546
FXUS63 KIWX 310738
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
338 AM EDT MON AUG 31 2026
KEY MESSAGES
- SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS WILL CONTINUE TO
BE POSSIBLE AGAIN TODAY, BUT LOW CONFIDENCE IN EXTENT OF
COVERAGE.
- ISOLATED THUNDERSTORMS ARE POSSIBLE TUESDAY AFTERNOON AND
AGAIN WEDNESDAY AFTERNOON AND EVENING, WITH THE GREATEST
CHANCES NORTH OF US ROUTE 30. THERE IS A MARGINAL RISK OF
SEVERE STORMS BOTH DAYS, BUT CONFIDENCE IN ISOLATED SEVERE
STORMS IS LOW AT THIS TIME.
- HOTTER AND MORE HUMID CONDITIONS BUILD THROUGH MIDWEEK,
PEAKING TUESDAY INTO WEDNESDAY WHEN AFTERNOON HEAT INDICES MAY
REACH TO AROUND 100 DEGREES. HEAT INDICES IN THE UPPER 90S TO
AROUND 100 MAY LINGER INTO THURSDAY MAINLY TO THE SOUTH OF US
ROUTE 30.
DISCUSSION
ISSUED AT 335 AM EDT MON AUG 31 2026
COVERAGE OF LIGHT SHOWERS HAS DIMINISHED AS OF 06Z AS RIDGE OF LOWER
LOW-MID LEVEL THETA-E AIR HAS ADVECTED INTO NORTHEAST IL/NORTHWEST
IN. A RIBBON OF MUCH HIGHER LOW-MID LEVEL THETA-E AIR IS ALREADY
RAPIDLY ADVECTING BACK ACROSS NORTH CENTRAL ILLINOIS AND IS EXPECTED
TO NOSE INTO LAKE MICHIGAN VICINITY, FAR NW IN, SW LOWER MI
THROUGH DAYBREAK. ISENTROPIC PROGS IN THE 310-315K LAYER DO
SHOW A DECENT SIGNAL OF STRONGER ISENTROPIC ASCENT CLOSER TO 12Z
ACROSS FAR NORTHEAST ILLINOIS INTO SOUTHWEST LOWER MICHIGAN
EVENTUALLY SHIFTING ACROSS FAR NORTHERN IN/SOUTHERN LOWER
MI/NORTHWEST OH THIS AFTERNOON. APPROACH OF THIS HIGHER LOW
LEVEL THETA-E AIR TODAY WILL FINALLY MARK AN UPTICK IN MORE
RESPECTABLE LOW LEVEL MOISTURE TRANSPORT INTO THE LOCAL AREA
ALONG WITH THE LEADING EDGE OF SOME STEEPER MID LEVEL LAPSE
RATES. ALONG WITH THIS ADVECTION WILL COME WARMER MID LEVEL
PROFILES THAT WILL LIKELY MAKE SFC BASED CONVECTION DIFFICULT TO
COME BY LOCALLY. NONETHELESS, DID CONTINUE SCATTERED POPS TODAY
TO ACCOUNT FOR THIS MORE SUBSTANTIAL ADVECTIVE PUSH, ALTHOUGH
COVERAGE REMAINS AN ITEM OF SOMEWHAT LOWER CONFIDENCE WITH
UNCERTAINTY IN HOW WARMER MID LEVEL PROFILES WILL AFFECT SHOWER
POTENTIAL.
BY MID AFTERNOON INTO THIS EVENING, ATTENTION WILL TURN TO AN UPPER
LEVEL SHORT WAVE WHICH HAS TS ORIGINS FROM SOUTHWEST CONUS AS
IT CONTINUES NORTHEAST FROM THE CENTRAL PLAINS. ISENTROPIC PROGS
OF THE SAME 310-315K LAYER DO SHOW A QUICK INCREASE IN STRENGTH
OF ISENTROPIC LIFT ACROSS NORTHERN ILLINOIS MID-LATE AFTERNOON
SHIFTING INTO NORTHERN IN LATE AFTERNOON/EVENING. THIS SECONDARY
ROUND OF FORCING COULD RESULT IN ANOTHER ROUND OF ISOLATED-
SCATTERED SHOWERS, PARTICULARLY ACROSS THE NORTH. MUCAPES OVER
1000 J/KG ARE POSSIBLE THIS AFTERNOON, ALTHOUGH THERE WILL
LIKELY BE SOME CIN IN A 100-MB MIXED LAYER SENSE. SEVERE WEATHER
IS NOT EXPECTED TODAY.
THE MAIN STORY FOR TODAY WILL BE THE INCREASED HEAT/HUMIDITY.
