734
FXUS63 KIWX 180718
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
316 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 /06Z TAFS THROUGH 06Z TUESDAY/
ISSUED AT 117 AM EDT MON MAY 18 2026
VFR CONDITIONS WILL CONTINUE THROUGH MIDDAY WITH THE ONLY
CONCERN BEING SOME MARGINAL LLWS AS THE LOW LEVEL FLOW BEGINS TO
RAMP UP SOMEWHAT. A DECAYING MCS OUT OF IOWA, MISSOURI, AND
ILLINOIS WILL BE THE FOCUS FOR POTENTIAL STRONG TO SEVERE STORMS
TODAY. THIS COMPLEX IS EXPECTED TO WEAKEN OVER ILLINOIS THIS
MORNING AND THEN REINTENSIFY ACROSS NORTHERN INDIANA AROUND
18Z. BREEZY SOUTHERLY WIND 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
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