917
FXUS63 KIWX 201750
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
150 PM EDT Mon Jul 20 2026

.KEY MESSAGES...

- There is a 30-60% chance of thunderstorms tonight. Confidence
  in severe weather occurring is low, but cannot completely
  rule out instances of damaging wind gusts or heavy rain.

- Air quality alerts remain in effect for the remainder of the
  day.

- High waves and strong currents are expected at southeast Lake
  Michigan beaches on Tuesday. Stay dry when waves are high.

&&

.DISCUSSION...
Issued at 150 PM EDT Mon Jul 20 2026

Primary item of interest continues to be the (murky) risk of severe
storms tonight and again on Tuesday. Water vapor, as of this midday
writing, depicts a sharp trough digging past the arrowhead of
Minnesota. Well south of this, perhaps on the far leading edge of
the right-front exit region of a 50-70 knot 500mb jet, lies a
cluster of thunderstorms that has persisted to some capacity
throughout the morning hours. The healthiest part of the line is
diving south of the Quad Cities posing no severe risk to our
local area. However, lingering outflow boundaries or trailing
MCVs appear to the focus for renewed, upstream convection early
this evening across Wisconsin and Iowa.

Guidance this morning has been in fair agreement that showers
or storms, likely sub- severe, move through after 11pm. Forecast
soundings depict rather dry, stable air below 600mb, as high
pressure over NYC continues to exert perhaps a hint of
influence locally. Since yesterday, forecast bulk shear values
near 30 knots are favorable over previous, lesser values. Fading
instability remains troublesome, though mid-level lapse rates
near 7 C/km continue to offer a glimmer of hope that some
convection could sustain itself. Like yesterday, we overall
remain doubtful of any significant convection this evening but
cannot completely rule out rogue instances of damaging wind
gusts or heavy rain.

With anticipated minimal severe weather concerns during the
overnight hours, attention then turns to the advertised cold front
now south of US 24 later Tuesday morning. This appears to be focus
for an isolated severe storm, but the upper-level support is
lackluster as the trough has become positively tilted. Shear is
notably improved toward 40 knots but instability remains
problematic, especially considering any cloud debris from early-
morning showers/storms. Here too, not overly concerned about
the severe weather chances on Tuesday.

Behind this cold front and period of showers and storms, a
reinforcing dose of cool air descends along a trailing secondary
upper-level vorticity maximum. This results in a 20-30% chance of
showers Tuesday night through Wednesday morning downwind of Lake
Michigan amid 10C delta-Ts and cloud tops near 10,000 ft. Otherwise,
a period of cooler and rather tranquil conditions lie ahead. Highs
in the low-70s are about 10 degrees below normal, while Thursday
morning lows near 50 will be fall-like. Temperatures trend back into
the 80s by the weekend and high pressure shifts east and warm
southerly flow resumes. We`ll keep an eye on an area of low pressure
moving through the Central Plains later Friday, but for now, this
feature continues to be advertised as passing to our west. Another
trough drops in from Canada later Sunday, representing the next best
chance for rain.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 124 PM EDT Mon Jul 20 2026

Chances for thunderstorms enter the area around midnight this
evening. There is some question about their intensity and whether or
not they`ll be able to continue much farther southeastward to SBN,
let alone get to FWA. At this point, plan to use Prob30 for SBN and
while the chances are lower for FWA than SBN, will use Prob30 for
FWA as well. The outflow boundary/cold front pushes southeastward
and probably gets far enough south of FWA to keep them out of
thunderstorm chances on Tuesday, but will leave this to
following TAF issuances. Also plan to any mention of smoke out
of the TAFs due to weaker concentration of particles. There
could be some smoke-induced MVFR visby across maybe SBN
tomorrow morning depending on where storms linger or the outflow
boundary gets through, but don`t have enough confidence to
place that in this issuance.

Otherwise, expect southwest winds to become more westerly Tuesday
morning. Gusts to 25 kts will be possible Tuesday with the low level
jet overhead. A few gusts to 25 kts will be possible at SBN
overnight tonight, but that really depends on thunderstorm chances.
Will cover that more in the sustained wind section instead.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Air Quality Alert until midnight EDT /11 PM CDT/ tonight for
     INZ005>009-012>015-017-018-020-022>027-032>034-103-104-
     116-203-204-216.
OH...None.
MI...Air Quality Alert until midnight EDT tonight for MIZ078>081-
     177-277.
     Beach Hazards Statement from late tonight through late
     Wednesday night for MIZ177-277.
MARINE...Small Craft Advisory from 2 AM Tuesday to 1 AM EDT Thursday
     for LMZ043.

&&

$$

DISCUSSION...Brown
AVIATION...Roller