Area Forecast Discussion
Issued by NWS Charleston, WV

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000
FXUS61 KRLX 211415
AFDRLX

AREA FORECAST DISCUSSION
National Weather Service Charleston WV
1015 AM EDT Mon Sep 21 2020

.SYNOPSIS...
High pressure maintains dry weather and plenty of sunshine for
the first half of the week. Weak system Thursday/Friday brings
rainfall to the south.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1015 AM Monday...

Made some minor adjustments to temperatures this morning as
temperatures are warning slightly quicker than previously
forecast based on current observations. Otherwise, current
forecast is on track.

As of 910 AM Monday...

Temperatures are in the low to mid 40s, above advisory criteria,
and will continue to rise throughout the morning. Thus, the
frost advisory has been allowed to expire as there should no
longer be a threat for frost this morning.

As of 611 AM Monday...

Lowered hourly temps a couple of degrees through 13z, accounting
for current conditions and trends. Probably seeing some patchy
frost across areas not currently included in the Frost Advisory.
Brief duration of this additional frost development, however,
has precluded expansion of ongoing Frost Advisory. Additional
frost advisories may later be required for tonight and Tuesday
morning.

As of 305 AM Monday...

River valley fog is currently developing across much of WV, E
KY, and SW VA (per GOES 11.2-3.9 micrometer imagery) thanks in
part to cool ambient air temps over warm water temps. This fog
should gradually mix out by mid morning with cobalt blue skies
then prevailing for the remainder of the day, as high pressure
continues to influence area weather.

Max temps this afternoon should be very similar to yesterday`s
values. Interestingly, all 00z guidance came in a little cooler
than previous runs for today`s highs...perhaps due to a brief
backing of the 925mb flow during the early/mid afternoon hours.
Given the very dry airmass, I still think the warming potential
exits to reach (or get very close to) Sunday`s highs.

Tonight also features more of the same. Unseasonably cool temps
and areas of frost across the NE CWA. Have undercut guidance by
a coupe of degrees for overnight lows, owing to a continued
very dry airmass in place.

&&

.SHORT TERM /TUESDAY THROUGH THURSDAY NIGHT/...
As of 245 AM Monday...

High pressure dominates until Wednesday when the ridge flattens
and the blocking pattern weakens and eventually falls apart
allowing the area to be vulnerable once again. Thursday is when
moisture is finally back and advected in from the southwest
associated with a cut off low forecast to spawn a system over
Texas. This fairly stacked system will affect us by late
Thursday raising chances for unsettled weather and adding POPs
from slight to chance as the system rides along to our south
with the northern half of the area mainly avoiding most of the
action. Chances for showers will be confined along the southern
mountains and the extreme south along with low probability for
thunderstorms into Friday until its associated upper level
trough exits completely. Not a whole lot of moisture/PWATs with
this system about average for this time of year so not expecting
a lot of rainfall accumulations, if any.

&&

.LONG TERM /FRIDAY THROUGH SUNDAY/...
As of 245 AM Monday...

Chances of showers will remain for the rest of Friday then high
pressure briefly builds in for Saturday although there will be
chances for showers later in the day as another disturbance to
the south funnels warm moist air into the region. For late
Saturday into Sunday, a broad trough will move in from the west,
originating from the Pacific, and will eventually bring a stout
upper level cutoff low in. Southerly flow along with a
disturbance in the south, which will merge with the
aforementioned system, will continue to bring moisture in from
the Gulf. A surface low will form in the wake of the main
feature as it amplifies which will push a cold front closer to
the area promoting showers all day Sunday. An increase in POPs
and thunderstorm probability will be on tap as the frontal band
pushes through into Monday. PWATs are 2 standard deviations
above normal, therefore rain chances and higher amounts will be
on the higher side of average. Accepted central guidance since
models seem like they have a good handle on the system as far as
timing and intensity goes and added in just a tad more likely
POPs for Sunday.

&&

.AVIATION /14Z MONDAY THROUGH FRIDAY/...
As of 607 AM Monday...

Ongoing river valley fog will mix out within an hour or two of
the start of the 12z TAF period. This will likely result in
about an hour of IFR or worse conditions at KCRW, and perhaps
brief MVFR VSBYs elsewhere. By 13/14z, nearly the entire region
should be VFR with CAVU prevailing at that time...and continuing
through the afternoon. Additional river valley fog is likely
later tonight (generally after 06z Tues) with greater impacts to
area aerodromes expected as wind fields just off the deck will
be weaker than what they are this morning.

Erly sfc winds around 5 kts (VRB at times) today. Exception
being KBKW where a more ESErly flow around 10 kts will be
common.

FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 12Z TUESDAY...

FORECAST CONFIDENCE: High.

ALTERNATE SCENARIOS: Timing of flight rule improvement at KCRW
may differ from TAF.

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       12   13   14   15   16   17   18   19   20   21   22   23
EDT 1HRLY       08   09   10   11   12   13   14   15   16   17   18   19
CRW CONSISTENCY  L    L    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    H    H    H    H    H    H    H    H    H
EKN CONSISTENCY  L    H    H    H    H    H    H    H    H    H    H    H
PKB CONSISTENCY  L    H    H    H    H    H    H    H    H    H    H    H
CKB CONSISTENCY  L    H    H    H    H    H    H    H    H    H    H    H

AFTER 12Z TUESDAY...
IFR possible with river valley fog Tuesday and Wednesday
mornings.

&&

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

&&

$$
SYNOPSIS...RH/JZ
NEAR TERM...RH/CG
SHORT TERM...JZ
LONG TERM...JZ
AVIATION...RH



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