Preview of NWS' New Version of Forecast
This preview is not operational and should not be used for support decisions.

Area Forecast Discussion (AFD)

Issued by Wilmington, OH (ILN)

FXUS61 KILN 131511

National Weather Service Wilmington OH
1111 AM EDT Fri Sep 13 2019

A cold front will shift through the Great Lakes and Ohio Valley
this afternoon and tonight with scattered to numerous
thunderstorms developing along its length. A few of these storms
could be strong to severe particularly across central and
northern Ohio and Indiana into southern Michigan. One more hot
day will be felt before the front brings slightly cooler and
drier air into the area for Saturday under plenty of sunshine.
The heat will once again begin building into early next week
with another week of 80s to near 90 with mostly dry conditions.


Dry conditions will start out the near term. A cold front will
approach the region later today. Two potential areas of
thunderstorms will be possible. There will be the potential for
a few isolated showers and storms to develop with afternoon
heating. Then there will be another chance later in the day
closer to the frontal boundary. The best chance for
precipitation chances will be across northern portions of the
forecast area with lower chances near and south of the Ohio
River. More on the hazard assessment for severe weather chances
can be found in the short term section below.

Southerly flow present today in advance of the cold front will
allow for one more day of heat and humidity will be present 
across the region today with high temperatures expected to be in
the upper 80s to the middle 90s. Heat index values will be in
the middle to upper 90s across a large portion of the region
today. Winds will be gusty today with wind gusts of 20 to up to
30 mph at times outside of thunderstorm activity.


As the scattered/broken band of storms moves further into Ohio,
expect coverage to begin to decrease and focus more to the north
of the area for a while. This is a signal that has been seen for
several days in the convective-permitting guidance - likely a
depiction of the convection running into less instability due 
to deeper mixing over the heart of the ILN CWA, and brief lull 
in forcing for a while. Later in the evening and actually more 
into the overnight, an approaching impulse from southern Indiana
will combine with right entrance region of the upper jet to 
allow a period of more enhanced coverage of showers/storms, so 
have rain chances increasing late in the evening and overnight 
in the Scioto Valley north of the Ohio River. 

Hazard assessment - despite stronger flow moving into the Ohio
Valley / Great Lakes atop the frontal boundary at peak heating,
effective shear values still only expected to peak around 30kts
for storms in west-central Ohio, and lesser values south. This 
suggests a few of the storms may briefly attain supercell 
structure, but overall organization will be kept in check. Low 
level shear /0-1km SRH < 100 m2/s2/ will also be muted given 
veered boundary layer flow ahead of the front. Much better low 
level shear signal north of the area over far NW Ohio and SE 
Lower Michigan where isallobaric component will keep winds more
backed to the south. That being said, forecast soundings show 
very steep low level lapse rates owing to strong heating and 
mixed dewpoint profile. Quite "inverted-V" especially 
NAM/RAP/HRRR soundings in west- central Ohio. With forecast 
DCAPE around 800-900 J/kg and 0-3km shear vector having at least some
modest orthogonal component to the frontal boundary, think any 
short line segments /frontal forcing/ or conglomerating 
multicells /cold pool/ will have the potential for a few swaths 
of wind damage. Most likely in west central Ohio between 5P-9P 
but can't really be ruled out with any deeper core given the 
inverted-v soundings and unidirectional flow in the soundings.
Think the SLGT/MRGL risks as they are currently laid out seem
well-placed for the data currently in-hand. 

Activity slowly comes to an end in the Scioto Valley later
Friday night as cooler air rushes in from west to east on
Saturday morning. The boundary layer airmass on Saturday will be
quite dry /dewpoints in the 50s/ and will heat quite
efficiently. Given very dry soils, most guidance has been
missing on the cool side of the MaxT forecasts, so have boosted
temps over the cooler MOS numbers given plenty of sunshine and
dry air should yield optimal heating on Saturday afternoon.


Surface high pressure will settle across the region Saturday night. 
Under mostly clear skies, lows will bottom out in the lower 50s in 
the normally sheltered/low-lying spots, to the mid/upper 50s 

On Sunday, the high will move east. Return flow will allow 
temperatures to rebound. Highs will range from the lower 80s north 
to the mid/upper 80s south.

Models continue to show a mid level ridge developing northward into 
the mid Mississippi River Valley early next week. This will develop 
northwest flow across our region, allowing a weak boundary to slip 
through the region Monday into Tuesday. It looks dry, so will keep 
the forecast dry. Surface high pressure will extend into the region 
from southeast Canada/New England on Tuesday in the wake of the 
boundary. Highs mostly in the mid and upper 80s on Monday will be a 
little cooler on Tuesday with lower to mid 80s expected. Lows will 
be in the lower to mid 60s.

For the remainder of the extended, the mid level ridge to our west 
will gradually move east across the Great Lakes and the Ohio Valley. 
Dry weather will continue. Highs will be in the 80s and lows will be 
in the 60s.


Weak stationary front as of 09Z remained from Chicago to Dayton
and southeast into WV. This will drift north this morning as a
warm front as cirrus blowoff from storms to the northwest drifts
across the area. Light southeast flow this morning will veer
southwesterly and increase today - becoming gusty this afternoon
with some sites (DAY/ILN/CMH/LCK) possibly seeing some 20kt 
gusts. Fair weather cumulus based at about 5kft will develop
with heating later this morning but should remain scattered.
Cold front approaches this evening with scattered to broken line
of storms along it. Highest potential impact TAFs would be
DAY/CMH/LCK with activity more scattered to the south. For DAY,
would be around 22Z or a little later, but expect better
coverage north of Dayton. For CMH/LCK, will be after 00Z when
frontal convection approaches. There is a very low chance at an
isolated downpour in the mid-late afternoon as widely scattered
activity may develop well out ahead of the cold front with peak
heating. Very low confidence in that scenario playing out, so
feel the better thing to do right now is focus on the frontal
convection which is more easily timed and of higher coverage

In the wake of the cold front later this evening and overnight,
could see a period of VFR ceilings as winds veer to
northwesterly and drier air filters in. 

OUTLOOK...No significant weather expected.


If today's forecast high temperatures are realized, this will be
one of the warmer 4 day September periods of the current decade.
Particularly at Dayton /KDAY/ where four day average high 
temperatures /including today/ will likely average out at 93F -
and the last time September had a 4-day MaxT average of 93F was
early September 2013, and before that one has to go back to 
early September of 1973. So definitely a period of anomalous
September warmth for the area.




LONG TERM...Hickman