Severe Thunderstorm Warning 147, NWS Northern Indiana

Area Forecast Discussion
National Weather Service Northern Indiana
1154 AM EDT Mon May 18 2026

.KEY MESSAGES...

- Severe storms are likely today between 12 PM to around 6 PM
  EDT. Damaging wind gusts to 60 mph and heavy rain are the main
  threats. Low but non-zero risk for large hail and an isolated
  tornado.

- Severe storms are anticipated again Tuesday afternoon and
  evening, with all hazards possible.

- Warm and humid through Tuesday with highs in the mid to upper 80s.

- Cooler with seasonable temperatures and dry midweek. Highs
  only in the 60s Wednesday and Thursday.

&&

.DISCUSSION...
Issued at 1014 AM EDT Mon May 18 2026

Main focus this forecast period is on the severe potential for
today and on Tuesday. For today, seems the one limiting factor
for today's storms will be the available shear, with values of
Bulk Shear is around 20 to 30 kts, this should keep
organization of storms minimal and current convective allowing
guidance and thinking points to a more linear feature moving
northeastward into the area over the next couple of hours from
central IL. A plume of dew points in the mid 60s is pushing
northeastward ahead of the convection currently pushing across
central IL. Surface based CAPE values will run about 2000 to
2500 J/kg over the CWA. With environmental profiles drier near
the surface and a moist plume maxing out around 850 mb this
creates an inverted-V sounding which is indicative of gusty
outflows/winds with thunderstorms this is further illustrated
with Downdraft CAPE values around 1000 J/kg. Storm relative
helicity values look to remain below the 100 m2/s2 threshold but
there is the possibility for an isolated tornado or two. This
first batch of storms will move through after Noon EDT and push
through the area into this evening til around the 8 PM EDT
timeframe. Moderate to heavy rainfall will accompany these
storms with precipitable water value sitting around 1.70 inches.
Of course, the storm motion speed will be important as if the
line moves through quicker that will limit the rainfall amounts
but either way looks like we should get a pretty good slug of
rain with today's event as trailing stratiform will bring some
moderate steady rainfall behind the initial line of
thunderstorms as it pushes eastward through the area. Storm
totals over the next two days looks to see some areas seeing
close to an inch of new rainfall.

A break in the action takes place tonight into the overnight
period before the better looking set up arrives tomorrow in the
form of a cold front associated with a low pressure circulation
centered over northern WI. SB CAPE values will be around
1500-2500 J/kg, surface dew points will get into the upper 60s
with a few locations seeing lower 70s, bulk shear values 30-40
kts, and mid level lapse rates around 6 deg/km and helicity
values of 100-200 m2/s2. At this time it looks as if all
threats will be on the table with the better helicity and shear
values associated with the close proximity of the frontal
boundary that will push eastward through the area. The exact
timing is still a bit hazy but current indications have the
frontal boundary approaching the western portions of our CWA
around 1 PM EDT and exiting the area by early morning Wednesday.
SPC currently has our entire area in a slight risk for severe
thunderstorms for Tuesday. Heavy to moderate rainfall will once
again be possible with the thunderstorms and as stated earlier
that around 1 inch of new rainfall will be possible with these
two batches of storms and locally heavier amounts if the
residence times of thunderstorms linger.

In the wake of the cold front a more zonal flow develops over
the region on Wednesday and cooler and drier conditions will
arrive. Highs on Wednesday will only get into the 60s which is
about a 20 degree drop from the 80s today and Tuesday. Upper
level ridging begins to push into the region by Thursday and
will start to see a gradual increase in temperatures into the
weekend. Highs Friday and Saturday will be in the 70s. Sunday
into the beginning of next week highs will return int 80s.
Chances for afternoon showers and thunderstorms will also
increase over the weekend and at this time the best chances will
be Friday afternoon and evening with a trough pushing through
the area but periods of showers/t-storms will be possible each
day into next week.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1149 AM EDT Mon May 18 2026

Primarily weather concern is an incoming squall line from the
west. Observation stations have had episodes of G30KT, with at
least one unofficial report of 58mph gust toward central IL.
Timing was adjusted to TSRA to align with the latest storm
motion. Behind this line, dry for the overnight hours unless
stratiform rain back builds over KFWA (low confidence, but will
monitor). Additional TSRA Tuesday, especially at KFWA, but just
beyond this TAF period.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...None.

&&

DISCUSSION...Andersen
AVIATION...Brown

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