Area Forecast Discussion
Issued by NWS Charleston, WV

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000
FXUS61 KRLX 191611 AAB
AFDRLX

Area Forecast Discussion...UPDATED
National Weather Service Charleston WV
Issued by National Weather Service Pittsburgh PA
1211 PM EDT Wed Sep 19 2018

.SYNOPSIS...
A weak cold front slips southward into the area today, as a weak
upper level disturbance crosses. Upper level ridge builds
through Thursday. A stronger cold front arrives Friday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1205 PM Wednesday...

Expanded mention of isolated convection across pretty much the
entire CWA for this afternoon. H5 vort maxes continue to advect
across the CWA around a strong H5 ridge (centered over W TN).
This increase in DPVA along with diurnal warming and sufficient
moisture depth should allow for isolated to perhaps scattered
convective development this afternoon. Capped POPs at only 20
percent, however, due to height fields prog to rise through the
afternoon...possibly negating greater development.

As of 748 AM Wednesday...

Increased POPs further through mid morning for the northern CWA
and also included isolated showers for our VA counties. Have
leaned POP forecast towards 00z NSSL WRF and NAM NEST guidance
as these suites have been the only guidance suites that have
handled this morning`s precip.

As of 635 AM Wednesday...

Updated to allow the encroachment of SHRA/TSRA into east
central Ohio counties before they fall apart this morning. Also
allowed for widely scattered SHRA/TSRA to pop up again this
afternoon, ahead of the west to east cold front sagging
southward into the area.

As of 320 AM Wednesday...

Dense valley fog early this morning will burn off by mid
morning, lifting briefly into stratus before mixing through.
This may be a bit more notable north, where a west to east cold
front will be sinking southward.

A weak upper level trough was evident over northern Ohio early
this morning, where a band of scattered convection was noted.
This activity may get close to our east central Ohio counties
by late this morning, before upper level ridging builds in from
the southwest.

While there is ample moisture for cumulus today, a mid level
inversion will otherwise keep the cumulus from getting too tall,
as the upper level ridge builds. So, while something may stand
up through midday today, the opportunity actually wanes this
afternoon. The mention is left out of the forecast for now.

The front dissolves beneath upper level ridging, as is slips
southward later today and tonight. A light southeast flow will
develop tonight, but still be light enough for some dense
valley fog to form overnight overnight, under a mainly clear
sky.

The high temperature forecast for today continues to reflect
slightly lower values north, with the cold front slipping
southward, and this was also reflected in most of the guidance.
Lows tonight were also not changed much in light of the latest
guidance, with a slightly cooler night on tap, given the
slightly cooler and drier air filtering in from the north.

&&

.SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...
As of 340 AM Wednesday...

Surface high pressure ahead of a 500 mb ridge rules the roost
to start the short term period. Easterly low level flow turns
southerly as the ridge axis approaches from the lower
Mississippi Valley early Thursday, bringing in a
warming/moistening trend. Dew points in the 60`s to near 70 will
try to work in as a result after recovering from a foggy
morning. Thus, expect a hot and muggy Thursday with lowland
highs in the upper 80`s and heat indices around 90. A good day
to be in the mountains, where temperatures are closer to 80, dew
points closer to 60. Convergence along the mtns introduces a
slight chance of showers during the afternoon, but warm mid-
levels limit convective potential.

The upper level ridge axis shifts across Appalachia and into the
Piedmont Thursday night allowing for stronger, deeper SW flow.
Thus, expect a warmer, muggier Friday morning with clouds on the
increase.

Models are in agreement for a shortwave trough to move across
the northern CONUS with a stout 120+ kt jet providing ample
dynamics for the development of a cyclone over the northern
Plains and into eastern Canada Thursday into Friday. Although
the low pressure center itself will pass well to the North of
the area, the associated trailing cold front will impact the
Ohio Valley and into Appalachia at the end of the work week
into the weekend.

Surface convergence along the spine of the Appalachians may lead
to scattered showers and storms Friday ahead of the approaching
system. Although the cold front/surface trough won`t approach SE
Ohio until late Friday, there is indication in multiple models
that a prefrontal trough/low to mid level jet may form somewhere
over the Ohio Valley which leaves severe storm potential in the
cards during peak heating. Though, there isn`t a great handle on
where the ingredients set up - so a relatively low-confidence Friday
afternoon precip forecast.

