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Area Forecast Discussion (AFD)

Issued by Wilmington, OH (ILN)

FXUS61 KILN 190258

National Weather Service Wilmington OH
1058 PM EDT Wed Sep 18 2019

Strong high pressure over the Northeast will slowly migrate
south towards the Mid Atlantic and Carolinas by the weekend.
Surface flow in the Ohio Valley will turn southerly on Thursday
with a slight increase in moisture expected through Friday. The
next cold front will pass on Monday, with an increasing chance
of showers and thunderstorms expected from late Sunday through


Surface dewpoints starting to moderate a bit, but still handled
poorly by models, so only very minor tweaks to hourly
temperature/dewpoint progression overnight with not much change
otherwise. Light easterly flow overnight and good radiational
cooling with some rural locations already in the low 60s. Lows
likely to have a decent range from mid to even lower 50s in
rural/low areas and lower 60s near urban centers. 


High pressure east of the region will see surface flow turn
south during the day. Some models are trying to squeeze out a
few light showers/sprinkles over Kentucky and some southern
portions of Ohio and southeast Indiana along a weak frontal
boundary. Given the hard-pressed nature these past few days to
even sprout some fair weather cu, do not believe that the threat
of precipitation is all that real. Do have increased cloud cover
and some increased pop below the 14% threshold over most of the
southern CWA, and have some very isolated pockets of showers
possible tomorrow afternoon. GFS is wholly overdone given over
.2" being painted south-southeast of metro Cincy. 

Cloud cover will be waning for the most part in the evening,
with some lingering cu possible nearer the surface trough. After
highs in the mid 80s, overnight lows will range from the mid 60s
in the west and southwest to around 60 in the east and Scioto
River Valley. Cloud cover may increase overnight in the west,
which was the main reasoning for warmer lows by Friday morning.


Main long term weather topic is still the extended warm, dry 
conditions across the region through the first half of the 
weekend and how much relief will come as the ridge is flattened 
by a weakening shortwave Sunday into Monday.

To begin the period, an anomalous high amplitude ridge will be 
centered over the Tennessee and Ohio Valleys with mid level 
trofs surrounding the ridge over the Great Basin and just off 
the East Coast. Low atmospheric moisture content, along with 
very dry ground, will likely continue to lead to large diurnal 
temperature variations, with cool nights and very warm 
afternoons. As with previous shifts, went on the high side of 
guidance, near the 90th percentile of the Euro ensemble.

As the Great Basin trof ejects northeast, the ridge flattens, 
allowing a surface low with an associated cold front to push 
southeast into the region. There is good agreement in the 
guidance showing rain showers accompanying the front from late 
Sunday/early Monday through Monday evening, with the GFS on the 
wetter end and the Euro/Canadian on the drier/more progressive 
end. Instability is limited, but decided to keep very isolated 
thunder chances with max heating and along the front.

High pressure builds in on Tuesday. Models show a reinforcing 
frontal system pushing through the region on Wednesday, but 
agreement is low on strength and position of the associated 


continued VFR conditions with the increasingly dry airmass
established over the region, along with abnormally dry
conditions reducing chances for BR/Fog development outside of
the favorable KLUK location. While MVFR possible here after
about 08z, could see brief IFR, but not expected to be
persistent, as was the case Wednesday morning briefly. Winds 
will back to the southeast as the surface high over the NE 
begins to sink a bit south, but some VFR cu expected mainly at 
KILN/KLUK/KCVG in the proximity of a weak surface trough that 
has persisted over WV/KY as the trough nudges slightly northward
again. While CAMs and NWP models indicate showers, am still 
under the thoughts of earlier discussions that the surface and 
far low levels are too dry to support anything other than an 
isolated sprinkle at best. Not worth mentioning in TAFs. 

OUTLOOK...Thunderstorms are possible on Sunday afternoon and