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Area Forecast Discussion (AFD)

Issued by Wilmington, OH (ILN)

FXUS61 KILN 231721

National Weather Service Wilmington OH
121 PM EDT Sun Jun 23 2019

A warm front will lift northwards today and a cold front will
move through Monday evening. High pressure will work into the
region for Tuesday. A weak frontal boundary move into the area
for Wednesday.


Not many changes needed to ongoing forecast at this moment.

21.12Z RAOBS show mid/upper level ridge axis firmly across the
ILN forecast area with weak tropospheric flow in place - mostly
less than 40kts through the EQL. Seasonable PWATs in place with
light southeasterly flow in the boundary layer - and satellite
shows warm advection-induced bank of mid cloud advancing across
eastern IN about to enter western OH. Behind that - about 4-5
hours of scattered/broken low clouds and then a slowly
organizing storm complex near the confluence of the OH/MS 
rivers which is our feature of interest for later this 

Warm front is draped from Chicago to Louisville /approximately/
and moving steadily northeast. Dewpoints behind the warm front
surge into the lower 70s quickly. Shortwave trough is across MO
moving up the western side of the deep- layer ridge and is 
/with support from increasing LLJ/ driving the storm complex to 
our southwest.

First peek at 23.12Z CAMS and NAM indicate that as shortwave
trough over MO moves toward us, convective complex over MO/IL
will maintain itself if not increase some in
coverage/intensity owing to 4-5 hours of diabatic heating
potential across southern ILL/IND. Expect a reservoir of 
moderate buoyancy /MLCAPE approaching 2000 J/kg/ to be in place 
for these storms to ingest later this afternoon immediately to 
our west and moving into our area. Dprog/DT of CAPE/shear 
parameter space is a little noisy from run to run on HRRR/RAP - 
but in general - expect weak effective shear /20-30kts/ in place
later this afternoon and evening over the western half of the 
ILN forecast area owing to the ridge axis being over the area. 
However, low level shear /0-1km bulk shear and 0-3km bulk shear/
will be a little more supportive of organized convection
especially with time into this evening, with 15-20kts and 25-30
kts, respectively. Most recent CAMSs suggest evolution of a 
linear MCS owing to cold pool amalgamation across IND moving 
into the ILN CWA around 21Z - and progressing steadily eastward 
into the mid evening hours where it will begin to encounter 
increasing SBCINH owing to nocturnal cooling and weakening 
forcing as the primary shortwave deamplifies. CAPE/Shear 
parameter space not overly favorable for any longer- lived 
supercell potential - but may be just enough for a brief line- 
embedded supercell structure or two. Given an anticipated 
linear/cold pool driven mode - 0-3km shear vector magnitude and 
orientation to the expected convective line is supportive of 
appropriate shear/cold pool balance to allow for the convective 
system /Indiana/ to at least make some inroads into eastern 
Indiana and the I-75 corridor of western Ohio. So while the SPC 
SLGT risk ends just before the ILN CWA border - can see some 
SLGT category potential to extend a few more tiers of counties 
downstream into eastern Indiana/far western Ohio before the line
is expected to weaken mid-evening - and there is good agreement
on that weakening trend past about 9 PM. The low level shear 
vector/orientation is also supportive of a line-embedded 
mesovortex or two this evening as LLJ begins to increase atop a 
weakening boundary layer flow with some modest backing, which 
supports an increasing low level hodograph curvature and length 
in the 23Z-02Z timeframe in the western third of the ILN CWA. So
a non-zero tornado potential for several hours this evening in 
southeast IND/western OH. 

As the line decelerates and weakens later this evening,
continued feed of moisture transport on modest LLJ means storm
complex could regenerate or see redevelopment right over the CWA
and could develop a localized flash flood threat for a few
counties where storms would tend to regenerate. Think this would
favor central Ohio given orientation of low/upper level jet
flows, but lower confidence on this scenario playing out.


During the day on Monday expect additional showers and
thunderstorms to develop in advance of a cold front. There is a
stronger low level wind field in place on Monday and therefore
damaging winds will be possible with storms that develop. In
addition, winds will be gusty around 30 mph even outside of
storms. A large portion of the region is under a slight risk for
severe weather on Monday with western portions of the region
under a marginal risk.

In addition to the potential for damaging winds, there is once
again a flash flood threat due to recent repetitive rounds of
rainfall. Have continued the damaging wind and flash flood
threat wording in the HWO for Monday.


Some storms may still be in eastern counties at the beginning of the 
period, but will quickly move off to the east. Behind the 
convection, there is still a chance of some additional showers 
through Monday evening as a secondary impulse swings northeast. 

In the wake of this system, upper heights will gradually rise. A 
short wave crossing the Great Lakes on Wednesday will push a front 
into at least the northern part of the forecast area which will 
bring a chance of storms. This boundary will wash out Wednesday 
night and be replaced by high pressure for Thursday and Friday. 
Upper flow will become more amplified at the end of the week. This 
will result in northwest flow over the Great Lakes. At this point, 
it appears that a short wave moving through this flow will bring 
another front into the area on Saturday which will result in another 
chance of storms.  

Temperatures near normal at the beginning of the period will warm 
with highs in the mid to upper 80s and lows in the upper 60s for the 
latter part of the week.


VFR conditions expected outside of thunderstorms through the
period. Main weather concerns will be storms this evening and
again on Monday. Current line of storms over southeast
IL/southwest IN - if it holds together - would impact
CVG/LUK/DAY/ILN terminals in the 21Z-23Z timeframe with the
potential for some gusty winds and IFR or MVFR visibilities in 
downpours. There are recent hints that this line may
weaken/dissipate before reaching the area, but even if it does,
there is likely to be redevelopment immediately behind the line
that would fill in and impact the same terminals a few hours
later /23Z-02Z/. So we have TEMPO for thunder in that general
period of 22Z to 02Z for many of the TAF sites except CMH/LCK -
who could be impacted later this evening but there is
considerably lower confidence in that scenario. Overnight -
expect scattered showers and storms to continue to threaten the
TAF sites - but expect that coverage will be less and location
is very low confidence - so have just indicated a VCSH for now
with further refinement coming in the next issuance. Cold front
will shift through the TAF sites on Monday with increasing
threats of showers and storms from west to east through the day.
The better potential will be at CMH/LCK on Monday afternoon -
just after the current TAF cycle ends. But it appears all areas
will likely need a prevailing shower/thunderstorm group in the
next set of TAFs for the period when the front shifts through. 

OUTLOOK...Thunderstorms are possible at times from Monday
afternoon through Monday night and then again on Wednesday.