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Area Forecast Discussion (AFD)

Issued by Wilmington, OH (ILN)

FXUS61 KILN 181805

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

Strong high pressure over New England will continue to influence
the weather over the Ohio Valley through the end of the work
week. Easterly winds will keep humidity levels comfortable,
while a dome of heat over much of the eastern half of the United
States keeps daytime highs well above normal and precipitation
chances slim. The next appreciable chance of rain will arrive
late in the weekend or early next week as a slow moving cold
front approaches the area.


Very few cirrus spilling into the western CWA and just as few
fair wx cu in the south are creating a very sunny day over the
Ohio Valley. This will permit temperatures to rise to the
forecast highs of the upper 80s in the south and mid 80s in the
north under seasonably dry conditions with dewpoints in the 50s
to lower 60s. 


Skies remain clear/mostly clear tonight with likely some more
valley fog in the favored areas of northern Kentucky/southern
Ohio where valleys are steep and provide the sheltering and cold
air drainage needed to support fog development. 

There is an area of modestly deeper moisture /seen clearly in
EPS/GEFS PWAT anomaly plots/ initially over eastern KY/TN that
rotates westward and then northwestward later tonight and into
Thursday afternoon into northern Kentucky/far southwest Ohio and
southeast Indiana. Some NWP use this moisture to generate
widely scattered showers or sprinkles that drift northwest
across the aforementioned areas during the day. Not sure about
biting on this just yet - the NWP doing this are all running a
heavy wet bias in the last 30 days /GFS and CMC as well as
HIRES-W-NMM/ and some other data remain dry. Forecast soundings
even from data which generate some sprinkles or showers show
meager if any instability, and there's very little if any
background forcing for ascent or moisture convergence. So even 
if a shower or sprinkle does develop, expect coverage will be 
minimal that it does not bear mentioning right now. In addition,
given how most NWP cannot grasp the dry soils and heating that 
is occurring every day, think sub-cloud layers may not permit 
sprinkles or light showers to make it all the way to surface, so
will hold off on inserting any showers to the forecast right 
now and evaluate trends and the potential to add a very small 
shower chance in northern KY/southeast IN in later forecasts.


A large scale mid level ridge will dominate the weather regime 
across the Great Lakes and the Ohio Valley from Thursday night into 
Saturday. The anomalous ridge should keep the forecast dry with high 
temperatures averaging much above normal for mid September. As has 
been pointed out in previous discussions, model performance with 
high temperatures have been poor, perhaps they are not capturing the 
very dry conditions that have developed across the region. Thus, 
have been starting with a model blend, then raising high 
temperatures 3 to 4 degrees, which fits more in line with 925 mb 
mixed temperature relationships. This results in highs in the upper 
80s to around 90 with lows in the lower to mid 60s.

Aforementioned mid level ridge is expected to become suppressed 
during the Sunday/Monday time frame as a mid level trough moves into 
the Great Lakes. This should eventually push a slow-moving cold 
front southeast into the area. An increase in deep moisture and the 
boundary will bring a chance of showers, perhaps a rumble of 
thunder, during the Sunday/Monday forecast. Highs in the mid and 
upper 80s Sunday should cool into the upper 70s to the lower 80s by 
Monday. Lows will remain in the lower to mid 60s.

High pressure is then expected to build into the Great Lakes Monday 
night and then remain across the area on Tuesday. Drier weather is 
expected.  Lows Monday night will range from the upper 50s to the 
lower 60s. Highs on Tuesday ranging from the upper 70s to the lower 


VFR conditions will prevail with an easterly wind around 10kt
this afternoon dropping off overnight to under 8kt, then turning
more southerly during the day Thursday. A weak surface trough
may provide a focus for isolated shower activity in the
afternoon for the Cincy/Lunken area but is not included in the
forecast attm. Main reason for omission is the dry nature of 
the airmass and several models not indicating this development,
or showing even more isolated light rain elsewhere, primarily in

Do not believe that Lunken will have much fog tonight given 
lack of fog this morning and a drier dewpoint working in. Do 
have a brief period of MVFR vsbys to account for possibility of 
some patchy fog in the predawn hours.

OUTLOOK...Thunderstorms are possible on Sunday afternoon and




NEAR TERM...Franks
LONG TERM...Hickman