MOISTURE ADVECTION TODAY SHOULD RESULT IN INCREASING SFC DEW POINTS
TO THE LOWER 70S. MIXING HEIGHTS REMAIN QUITE SHALLOW TODAY
UNDER THE INFLUENCE OF THE WARM ADVECTION, BUT EVEN MIXING UP
TO 900 MB WOULD SUPPORT HIGHS IN MID 80S TO AROUND 90. THIS
COMBINATION OF TEMPS/DEW POINTS SHOULD PUSH HEAT INDICES INTO
THE 90 TO 95 RANGE, ALTHOUGH LIKE YESTERDAY WILL HAVE TO MONITOR
HOW CONVECTIVE TRENDS/CLOUD COVER IMPACT HOURLY TEMPS/HEAT
INDICES.
THE AFORMENTIONED CENTRAL PLAINS VORT MAX SHOULD PUSH ACROSS
NORTHERN INDIANA TONIGHT WITH A CONTINUED POTENTIAL OF
ISOLATED/SCATTERED SHOWERS IN THE EVENING IN A ZONE OF
PRECEDING ISENTROPIC ASCENT. LATE TONIGHT CONFIDENCE WANES IN
SHOWER POTENTIAL AS WARMER MID LEVEL PROFILES BECOME MORE
ESTABLISHED. ONE INTERESTING ITEM TO NOTE IN HIGHER RES
GUIDANCE IS DEVELOPMENT OF CONVECTION LATE TONIGHT ACROSS CORN
BELT IN RIGHT ENTRANCE REGION OF UPPER MIDWEST JET STREAK, AND
AT THE NOSE OF WEAK TO MODEST LOW LEVEL JET IMPINGING ON THE
STRONG 925-800 MB THETA-E GRADIENT. SOME CAMS ATTEMPT TO BRING
THIS CONVECTION ACROSS NORTHEAST IL INTO SOUTHERN LOWER MI
TOWARD MIDDAY TUESDAY, BUT CONFIDENCE IN THIS SCENARIO IS VERY
LOW GIVEN POSSIBILITY THAT CONVECTION MAY REMAIN MORE ELEVATED
AND TAKE A NORTHWARD ROUTE. SOME INDICATIONS IN GUIDANCE THAT A
WEAK MID LEVEL TROUGH (POSSIBLY CONVECTIVELY ENHANCED) COULD
DAMPEN THE MID LEVEL HEIGHTS/TEMPS JUST A BIT BY TUESDAY
AFTERNOON TO CAUSE SOME CONCERN FOR ISOLATED STORMS DEVELOPING
IN WHAT COULD BE MODERATELY TO STRONGLY BUOYANT ENVIRONMENT.
THERE SHOULD BE SOME DECENT WESTERLY DEEP LAYER SHEAR ACROSS FAR
NORTHERN IN/SOUTHERN LOWER MI TUESDAY AFTERNOON (~30-35 KNOTS).
MAIN ITEM OF UNCERTAINTY IS A FORCING MECHANISM ON TUESDAY, AS
THE POTENTIAL WEAK MID LEVEL TROUGH COULD EXIT EARLY IN THE
AFTERNOON WITH SOME SUBTLE MID LEVEL HEIGHT RISES LATER IN THE
DAY. GIVEN THIS LOW CONFIDENCE SCENARIO HAVE INCLUDED SOME
SLIGHT CHANCE POPS TUESDAY ACROSS THE NORTH, WITH A POTENTIAL OF
AN ISOLATED STRONG TO SEVERE STORM (WIND/HAIL) DUE TO
BACKGROUND SHEAR/INSTABILITY.
FOR WEDNESDAY, THE STRONGER NEGATIVE UPPER HEIGHT ANOMALY ACROSS
ONTARIO WILL SHIFT INTO WESTERN QUEBEC HELPING TO DRIVE A COLD
FRONTAL BOUNDARY ACROSS CENTRAL LOWER MICHIGAN DURING THE DAY.
INSTABILITY/SHEAR PROFILES COULD POTENTIALLY SUPPORT ANOTHER DAY OF
AT LEAST AN ISOLATED SEVERE RISK, BUT A GOOD DEAL OF UNCERTAINTY
EXISTS AGAIN WEDNESDAY DEALING WITH THE FACT STRONGER MID/UPPER
LEVEL FORCING MAY BE VACATING THE AREA LATE IN THE DAY, AND SOME
QUESTION AS TO EXISTENCE OF ANY WEAK TO MODERATE SURFACE BASED CIN
INTO EARLY EVENING.
