Area Forecast Discussion
Issued by NWS Charleston, WV

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FXUS61 KRLX 202031
AFDRLX

Area Forecast Discussion
National Weather Service Charleston WV
431 PM EDT Sun May 20 2018

.SYNOPSIS...
Weak cold front sags into the area tonight, only to return
northward, as a warm front, Monday and Monday night. New cold
front crosses Tuesday night. High pressure mid-late week.

&&

.NEAR TERM /THROUGH MONDAY/...
As of 115 PM Sunday...

Did elect to reduce pops quite a bit this afternoon. Not seeing
much in the way of development yet on radar or satellite, and
recent model runs seem to indicate conditions too stable for
much to form. Went ahead and elected to maintain a slight chance
during peak heating, but not overly confident in that.

The frontal boundary continues to linger across southeast Ohio
this afternoon, but should continue to slowly sag south a little
more today, before generally stalling out just south of or close
to the Ohio River. The front will return north on Monday, as low
pressure moves northeast into Ohio, with warm and humid
conditions on Monday. More convection expected on Monday in warm
sector, with most convection expected across southeast Ohio and
the mountains, with less expected across lowlands of WV. We are
still in a marginal risk for severe on Monday, but thinking
overall threat looks low, as lacking significant shear/dynamics.
Heavy downpours will accompany any convection.

As with last night, any areas that are able to clear, will see
fog development, particularly in favored river valleys.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/...
As of 430 PM Sunday...

Period starts with a warm front / outflow boundary over the
middle Ohio Valley, out ahead of a low pressure system to the
west. Showers and thunderstorms are likely near and north of
this front Monday night. Storms can be a bit strong near the
front early on with modest bulk shear, but decreasing CAPE
after sunset should limit the strength of storms going into the
overnight. Locally heavy downpours are also possible Monday
night, as pw values remain up around 1.5 in.

The boundary pushes back north overnight Monday night into
Tuesday, but showers and thunderstorms become likely throughout
the area Tuesday morning, as a cold front approaches from the
west. The mid stream short wave trough driving the cold front
also draws a piece of energy from a southern stream low
northward ahead of it. This subtle forcing will have dew points
in the upper 60s and pw values up to 1.5 inches to work with.

Thunderstorms can be locally heavy Tuesday, but bulk shear
greater than 30 kts staying mostly north of the cold front
advancing into the Ohio Valley should limit the strength of the
thunderstorms.

Models are in better, but not total, agreement on the passage
of the cold front by Wednesday morning, Thus, a slight chance
for showers and thunderstorms was maintained for southern
portions of the area Wednesday, The weather will settle down
promptly Wednesday evening, with a clear, calm radiation night,
as high pressure builds into the area from the north.

Central guidance temperatures accepted, except lowered closer to
the MEX in the valleys Wednesday night. The cooler air is
balanced by increased sunshine for highs Wednesday, compared
with highs Tuesday. The nights get cooler, especially in the
valleys by Thursday morning.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 430 PM Sunday...

High pressure over the area Thursday, moves east of the area
Friday and Saturday, allowing a return southerly flow of
increasingly warm and humid air. After a pair of dry days Thursday
and Friday, the chance for mainly diurnally driven showers and
thunderstorms returns on Saturday, to start the Memorial Day
weekend.

Models diverge on the track of a tropical system and progress of
the next cold front Sunday and beyond, arising from differences
in the southward extent of the next upper level short wave
trough. One camp has a deeper trough, which pulls the tropical
storm northward faster and farther east ahead of it, along or
just east of the Appalachians, while the other camp leaves the
tropical system loitering over the deep south, left behind by a
less amplified northern stream trough.

Central guidance temperatures looked good, with a warming trend
through Saturday.

&&

.AVIATION /20Z SUNDAY THROUGH FRIDAY/...
As of 125 PM Sunday...

VFR conditions for much of the area through 04Z, when LIFR/VLIFR
valley fog is expected to develop. Any fog will generally
dissipate after 13Z for a return of VFR conditions area wide.
However, convection will increase again particularly after 15Z,
especially across southeast Ohio and mountains.

FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 18Z MONDAY...

FORECAST CONFIDENCE: Medium

ALTERNATE SCENARIOS: Development and extent 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.

UTC 1HRLY       18   19   20   21   22   23   00   01   02   03   04   05
EDT 1HRLY       14   15   16   17   18   19   20   21   22   23   00   01
CRW CONSISTENCY  H    H    H    H    H    H    H    H    H    H    M    L
HTS CONSISTENCY  H    H    H    H    H    H    H    H    H    H    M    L
BKW CONSISTENCY  H    H    H    H    H    H    H    H    H    H    H    L
EKN CONSISTENCY  H    H    H    H    H    H    H    H    H    H    L    L
PKB CONSISTENCY  H    H    H    H    H    H    H    H    H    H    M    L
CKB CONSISTENCY  H    H    H    H    H    H    H    H    H    H    M    L

AFTER 18Z 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...TRM/SL
NEAR TERM...SL
SHORT TERM...TRM
LONG TERM...TRM
AVIATION...SL



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