FXUS63 KIWX 181006
AFDIWX

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

.KEY MESSAGES...

- Strong to severe storms are likely today between 12 PM to 8 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.

- Strong to 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 316 AM EDT Mon May 18 2026

Satellite and radar imagery currently shows a line of strong to 
severe thunderstorms persisting across parts of Iowa and Missouri. 
This activity is expected to weaken as it moves east into Illinois 
before daybreak. As an upper level trough digs across the Four 
Corners region on today, an impressive and expansive Gulf connection 
will strengthen, sending even stronger surges of moisture and warmth 
into the Upper Great Lakes region. Dewpoints will increase to the 
upper 60s to near 70 degrees in response. A prefrontal trough and 
several 500mb shortwaves will provide a source of lift as storms 
from Illinois are likely to reintensify as they move into our 
forecast area around midday. SPC maintains a Slight Risk (level 2 of 
5) for much of our forecast area. With highs in the mid to upper 80s 
again today, the atmosphere will be unstable with 1500-2000 J/kg of 
SBCAPE and steep low level lapse rates as high as 8 C/km. The 
greatest instability and lapse rates will be along and east of IN-
15, as these areas will have the longest to destabilize before 
storms come through. Despite a lack of organized bulk shear (only 
~20 kts), forecast soundings depict a favorable environment for 
damaging winds with inverted v soundings and DCAPE around 1000 J/kg. 
Cannot rule out hail or an isolated tornado from any discrete storms 
that develop ahead of the line. With PWATs around 1.25-1.5", even if 
storms are not severe, they will likely be efficient with rainfall 
rates in excess of 1"/hr.

Our forecast area will be in a favorable region for severe weather 
again on Tuesday afternoon and evening ahead of an incoming cold 
front. SPC once again has a Slight Risk (level 2 of 5) for much of 
our forecast area. The environment will be very similar to 
Monday with highs in the mid to upper 80s and dewpoints in the 
upper 60s. This will boost SBCAPE to 1500-2000 J/kg during peak 
heating hours. With the cold front as the source of lift, 
forecast soundings depict slightly better shear of 30 kts and 0-1 
SRH up to 200 m2/s2. At this point, all hazards are possible, but 
damaging winds appear to be the main threat. There is some veering 
present in the lowest 1km per forecast soundings, but then the 
vertical wind profile is unidirectional above 1 km. Given low level 
clockwise turning of winds with height and LCLs below 1000m, I can't 
rule out isolated tornadoes occuring Tuesday ahead of the cold front.

It will be noticeably drier with much more seasonable conditions 
midweek behind the cold front. High pressure builds in on 
Wednesday and Thursday across the Great Lakes region. Highs will
be in the 60s and it will feel much cooler than the previous 
stretch of warm and humid days. Summer-like temperatures return 
next week with additional chances for rain/storms.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 604 AM EDT Mon May 18 2026

Minimal changes made to the 12Z TAFs. VFR conditions will continue
through midday. A decaying MCS out of Iowa and Missouri has
produced an outflow boundary in Illinois and storms are forming
along it. This complex of developing storms is expected to 
weaken over Illinois this morning and then reintensify over 
northern Indiana around 18Z becoming strong to severe. Breezy 
southerly winds will gust as high as 30 kts today, even outside 
of any showers or storms. The strongest storms may end up east 
of IN-15 towards KFWA, but have maintained a PROB30 at KSBN for 
17-20Z and a few hours later at KFWA from 19-22Z. MVFR ceilings 
and visibilities possible within any storms. The main threats 
today will be heavy rain and damaging wind gusts up to 50kts.

&&

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

&&

$$

DISCUSSION...Johnson
AVIATION...Johnson