Flash Flood Watch 16, NWS Blacksburg, VA

Area Forecast Discussion
National Weather Service Blacksburg VA
946 AM EST Wed Nov 11 2020

.SYNOPSIS...
High pressure over the Atlantic ocean will continue to pump
moisture into the region with widespread rainfall expected
today, especially in the mountains. Tonight, an approaching cold
front will combine with moisture from tropical cyclone Eta over
the Gulf of Mexico to bring another round of locally heavy
rainfall to the Appalachians and central mid Atlantic region
tonight. High pressure will bring drier conditions for the end
of the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 945 AM EST Wednesday...

Rain this morning has been heaviest along the spine of the Blue
Ridge, as expected. Starting to see a break in the southern
Appalachians, which will be a nice reprieve for northwestern NC,
where totals as of this morning were approaching 3", and had a
report of 3.37" at Blowing Rock, NC, which is typically on the
higher end during rain events.

Have adjusted PoPs the next couple of hours to account for the
breaks and patterns developing on radar, but nothing lower than
likely PoPs for the CWA. Temperatures east of the Blue Ridge
were running a couple degrees warmer than the forecast, so those
values have been nudged up.

From the previous discussion...

Current weather across the Appalachians and central mid Atlantic
region is unfolding as expected. Deep moisture transport is
becoming established in a very moist airmass with precipitable
water values expected to approach 4 standard deviations above
normal this morning. Deep layer ascent will be aided by an upper
level jet sliding by to our northwest and placing the area
under the good diffluence in the right rear quadrant. And the
amplifying low level wind field ahead of an approaching cold
front will bring good isentropic lift over the region. Can
already see these ingredients manifesting themselves with areas
of moderate to heavy rainfall across the Carolinas on radar
heading in our direction.

Expect the surge of heaviest precipitation will start entering
from the south before daybreak and slide through the region
during the morning. A rumble of thunder is not out of the
question. Anticipate efficient warm rain processes will yield
significant rainfall by daybreak Wednesday especially along the
southern Blue Ridge/NC mountains where upslope will boost local
amounts to around 2.0" through the morning. Confidence in this
heavy rain scenario is high from the southern Blue Ridge into
the mountains of NC, and has increased enough further east to
expand the flood watch into the foothills and piedmont including
Southside.

The widespread precipitation looks to pull off to the northeast
along with the best surge of dynamics, but expect some ribbons
of locally heavy rainfall to linger through this afternoon,
along with continued upslope precipitation in the mountains.
Also see some indications for minimal surface based destabilization
so a rumble of thunder remains possible. Will have to remain
alert for hydro concerns since any mesoscale features that become
anchored over a location for a period of time will be able to
produce a lot of rainfall.

The approaching cold front will bring one last round of heavy
rain to the region Wednesday night. Based on where heavy rain
falls today, expansion of the flood watch may be necessary to
account for this last surge of rain.

Temperatures will continue running well above normal with highs
today generally in the low/mid 70s. Lows tonight will start to
cool off once the front passes but will still be above normal
with low/mid 60s east, low/mid 50s west.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/...
As of 215 AM EST Wednesday...

The cold front should pass over central Virginia during the day,
while the remnant low of Tropical Storm Eta will merge in behind
the frontal boundary across northern Florida. Rain chances will
diminish from west to east as the front approaches the East
Coast by Thursday evening. There may still be ongoing
hydrological issues regarding minor flooding of creeks and
rivers, but that focus will shift eastward into Southside
Virginia and the North Carolina Piedmont. Lingering moisture
could persist through Thursday night, so a chance of showers
will stay in the forecast during that time period.

Finally, the major discrepancies among the model guidance are
clearing up as the latest ECMWF has swung into agreement with
the NAM and GFS. The remnant low of Eta should follow the cold
front into the Atlantic Ocean and stay well east of the
Appalachian Mountains. As a result, Friday and Saturday appear
dry as high pressure builds over the Mid Atlantic. Wind speeds
were bumped upward on Friday afternoon as model soundings show
good boundary layer mixing that may bring down northwest wind
gusts up to 25 MPH along the higher terrain. Saturday morning
lows were also lowered a few degrees to account for the
increased cold air advection and clearing skies. By Saturday
night, high pressure should head offshore as the next cold front
enters the Ohio River Valley.

&&

.LONG TERM /SUNDAY THROUGH TUESDAY/...
As of 215 AM EST Wednesday...

A cold front should approach the Appalachian Mountains on Sunday
to bring the next chance of showers into Sunday night. Breezy
conditions could follow behind the front by Monday. It appears
by early next week temperatures could cool a bit, but we would
still be 5-10 degrees above normal for mid-November.

&&

.AVIATION /15Z WEDNESDAY THROUGH SUNDAY/...
As of 630 AM EST Wednesday...

