Area Forecast Discussion


491 
FXUS61 KRLX 220546
AFDRLX
AREA FORECAST DISCUSSION
National Weather Service Charleston WV
1246 AM EST Fri Feb 22 2019
.SYNOPSIS...
Several systems will bring unsettled weather this weekend. Mainly
across the south through Friday night and then spreading north 
for the weekend.
&&
.NEAR TERM /THROUGH TONIGHT/...
As of 1245 AM Friday...
Rain ongoing generally along and south of I-64. This is
associated with a series of shortwave troughs in advance of a
much stronger upper trough moving into the southern Rockies
today. Not expecting this rain to make it much farther into the
middle Ohio River Valley, but do expect it to make its way into
the eastern slopes and northern mountains of WV. Temperatures at
this time are near to just below freezing along some of the
higher ridges. The NAMNest seemed to have an OK handle on
current temperatures, so blended toward that through the rest of
the night. This keeps freezing rain as the predominant p-type
for the mountain ridges. Came up with fairly similar ice
accumulations through the morning, with up to around 0.1". This
matches well with the winter weather advisory so no changes
planned at this time. 
Expect rain to continue across the southern coal fields of WV
into southwestern VA through much of the day. The higher
resolution NAM does try to show some drier time late afternoon
into evening while the GFS and ECMWF keep a broader
precipitation shield in place. With uncertainty in timing of
these features, will keep PoPs going. If higher resolution
models consistently show a drier period may start cutting back
some before the end of the shift. Overnight, rain will start
spreading northward as a warm front and the upper trough to our
west approach. Temperatures will remain above freezing for all
except the northern mountain ridges, where some light icing is
possible. Temperatures are borderline, so will let current WSW
run its course before making decision on whether another
headline is needed for late Friday night into early Saturday.
QPF wise, have generally half an inch of rain every 12 hours
across southwestern VA, tapering down to a tenth of an inch or
less from northeastern KY across HTS/CRW and the up into the
northern mountainous counties of WV. 
&&
.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
As of 310 PM Thursday...
The trough of interest rotates negatively into the Plains 
Saturday, strengthening southwest flow to 50 kts at 850 mb, 
lifting the remnant boundary North as a warm front in the Ohio
Valley. As a result, moisture increases to 1.3"+ PWAT area-wide
by Saturday afternoon. This leaves ample opportunity for 
moderate to heavy rainfall basically everywhere Saturday into 
Saturday night. While many long-range models have consistently 
placed an axis of heavy rainfall of 1-2" near and South of the 
64 corridor, the NAM and SREF have trended and shifted the 
corridor further North into the Middle Ohio Valley and into SE 
Ohio. Most of these lowland areas are already saturated, and 
have streams already running high, and the mountains have 
considerable liquid captured in snowpack, so flood vulnerability
exists basically everywhere. The greatest threat would 
therefore exist where any axis of heavy precipitation sets up.
Fortunately, convective rainfall looks unlikely on Saturday with
a strong low-level temperature inversion keeping things pretty 
well capped in this warm frontal scenario. Some elevated 
instability exists in the OH/KY/WV Tri-state region Saturday 
afternoon, but currently not enough confidence to include thunder
in that portion of the forecast. Saturday night, thunderstorm 
threat increases in spite of fairly limited instability, and is
chiefly tied to the cold front itself, where frontal lift can 
tap into modest elevated CAPE on the order of 500 J/KG CAPE. 
Very high shear on the order of 80+ kts 0-6km means that one or 
more potent lines of thunderstorms will form ahead of the front 
packing isolated damaging wind gusts. Storms will tend to be 
much stronger toward the West over parts of the lower Ohio and 
Tennessee Valleys where stronger daytime instability exists, 
however those storms will likely spill into Appalachia as they 
weaken with the setting sun thanks to aforementioned strong low-
and mid- level flow. So, strong gusts, mainly sub-severe, are
likely area-wide, but saturated grounds mean trees and power 
lines can come down with wind gusts well below severe criteria.
Models place the cold front near the Ohio River during the pre-
dawn hours of Sunday and then quickly shoves it across the WV 
mountains by late morning. Moisture aloft quickly diminishes 
behind the front, ending the flood and thunderstorm threat. Low-
to mid-level moisture remains in the cold-advective scheme, so 
do expect area-wide cloud cover to remain through the period 
with lingering drizzle/freezing drizzle in the mountains 
tapering off Sunday evening. Strong winds do linger however
through Sunday as the upper level trough rotates up and out
toward the northeast, with gusts 30-40+ kts possible everywhere.
&&
.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 315 PM Thursday...
Zonal flow takes hold across much of the CONUS with the departure of the short-
term period's trough, which makes for a relatively quiet and
much-needed dry period, albeit with a degree of temperature 
uncertainty given weak forcing. The GFS tends to keep the region
on the warm side and the ECMWF on the cool side. Long- range 
models bring in the next system by mid-week.
&&
.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
As of 1245 AM Friday...
Generally a quiet TAF period across northern sites, with light
winds an broken to overcast mid to high clouds giving VFR
throughout. Currently have rain across the southern sites,
expect this to gradually end at HTS and CRW with ceilings rising
some. At BKW, expect rain to linger through most of the TAF
period. Went with some MVFR ceilings into Friday morning here,
with a tempo for MVFR visibilities as radar shows some higher
reflectivities moving that direction.
FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 06Z SATURDAY...
     
FORECAST CONFIDENCE: High. 
ALTERNATE SCENARIOS: Timing of rain at southern sites 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 02/22/19
UTC 1HRLY       03   04   05   06   07   08   09   10   11   12   13   14
EST 1HRLY       22   23   00   01   02   03   04   05   06   07   08   09
CRW CONSISTENCY  H    H    H    H    H    H    H    H    H    H    H    H
HTS CONSISTENCY  H    H    H    H    H    H    H    H    H    H    H    H
BKW CONSISTENCY  H    H    H    M    H    M    H    M    M    L    M    H
EKN CONSISTENCY  H    H    H    H    H    H    H    H    H    M    M    H
PKB CONSISTENCY  H    H    H    H    H    H    H    H    H    H    H    H
CKB CONSISTENCY  H    H    H    H    H    H    H    H    H    H    H    H
AFTER 06Z SATURDAY...
IFR possible in rain beginning Friday night and continuing
through Saturday night.
&&
.RLX WATCHES/WARNINGS/ADVISORIES...
WV...Winter Weather Advisory until 10 AM EST this morning for 
     WVZ523-526.
     Flood Watch through Sunday morning for WVZ005>007-013>015-
     024>027-033-034-515>520.
OH...Flood Watch through Sunday morning for OHZ083-086-087.
KY...Flood Watch through Sunday morning for KYZ101>103-105.
VA...Flood Watch through Sunday morning for VAZ003-004.
&&
$$
SYNOPSIS...MZ/MC
NEAR TERM...MZ
SHORT TERM...MC
LONG TERM...MC
AVIATION...MZ