Area Forecast Discussion
Issued by NWS Charleston, WV

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FXUS61 KRLX 201037
AFDRLX

Area Forecast Discussion
National Weather Service Charleston WV
637 AM EDT Thu Jul 20 2017

.SYNOPSIS...
Convective activity on the increase into the weekend with heat
persisting. Frontal system passes early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 620 AM Thursday...

Inserted low pops this afternoon over southeast Ohio for pop up
convection, as the models shift the aforementioned dry slot
eastward faster. Organized convection is still uncertain for
tonight and will maintain high chance pops in the north.

As of 315 AM Thursday...

Models have upper ridging over the Ohio Valley continuing to
weaken with upper flow west northwesterly. A short wave will
cross the Great Lakes into New England later today and tonight,
and this will allow a frontal boundary to drop southward. Most
of the model guidance keeps the front just north of our area by
12Z Friday. A mid level dry slot crossing the area today, and
the front still well to the north, will keep convection at bay
today, despite the high low level moisture. So, will keep the
area precip free today. It will be hot and humid with highs
mainly in the lower 90s, but heat indices are still expected to
remain below advisory criteria. Deeper moisture with pw`s aoa 2
inches pools along the front today as it drops south through
the Great Lakes, which will likely generate convection with the
front.

The big forecast problem will be for tonight, concerning
convective that develops along the front to the north this
afternoon. Corfidi vectors with west northwest flow aloft will
tend to push any frontal convection south and east ahead of the
front. Although model pops are not aggressive at all, they do
show the deeper moisture driving southward thru the northern
half of the area by 12Z Friday. So, will bring convection
southward into central WV by Friday morning, but given the
diurnal factor and low model pops, will keep convection on the
scattered side for now. Will leave for the day shift to monitor
for a possible MCS tonight. Finally, it will be warm and muggy
tonight.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 305 AM Thursday...

The short term transition brings an increase in the mid level
dewpoints and a marked increase in the surface based instability
Friday and especially into Saturday. As advertised, northwest
flow aloft will drop into the CWA, as well as a weaker surface
boundary from a surface low lingering in the plains states. The
low level frontogenetic forcing with the boundary will be less
than impressive, but even weak forcing with the temperatures
nearing their convective temperatures and disturbances aloft in
the 500mb gradient should be able to initiate convection. In the
meantime, lowland dewpoints and temperatures will couple to push
and exceed the 100 heat index criteria Friday and Saturday. Will
mention again in the HWO. Some concern about cloud cover and
showers possibly keeping those values at bay a bit, but need to
push that threat.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 305 AM Thursday...

As the upper ridge retreats to the west, plains area surface low
will finally track eastward as an upper level open wave drops
into the Great Lakes. Expect some organization to the convection
as the frontal system approaches and the magnitude of the low
level frontogenesis increases. This should lead to some early
next week relief to the temperatures and dewpoints for a short
period of time.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
12Z Thursday thru 12Z Friday...
As of 620 AM Thursday...

Upper ridging continues to weaken. A frontal system over the
upper midwest early this morning will drop southeastward today
and tonight, but staying just north of our area by 12Z Friday.

Today...
The more widespread MVFR/patchy IFR haze/fog for the river
valley areas will dissipate by 13Z. Thereafter, generally SCT
5000-7000 feet AGL except becoming BKN far northwestern portions
of area by 00Z. Models have a mid level dry slot crossing today
ahead of the front, bu deeper moisture moves back into
southeast Ohio later this afternoon. Associated convection and
deepest moisture associated with the front is expected to
remain mostly north of our area until around 00Z. Thus, except
for popup convection southeast Ohio later this afternoon, will
leave convection out of the area and the major TAF sites today.

Tonight...
Even though frontal system sags ever so slowly southward and
will remain just north of our area by 12Z Friday, west to
northwest flow aloft is expected to carry the frontal deeper
moisture and convection southward across the north and into
central sections of WV by 12Z Friday. However, despite deep
moisture, the diurnal timing will tend to diminish the
convection, and will keep the convection as scattered. So, given
this uncertainty with the convection, will go with VCSH after
04Z for the northern TAFS of PKB, CKB and EKN for now. Dry
south. Generally VFR ceilings 4000-7000 feet across the north,
except lower in scattered convection, while SCT mid level clouds
prevail in the south.

Near calm winds by night, and west winds 5 to 10 KTS by day.

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



FORECAST CONFIDENCE: Medium

ALTERNATE SCENARIOS: IFR Fog development early this morning may
vary from forecast. Timing and southward extent of convection may
also vary.


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       10   11   12   13   14   15   16   17   18   19   20   21
EDT 1HRLY       06   07   08   09   10   11   12   13   14   15   16   17
CRW CONSISTENCY  L    L    M    H    H    H    H    H    H    H    M    M
HTS CONSISTENCY  M    M    M    H    H    H    H    H    H    H    M    M
BKW CONSISTENCY  H    M    H    H    H    H    H    H    H    H    M    M
EKN CONSISTENCY  L    L    M    H    H    H    H    H    H    H    M    M
PKB CONSISTENCY  L    L    M    H    H    H    H    H    H    H    M    M
CKB CONSISTENCY  L    L    M    H    H    H    H    H    H    H    M    M

AFTER 12Z FRIDAY...
Patchy IFR river valley fog is possible Friday morning, and
Friday and Saturday in showers and thunderstorms.

&&

.RLX WATCHES/WARNINGS/ADVISORIES...
WV...None.
OH...None.
KY...None.
VA...None.

&&

$$
SYNOPSIS...JMV/26
NEAR TERM...JMV
SHORT TERM...26
LONG TERM...26
AVIATION...JMV


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