday, western and northern parts of the
area may start experiencing precipitation from this system. Models
are in pretty good agreement that conditions at the surface and
within the low level profile will be cold enough for snow at the
onset.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 130 PM EST Saturday...

Key Points:

1. Increasing confidence of a winter storm Wednesday into Thursday.
2. Drier and trending slightly milder Friday into Saturday.

A look at the 15 Feb 00Z NCEP Ensemble Mean 500mb Geopotential
Heights shows the formation of a closed low Wednesday into Wednesday
night over the Great Lakes region. An associated shortwave trough
extends south into the Mississippi Valley. By Thursday into Thursday
night, the low opens into a progressive trough moving across the
Great Lakes region. Its associated trough axis moves across the mid-
Atlantic region. For Friday into Friday night, the trough progresses
to the area of Newfoundland and Labrador, a shortwave ridge builds
over the Midwest, and a new trough starts developing from the
Northern Plains States, southwest into the Four Corners region. On
Saturday, the trough to our west moves eastward and evolves to
longwave trough pattern centered over the Mississippi Valley.

At the surface, the axis of the ridge over our region weakens in
response to the southern US inverted trough progressing eastward. As
it moves eastward, its influence is expected to expand northeastward
with its axis extending from Florida to just off the coast of the
Carolinas by Wednesday evening. For Thursday into Thursday night,
the inverted trough deepens into a closed low in the western
Atlantic east of New England and south of Nova Scotia. High pressure
over the central US expends eastward into the Tennessee Valley. For
Friday into Friday night, the central US high continues its
expansion eastward. Saturday into early Saturday night, the center
of the high shifts to the Southern Appalachians.

A look at the 15 Feb 00Z NAEFS Ensemble Situational Awareness data
shows 850mb temperatures by the early evening on Wednesday are
expected to range from -6C to -2C, nw-se. Wednesday night through
Thursday, values will trend lower, reaching a range of -13C to -10C,
nw-se by Thursday evening. These values will correspond to the 2.5
to 10 percentile of the 30-year CFSR climatology. For the far
southwest portion of the area, the numbers represent the 1 to 2.5
percentile. On Thursday night, only small moderation is expected
with daybreak Friday values ranging from -12C to -8C, nw-se. On
Friday, values start to moderate, reaching -8C to -6C, nw-se by the
early evening. Friday night into early Saturday morning, values
increase to -6C north to -4C south. By Saturday evening, expect a
range of -5C to -3C, n-s.

The above weather patterns offers a broad shield of precipitation
progressing into our region on Wednesday in association with the
southern stream system. For most of our region, surface and low
level thermal profiles are offering a snow forecast. Enough of a
warm nose may infiltrate the southeastern sections of the region to
offer a p-type challenge. An additional challenge, is how much
influence will a northern stream system have on the potentially
multi-day wintry event. The deterministic solutions offer too broad
of a spectrum of solutions for there to be good confidence on this
question just yet. However, the various guidance equally does not
suggest there will be no influence from the northern system. The
question is more will the two work in tandem with each other, a
unique distinction between the two, or some hybrid solution where
there is some interaction between the two. Our most recent forecast
is leaning toward the third option with at least some interaction
between the two.

Taking a look at snowfall probabilities from DESI for the 48 hours
concluding 7pm Thursday, currently there is a 50 percent probability
or greater of five inches or greater of snowfall across all of our
Southeast West Virginia counties, most of our Southwest Virginia
counties except those nearest the North Carolina border, and
southwest of Wytheville along the I-81 corridor. Areas along and
southeast of a Reidsville to South Boston line have a 30 to 40
percent probability of experiencing 0.1 inch or more of freezing
rain during the same time period.

As we progress into Friday and Saturday, for the most part,
precipitation-free conditions are expected. The exception may be
some residual upslope snow showers across portions of Southeast West
Virginia. Temperatures are expected to trend slightly milder.

&&

.AVIATION /20Z SATURDAY THROUGH THURSDAY/...
As of 300 PM EST Saturday...

Ceilings were MVFR to IFR and visibility was MVFR in moderate to
heavy rain.

The southern edge of the warm front and isentropic lift advance
north of I-64 west of Lexington during the evening. South of
the warm front precipitation will stop or become much lighter.
However, with a light wind at the surface and abundant low level
moisture, IFR to LIFR fog will develop overnight. There will
also be significant LLWS until the front goes through on Sunday.

Significant change in air mass and intense cold air advection starts
Sunday afternoon behind a cold front. Bufkit forecast soundings
from the 3KM NAM showed a surge in wind immediately behind a
cold front. Expect gusts of 30 to 50 kts after 12Z Sunday behind
the front.

.EXTENDED AVIATION OUTLOOK...

Deep convection along the front will produce moderate-heavy
intensity rain with potential for embedded thunderstorms Timing
of the front Sunday...12-16Z for BLF/LWB/BCB and 14-18Z
ROA/LYH/DAN.

Behind the front ceilings/vsbys improve east of the mountains
but windward slopes may keep sub-VFR with snow showers across
BLF/LWB into early Monday. Also west to northwest winds behind
the front Sunday could gust over 40 mph along/west of the Blue
Ridge.

Should be VFR into late Tuesday maybe even Tuesday night but
another winter storm could bring poor aviation conditions across
the Mid-Atlantic and Carolinas Wednesday and Thursday.

&&

.HYDROLOGY...
As of 230 PM EST Saturday...

