Area Forecast Discussion
Issued by NWS Charleston, WV

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FXUS61 KRLX 210548
AFDRLX

Area Forecast Discussion
National Weather Service Charleston WV
1248 AM EST Wed Feb 21 2018

.SYNOPSIS...
After another mild night, a cold front crosses the Middle Ohio
Valley Wednesday. The front stalls or wavers through the end of
the week, with significant rainfall possible into the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1245 AM Wednesday...

A mild morning expected today, with southerly flow ahead of an
approaching cold front. The cold front will move through from
west to east this afternoon and evening. The surface front
eventually outruns its mid and upper level support, so have
80-90 POPs through the middle Ohio River Valley early to mid
afternoon, and then gradually decrease POPs along the front as
it moves eastward into and through the mountains late this
afternoon. Did include isolated to scattered thunder, with the
best chance across the Tri-state and Tug Valley. Also included a
non-diurnal trend for temperatures as the front and showers
move through this afternoon.

The front weakens and eventually stalls out this evening before
another wave approaches from the west and the boundary starts
moving northward/reforming across southern forecast area. This
wave will bring another round of precipitation, mainly along
and NW of the front -- so have 90-100 POPs in the Ohio River
Valley with generally chance POPs across the mountains. Expect a
decent spread in temperatures tonight, with lows in the upper
30s across the NW, and lows near 60 across the SE.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 245 PM Monday...

Being on the cool side of the front, Thursday will be cooler
especially toward the North with high temperatures near 50 in SE
Ohio and warmer conditions in the 60`s in southern WV and SW
VA. The heaviest bout of rainfall will move through the Mid-Ohio
valley and northern WV Thursday morning, coincident with an
area of healthy synoptic lift in the right entrance region of a
strong jet. PWAT nearing 1.4" and strong equivalent potential
temperature convergence indicates this enhancement would
generate moderate rainfall rates with this wave. Total
precipitation through this period will near an inch at the
highest in the Tristate area of WV/KY/OH waning to less than
0.5" in SE WV and SW VA.

Friday, the front lifts back northward increasing afternoon
temperatures back into the 70`s in the lowlands. Destabilization
will occur with afternoon heating with SFC based CAPE reaching
up around 500 J/kg, so have opted to include the possibility
for thunder with any warm front/warm sector shower activity. In
spite of strong winds aloft lending decent sheer, lack of
instability and a water-logged profile aloft doesn`t leave much
in the way of strong updraft development. So, there is low
severe potential. rain showers continue through Friday night
with the same frontal boundary draped across the northern tier
of zones.

Given uncertainty in the location of the axis of heaviest
precipitation, have opted to leave flood threat in the HWO for
now.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 315 PM Monday...

Multiple waves not unlike the prior (Thu AM) move across the
the frontal boundary through the weekend - specifically,
Saturday evening and Sunday morning, meaning this time frame
will have to be refined and paid special attention to for
possible flooding concerns. High moisture availability remains
while strong eastern Canadian jets continue to generate large
scale ascent and induce surface waves along the front.

Highest precipitation amounts will again fall in the
northwestern half of the CWA across SE Ohio and northern West
Virginia near the frontal boundary. Quite aggressive models
like the GFS peg as much 4+" of rain from Friday through Sunday,
however the conservative blended approach yields an axis of
2-3" or so up through the Ohio Valley and northern WV. This
seems realistic for widespread amounts across this heaviest axis
but storm training will bear watching as we approach the event
itself armed with higher resolution forecast information.

By the weekend, soils will already be saturated, so hydrological
systems will be quite prone to flooding. Although there is not
the confidence in flooding on specific small-scale basins given
location uncertainty, heavy rain in the Mid to Upper Ohio River
basin as a whole could lead to another flood of the Ohio River.
While not forecast at this time, probabilistic forecasts like
those found at weather.gov/erh/mmefs indicate a strong
possibility given recent model trends.

A break in the pattern shows late Sunday as an upper-level
trough rotates through the Great Lakes region, pushing the front
past the mountains and out to the East Coast. High pressure
quickly builds in behind to dry out the region. A small handful
of models quickly brings another trough/front pair through
Monday night/Tuesday, so have kept PoPs from the blend of models
for this period to indicate this chance.

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
As of 1245 AM Wednesday...

VFR conditions are expected into today. A cold front, with
showers along and behind it will bring MVFR to possibly IFR this
afternoon into tonight. Also included some VCTS at across the
south. MVFR to IFR is expected tonight in stratus and rain.
Southerly winds this morning will become W to NW with the
frontal passage, and more northerly overnight. Debated putting
low level wind shear in TAFs, but with some flow remaining at
the surface opted to keep it out for now. Will monitor this and
may need to amened to add it eventually.

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

FORECAST CONFIDENCE: High.

ALTERNATE SCENARIOS: Restrictions along and behind the front
could 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                                                  WED 02/21/18
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    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    H    H    H    H    H    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 THURSDAY...
IFR possible in showers late Wednesday night into Thursday.

&&

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

&&

$$
SYNOPSIS...MZ/MC
NEAR TERM...MZ
SHORT TERM...MC
LONG TERM...MC
AVIATION...MZ


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