-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KRLX 210547
AFDRLX

Area Forecast Discussion
National Weather Service Charleston WV
147 AM EDT Sat Oct 21 2017

.SYNOPSIS...
High pressure remains in control, with cool nights and warm
afternoons through the weekend. A strong cold front and low
pressure system crosses early next week.

&&

.NEAR TERM /THROUGH TODAY/...
As of 1240 AM Saturday...Temperatures are running a bit cooler
than previously forecast with efficient radiational cooling
under clear skies and light winds, so dropped low temperatures
down a couple of degrees. With temps running a bit lower, there
is some concern we will see a bit more fog as we will be much
closer to crossover temperatures, but still not enough
confidence at this time on what valleys will actually get the
fog, so will leave fog forecast as is for now.

As of 820 PM Friday...

No changes.

As of 150 PM Friday...

Mainly clear overnight...though cirrus will try to spread into
the area toward dawn. Another beautiful warm day Saturday with
some passing cirrus. I continue to go a little below guidance
for overnight lows, especially in the mountain valleys with near
ideal radiational cooling once again. Highs on Saturday were
nudged near the warm side of the envelope with 10 t0 15 degrees
above average expected.

&&

.SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/...
As of 345 PM Friday...

High pressure remains in control with deep southwesterly flow
continuing to bring above-average warmth into the Mid-Ohio
Valley and Central Appalachia. Low-level cloud cover will begin
to build in from the southeast with the approach of a deep
trough late Sunday.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
As of 345 PM Friday...

A briefly cut-off low will merge again with the northern jet
and undergo cyclogenesis in the central to eastern CONUS by the
start of the next work week. Models are beginning to hone in on
a solution that suggests a storm track through the Ohio Valley
though substantial track differences still exist. More
expeditious guidance brings rain showers in starting midday
Monday, although downsloping would favor a delayed onset until
Monday night - closer to a consensus blend of guidance. An even
greater delay in rain is possible if cyclogenesis is
concentrated further south allowing greater warm air advection
to push the frontal zone north. Nevertheless, the forecast
depicts an elongated frontal zone passing through the area early
Tuesday morning. Though exact frontal position is up for
debate, high confidence exists for gusty, widespread rainfall
Monday night through Tuesday.

Being that cyclogenesis in this case is aided by strong
divergence associated with a 120+ kt 300mb jet, and the
deepening of this low tightens height gradients through the
column, winds are expected to increase first with system onset
Tuesday morning and again with the secondary cold front on the
back side of the system Wednesday morning. The secondary cold
front will usher in the coldest air experienced thus far this
season with northwest flow behind. Showers may linger through
Wednesday tapering off Thursday under the influence of a brief
ridge. Pattern remains active with another trough to round out
the week.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...

-- Changed Discussion --
As of 145 AM Saturday...

High pressure has pushed over the region and low level winds are
weaker early this morning than they were last night. However,
there remains a lot of uncertainty on how much valley fog will
develop. Forecast model guidance is not interested in any fog
until most recent runs pinning IFR fog at EKN around sunrise.
Decided to use UPS Crossover technique for this mornings fog
forecast, and although guidance is not indicating fog, EKN and
HTS should at the very least hit their crossover temperatures,
so have only included IFR conditions at those locations. CRW
will be a bit tougher to fog so have left at MVFR for now.

VFR conditions are expected through the day Saturday with dry
high pressure remaining over the area.


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

FORECAST CONFIDENCE: Medium overnight.

ALTERNATE SCENARIOS: IFR or worse fog is still uncertain at this
time.


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                              SAT 10/21/17
UTC 1HRLY       06   07   08   09   10   11   12   13   14   15   16   17
EDT 1HRLY       02   03   04   05   06   07   08   09   10   11   12   13
CRW CONSISTENCY  H    H    H    H    H    M    L    H    H    H    H    M
HTS CONSISTENCY  H    H    H    H    H    H    H    H    H    H    H    M
BKW CONSISTENCY  H    H    H    H    H    H    H    H    H    H    H    M
EKN CONSISTENCY  H    H    H    L    L    L    L    M    H    H    H    M
PKB CONSISTENCY  H    H    H    H    H    H    H    H    H    H    H    M
CKB CONSISTENCY  H    H    H    H    H    H    H    H    H    H    H    M

AFTER 06Z SUNDAY...
Dense valley fog possible Sunday morning. Heavy rain at times
early next week could also bring IFR conditions.
-- End Changed Discussion --

&&

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

&&

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