612
FXUS63 KIWX 190550
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
150 AM EDT WED AUG 19 2026
KEY MESSAGES
- RAIN SHOWERS WILL CONTINUE TO DIMINISH THROUGH THE REMAINDER
OF THE OVERNIGHT HOURS.
- SCATTERED SHOWERS AND THUNDERSTORMS EXPECTED THIS AFTERNOON,
ESPECIALLY SOUTH OF US ROUTE 30. WIDESPREAD SEVERE WEATHER IS
NOT EXPECTED, BUT SOME STORMS MAY PRODUCE BRIEF HEAVY RAIN AND
WIND GUSTS TO 40 MPH.
- AFTER PLEASANT CONDITIONS THURSDAY AND FRIDAY, MORE LIGHT RAIN
IS EXPECTED ON SATURDAY.
UPDATE
ISSUED AT 830 PM EDT TUE AUG 18 2026
BROAD PRE-FRONTAL CONFLUENCE AND LOW-MID LEVEL THETA-E ADVECTION
HAVE ALLOWED A BAND OF SHOWERS AND STORMS TO FORM ALONG A MODEST
MLCAPE AXIS. THIS INSTABILITY AXIS FROM EASTERN IOWA INTO
SOUTHEAST WISCONSIN SHOULD BUILD SOUTHEAST INTO SW LOWER
MI/NORTHWEST INDIANA THROUGH 04Z. INSTABILITY MAY BECOME
SLIGHTLY ELEVATED THROUGH TIME PROGRESSING THROUGH LATE EVENING.
THIS LEADS TO SOME QUESTION AS TO MAINTENANCE OF STRONGER 50-60
MPH GUSTS CURRENTLY BEING OBSERVED WITH THIS LINE ACROSS SE
WISCONSIN. A 50-60 KNOT SPEED MAX AT 500 MB IS PROGRESSING
THROUGH A LOW AMPLITUDE UPPER TROUGH ACROSS THE SOUTHERN GREAT
LAKES TONIGHT WITH PLENTY OF LOW LEVEL AND DEEP LAYER SHEAR TO
SUSTAIN THIS CONVECTION THROUGH AT LEAST LOWER MICHIGAN/FAR
NORTHERN INDIANA, AT LEAST PARTIALLY COMPENSATING FOR MORE
MARGINAL INSTABILITY. THERE ALSO COULD BE SOME MCV-TYPE FEATURE
FORMING ON NORTHERN PERIPHERY OF THIS CONVECTION ACROSS SE
WISCONSIN THAT COULD HELP SUSTAIN STORMS THROUGH 05Z-06Z. BASED
ON CURRENT TRENDS, DID INCREASE POPS TO CATEGORICAL ACROSS THE
NORTHWEST WITH EXPECTATION THAT SOME TEMPORAL WINDOW EXISTS LATE
EVENING/EARLY OVERNIGHT FOR 40-50 MPH GUSTS ACROSS SW LOWER
MICHIGAN/NORTHWEST INDIANA, WITH A GRADUAL WEAKENING WITH
EAST/SOUTHEAST EXTENT OVERNIGHT AS SOME BOUNDARY LAYER
STABILIZATION OCCURS AND BETTER MLCAPE AXIS GETS PINCHED OFF
TO THE WEST. IN ADDITION TO THE POTENTIAL OF GUSTY WINDS, SOME
BRIEF HEAVY RAINFALL IS EXPECTED THAT COULD LEAD TO SOME
LOCALIZED PONDING. HOWEVER, OVERALL PROGRESSIVE SHOULD KEEP
RAINFALL AMOUNTS IN CHECK MOST LOCATIONS. IT IS POSSIBLE SOME
LOCALIZED 1+" INCH AMOUNTS COULD BE REALIZED ACROSS FAR NW
INDIANA/SW LOWER MICHIGAN.
DISCUSSION
ISSUED AT 206 PM EDT TUE AUG 18 2026
NOT A LOT OF WHOLESALE CHANGES TO THIS FORECAST PERIOD. COOL
FRONT CURRENTLY SITTING OVER SOUTHCENTRAL MI AND ORIENTATED TO
THE SOUTHWEST INTO CENTRAL IL STILL ON SCHEDULE TO BEGIN PUSHING
SOUTHEASTWARD INTO THE AREA THIS EVENING. LOOKS LIKE AFTER 6 PM
EDT CHANCES FOR SOME LIGHT SHOWERS INCREASE OUT AHEAD OF THE
INCOMING FRONTAL BOUNDARY FOR OUR FAR NORTHWESTERN PARTS OF THE
CWA BEFORE SOME SCATTERED THUNDERSTORMS ALONG THE FRONT PUSH IN
SHORTLY AFTERWARDS AND CONTINUES TO MOVE SOUTHEASTWARD THROUGH
THE AREA OVERNIGHT INTO WEDNESDAY. FORECASTED INSTABILITY,
MAINLY ELEVATED, WITH VALUES LESS THAN 1000 J/KG COUPLED WITH
DECENT SHEAR VALUES AHEAD OF AND ALONG THE FRONT WITH VALUES
AROUND 70-80 KTS, AND SURFACE DEW POINTS CURRENTLY IN THE 60S
ACROSS THE AREA. EXPECTATION IN THIS ENVIRONMENT WITH THE LATER
DIURNAL TIMING THAT SOME OF THE STORMS MAY BECOME STRONG BUT
WOULD TREND WEAKER THROUGH THE EVENING AS THE FRONT
SOUTHEASTWARD.
