Flash Flood Watch 6, NWS Blacksburg, VA

Area Forecast Discussion
National Weather Service Blacksburg VA
1001 AM EDT Wed Jun 17 2020

.SYNOPSIS...
A slow moving upper low pressure system will make for a few days
of showery weather.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 955 AM EDT Wednesday...

Periods of moderate to heavy rainfall have been streaming into
the region from Southside into the Roanoke valley with
significant rainfall in a relatively narrow corridor from
roughly South Boston up through Roanoke. Anticipate this
corridor of rainfall will become less concentrated over the
next couple of hours, though locally heavy rainfall will remain
possible especially if more convective elements become
embedded.

Previous discussion...

Expect another day of off and on again rain/showers. Closed upper
low center south of the Triad of NC this morning and will slide
slowly north/northwest into SW Va later today into tonight. We will
see best lift ahead of it across the VA/NC piedmont into the
foothills of the Blue Ridge in VA this morning, then as we head
through the day best moisture transport starts to head northward,
while at the same time low and mid level lapse rates increase under
the upper low. The big question is instability as clouds look to
hang tough limiting solar insolation. However, elevated instability
is there, so expect a few pockets of thunder area wide this
afternoon/early evening. These heavier storms could bring 2-4
inch/hour rates as pwats hang in the 1 to 1.5 inch range.  See hydro
section below for more details.

Given coverage of heavier rain will be sporadic, and rates overall
will run about a quarter to half inch an hour, not really seeing a
need for a flood watch, plus there are some differences in models on
the exact bullseye of heavier rainfall, ranging from the 00z Euro
lined up north of the Roanoke River and U.S./ 460, similar to the
NAM but with some differences on exact location of heavier qpf, with
the GFS further south across the NC/VA border. With the sfc
flow/upper flow as advertised by the models and looking at WV loop
trends, think a northern shift in the higher amounts seems
reasonable.

As we head into tonight, models start to "dry" things out across
southern VA into NC with a dry slot working across the piedmont.
Since the upper low will be close by not going to be going too dry
but will lean toward low chance pops late tonight from the mountain
empire of SW VA into the NC piedmont, with higher pops north of U.S.
460 and especially north of I-64/U.S. 60.

As for temperatures should see a continuation of cooler than normal
highs today, but maybe a few degrees warmer, with most in the 60s.

Tonight, with increasing dewpoints appears lows should be milder in
the mid to upper 50s west, to lower 60s east.

Forecast confidence is high for all parameters except rainfall
amounts, which is average.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 150 AM EDT Wednesday...

The models continue to trend slower and slower with each run on the
closed upper level low ever leaving the Mid Atlantic. The Canadian,
ECMWF, and UKMET models have the closed low retrograding from
southwest Virginia toward West Virginia during Thursday and
eventually reaching southeastern Ohio by Friday. The GFS has also
slowed down and come into better agreement with the other global
models through this same time period. As a result, confidence has
risen on keeping conditions unsettled through Friday with higher
rain chances and sky cover. Temperatures were also kept on the
cooler side of the blended guidance. The threat of thunderstorms has
also been increased slightly during the afternoon and evening hours
due to the pool of cooler air aloft.

By Friday night, the GFS become mores progressive and diverges from
the other global models as it opens the closed low into an open wave
trough due to an approaching upper level trough crossing over the
northern Plains. However, because the GFS continues to trend slower
with each run as previously mentioned, this forecast will be steered
toward the slower consensus solution from the other global models
with the closed low wobbling eastward from the Ohio River across the
Appalachian Mountains by Saturday and getting close to the
Chesapeake Bay by Saturday night. Thus, unsettled weather should
persist through the first half of this weekend. Some drier air could
work its way from the west by Saturday night, but this pattern
insists on not clearing things up so quickly due to how poorly the
models already have handled this blocking pattern with a closed low
embedded in a broad upper level ridge that spans the eastern United
States. Several days ago, all the models had the closed low exiting
the Mid Atlantic by Friday, which is clearly not the case now.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 200 PM EDT Tuesday...

The cutoff low will gradually weaken and head offshore by the
end of the weekend. Some ridging over us should clear the skies
a bit and let some peeks of sunshine through, helping warm us
back to normal temperatures for mid- June. Persistent rain
coverage will be replaced by afternoon convection, especially
along the mountains. By Monday, areal coverage of precipitation
will expand again, as the next upper trough approaches bringing
showers and storms to the region.

&&

.AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
As of 640 AM EDT Wednesday...

Not much change from previous forecast, though some areas have
maintained better ceilings early, but however, this will change
as rain moves across lowering cigs/vsbys to MVFR or lower, with
IFR likely at most spots by midday. Should see this continue
through tonight with models showing showers starting to taper
off from south to north overnight, mainly south of a BLF-DAN
line, but a possibility that showers will be around through most
of the period off an on. Fog may be an issue late tonight, along
and south of a BLF-DAN line including BCB, if rain ends and
light winds occur. Some models have LIFR vsbys before 12z. Will
not go this low given extent of cloud cover expected.

