Area Forecast Discussion
Issued by NWS Charleston, WV

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FXUS61 KRLX 221037
AFDRLX

Area Forecast Discussion
National Weather Service Charleston WV
637 AM EDT Tue Aug 22 2017

.SYNOPSIS...
Strong cold front with strong to possibly severe storms later
today into tonight. Cooler and drier high pressure into the
weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 630 AM Tuesday...

No significant changes.

As of 315 AM Tuesday...

Models are in agreement on a strong cold front dropping
southeast through the area tonight under an amplifying northern
stream upper trough. This system has both dynamics and a very
moist and unstable airmass in place ahead of the front. This
will likely result in a well defined line of strong to severe
thunderstorms, supported by SPC forecasts. The big forecast
question then is the timing of this line to move across. There
are model differences in that some are initially prefrontal
along a surface boundary laid out by overnight convection back
in Indiana, while others are closer to the front itself. Will go
with the prefrontal boundary scenario, in which the line should
regenerate by early this afternoon from northeast Ohio to north
central Kentucky. The line is expected to intensify and
accelerate southeast across the area this afternoon into early
tonight, possibly accompanied by damaging winds and large hail.
The most likely areas for potential severe thunderstorms will be
over northeast Kentucky, southeast Ohio and the northwest half
of West Virginia this afternoon and evening, then weakening as
the line gets into the southeastern half of West Virginia and
southwest Virginia late this evening and early tonight. Ahead of
this line, there may be isolated pop up storms this afternoon.
This scenario will take away much of the convection with the
cold front itself that follows tonight, so will keep much lower
pops behind this line and until the front passes. It will be hot
and more humid today under sunshine ahead of the line, with
highs 85 to 91.

For tonight, intensity of the line of convection as it moves
across the south and east will diminish with loss of heating,
while showers will be ending from west to east in the low lands
following the front, as drier air filters in. Any lingering
showers by dawn will mostly be confined to the central and
southeast mountains with some cold advection northwest upslope
flow acts on some remaining low level moisture behind the
front.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/...
As of 220 AM Tuesday...

The post frontal environment will dry out quickly in northwest
flow with broad scale surface high pressure building into the
Ohio Valley. Some low level moisture advects back into the area
in wrap around moisture, which would suggest sprinkles to
isolated shower chances over the far northern CWA. However,
leaving this out for now, and should be firmly entrenched north
in the PBZ area.

Temperatures give a slight hint to the twilight of summer with
lowland 70s and dewpoints in the 50s for the short term.

&&

.LONG TERM /SATURDAY THROUGH MONDAY/...
As of 220 AM Tuesday...

Outside of some isolated mountain showers, the extended is dry
on the front end, with high pressure centered over eastern
Canada controlling our forecast area. An upper level low will
dig into the upper Mississippi Valley, meander eastward as it
becomes cut off, and slow advects chances for showers into the
western zones. As mentioned in past discussions, the dominant
ridge/trough pattern across the CONUS from west to east will
remain dominant. Expecting a slight increase in temperatures
from the short term.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
12Z Tuesday thru 12Z Wednesday...
As of 630 AM Tuesday...

Strong cold front moves across the area late this afternoon and
tonight, well preceded by a line of strong to severe
thunderstorms.

Thru 13Z...
Cirrus on the increase early morning. This, and some flow
should keep dense fog in only the most protected valleys. Did
include LIFR at EKN in the deeper valley and with the thinest
clouds til 13Z. Elsewhere, marginal MVFR valley fog at best possible.

Today after 13Z...
Out ahead of aforementioned line of thunderstorms, VFR with
generally cirrus this morning, then SCT-BKN clouds 4000-6000
feet AGL after 17Z with isolated thunderstorms mainly west.
Light south winds becoming southwest 10 to 20 KTS and gusty by
late morning.

Best estimate. Line of TSTMS expected to arrive at Ohio River
20Z-22Z and CKB-CRW line 23Z-01Z and into the mountains 01Z-
03Z. Conditions varying greatly within this line, lowering to
IFR at times, so will put PROB30 in TAFS at this distant time
frame, with strong gusty west winds and hail possible.

Behind this line, outside of mountains generally VFR ceilings
3500-5000 feet, with scattered showers for 2-4 hours, then
clouds decreasing in the west. In the mountains, MVFR/IFR
ceilings, and showers will linger thru rest of period. Winds
becoming west 5 to 8 KTS behind the front which will reach the
mountains around 06Z.


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

FORECAST CONFIDENCE: Medium.

ALTERNATE SCENARIOS: Main line of storms with cold front
later today could arrive a bit earlier than 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       10   11   12   13   14   15   16   17   18   19   20   21
EDT 1HRLY       06   07   08   09   10   11   12   13   14   15   16   17
CRW CONSISTENCY  H    M    H    H    H    H    H    H    H    H    M    M
HTS CONSISTENCY  H    H    H    H    H    H    H    H    H    H    M    M
BKW CONSISTENCY  H    H    H    H    H    H    H    H    H    H    M    M
EKN CONSISTENCY  L    L    L    H    H    H    H    H    H    H    M    M
PKB CONSISTENCY  M    M    M    H    H    H    H    H    H    H    M    L
CKB CONSISTENCY  H    H    H    H    H    H    H    H    H    H    M    M

AFTER 12Z WEDNESDAY...
IFR possible in low stratus and showers/fog into early
Wednesday for mountains. River valley fog possible each morning
through the weekend.

&&

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

&&

$$
SYNOPSIS...JMV/26
NEAR TERM...JMV
SHORT TERM...26
LONG TERM...26
AVIATION...JMV



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