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Area Forecast Discussion (AFD)

Issued by Wilmington, OH (ILN)

                            
000
FXUS61 KILN 181038
AFDILN

AREA FORECAST DISCUSSION
National Weather Service Wilmington OH
638 AM EDT Wed Sep 18 2019

.SYNOPSIS...
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.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Rinse and repeat. Another day under control of strong surface
high pressure drifting through New England, and a
strong/amplified mid-level ridge axis oriented from the lower MS
River Valley northeast through the Ohio Valley into eastern
Canada. The former will keep dry easterly flow in place across
the forecast area today with easterly winds of 10 mph or so
continuing to stave off any moisture advection from the
south/west. Thus, expect surface dewpoints today to remain in
the 50s with some potential for central Ohio to mix back into
the upper 40s at peak heating/mixing. Multi-model consensus
suggests 925mb temps modify a little today and push toward 20C
/central Ohio/ and 22C /northern Kentucky and southeast
Indiana/. Mixing that to the surface and adjusting upward for
very steep lapse rates from extremely dry topsoil yields a 
forecast high temperature a degree or two warmer than yesterday.
As it has been with previous days - this values end up very 
close to ECMWF MOS which is on the very warm side of guidance 
and much warmer than way-too-cold GFS MOS and raw 2m 
temperatures - the latter of which is about 7-10F too cold. 

Mostly sunny skies anticipated today. With the enhanced low
level drying across our northern counties, expect what few
cumulus that form will tend to be on the southern half of the
forecast area. GOES IR imagery this morning indicates plenty of
waves of cirrus upstream, so expect some high clouds from time
to time.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
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.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
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 
80s.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
VFR conditions expected across the TAF sites through the period.
Only exception is at KLUK where valley fog may lower visibility
to MVFR thresholds and possibly IFR later tonight into the
sunrise hours on Thursday morning. Moderate east-northeasterly
breezes today /7-10kts/ will slowly veer to the east-southeast
which will keep dry air funneling into the area. Not much if any
cumulus today - will be VFR where it forms and will tend to be
more down toward CVG/LUK where a little higher moisture exists.
Few/scattered cirrus will continue to drop around the large
ridge over the Ohio Valley.   


OUTLOOK...Thunderstorms are possible on Sunday afternoon and
evening.

&&

.ILN WATCHES/WARNINGS/ADVISORIES...
OH...None.
KY...None.
IN...None.

&&

$$
SYNOPSIS...Binau
NEAR TERM...Binau
SHORT TERM...Binau
LONG TERM...Hickman
AVIATION...Binau