It is a high confidence forecast for sub-VFR through most of the
period, but lower on how low cigs/vsbys go in relation to
rainfall, which will be moderate to heavy at times from LWB-
ROA-LYH this morning and possibly BCB/DAN.

Some thunder may occur later this afternoon, but overall
coverage is isolated so not mentioning in the tafs. Winds are
generally east to northeast under 10 kts with occasional higher
gusts through midday, mainly east of the Blue Ridge, then calmer
later Wed evening.

Extended Aviation Discussion...

The closed upper low will continue to meander about the central
and southern Appalachians through Friday, finally beginning to
lift slowly to the north by the weekend. As the low weakens,
the threat for prevailing IFR conditions and persistent -RA will
begin to decrease.

Showers and thunderstorms, with MVFR ceilings and visibilities
are expected Saturday and Sunday, mainly each afternoon and
evening.

&&

.HYDROLOGY...
As of 215 AM EDT Wednesday...

Overall rainfall amounts will again vary by location, but
models overall are pinpoint higher amounts from the Blue Ridge
north of the VA/NC border through tonight north and east into
the piedmont. Amounts on average should be half inch, but some
thunderstorms could be embedded with locally 1-2 inch amounts
not out of the question. However, given how spread out the
rainfall has been, rivers/streams are slowly responding, but no
flooding concerns.

Through the end of the week, a culmination of rainfall in the 2
to 5 inch range is not of out of the question, so some hydro
issues may occur. Ensemble model river forecasts though are not
indicating any flooding. Of note, the National Water Model
(NWM) experimental products based HRRR short-range (0-18 hr) and
GFS ensemble QPFs (18-hr to 10-days) are showing low
probabilities for bankfull stages to be reached in any of the
Blacksburg WFO rivers and streams.

&&

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

&&

SYNOPSIS...AMS/WP
NEAR TERM...MBS/WP
SHORT TERM...PW
LONG TERM...VFJ
AVIATION...AMS/PC/WP
HYDROLOGY...PC/WP

Hazardous Weather Outlook
National Weather Service Blacksburg VA
424 AM EDT Wed Jun 17 2020

VAZ010>020-022>024-032>035-043>047-058-059-WVZ044-507-180830-
Bland-Giles-Wythe-Pulaski-Montgomery-Grayson-Carroll-Floyd-Craig-
Alleghany VA-Bath-Roanoke-Botetourt-Rockbridge-Patrick-Franklin-
Bedford-Amherst-Henry-Pittsylvania-Campbell-Appomattox-Buckingham-
Halifax-Charlotte-Monroe-Eastern Greenbrier-
424 AM EDT Wed Jun 17 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.

Locally heavy rainfall today may lead to isolated flooding.

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

There is a low probability for widespread hazardous weather.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

NCZ001>006-018>020-VAZ007-009-WVZ042-043-508-180830-
Ashe-Alleghany NC-Surry-Stokes-Rockingham-Caswell-Watauga-Wilkes-
Yadkin-Tazewell-Smyth-Mercer-Summers-Western Greenbrier-
424 AM EDT Wed Jun 17 2020

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

.DAY ONE...Today and tonight.

The probability for widespread hazardous weather is low.

.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.

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BLACKSBURG VA
1051 AM EDT WED JUN 17 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1050 AM     FLOOD            2 SE THAXTON            37.33N 79.61W
06/17/2020                   BEDFORD            VA   911 CALL CENTER

            INTERSECTION OF ROCKY FORD ROAD AND
            CULPEPPER LANE CLOSED DUE TO FLOODING.

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BLACKSBURG VA
1052 AM EDT WED JUN 17 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1051 AM     FLOOD            3 ESE MONTVALE          37.37N 79.69W
06/17/2020                   BEDFORD            VA   911 CALL CENTER

            WILKERSON MILL ROAD CLOSED AT ROUTE 460.

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BLACKSBURG VA
1105 AM EDT WED JUN 17 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1104 AM     FLOOD            2 NE CHATHAM            36.83N 79.38W
06/17/2020                   PITTSYLVANIA       VA   911 CALL CENTER

            WATER OVER CHALK LEVEL ROAD.

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BLACKSBURG VA
1134 AM EDT WED JUN 17 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1133 AM     FLASH FLOOD      3 NNE VINTON            37.32N 79.88W
06/17/2020                   ROANOKE            VA   PUBLIC

            BONSACK ROAD CLOSED DUE TO FLOODING.

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BLACKSBURG VA
1135 AM EDT WED JUN 17 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1134 AM     FLOOD            3 S LAYMANTOWN          37.33N 79.86W
06/17/2020                   ROANOKE            VA   911 CALL CENTER

            GLADE CREEK ROAD CLOSED DUE TO FLOODING.

&&