Area Forecast Discussion
Issued by NWS Charleston, WV

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FXUS61 KRLX 200621
AFDRLX

Area Forecast Discussion
National Weather Service Charleston WV
221 AM EDT Sun May 20 2018

.SYNOPSIS...
Weak cold front sags into the area today. Weak disturbances
cross early next week. Cold front crosses mid week, followed by
high pressure to end the work week. Unsettled to start the
Memorial Day weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 200 AM Sunday...

Surface front as of 06Z was located near Dayton to Youngstown.
Isolated showers were noted along the boundary. This front will
slowly sag into our northern counties in southeast Ohio this
morning. Meanwhile, low level moisture will pool along and
ahead of the boundary in the form of low stratus, most
predominate say from the Parkersburg to Elkins corridor.
Orographic enhancement to the flow may provide enough lift to
wring out some showers this morning in the northern mountains.
Elsewhere, dense river valley fog should stay confined to the
southern West Virginia and southwest Virginia with a stiff
boundary layer wind mitigating fog elsewhere.

Low stratus across the north will slowly mix out by late morning
to midday. The front will continue to sag south as the day
progresses, before putting on the breaks generally along the
Route 33 corridor. It is hear where CAMs along with other models
focus afternoon showers and thunderstorms along the front. I`ve
focused on this corridor for the highest pops, though still
capping at high chance for now and rolling with coverage
wording. SPC has painted the area in a marginal risk. Mixed
layer cape values pooling along/ahead of the boundary peak just
shy of 2 grand though deep layer shear values are only about 25
kts. This combined with lackluster mid level lapse rates spells
more of downpour scenario with the potential for some decent
downdrafts. Cell motions along with potential cold pool
propagation may allow some of these to make it to the HTS/CRW
corridor late afternoon. Elsewhere, only an isolated shower or
thundershower is expected with an overall lack of a lifting
mechanism.

Activity winds down this evening as the front settles along the
I64 corridor. With the boundary layer winds relaxing tonight,
dense river valley fog will become a concern, especially if
the area remains largely void of cloud cover. We will watch
upstream in the middle Ohio Valley for an MCS diving southeast
toward the region late. Current indications this will stay west
of the CWA as it reorganizes toward the better instability
across western and central Kentucky.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
As of 335 PM Saturday...

NAM12 and HIRESWnmm develop a convective complex over southwest
Ohio Sunday afternoon, in response to a low level jet max and
moisture feed out of the SSW, intersecting with a west to east
oriented front sagging down from the north, possibly enhanced
by an outflow boundary from upstream convection tonight. They
then prog this complex to move ESEWD across the forecast area
Sunday night, with rainfall totals up to two inches from the
NAM12, and a much more confined axis of up to 1.5 inches off the
HIRESWnmm.

HIRESWarw shows this to a lesser extent, and faster, more of a
late day event than a nocturnal one. Other models are not so
bullish on this scenario, but show smaller pockets of convection
to the south, and to the north, and central guidance reflects
the smoothing resulting from a blended solution.

The details of the forecast remain fuzzy through Tuesday,
beneath zonal upper level flow, with the surface boundary
remaining north of the area. Ripples in the zonal flow, and left
over outflow boundaries will focus convection, which will be
diurnally enhanced during the afternoon and evening hours.

A cold front is forecast to cross or at least approach Tuesday
night, from northwest to southeast, but most of the forcing and
the better bulk shear is is progged to pass north of the
forecast area, and the day 3 SPC marginal outlook for severe
looks good.

Above normal temperatures continue.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 335 PM Saturday...

Models continue to differ on the timing of a cold front crossing
Tuesday night into Wednesday, and central guidance reflects this
with the chance for showers and thunderstorms south on
Wednesday.

Models do concur on dry weather Thursday and Friday, with high
pressure beneath upper level ridging.

A mid stream short wave trough approaching from the northwest,
a southern stream low approaching from the south, and low level
southerly flow of increasingly warm and moist air, will all
conspire to bring unsettled weather back into the area in time
for the start of the Memorial Day weekend.

Temperatures remain above normal in the wake of the cold front.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
As of 215 AM Sunday...

A weak cold front will sag into southeast Ohio and far northern
West Virginia toward morning. Low level moisture will pool ahead
of the boundary, with MVFR cigs develop across northern
terminals, lowering into IFR by 09Z. Farther south, dense river
valley fog will be noted, but with a decent boundary layer wind,
remaining terminals should stay void of fog. A few showers will
be noted across the mountains early this morning and may sneak
into EKN.

Low stratus will be slow to mix out today at PKB/CKB/EKN, taking
until late morning perhaps to lift out of IFR. However, by early
afternoon most of the stratus should have scattered out into a
VFR CU field.

The front will continue to sag southeast today, becoming nearly
stationary along the I64 corridor late. Isolate to scattered
convection is expected this afternoon along the boundary with
PKB/CRW the most likely terminals to experience any impacts.
This was handled with PROB30 groups at this distance.

Convection wanes this evening with dense river valley fog
developing. There is some question as to how much cloud cover
will be around, though it appears that most terminals will be
impacted by fog toward the end of the TAF period.

Southwesterly winds, with occasional gusts 15-20kts today
before going calm at the surface this evening.

FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 06Z MONDAY...

FORECAST CONFIDENCE: Medium

ALTERNATE SCENARIOS: Development and extent of low stratus or
fog overnight may vary from forecast.

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.

DATE                                             SUN 05/20/18
UTC 1HRLY       03   04   05   06   07   08   09   10   11   12   13   14
EDT 1HRLY       23   00   01   02   03   04   05   06   07   08   09   10
CRW CONSISTENCY  H    H    H    H    H    H    H    H    M    M    M    L
HTS CONSISTENCY  H    H    H    H    H    H    H    H    H    H    H    M
BKW CONSISTENCY  H    H    H    H    H    H    H    H    M    M    M    L
EKN CONSISTENCY  H    H    M    H    H    H    H    H    H    H    H    M
PKB CONSISTENCY  H    H    H    H    H    M    M    M    M    M    M    L
CKB CONSISTENCY  H    H    H    H    M    H    H    H    H    H    M    L

AFTER 06Z MONDAY...
Brief periods of IFR possible in showers and storms into the
beginning of the work week.

&&

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

&&

$$
SYNOPSIS...RPY/30
NEAR TERM...30
SHORT TERM...TRM
LONG TERM...TRM
AVIATION...30



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