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Area Forecast Discussion (AFD)

Issued by Wilmington, OH (ILN)

FXUS61 KILN 230603

National Weather Service Wilmington OH
203 AM EDT Sun Jun 23 2019

Weak high pressure building into northeast Ohio this evening
will allow for dry conditions overnight into Sunday afternoon. A
weather disturbance moving out of the Mississippi Valley will
combine with a warm frontal passage on Sunday afternoon and
evening to bring increasing warmth and humidity and the next
chance for showers and thunderstorms - which will last into
Monday as a cold front swings through the Great Lakes. Dry
weather is expected on Tuesday as high pressure builds back into
the Great Lakes.


Weak high pressure ridge over the region attm will provide dry
conditions over night. Latest runs of the mesoscale models are
indicating that some isolated showers associated with weak
convergence will stay west of the region later tonight.

Kept the high clouds scattered overnight, since the ridge axis
stays west of the region. 

Lows tonight are forecast to range form the mid to upper 50s in
Central Ohio to the mid 60s southwest of CVG.


Late in the afternoon into early Sunday evening - a shortwave
trough in TX/OK will move quickly northeast as it deamplifies as
it enters the Ohio. Initially very weak mid/upper level winds - 
as the deep layer ridge axis is over the Ohio Valley - will
slowly strengthen after 21Z as weak height falls cross the area
attendant to the shortwave progressing into Indiana/Ohio. Old
convectively reinforced surface boundary which has been pinned
to our south/west the last 48 hours will begin to advance bodily
northeastward as a warm front with help from surface pressure 
falls and approaching trough. Dewpoints which will start the day
in the upper 50s to around 60, will surge as the front passes
into the lower 70s - such that by Sunday evening dewpoints
across all of southeast Indiana/northeast KY/southwest Ohio will
be around/just above 70F. Ample instability will develop just
behind the peak heating cycle - with MLCAPES > 1500 J/kg
spreading over much of the aforementioned area. Forcing from the
trough should begin to ignite scattered/broken cluster(s) of 
storms over Indiana late in the afternoon /or maintain a cluster
from the southwest from overnight and early morning/ with these
storms approaching the Ohio/Indiana border on Sunday evening. 
Expect storms to spread across much of western Ohio before 
midnight with focus more north of the Ohio River - and more 
specifically - across west-central Ohio and east-central 
Indiana closer to the track of the better dynamics of the 
shortwave trough. These storms should hold together into 
central Ohio Sunday night as the low level jet tied to the 
advancing shortwave trough - begins to enhance thanks to height 
falls with a stronger trough to the west /Monday's weather 
maker/. In fact, there is some concern /although not really 
hinted at in the QPF output but moreso in the mass fields/ that 
the southern/southwestern flank of any Sunday evening storm 
cluster may slowly begin to backbuild/regenerate on Sunday night
into a heavy rain/flash flood threat given Corfidi Vectors 
which go to zero in magnitude owing to the presence of the 
mid/upper layer ridge axis still over the area, weak mid/upper 
level winds, but an ever increasing LLJ which surpasses 
windspeed magnitudes of the mid level flows. Will need to watch 
this closely in further runs to see if a flash flood watch could
be needed Sunday night for parts of the northern CWA where they
have been hard hit with heavy rain in the past week. 

Speaking to the severe threat - SWODY2 maintained MRGL
probabilities today and this appears reasonable on the larger
scale. There is the possibility of a more localized corridor of
potentially higher severe threat centered on Sunday evening into
the early overnight as storms tied to the shortwave trough will
be close to the synoptic warm front where backed /albeit weak/
low level flow with instability will be present. Dropping some
forecast soundings from a wealth of models across west-central
Ohio into southeast Indiana/southwest Ohio all present similar
ideas: 1) effective shear over the depth of the troposphere is 
weak (but slowly increasing) - around 25kts owing to the ridge 
axis over the area 2) instability is plenty adequate to support 
a severe threat 3) low level shear is generally weak south of
the warm front over southeast Indiana/southwest Ohio/northern KY
but gets better over east-central Indiana/west-central Ohio
Sunday evening as the low level jet starts to increase atop the
still-backed flow along and north of the warm front. Therefore - a
brief/weak tornado threat is in play across the northwest 1/3 
of the CWA before surface based CINH builds quickly with the 
onset of nocturnal cooling, and there will be a wind (primary) 
or hail (secondary) threat with the strongest cores through the 
night owing to the large reservoir of elevated instability. The 
residence time of storms along the warm front will be key for
higher-end severe threats - as will the timing of storms 
overall in relation to the building SBCINH field Sunday evening.
Still feel - overall - that flash flooding will end up being 
the primary concern due to the slower storm motions and 
tendency/potential to backbuild through the night.


Monday will be the more active day of the period, starting with a 
decrease in shower/thunderstorm activity in the morning that may be 
left over from the prior night's convection. The overnight 
convection that may linger early on is expected to be primarily from 
shortwave energy pushing through an established upper ridge, which 
will have shifted east of the area by daybreak. By afternoon 
however, another more organized shortwave and associated spin will 
butt into the western edge of the ridge. This will occur with 
maximum daytime heating (~21Z) as a surface front gets shoved east 
through the region at the apex of the negatively tilting upper low 
over MN/WI. Severe weather potential with this system bears watching 
as subsequent model runs bring continued clarification on timing and 
specific threats. 

Do not think that much of a threat of any lingering rain will be 
present overnight as drier and more stable air works in on westerly 
winds. GFS was showing a southern piece of energy crossing the TN 
Valley Tuesday with a northern extent skimming southern CWA, but 
this solution seems to be an outlier and will opt for a dry forecast 
until daytime Wednesday when a front is progged to move closer to 
the region from the northwest. Models are vastly different on 
surface features and strength/timing of the upper s/w here. Enough 
indicators exist to expect diurnal storms to develop Wednesday. 

Beyond Wednesday, a surface high will build underneath a 
strengthening upper ridge in the Ohio Valley. Pop-up storms or a 
ridge-rider may be possible Saturday but see a better chance on 

Temperature forecasts are pretty stable in a low to moderate spread 
that has the ILN forecast nicely in-between. Generally on the high 
end for daytime maxima with low to mid 80s and low end for the 
nighttime minima sporting mid to upper 60s. 

Drier air will work into the region behind the front Monday night 
and linger through Tuesday with a return to more humid but not 
oppressively so conditions for the latter half of the week.


VFR and dry conditions are expected to start out the TAF period.
Cannot rule out a few MVFR vsbys overnight, however believe the
probability is low with increasing high clouds and therefore
kept out of the TAFs at this time. High clouds will move across
the TAF sites overnight and during the day on Sunday. A few cu
will also be possible during the day on Sunday.

Sunday evening into Sunday night showers and thunderstorms will
move into the TAF sites. Timed in VCTS and TSRA into the TAFs
during this time.  

OUTLOOK...Thunderstorms are possible at times from Sunday
night through Monday night.




LONG TERM...Franks