Area Forecast Discussion
Issued by NWS Wilmington, OH

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000
FXUS61 KILN 271429
AFDILN

AREA FORECAST DISCUSSION
National Weather Service Wilmington OH
929 AM EST Sat Feb 27 2021

.SYNOPSIS...
Weak high pressure will bring a temporary dry period into the
evening. A wave of low pressure will provide additional rain
overnight into Sunday, with heavy rain possible along and south
of the Ohio River. High pressure will result in dry weather for
the beginning of the work week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Rain has moved east of the forecast area which will leave the
region dry through the rest of the day. Satellite imagery shows
breaks in the clouds across parts of eastern Indiana and western
Ohio. Breaks should spread across the rest of the area, however
there is a fair amount low level moisture lingering through the
day. So a broken to scattered cloud deck should persist.
Forecast highs look reasonable at this point.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
Focus revolves around the potential for heavy rain and flooding
across ILN/s southern counties.

Surface low pressure to eject northeast from the Central Plains
this evening into the Upper MS VLY by Sunday morning. A warm
front to lift north across the TN VLY into KY overnight with a
50 kt southerly low level jet developing. Very favorable
moisture transport will take place with precipitable water
values increasing to 1.2 to 1.3 inches. These values are 250
to 300 percent above normal.

Favorable isentropic lift will result in widespread coverage of rain
showers after 04Z with the best forcing between 09Z and 14Z.

Elevated instability develops north of the warm front with some
thunderstorms possible across the south late tonight into early
Sunday. Strong signal for heavy rain. Storm total QPF thru
Sunday of 1.5 to 2.5 inches with locally higher amounts
possible.

Uncertainty exists on the exact placement of the heavy rain
which is tied to the elevated convection late tonight into early
Sunday. The model consensus continues to point to an axis of
heavy rain across Northern KY into South Central Ohio. There are
a couple of solutions including the WRF-ARW and WRF-NMM which
have this heavy rain axis farther north.

Even disregarding these northern outlier solutions, there is
evidence in the consensus for heavy rain/flood threat a little
north of the existing flood watch. Therefore, have expanded the
flood watch to include Carroll, and Gallatin counties in KY and
Adams and Scioto counties in Ohio.

As the surface cold front slips into the area Sunday aftn the
pcpn begins to end from the west and the heavy rain threat
shifts east.

Warm temperatures with lows tonight of 40 north to near 50
south and highs Sunday from the upper 50s to the lower 60s.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
On Sunday evening, deep-layer southwesterly flow will still be in
place across the Ohio Valley, with a sharp mid-level shortwave
moving NE through the Great Lakes, and associated broader troughing
upstream over the upper Midwest. At the surface, a closed low will
be moving into northern Quebec, with a trailing cold front extending
SSW through the Ohio Valley and into the deep south. This cold front
will likely be somewhere in the ILN CWA at the start of this
forecast period -- 00Z on Sunday evening. Ahead of the front,
boundary layer theta-e advection will be continuing. Although
chances for precipitation will be decreasing, the final swaths of
rain from the Sunday heavy rain situation will likely still be
departing the southeastern ILN counties. Behind the front, drier air
will be advecting in, with just a low-end chance of some additional
showers in the cold advection. Based on BUFKIT soundings, the
frontal passage is likely to bring a period of gusty winds, well
above what raw planar model output seems to be suggesting. Some
gusts of around 30 knots may occur, particularly in the northern
sections of the ILN CWA. Min temps are generally expected to be in
the lower to upper 30s early Monday morning, with a gradient from NW
to SE as a result of the frontal passage.

Much cooler conditions are expected on Monday behind the cold front,
with temperatures only reaching the lower to upper 40s in a regime
of strong deep-layer WNW flow. A tightening pressure gradient in
advance of a second (dry) cold front will lead to more gusty
conditions on Monday afternoon, with gusts well into the 20 knot
range possible for most of the forecast area, and some 30 knot gusts
possible in the northern ILN counties. Surface high pressure will
move into the area for Tuesday, with temperatures a couple degrees
cooler than Monday thanks to the continued cold advection leading
into the day.

After Tuesday, model agreement on the rest of the extended forecast
period remains quite poor. For example, several operational ECMWF
runs suggest a weak system moving through the Ohio Valley on Tuesday
night and Wednesday morning, while the operational GFS has been
consistent in keeping this system to the south. With some weak GEFS
support for a more northerly solution, some low-end PoPs will be
kept in the forecast for this time frame. The 00Z GFS has also
continued to show a very wound-up closed low moving into the
southeastern states on Friday, bringing precipitation to the Ohio
Valley and other nearby regions. This feature remains essentially
absent from the ECMWF. Once again, only low-end PoPs will be used,
reflecting the considerable uncertainty in the forecast.

Overall, slightly warmer temperatures (upper 40s to mid 50s) appear
likely on Wed-Thu-Fri.

&&

.AVIATION /14Z SATURDAY THROUGH WEDNESDAY/...
IFR ceilings will lifting to MVFR by early afternoon. As weak
surface high pressure builds across the area this aftn expect to
see continued improvement. Uncertainty exists if clouds scatter
out with VFR conditions developing. Have kept MVFR conditions
at KCVG/KLUK and KILN with a period of VFR conditions at the
remainder of the TAF sites later in the day into this evening.

Moisture increases late this evening with clouds and rain
showers overspreading the area from the southwest between 04Z
and 09Z. Have MVFR to IFR conditions redeveloping as rain
showers overspread all TAF sites. Some elevated instability
develops across the far south late tonight which will offer the
potential for thunderstorms. Have left any mention of thunder
out of the TAF/s at this time due to uncertainty and limited
coverage.


OUTLOOK... MVFR/IFR CIGs and MVFR VSBYs likely into Sunday
morning.

&&

.ILN WATCHES/WARNINGS/ADVISORIES...
OH...Flood Watch from late tonight through Sunday evening for
     OHZ081-088.
KY...Flood Watch from late tonight through Sunday evening for
     KYZ089-090-094>100.
IN...None.

&&

$$
SYNOPSIS...AR
NEAR TERM...
SHORT TERM...AR
LONG TERM...Hatzos
AVIATION...AR


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