Sky conditions have become chaotic with changes in precipitation
intensity periodically mixing out low deck of clouds. Some
improvement is possible as initial surge of rain diminishes this
afternoon but may only see a rise into the lower end of MVFR.
Will err pessimistic and stay with generally IFR and amend if a
clear trend materializes. While guidance has a good handle on
the flavor of conditions, timing and placement of features is
varying considerably and lowering confidence in solutions. Will
paint with a broad brush and attempt to capture the trend with
more rain and IFR/LIFR developing after dark.

Winds may be a bit gusty west of the Blue Ridge this morning,
then diminishing for this afternoon.

.Extended Aviation Discussion...

High probability for sub-VFR conditions with widespread rainfall
into Thursday as moisture from the tropics combines with an
upper level trough and surface front over the region. Models
diverge for the weekend with some indication that clearing will
take place as high pressure builds into the north for the
weekend, but maintaining cloudy wet weather along the southeast
Atlantic Coast from the remnants of Eta.

&&

.HYDROLOGY...
As of 200 AM EST Wednesday...

No change to previous thinking with locally heavy rainfall
poised to move up from the south this morning. Expect widespread
1 to 2 inch amounts for the piedmont and foothills, with 2 to
locally 3 inches expected along the crest of the Blue Ridge of
the North Carolina Highlands through southern Roanoke County
this morning. Training of rain bands over the same areas is also
possible, which may lead to locally higher amounts and the
possibility of minor flooding of small creeks and streams. A
flood watch has been issued for the counties on either side of
the crest of the Blue Ridge from Roanoke southward as a result
of the potential for heavy rain.

A cold front will pass eastward across the central Appalachians
Wednesday night/early Thursday, bringing a renewed threat of
heavy rain, where an additional 1 to 2 inches is possible, more
so along and east of the Blue Ridge. Localized flooding will
again be a possibility with this rain before it exits the area
to the east by Thursday afternoon.

The strongest potential for mainstem river flooding is found
across the Dan River basin and the Roanoke River downstream of
Roanoke, where bankfull conditions are expected, possibly minor
flooding. The James River basin, as well as basins west of the
Blue Ridge, are not expected to be as heavily impacted.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...Flood Watch through Thursday evening for VAZ015>017-022-032-
     033-043-044-058.
NC...Flood Watch through Thursday evening for NCZ001>006-018>020.
WV...None.

&&

SYNOPSIS...MBS
NEAR TERM...MBS/VFJ
SHORT TERM...PW
LONG TERM...NF
AVIATION...MBS/PM
HYDROLOGY...MBS/PW

Hazardous Weather Outlook
National Weather Service Blacksburg VA
323 AM EST Wed Nov 11 2020

VAZ007-009>014-018>020-023-024-034-035-045>047-059-WVZ042>044-507-
508-121000-
Tazewell-Smyth-Bland-Giles-Wythe-Pulaski-Montgomery-Craig-
Alleghany VA-Bath-Botetourt-Rockbridge-Bedford-Amherst-Campbell-
Appomattox-Buckingham-Charlotte-Mercer-Summers-Monroe-
Eastern Greenbrier-Western Greenbrier-
323 AM EST Wed Nov 11 2020

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

.DAY ONE...Today and tonight.

Heavy rainfall may produce localized flooding today and tonight.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

The probability for widespread hazardous weather is low.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

NCZ001>006-018>020-VAZ015>017-022-032-033-043-044-058-121000-
Ashe-Alleghany NC-Surry-Stokes-Rockingham-Caswell-Watauga-Wilkes-
Yadkin-Grayson-Carroll-Floyd-Roanoke-Patrick-Franklin-Henry-
Pittsylvania-Halifax-
323 AM EST Wed Nov 11 2020

...FLOOD WATCH IN EFFECT THROUGH THURSDAY EVENING...

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

.DAY ONE...Today and 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...Thursday through Tuesday.

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

   Flood Watch.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Service Notice</title>
  <link rel="stylesheet" href="index.css">
</head>
<body>
  <main class="wrap">
    <section class="card" role="status" aria-live="polite">
      <div class="status" id="status">Temporary Notice</div>
      <h1 id="headline">This service is currently unavailable.</h1>
      <p id="message1">
        The site you requested is temporarily down for maintenance or an unexpected outage.
      </p>
      <p id="message2">
        Please try again in a few minutes.
      </p>
      <p class="small" id="detail">
        If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
      </p>
    </section>
  </main>
  <script src="index.js"></script>
</body>
</html>

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Service Notice</title>
  <link rel="stylesheet" href="index.css">
</head>
<body>
  <main class="wrap">
    <section class="card" role="status" aria-live="polite">
      <div class="status" id="status">Temporary Notice</div>
      <h1 id="headline">This service is currently unavailable.</h1>
      <p id="message1">
        The site you requested is temporarily down for maintenance or an unexpected outage.
      </p>
      <p id="message2">
        Please try again in a few minutes.
      </p>
      <p class="small" id="detail">
        If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
      </p>
    </section>
  </main>
  <script src="index.js"></script>
</body>
</html>