As for the main front, models indicate a nocturnal passage with
instability generally lacking and the best shear, both
directional and speed, lying well North of the area coincident
with the jet aloft. So, over-all a low severe threat with a line
or lines of showers and storms accompanying the front Friday
night. Mainly-unidirectional bulk shear on the order of 30-40
mph indicates some longevity and sustaining power to storms...
but, again, surface-based instability is severely limited
overnight.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
As of 350 AM Wednesday...

The surface front and associated showers from the short term reach
southern WV/SWVA and stall Saturday with afternoon storms
possible in the proximity of the front. Zonal flow aloft yields
to occasional ripples, generating periods of enhanced precip
along the front during the generally unsettled weekend. Models
waffle the front NW/SE across the region with each ripple, so
have kept precip chances/diurnal storms painted with a
relatively wide brush through the weekend.

The good news is that with the front draped across the southern
portions of the area, the majority of the forecast area will be
on the cooler side of the front. Reasonable high temperatures
in the 70`s are forecast Saturday and Sunday with dew points in
the upper 50`s nosing into SE Ohio and northern WV Sunday into
early Monday.

Upstream, a Rocky Mountain trough ejects into the Plains at the
start of next week with a strong, persistent moisture feed
setting up from the Gulf into the eastern CONUS including
Central Appalachia by Monday. This lends mainly to showers and
diurnally driven convection in the unstable environment early
next work-week, especially as the remnant boundary across the
southern mountains lifts northward as a warm front on Monday.
Conditions could get interesting with the approaching trough,
depending on where its best dynamics end up, and when. Earliest
indications place the cold front associated with the trough passage
in the Wednesday to Thursday timeframe.

&&

.AVIATION /16Z WEDNESDAY THROUGH SUNDAY/...
As of 635 AM Wednesday...

Valley fog this morning was already beginning to thin out, and
this was most evident on GOES-0R over the middle Ohio valley, on
account of low level stirring ahead of a cold front approaching
from the north-northwest, and associated SHRA/TSRA. The fog
should be gone by 13Z.

As the cold front slips slowly southward into the area, and a
weak upper level disturbance crosses, SHRA/TSRA may form from
the middle Ohio Valley through central WV this afternoon. The
isolated to scattered coverage anticipated lends insufficient
confidence to code anything more than VCTS/CB in the TAFs for
now.

Outside any SHRA/TSRA, expect VFR conditions to prevail
this afternoon and this continues tonight, with the loss of
heating, and the front starts to dissolve beneath upper level
ridging.

Fog may form in the mountain valleys tonight, but there will be
a little more surface flow, compared with this early this
morning. However, an airport directly impacted by SHRA/TSRA this
afternoon will have a higher chance for dense fog formation
tonight.

Light south to southwest surface flow this morning will become
light north later today, as the front slowly sinks south, and
then light and variable to light southeast tonight, as the front
dissolves. Light northwest flow aloft today into tonight will
become light southwest overnight tonight.
FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 18Z THURSDAY...

FORECAST CONFIDENCE: High.

ALTERNATE SCENARIOS: Amendments may be needed later today if it
becomes evident SHRA/TSRA will directly impact a TAF site.
Timing of fog development and duration may vary 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       11   12   13   14   15   16   17   18   19   20   21   22
EDT 1HRLY       07   08   09   10   11   12   13   14   15   16   17   18
CRW CONSISTENCY  H    H    L    L    L    L    L    L    L    L    L    L
HTS CONSISTENCY  H    H    L    L    L    L    L    L    L    L    L    L
BKW CONSISTENCY  L    L    L    L    L    L    L    L    L    L    L    L
EKN CONSISTENCY  H    H    L    L    L    L    L    L    L    L    L    L
PKB CONSISTENCY  H    H    L    L    L    L    L    L    L    L    L    L
CKB CONSISTENCY  H    L    L    L    L    L    L    L    L    L    L    L

AFTER 18Z THURSDAY...
IFR possible in SHRA/TSRA late Friday or Friday night. This may
continue through the weekend in the mountains and southern WV
coal fields.

&&

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

&&

$$
SYNOPSIS...TRM/MC
NEAR TERM...RH/TRM
SHORT TERM...MC
LONG TERM...MC
AVIATION...TRM



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