Area Forecast Discussion
Issued by NWS Charleston, WV

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019
FXUS61 KRLX 161949
AFDRLX

Area Forecast Discussion
National Weather Service Charleston WV
249 PM EST Sun Dec 16 2018

.SYNOPSIS...
Low will slide off to the east tonight, with cooler air moving
in behind the system for the beginning of next week. High
pressure mid week. Another system due late next week.

&&

.NEAR TERM /THROUGH MONDAY/...
As of 1255 PM Sunday...

Subsidence inversion will keep an abundance of low stratus in
place heading into the evening hours. Meanwhile, areas of light
rain or drizzle will become confined to the mountains. Above
4000 feet, this will tend to transition to light freezing
rain/drizzle. I have elected to handle this in the HWO for now,
as coverage and impacts are in question overnight. Some clearing
will work in from the west tonight, but likely not making it
east of the Ohio River until late.

There is some uncertainty whether low stratus holds into Monday
across the mountains with the NAM locking in moisture beneath
the inversion actually for most of the area. This solution was
largely discounted outside of the mountains, with some nod to
the model in the high terrain. There is some weak, mainly
orographically enhanced, lift persisting Monday in the mountains
which may keep some patchy drizzle/freezing drizzle going but
confidence is low on this panning out.

A s/w trof and associated cold front will drop into the area
Monday afternoon. Models indicate there will be scant moisture
except beneath the persisting inversion, mainly across northern
counties. I kept with previous forecaster thinking with some low
pops across the northern mountains, taking the form of light
snow showers or drizzle/freezing drizzle.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
As of 200 PM Sunday...

Favorable upslope flow continues to squeeze out
drizzle/freezing drizzle Monday night with shallow moisture
lapping up against the western slopes of the mountains. A couple
flakes of snow are possible in the mix with the top of the
saturated layer clipping the bottom of the DGZ. Regardless of
crystal growth, a stout subsidence inversion aloft suppresses
any development outside of the upslopes thus limiting impacts.

High pressure builds from the NW starting early Tuesday and
erodes low- level moisture, gradually clearing out and
precipitation and low- level stratocu through the day. The high
pressure center drifts SEward from the Mitten state into
western PA by Tuesday evening, into the Mid- Atlantic by early
Wednesday. This turns low-level winds southerly and in turn
increases warm air advection and baroclinicity especially in the
Ohio Valley to round out the period. High clouds associated
with the next weather- maker begin streaming in from the SW
Wednesday as temperatures reach into the 40`s in the mountains,
50`s across the lowlands, around 10 degrees above normal for
this time of year.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
As of 215 PM Sunday...

Attention turns to an approaching trough ejecting from the
Rockies during the middle of the week. Trekking eastward into
the Plains, the northern and southern streams come into phase,
amplifying the unified trough, and extending a surface pressure
trough extending from central Canada down into the lower
Mississippi Valley.

Ahead of the trough, deep southerly flow allows warm/moist
advection to continue Wednesday night with PWAT increasing to
near 1" by the end of Thursday in our area. Sky coverage will
continue to increase and cloud bases will lower through
Thursday. Temperatures do again reach the 40`s/50`s Thursday
afternoon with ample sky coverage likely canceling out
additional warm advection.

Meanwhile, further upstream, strong jet-level winds migrate from
the upstream to the downstream portion of the trough, spurring
cyclogenesis along the elongated pressure trough under
favorable jet dynamics. The resulting low will track from from
WSW to ENE across the eastern CONUS as the parent trough axis
pivots negatively in a similar manner. Expect the first rain
showers associated with warm advection to enter the area from
the SW by mid- to late-Thursday with showers continuing through
Friday night as the low sails past. 1-2" of rain are possible
across the area with this system.

Synoptic-scale model differences are relatively slight between
major long-range models; the GFS yields a somewhat deeper
system tracking directly through our Ohio Valley counties while
the ECMWF paints a slightly more progressive picture with a low
tracking up the lee of the Appalachians. The main impacts here
are that a more progressive solution tends to a) rain out more
over the eastern upslope areas of the eastern mountains and
downslope/dry into the lowlands and b) bring in cooler
conditions faster in the wake of the system, Friday night into
Saturday.

Decided to expand/extend PoPs Saturday with models agreeing on
strong northwesterly flow and cold air advection, and the
assumption of left-over moisture in the low-levels, as is often
the case in this locale during the cool season. Thus Saturday
would bring widespread rain/snow/mix showers (mostly rain in
the lowlands, snow in the mountains during the day) depending
on how efficiently cold air makes it into the area.

&&

.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
As of 115 PM Sunday...

Widespread IFR cigs continue through 00Z, with some improving of
bases into MVFR at HTS/PKB. Some light rain/drizzle will persist
across CRW/CKB/BKW/EKN as well, with some occasional IFR vsby.

After 00Z, some clearing may work into southeast OH and into
HTS/PKB after 06Z. Farther east, IFR cigs look to hold for much
of the night, especially in the mountains where some
drizzle/freezing drizzle will persist.

There is some uncertainty regarding how long stratus holds on
Monday, especially across the mountains. For now, I have allowed
improvement into MVFR and eventually VFR by the end of the TAF
period.

Winds becoming West-northwesterly, with occasional gusts in
the teen to lower 20 kt range, mainly mountains.

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

FORECAST CONFIDENCE: Medium.

ALTERNATE SCENARIOS: Timing improving conditions 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
EST 1HRLY       13   14   15   16   17   18   19   20   21   22   23   00
CRW CONSISTENCY  M    M    M    H    H    H    H    H    H    H    M    H
HTS CONSISTENCY  H    M    H    H    H    H    H    H    H    H    H    H
BKW CONSISTENCY  H    H    H    H    H    H    H    H    H    H    H    H
EKN CONSISTENCY  H    H    M    H    L    M    H    L    M    M    M    H
PKB CONSISTENCY  M    H    H    H    H    H    H    H    M    H    L    H
CKB CONSISTENCY  H    H    H    H    L    M    M    M    M    H    H    H

AFTER 18Z MONDAY...
Periods of IFR possible in rain or stratus Sunday night
particularly in the mountainous counties. IFR possible in mixed
wintry precipitation and stratus in the northern WV mountains at
times Sunday night into Monday night.

&&

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

&&

$$
SYNOPSIS...30/MC
NEAR TERM...30
SHORT TERM...MC
LONG TERM...MC
AVIATION...30



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