AN ITEM OF HIGHER FORECAST CONFIDENCE FOR TUESDAY AND WEDNESDAY
CONTINUES TO BE THE POTENTIAL OF HEAT INDICES AROUND THE 100 DEGREE
MARK FOR MUCH OF THE AREA. FORECAST THERMAL PROFILES SUPPORT HIGHS
AROUND 90 ON TUESDAY AND IN THE LOW TO POTENTIALLY MID 90S
WEDNESDAY, WHICH COMBINED WITH DEW POINTS IN LOWER 70S COULD
PUSH HEAT INDICES PAST THE 100 MARK. HEAT HEADLINES COULD VERY
WELL BE NEEDED FOR BOTH OF THESE DAYS. COOL FRONT WILL LOSE SOME
INTEGRITY ACROSS SOUTHERN GREAT LAKES ON THURSDAY AS THE
STRONGER FORCING SHIFTS ACROSS SE CANADA, SO ANOTHER DAY OF HEAT
HEADLINES DOES APPEAR POSSIBLE ESPECIALLY SOUTH OF US ROUTE 30
ON THURSDAY.
NO SIGNIFICANT CHANGES HAVE BEEN MADE TO THE LONGER TERM PERIOD
WITH REASONABLE AGREEMENT IN MEDIUM RANGE GUIDANCE OF RE-
AMPLIFICATION OF LONGWAVE PATTERN, AND BUILDING CENTRAL CONUS
RIDGE THAT WOULD KEEP WARMER LOW LEVEL PROFILES WEST OF THE
AREA, AND A GRADUAL DAY TO DAY COOLING HEADING INTO THE WEEKEND.
ADDITIONAL CHANCES OF PRECIP WOULD LIKELY ACCOMPANY THIS
PATTERN WITH SOME ADDITIONAL NW FLOW WAVES POSSIBLE GIVEN RIDGE
POSITIONING.
AVIATION /06Z TAFS THROUGH 06Z TUESDAY/
ISSUED AT 143 AM EDT MON AUG 31 2026
A STUBBORN ADVECTIVE FORCING PATTERN CONTINUES FOR NORTHERN
INDIANA TONIGHT WITH A STRONG MID LEVEL THETA-E GRADIENT
RESIDING ACROSS THE WESTERN GREAT LAKES. THIS GRADIENT COMBINED
WITH MODEST WEST-SOUTHWEST FLOW IMPINGING ON THE AREA SHOULD
RESULT IN SOME RENEWED ELEVATED SHOWERS AND PERHAPS A
THUNDERSTORM TOWARD DAYBREAK AND INTO THE MID MORNING HOURS
ACROSS LAKE MICHIGAN/NORTHWEST INDIANA/SOUTHWEST LOWER MICHIGAN
VICINITIES. DID INCLUDE A PROB30 GROUP FOR SHOWERS AT KSBN TO
COVER THIS EXPECTED INCREASE IN ADVECTIVE FORCING OVER THE NEXT
SEVERAL HOURS. STRONG ISENTROPIC ASCENT SHOULD SHIFT ACROSS FAR
NORTHERN INDIANA FROM THIS MORNING THROUGH EARLY AFTERNOON. BY
MID AFTERNOON ANOTHER SURGE OF ADVECTIVE FORCING IS LIKELY TO
TAKE PLACE ACROSS NORTHERN ILLINOIS DOWNSTREAM OF A SHORT WAVE
KICKING EAST NORTHEAST OUT OF THE CENTRAL PLAINS. ADDITIONAL
SHOWERS/ISOLATED STORMS COULD MOVE INTO NORTHWEST INDIANA LATER
THIS AFTERNOON/EVENING ASSOCIATED WITH THIS FORCING.
BY LATE TONIGHT, THE PLAINS WAVE WILL APPROACH BUT MID LEVEL
THERMAL PROFILES BECOME INCREASINGLY WARM AND POTENTIALLY LESS
LIKELY TO SUPPORT CONVECTION. CONFIDENCE IN TIMING PRECIP
CHANCES IS RELATIVELY LOW IN THIS PATTERN GIVEN SUBTLE NATURE OF
SHORT WAVE FORCING, BUT KSBN SHOULD REMAIN IN MORE FAVORED AREA
FOR ISOLATED/SCATTERED SHOWERS TODAY IN COMPARISON TO KFWA.
SOUTHWEST WINDS LIKELY TO GUST INTO THE 15 TO 20 KNOT RANGE
DURING PEAK MIXING ONCE AGAIN TODAY, WITH GUSTS DIMINISHING
EARLY EVENING. PRIMARILY VFR CONDITIONS EXPECTED THIS PERIOD
WITH POSSIBLE EXCEPTION OF BRIEF REDUCTIONS WITH ANY SHORT-LIVED
SHOWERS.
IWX WATCHES/WARNINGS/ADVISORIES
IN...NONE.
OH...NONE.
MI...NONE.
MARINE...NONE.
DISCUSSION...MARSILI
AVIATION...MARSILI
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page