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473
FXUS61 KRLX 231351
AFDRLX

Area Forecast Discussion
National Weather Service Charleston WV
951 AM EDT Sun Jul 23 2017

.SYNOPSIS...
Strong to severe thunderstorms are still possible today, with a
risk for heavy downpours as well. A cold front crosses tonight,
and then another crosses Monday night. High pressure midweek.

&&

.NEAR TERM /THROUGH TONIGHT/...
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As of 945 AM Sunday...

Quick update this morning to several forecast variables. First,
bulk of convection moving across the area this morning,
associated with upper disturbances moving along a weak boundary,
has decreased somewhat. Already starting to see a few breaks in
the cloud cover this morning, and this will only help to aid in
destabilization once again.Cold frontal boundary still to our
north and west, but will gradually sag south towards the region
later tonight and on Monday, as a shortwave trough deepens
across the area. As it does so, strong unidirectional wind
profiles will develop, with 30-40 kts 0-6km bulk shear. With
heavy rains previous days, and more on the way, have kept the
FFA in place, and also expanded in area to include the entire
CWA. Although coal fields and southwest VA counties are drier
than other counties, with models indicating areas of heavier
convection setting up across these areas today, and WPC
guidance, along with the fact that coal fields tend to be rather
flash flood prone, in coordination with JKL, decided just to
expand the watch area wide through midnight tonight. Area
continues to remain in a slight risk for severe today.

As of 600 AM Sunday...

Convection continues to track east-southeast along the Ohio
River into southern WV early this morning. Latest HRRR suggests
showers/thunderstorms won`t exit the southern 1/2-1/3 of the
area until mid to late morning and have updated POPs to show
higher precip probs with longer duration. The other change was
to expand Flash Flood Watch to cover more of the southwest
portion of the CWA where locally heavy rain continues. The
overnight convective rainfall should sufficiently lower 1-3hr
FFGs in this area.

Well-defined shortwave over northern MN early this morning will
move east through the Great Lakes with general synoptic trough
amplification into the central Appalachians by the end of the
period. Several vorticity maxima will rotate through the
southern edge of the trough and ahead of a cold front pressing
southeast through the OH Valley. The combination of increasing
large scale forcing/ascent associated with vort maxes, residual
outflow boundaries, rich moisture (70+ dewpoints) and moderate
instability should all prove effective in generating more storms
this afternoon into tonight. Much like yesterday, storms will be
capable of isolated damaging winds and localized heavy rainfall.
1-3hr FFG is quite low (an inch or less) across the northern 1/2
of the CWA and may need to extend FFA beyond 12z expiration.
Lastly, max HX values approach 100F around the Tri-State area
and will need to monitor convective/cloud trends for possible
advisory.
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&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/...
As of 420 AM Sunday...

Monday begins with low cloud given lots of low level moisture in
place in the wake of rounds of convection over the weekend. With
the morning cu effect, it may take much of the morning for these
clouds to mix higher and then mix out. This will then modulate
the amount of instability we could realize Monday afternoon, to
take advantage of marginal deep layer bulk shear, ahead of a
cold front approaching from the northwest.

With drier mid level air limiting high PW values to smaller
pockets, coverage of storms should be limited, and so should the
excessive rainfall threat.

The front will cross Monday night, with dry weather overnight
through Tuesday night, and into Wednesday morning, as high
pressure crosses. That high exits on Wednesday, allowing a
return flow of warmer and more humid air from the south. This
may be sufficient for elevated heat source effect convection in
the mountains Wednesday afternoon and evening. That diurnal
convection will wane Wednesday night.

Temperatures only get a scosh below normal in the relatively
refreshing canadian air, in which central guidance was below the
MEX for lows in the Tygart Valley Tuesday.

&&

.LONG TERM /THURSDAY THROUGH SATURDAY/...
As of 420 AM Sunday...

Models agree on a new cold front approaching from the northwest
late Thursday and Thursday night, and then crossing the area
Friday. The chance for showers and thunderstorms increases in
the warmer and more humid air ahead of the front Thursday
afternoon, with the help of diurnal heating. Showers and
thunderstorms are likely Thursday night into Friday, as the
front approaches. The passage of the front will bring drier
weather into the middle Ohio Valley Friday afternoon, and then
the central Appalachians Friday night.

High pressure will build in behind the front, for a dry, cooler
and less humid weekend.

Temperatures reflect a return to the very warm weather on
Thursday, followed by a cooling trend, largely on account of the
clouds and rain associated with the front on Friday, and then
below normal in the wake of the front over the weekend. Central
guidance is again below the MEX for lows in the Tygart Valley
over the weekend.

&&

.AVIATION /14Z SUNDAY THROUGH THURSDAY/...
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As of 600 AM Sunday...

Thunderstorm clusters continue tracking east-southeast along
the OH River and gradually weaken across southern WV. Updated
23/09z TAFs to show longer duration of rain over the southern
airfields, with pcpn ending 15-17z from west to east based on
the latest HRRR. Showers remain isolated over the northeast
airspace (in vicinity of KEKN). Also cut back on fog and lower
cigs given cloud cover. Additional storms are expected to
develop later this afternoon/evening and have indicated VCTS
18-21z. Showers/storms could persist through tonight but
confidence is low in the details.

FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 12Z MONDAY...

FORECAST CONFIDENCE: Medium.

ALTERNATE SCENARIOS: Thunderstorm coverage could be more limited
later today/tonight.

EXPERIMENTAL TABLE OF FLIGHT CATEGORY OBJECTIVELY SHOWS CONSISTENCY
OF WFO FORECAST TO AVAILABLE MODEL INFORMATION:
H = HIGH:   TAF CONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL.
M = MEDIUM: TAF HAS VARYING LEVEL OF CONSISTENCY WITH MODELS.
L = LOW:    TAF INCONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL.

UTC 1HRLY       12   13   14   15   16   17   18   19   20   21   22   23
EDT 1HRLY       08   09   10   11   12   13   14   15   16   17   18   19
CRW CONSISTENCY  H    H    L    L    L    H    H    H    H    H    H    M
HTS CONSISTENCY  H    H    H    H    H    H    H    H    H    H    H    M
BKW CONSISTENCY  H    M    H    H    H    H    H    H    H    H    H    M
EKN CONSISTENCY  H    M    M    M    H    M    H    H    H    H    H    M
PKB CONSISTENCY  H    H    H    H    H    H    H    H    H    H    H    M
CKB CONSISTENCY  M    M    M    M    M    L    M    H    H    H    H    M

AFTER 12Z MONDAY...
IFR possible Sunday night in heavy showers and thunderstorms.
Fog and low ceilings possible early monday morning.
-- End Changed Discussion --

&&

.RLX WATCHES/WARNINGS/ADVISORIES...
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WV...Flash Flood Watch through this evening for WVZ005>011-013>020-
     024>034-039-040-515>526.
OH...Flash Flood Watch through this evening for OHZ066-067-075-076-
     083>087.
KY...Flash Flood Watch through this evening for KYZ101>103-105.
VA...Flash Flood Watch through this evening for VAZ003-004.
-- End Changed Discussion --

&&

$$
SYNOPSIS...TRM/99
NEAR TERM...SL/99
SHORT TERM...TRM
LONG TERM...TRM
AVIATION...99