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FXUS61 KRLX 180918
AFDRLX

AREA FORECAST DISCUSSION
National Weather Service Charleston WV
418 AM EST Fri Jan 18 2019

.SYNOPSIS...
Weak system moves through overnight into Friday. A stronger
storm Saturday and Saturday night, followed by much colder air
and upslope snow Sunday/Sunday night.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 345 AM Friday...

Very light precipitation lingers over the area, mainly east of
the Ohio River, early this morning, as deep layer forcing /
moisture associated with an upper level short wave trough, had
already shifted to the east of the area. The light rain and
drizzle will taper off across the lowlands will taper off first
thing this morning, but light snow and freezing drizzle will
persist into this afternoon over the higher terrain, as the top
of the shallow moist layer beneath the seemingly ever present
inversion wavers right in the -6 to -10C range, marginal for the
presence of ice crystals in cloud.

Thus will leave advisory up across the highest ridges which
currently expires 10 AM this morning, while canceling the
remainder of it.

Otherwise the stratus in the moist layer beneath the inversion,
which becomes a bit more shallow in time, persists right up
until the approach of the next system, early Saturday morning.

Temperatures and dew points close to previous and near term
guidance, with continuing small diurnal ranges beneath the
stratus. Temperatures will be below freezing across the northern
lowlands as precipitation arrives there toward dawn Saturday.
Models bring in low level moisture ahead of the mid level
moisture, resulting in a nearly isothermal layer near 0C in the
saturated layer, up through h8, thus light freezing rain.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
As of 415 AM Friday...

A complex storm system will drive the weather through the short term
period. Starting off Saturday, a surface low will be moving through
the lower Ohio River Valley. Cut back POPs a touch to start things,
but then ramp them up very quickly through the morning. Precip type
is a bit tricky early on, as sub-freezing surface air will be in
place across the north. Model soundings show two layers of moisture,
one near the surface, and another up near 500mb. Think the dry layer
between is too dry and thick to allow a seeder feeder process, so
went with freezing rain as the precipitation starts across the
north, with just rain farther south with temperatures above
freezing. Expecting temperatures to slowly warm above freezing
across the north through the morning, with a transition to rain
for most of the forecast area by Saturday afternoon. A period
of moderate to heavy rain on Saturday afternoon will provide
totals of 0.6" to 1.0", with locally higher amounts possible --
especially in the Tri-state region. This could lead to some
water issues, and will continue mention in the HWO.

As the surface low crosses and heads east, cold air rushes in from
the NW. This will transition the rain to snow from west to east
after sunset Saturday night. Still some uncertainty on just how the
cold air and best moisture line up, but ECMWF and NAM show a good
slug of moisture, and strong frotogenesis near the Ohio River as the
cold air plows in, resulting in a period of heavy snowfall across
portions of SE Ohio. Have issued a winter storm watch for snowfall
amounts of 4-6 inches Saturday night across Vinton, Athens, Perry,
Morgan and Washington Counties. The moisture pulls out pretty
quickly, so these counties represent the area of higher confidence.
Some adjustments south and east may be necessary if the
moisture looks to linger longer.

Upslope snow showers will linger into Sunday night across the
western slopes and mountains. Generally have 1-2" across lower
elevations south and east of the Ohio River with 3-5" for the
northern mountainous counties of WV. As skies begin to clear Sunday
night, temperatures will drop like a rock with most areas in the
single digits above/below zero.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 415 AM Friday...

Arctic high pressure skirts by to the north Monday, with a very
chilly day expected. Flow then turns southerly on the back side
of this high, and we get a good rebound of temperatures Tuesday
into Wednesday. This is fairly shortlived however, as a cold
front pushes through Tuesday night or Wednesday -- based on
model preference. The GFS is faster than the ECMWF here. Either
way, expect rain to begin with, changing over to snow as another
shot of cold air drains in. This front looks to pick up a
southern stream surface low Wednesday night into Thursday.
Again, models differ some on this, but this should give another
shot of moisture to keep precipitation going into Thursday. With
this tracking east of the Appalachians, our forecast area
remains cold enough for mostly snow, but this far out confidence
is pretty low and stuck close to the consensus blend.

&&

.AVIATION /09Z FRIDAY THROUGH TUESDAY/...
As of 100 AM Friday...

Widespread IFR ceilings across the area except for the Tygart
Valley, which should go IFR by 10Z, when a weak front causes a
wind shift to the west. IFR ceilings, lowest at BKW which
should remain 200 to 400 feet through daybreak, will improve to
low MVFR later Friday morning, except remaining IFR BKW, with a
slow improvement toward 1000 feet there by Friday night.

Visibility will fluctuate from MVFR to IFR in light rain,
drizzle and mist, and snow over the northern and central
mountains including EKN. Precipitation will end, and visibility
will improve to VFR from southwest to northeast late overnight
through Friday morning, except remaining MVFR in the mountains
through Friday night.

Light south flow at the surface will continue to switch to west
overnight, as a weak front crosses, and then become light and
variable Friday night. Light to moderate west flow aloft
overnight through Friday will become light southwest Friday
night.

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


FORECAST CONFIDENCE: Medium.

ALTERNATE SCENARIOS: Ceilings and visibility will fluctuate
overnight, and then timing and degree of improvement Friday may
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.

DATE FRI 01/18/19
UTC 1HRLY 09 10 11 12 13 14 15 16 17 18 19 20
EST 1HRLY 04 05 06 07 08 09 10 11 12 13 14 15
CRW CONSISTENCY M M M L M M M M M H H H
HTS CONSISTENCY L L L M M M M M H H H H
BKW CONSISTENCY H L M M M L M M M M M M
EKN CONSISTENCY M M M M M M M M M M L M
PKB CONSISTENCY H M M L L M M M M M M H
CKB CONSISTENCY H H M M M M M L M M M M

AFTER 06Z SATURDAY...
IFR/LIFR possible in mainly rain Saturday, and then snow
showers by Sunday morning, persisting into Sunday afternoon, as
a strong system moves through. Windy and sharply colder Sunday.

&&

.RLX WATCHES/WARNINGS/ADVISORIES...
WV...Winter Weather Advisory until 10 AM EST this morning for
WVZ522-523-526.
OH...Winter Storm Watch from Saturday morning through Sunday
morning for OHZ066-067-075-076-084.
KY...None.
VA...None.

&&

$$
SYNOPSIS...TRM/MZ
NEAR TERM...TRM
SHORT TERM...MZ
LONG TERM...MZ
AVIATION...TRM
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