FXUS63 KIWX 090046

Area Forecast Discussion
National Weather Service Northern Indiana
846 PM EDT Wed Jul 8 2020

Issued at 830 PM EDT Wed Jul 8 2020

Lingering showers will dissipate this evening with mainly dry
conditions for the remainder of the night. Heat Index values
increase around the century mark tomorrow afternoon for northwest
Ohio and eastern Indiana while the remainder of the area holds in
the mid to upper 90s. Another round of thunderstorms are expected
on Thursday and again late Thursday night through Friday. A few
of the storms could be strong, with gusty winds and heavy rain the
primary threats.


Issued at 830 PM EDT Wed Jul 8 2020

Series of outflows with earlier thunderstorms have pushed the most
unstable conditions out of the forecast area. Greatest uptick in
convection past few hours has been across northeast Illinois where
westward propagating outflows have interacted with lake breeze.
While cannot completely rule out an isolated shower or storm
through 03Z, expecting mainly dry conditions should persist most
areas this evening as convective inhibition for sfc/near sfc based
parcels slowly builds. Some shallow patchy fog possible once
again toward daybreak, but with potentially more lingering cloud
cover tonight and limited impacts, will omit any mention at this


.SHORT TERM...(This Evening through Thursday)
Issued at 356 PM EDT Wed Jul 8 2020

Scattered showers and thunderstorms have developed once again across
the area as temperatures/heat index values reach into the mid to
upper 90s. Much like yesterday, deep layer shear is very weak with
strong instability in the 1500 - 2500 J/kg range. Storm organization
is not anticipated given the weak shear, but storms will be able to
pulse into the strong to marginally severe category. DCAPE across
the area of 1000 - 1500 J/kg, will sustain the chance for storms to
produce localized downbursts as cores collapse. Locally heavy
rainfall, briefly torrential, is expected for locations where storms
move over. Should see storms wain after sunset, but a stalled
shortwave just SW of the forecast area could cause an isolated storm
to develop during the overnight hours. CAMs do generate a few storms
overnight, but the location is different between the various models.
Will broad brush an isolated mention of storms after 06z to account
for this chance, but confidence is low. Other than this chance for a
storm, overnight lows should drop into the lower 70s.

Thursday will see the stalled shortwave over IL lift northeastwards
over the course of the day in response to a stronger low propagating
eastwards from the northern Plains/upper Midwest. This could help
initiate a greater coverage of convection during the daytime hours.
There is some uncertainty as to how much upper support this
shortwave will provide given that it will start to be ingested by
the western low as we approach peak heating. Will keep POPs in the
40 to 50 percent range with this issuance given that there will be
more upper support than on previous days. Shear will be a little
better, but still around 15kt. The combination of instability and
weak upper support could allow for thunderstorms to become strong to
marginally severe. Primary hazard with these storms will be strong
to damaging winds, hail up to 1 inch, and locally heavy rainfall.

Looking at the heat concern, will go with a Heat Advisory for NW
OH and portions of NE IN where heat index values are 98 to 100
degrees. Will continue the SPS for the remainder of the area, as
there is greater concern with cloud cover preventing temps from
warming sufficiently to hold heat index values in that range.


.LONG TERM...(Thursday Night through Wednesday)
Issued at 356 PM EDT Wed Jul 8 2020

A brief decrease in convective area is possible Thursday night prior
to midnight before the eastward progressing low mentioned above
pushes into the forecast area. This will allow convection to spread
across the area over the remainder of the overnight hours and
daytime Friday. The increased cloud cover and widespread precip
should help to keep afternoon high temperatures in the 80s. This
should also help to limit instability and storm strength despite
better shear. As such, severe weather is not anticipated at this
time. Still some differences between models concerning end timing,
but think storms should start to diminish after sunset Friday.

Another round of showers and thunderstorms possible Saturday and
Sunday as the upper low (now east of the area) begins to stall. Have
stayed slower to the ECMWF for this time frame and beyond as it has
been the most consistent with the upper pattern evolution for
several days. This results in dry conditions returning for next week
with a gradual warming trends as an upper ridge builds back over the
forecast area.


.AVIATION...(For the 00Z TAFS through 00Z Thursday Evening)
Issued at 830 PM EDT Wed Jul 8 2020

Series of outflows with earlier scattered thunderstorms have
lessened instability magnitudes this evening with weak inhibition
for near sfc parcels. Cannot completely rule out an isolated
shower or storm over next few hours along old boundaries, but
will maintain dry terminal forecast tonight. Weak short wave cut-
off in weak steering flow across northern/central Illinois will
drift northeast across the southern Great Lakes on Thursday which
may result in fairly early initiation of more scattered showers
and storms late Thursday morning/early afternoon. Best chances may
be across far northern Indiana into southern Lower Michigan given
expected track of this short wave. With uncertainty in coverage
and timing, will cover this with VCSH mention for Thursday
afternoon and let later forecasts resolve window for possible TS
mention. Lull in shower/storm chances possible Thursday evening,
but should increase again late Thursday night into Friday morning
as a slightly more progressive and stronger upper trough
approaches from the mid MS Valley with some elevated instability
to work with. Some patchy shallow fog is possible again early
Thursday morning, but potential greater cloud cover tonight and
limited impacts argues for continuing to keep out of the 00Z TAFs
for both terminals.


IN...Heat Advisory from 11 AM to 9 PM EDT Thursday for INZ009-017-018-

OH...Heat Advisory from 11 AM to 9 PM EDT Thursday for OHZ001-002-004-




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