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-- Discussion containing changed information from previous version are highlighted. --
056
FXUS61 KRLX 211249
AFDRLX

Area Forecast Discussion
National Weather Service Charleston WV
849 AM EDT Fri Jul 21 2017

.SYNOPSIS...
Thunderstorm activity on the increase, with strong to severe
storms possible this weekend. Frontal system passes early next
week. Cooler high pressure crosses midweek.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
As of 845 AM Friday...
Increased pops across the area this morning as MCS is knocking
on our doorstep. Generally 30-40 kts of wind has been reported
across western Ohio so far, and expect similar conditions, at
least across southeast Ohio and northeast KY in the next couple
of hours. Overall though, satellite indicates warming cloud
tops, and an overall weakening trend.

Still expecting additional convection to fire up this afternoon
during peak heating, particularly across eastern zones.

As of 630 AM Friday...

Recent radar trends show a slight uptick in convection over the
eastern 1/3 of the CWA. The bigger story is thunderstorm
complex pushing east-southeast across Indiana. The latest
HRRR/HRRRx are both in agreement along with most other high res
models in tracking this feature or its remnants into the area by
late morning. This should result in a broader area of convection
by early afternoon and have increased POPS into the likely range
by 18z.

As of 400 AM Friday...

A consensus of the latest high res model guidance continues to
indicate max precip potential across the northern portions of
the area this morning. An isolated/brief heavy downpour is psbl.
Both high res and larger scale model guidance remain fairly
bullish on scattered thunderstorm development during the
afternoon. SPC has shifted the MRGL severe storm risk to the
northwest, with lack of deep-layer shear likely the limiting
factor. Locally heavy rain is a concern with moderate
instability and PW values 1.5-2.0+ inches. Some convection may
linger into early tonight but overall expect a gradual decrease
in coverage/intensity. Hot/humid conditions are expected again
this afternoon with max heat index values in the upper 90s to
low 100s from the southern WV lowlands into northeast KY/srn OH.
No changes to the heat advisory.
-- End Changed Discussion --

&&

.SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/...
As of 430 AM Friday...

Saturday begins with a warm front over northeastern WV, which
pushes to the north and east of the area in the morning. This
paves the way for southwest flow to keep the high heat and
humidity going throughout the area Saturday. PoP grids reflect
diurnal convection beginning by midday given the high dew
points, perhaps slower timing of the warm front, and/or outflow
boundaries from previous convection.

An upper level short wave trough and low pressure system passing
north of the area drive a cold front southward through the area
Saturday night through Sunday night. This gives rise to the
increasing chance for thunderstorms, especially during the
afternoon and evening hours, as the strengthening flow
associated with the system provide sufficient deep shear to
take advantage of CAPE values up to 3 kj/kg Saturday and even 4
kj/kg on Sunday, and PW values near two inches in a narrower
axis closer to the front.

The SPC slight risk area across the north on Saturday, and then
throughout the area Sunday, reflect the southward progress of
the front, along with the higher CAPE values on Sunday, when
the slight risk is area wide.

The high PW values, together with the slow moving front, could
lead to excessive rainfall over the weekend.

A second upper level short wave trough drives a second cold
front through the area Monday night, bringing another chance
for thunderstorms Monday, again mainly during the afternoon and
evening.

Temperatures and dew points reflect the soupy summer air mass in
place this weekend, with another heat advisory possibly needed
for Saturday afternoon, in a similar areas as the current one in
northeast KY, southeast Ohio and the southern lowlands of WV.
The cold fronts bring a downturn in temperatures and dew points
Monday and Monday night, with values getting back to near
normal for late July.

&&

.LONG TERM /TUESDAY THROUGH THURSDAY/...
As of 400 AM Friday...

The long term period brings a relief in the heat and humidity,
with high pressure providing dry weather through Thursday.
A persistent upper level high bulges farthest north over the
plains, keeping the upper level flow mainly out of the west
northwest, and another system or complex may approach from that
direction Thursday night, as the portion of the upper level
high over the southeastern U.S. backs off.

Highs, lows and dew points will be lowest Tuesday and Tuesday
night, in the fresh canadian air, and then slowly moderate to at
least normal by Thursday.

&&

.AVIATION /13Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --
As of 630 AM Friday...

Radar shows convective complex pushing southeast from Indiana
early this morning. High res models agree that this feature
will impact the airspace btwn 15-18z. Confidence has increased
for thunderstorms impacts at all terminals during this time and
this will be reflected in the 21/12z TAFs. Expect brief periods
of sub-VFR conditions in heavy downpours.

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

FORECAST CONFIDENCE: Medium-High.

ALTERNATE SCENARIOS: Thunderstorms weaken/dissipate with little
to no impacts on the airspace.

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  M    H    H    H    H    H    M    M    H    H    H    M
HTS CONSISTENCY  M    H    H    H    H    H    M    M    H    H    H    M
BKW CONSISTENCY  H    H    H    H    H    H    H    H    H    H    H    M
EKN CONSISTENCY  H    H    L    H    H    H    H    H    H    H    H    M
PKB CONSISTENCY  M    H    H    H    H    H    H    H    H    H    H    M
CKB CONSISTENCY  H    L    L    H    H    H    H    H    H    H    H    M

AFTER 12Z SATURDAY...
IFR possible Saturday and Sunday in heavy showers and thunderstorms.
-- End Changed Discussion --

&&

.RLX WATCHES/WARNINGS/ADVISORIES...
WV...Heat Advisory from noon today to 7 PM EDT this evening for
     WVZ005>008-013>015-024>026.
OH...Heat Advisory from noon today to 7 PM EDT this evening for
     OHZ083-086-087.
KY...Heat Advisory from noon today to 7 PM EDT this evening for
     KYZ101>103-105.
VA...None.

&&

$$
SYNOPSIS...TRM/99
NEAR TERM...SL/99
SHORT TERM...TRM
LONG TERM...TRM
AVIATION...99