979
FXUS63 KIWX 161840
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
240 PM EDT Wed Jul 16 2025

.KEY MESSAGES...

- Hot and humid conditions through the remainder of today with
  heat indices in the lower to middle 90s expected.

- Scattered showers and thunderstorms continue today, most
  numerous along and east of Interstate 69. Severe weather is
  not expected, but brief heavy rainfall and wind gusts to
  around 40 mph possible with a few storms.

- Thunderstorms chances continue into tonight, especially west
  of US Route 31. There is mainly a Marginal risk (with a small
  area of slight risk for areas close to Lake Michigan in
  northwest IN and southwest MI) of severe storms with isolated
  damaging wind gusts possible. The most favored time period
  for an isolated severe weather threat is from approximately
  7pm to 11pm EDT.

- Brief return of less humid conditions Thursday/Friday behind a
  cold front. This front will also likely bring an increased
  swim risk for southeast Lake Michigan beaches later Thursday
  and Friday.

&&

.DISCUSSION...
Issued at 113 PM EDT Wed Jul 16 2025

With a very humid and hot airmass over the area today, scattered
pop up showers and thunderstorms have developed. Main threats
with these storms is brief heavy downpours, gusty outflow winds,
and of course lightning. Even with PWATs around 2", the fairly
quick northeasterly movement of the storms has minimized any
localized flooding or ponding issues.

Outside of these pop up storms this afternoon the focus then
becomes the development of convection along a north to south
orientated cold front over western IL/WI that will move
eastward this evening. The time of arrival for this boundary
into our western and northeastern parts of the CWA is around 6PM
CDT/7PM EDT. This is early enough in the diurnal period that
any storms forming over IL could certainly maintain their
strength into our western and northwestern areas of the CWA.
Also, the latest guidance suggests bulk shear values of 25-40
kts for mainly over southern Lake Michigan and southwestern MI
with the frontal boundary which will allow for some continued
organization. The main threats with any of the strong to severe
storms would be the associated winds. An isolated tornado would
not be out of the question with these storms along the boundary
as SR Helicity values of 50-100 m2/s2 will also be available.

This frontal boundary will continue to move eastward through
the rest of the CWA through about 06z Thursday morning keeping
increased chances of showers and thunderstorms along and ahead
of the front, however with the loss of the diurnal heating
storms should remain on the weaker side.

In the wake of the cool front, drier and cooler airmass will
advect into the area for Thursday and Friday. There will still
be the potential each afternoon for pop up thunderstorms with
the increased vertical instability. Surface dew points will go
from low to mid 70s today to the low 60s to upper 50s by
Thursday evening. And highs for Thursday and Friday will only be
in the upper 70s to low 80s. This will make for much more
comfortable conditions. Unfortunately, this relief will be
somewhat short- lived as a southeastern ridge squeezes some
moisture and warmer temperatures northward against a zonal flow
that will be centered over our heads. This will allow for
surface dew points to jump into the low to mid 70s by Saturday
afternoon. High temperatures will luckily be somewhat restrained
by the fact that the thermal gradient will mainly remain stable
due to the flat zonal flow present over the area. The bad news
is that this broad southeastern CONUS ridging does ultimately
push northward by Tuesday. This will allow for much hotter
temperatures along with the humid airmass to stream northward
over the region with highs on Tuesday in the upper 80s to lower
90s and warmer yet on Wednesday and beyond with high
temperatures in the low to mid 90s.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 646 AM EDT Wed Jul 16 2025

A very moist environment will remain over the area as isolated
showers continue to develop over northern Indiana this morning.
The activity will increase with daytime heating. The latest HRRR
indicates the best chances for storms will be after 00Z. Rapid
development is expected as the cells develop over northwest
Indiana and move southeast.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Air Quality Alert until 4 AM CDT Thursday for INZ103-203.
OH...None.
MI...Air Quality Alert until 5 AM EDT Thursday for MIZ078-177-277.
MARINE...None.

&&

$$

DISCUSSION...Andersen
AVIATION...Skipper