Key Message:

     -Flood Watch in effect until Sunday evening along and west of
      the Blue Ridge

Moderate flooding is forecast for the Greenbrier River at
Alderson.

Minor flooding is in effect for the Clinch River at Richlands.

Rainfall rates in the band of warm air advection isentropic lift
from western Kentucky into central Virginia have been around 0.5
inches per hour. Rainfall total through 18z/1PM were roughly 0.25 to
1.25 inches west of the Blue Ridge. Even with the relative break in
the rain overnight, since the second rounds will still be crossing
the area with the cold front, including a band of showers and
isolated thunderstorms with heavier rainfall rates, no changes are
planned to the Flood Watch.

Will continue to monitor area mainstem Rivers. The highest
concern remains in the Greenbrier, Clinch, Bluestone, New, and
upper James basins. River forecasts will be updated again be the
River Forecast Centers after 00Z/7PM or as needed.

At the very least, those near small streams and rivers should
prepare for potential flooding. Small streams and creeks will
rise very quickly when the ground is saturated. Rivers will
respond a little slower (lag time) but can rise just as rapidly
if thunderstorms with heavy rain enter the equation.

The Greenbrier, Upper James, and upper Clinch river valleys are
especially susceptible to river flooding due to the wet
antecedent conditions and headwater higher elevation snow pack.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...Flood Watch through Sunday evening for VAZ007-009>020-022>024-
     035.
     Wind Advisory from noon Sunday to 4 PM EST Monday for
     VAZ014>017-022>024-032>035-043>047-058-059.
     Wind Advisory from noon Sunday to 1 PM EST Monday for VAZ007-
     009>013-018>020.
     Winter Weather Advisory until 7 PM EST this evening for VAZ011-
     013-014-017>020-022>024-032>035.
NC...Flood Watch through Sunday evening for NCZ001-002-018.
     Wind Advisory from noon Sunday to 4 PM EST Monday for
     NCZ001>006-018>020.
WV...Flood Watch through Sunday evening for WVZ042>044-507-508.
     Wind Advisory from noon Sunday to 1 PM EST Monday for
     WVZ042>044-507-508.
     Winter Weather Advisory until 7 PM EST this evening for WVZ043-
     044-507-508.

&&

SYNOPSIS...PM
NEAR TERM...AMS
SHORT TERM...DS
LONG TERM...DS
AVIATION...AMS/PM
HYDROLOGY...AMS

Hazardous Weather Outlook
National Weather Service Blacksburg VA
511 PM EST Sat Feb 15 2025

VAZ007-009>013-018>020-WVZ042>044-507-508-162215-
Tazewell-Smyth-Bland-Giles-Wythe-Pulaski-Craig-Alleghany VA-Bath-
Mercer-Summers-Monroe-Eastern Greenbrier-Western Greenbrier-
511 PM EST Sat Feb 15 2025

...FLOOD WATCH REMAINS IN EFFECT THROUGH SUNDAY EVENING...
...WIND ADVISORY IN EFFECT FROM NOON SUNDAY TO 1 PM EST MONDAY...

This Hazardous Weather Outlook is for southwest Virginia, west
central Virginia and southeast West Virginia.

.DAY ONE...Tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Flood Watch.

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

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Flood Watch.
   Wind Advisory.

Another winter storm system may impact the region Wednesday and
Thursday.

.SPOTTER INFORMATION STATEMENT...

Weather spotters are requested to report flooding or wind damage in
their area.

NCZ001-002-018-VAZ014>017-022>024-035-162215-
Ashe-Alleghany NC-Watauga-Montgomery-Grayson-Carroll-Floyd-Roanoke-
Botetourt-Rockbridge-Amherst-
511 PM EST Sat Feb 15 2025

...FLOOD WATCH REMAINS IN EFFECT THROUGH SUNDAY EVENING...
...WIND ADVISORY IN EFFECT FROM NOON SUNDAY TO 4 PM EST MONDAY...

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

.DAY ONE...Tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Flood Watch.

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

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Flood Watch.
   Wind Advisory.

Another winter storm system may impact the region Wednesday and
Thursday.

.SPOTTER INFORMATION STATEMENT...

Weather spotters are requested to report flooding, or wind damage in
their area.

VAZ032>034-162215-
Patrick-Franklin-Bedford-
511 PM EST Sat Feb 15 2025

...WIND ADVISORY IN EFFECT FROM NOON SUNDAY TO 4 PM EST MONDAY...

This Hazardous Weather Outlook is for south central Virginia,
southwest Virginia and west central Virginia.

.DAY ONE...Tonight.

There is a low probability for widespread hazardous weather.

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

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Wind Advisory.

Another winter storm system may impact the region Wednesday and
Thursday.

.SPOTTER INFORMATION STATEMENT...

Weather spotters are requested to report wind damage in their area.

NCZ003>006-019-020-VAZ043>047-058-059-162215-
Surry-Stokes-Rockingham-Caswell-Wilkes-Yadkin-Henry-Pittsylvania-
Campbell-Appomattox-Buckingham-Halifax-Charlotte-
511 PM EST Sat Feb 15 2025

...WIND ADVISORY IN EFFECT FROM NOON SUNDAY TO 4 PM EST MONDAY...

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

.DAY ONE...Tonight.

There is a low probability for widespread hazardous weather.

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

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Wind Advisory.

.SPOTTER INFORMATION STATEMENT...

Weather spotters are requested to report wind damage in their area.

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