ON WEDNESDAY, DEPENDING ON THE EXACT POSITION OF THE FRONTAL
BOUNDARY, WHICH AT THIS TIME WILL MOST LIKELY BE OVER OUR FAR
SOUTH/SOUTHEASTERN PARTS OF THE CWA. WHICH IF THIS DOES PAN OUT
THEN THERE WILL BE AFTERNOON SLIGHT CHANCES OF SHOWERS AND
STORMS MAINLY FOR THE SOUTHERN HALF OF THE CWA WITH THE CLOSE
PROXIMITY OF THE FRONTAL BOUNDARY TO PROVIDE A BIT OF LIFT.
HOWEVER, SEVERE STORMS ARE NOT EXPECTED WITH MOST OF THE AREA TO
THE NORTH OF THE BOUNDARY WITH A LESS THAN IDEAL ENVIRONMENT
ESPECIALLY WITH A DRIER AIRMASS PUSHING IN FROM THE NORTH IN THE
WAKE OF THE FRONT BY WEDNESDAY AFTERNOON AND EVENING. ZONAL FLOW
ALOFT ACROSS THE REGION WILL BRING SLIGHTLY COOLER TEMPERATURES
ACROSS THE AREA INTO FRIDAY WITH HIGHS IN THE UPPER 70S
EXPECTED. FAIRLY NICE WEATHER WITH COMFORTABLE CONDITIONS WILL
BE IN PLACE FOR THURSDAY AND FRIDAY BEFORE ANOTHER COOL FRONT
ASSOCIATED WITH A TROUGH DROPPING SOUTHEASTWARD INTO THE GREAT
LAKES ARRIVES LATE FRIDAY AND INTO SATURDAY INCREASING CHANCES
ONCE AGAIN FOR SHOWERS AND STORMS AND BEFORE PUSHING QUICKLY
EASTWARD.
BY SUNDAY, RIDGING OVER THE CENTRAL CONUS THEN BEGINS TO
BUILD NORTHWARD INTO THE REGION BRINGING ANOTHER PERIOD OF DRY
WEATHER AND A SLIGHT WARMING TREND INTO NEXT WEEK WITH HIGHS
BACK INTO THE LOW 80S.
AVIATION /06Z TAFS THROUGH 06Z THURSDAY/
ISSUED AT 145 AM EDT WED AUG 19 2026
CONVECTIVE COMPLEX WHICH MOVED INTO THE AREA FROM SOUTHEAST
WISCONSIN CONTINUES TO DIMINISH IN INTENSITY AS WEAK MLCIN HAS
DEVELOPED LOCALLY WITH APPROACH OF THE WEAKENING MLCAPE AXIS.
AN UPPER SPEED MAX AND INCREASED DEEP LAYER SHEAR HAS PROVIDED
SOME LONGEVITY TO THE ORGANIZATION OF THIS CONVECTION DESPITE
THE WANING INSTABILITY, AND A PERIOD OF SHOWERS IS STILL
POSSIBLE AT KFWA IN THE 07Z-09Z BEFORE THE LINE DISSIPATES.
A LAGGING FRONTAL BOUNDARY WILL DROP ACROSS THE SOUTHERN GREAT
LAKES OVERNIGHT, AND WITH PLENTY OF RESIDUAL LOW LEVEL MOISTURE,
SOME LOWER END MVFR OR IFR CIGS ARE POSSIBLE BEFORE IMPROVING
MID MORNING.
FOR TODAY, STRONGER MID/UPPER LEVEL SHORT WAVE WILL BYPASS THE
AREA ACROSS THE NORTHERN GREAT LAKES, BUT LOW LEVEL TROUGH AXIS
WILL BE SAGGING INTO NORTHERN INDIANA COUPLED WITH SOME
ADDITIONAL SHEARED VORTICITY MAXIMA PROGRESSING THROUGH BROAD
CYCLONIC UPPER FLOW. THIS SHOULD GIVE RISE TO SOME SCATTERED
AFTERNOON SHOWERS, PARTICULARLY ACROSS KFWA AND POINTS
SOUTHWARD WHERE BETTER SFC BASED INSTABILITY AXIS IS EXPECTED TO
RESIDE. INSTABILITY MAGNITUDES DO APPEAR TO BE SOMEWHAT LIMITED
AS FAR NORTH AS KFWA, AND WITH WEAK MID LEVEL LAPSE RATES,
GREATER CONFIDENCE IN THUNDER AT THIS TIME IS SOUTH OF KFWA THIS
AFTERNOON. WILL INCLUDE PROB30 GROUP AT KFWA TO COVER THIS
POTENTIAL, BUT SOME THUNDER MAY NEED TO BE ADDED IN LATER
FORECASTS IF SUFFICIENT DESTABLIZATION CAN BE REALIZED.
IWX WATCHES/WARNINGS/ADVISORIES
IN...NONE.
OH...NONE.
MI...NONE.
MARINE...NONE.
UPDATE...MARSILI
DISCUSSION...ANDERSEN
AVIATION...MARSILI
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