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FXUS63 KLOT 301931
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
231 PM CDT SUN AUG 30 2026
KEY MESSAGES
- PERIODIC SHOWER AND STORMS THROUGH THE EARLY PART OF THE WEEK,
THOUGH THERE WILL AMPLE DRY PERIODS.
- HOTTER AND MORE HUMID CONDITIONS BUILD THROUGH MIDWEEK.
DISCUSSION
ISSUED AT 231 PM CDT SUN AUG 30 2026
A SHORTWAVE DISTURBANCE OVER NORTHEASTERN IOWA WILL CONTINUE TO
DRIVE SHOWERS AND EMBEDDED THUNDERSTORMS EASTWARD THROUGH EARLY
THIS EVENING, WITH THE GREATEST COVERAGE EXPECTED NORTH OF
I-80. WHILE A 20% CHANCE FOR LIGHTNING REMAINS, POOR MID-LEVEL
LAPSE RATES ACROSS NORTHERN ILLINOIS SHOULD LIMIT THUNDERSTORMS
TO ISOLATED COVERAGE.
FOLLOWING THE EASTWARD DEPARTURE OF THIS SHORT-WAVE IMPULSE
THIS EVENING, A SOUTHWESTERLY LOW-LEVEL JET WILL RAMP UP AGAIN
OVERNIGHT, WITH THE CORE EXPECTED TO RESIDE OVER IA
NORTHEASTWARD INTO SOUTHERN WI. ASSOCIATED ISENTROPIC UPGLIDE
(WARM AIR ADVECTION) MAY THUS FOSTER MORE ISOLATED TO SCATTERED
SHOWERS AND THUNDERSTORMS LATE TONIGHT INTO EARLY MONDAY
MORNING. THEREAFTER, CAPPING IS LIKELY TO CURTAIL THE THREAT OF
CONVECTION FOR MUCH OF THE AREA INTO MONDAY AFTERNOON. HOWEVER,
ANOTHER SHORT-WAVE IMPULSE IS PROGGED TO TRANSLATE EASTWARD
TOWARDS NORTHWESTERN IL LATE IN THE DAY, AND THUS MAY ACT AS THE
IMPETUS FOR ISOLATED TO WIDELY SCATTERED AFTERNOON DEVELOPMENT
ACROSS NORTHWESTERN IL AFTER 2 PM. SHOULD THIS ACTIVITY OCCUR,
~40 KT OF MID-LEVEL WESTERLY FLOW COULD SUPPORT A FEW STRONGER
STORMS ACROSS NORTHWESTERN IL LATE IN THE AFTERNOON. CONFIDENCE
REMAINS LOW WITH THE EXTENT OF THIS THREAT.
CONVECTIVE TRENDS CONTINUE TO BE OF LOW CONFIDENCE MONDAY NIGHT
INTO TUESDAY MORNING. NEVERTHELESS, LOW (20-30%)CHANCES FOR
STORMS CONTINUE DUE TO THE PERSISTENT WARM-AIR ADVECTION PATTERN
IN COMBINATION WITH ADDITIONAL SMALLER SCALE PERTURBATIONS
LIKELY TO TRANSITION EASTWARD ACROSS SOUTHERN WI THROUGH THE
MID-LEVEL RIDGE AXIS. THE BETTER FOCUS FOR STORMS MAY REMAIN IN
SOUTHERN WI, BUT AT THIS TIME, CANNOT RULE OUT STORMS AS FAR
SOUTH AS THE I-80 CORRIDOR. THE SPC DAY 3 SEVERE OUTLOOK (FOR
TUESDAY) PLACES MOST AREAS NORTH OF I-80 IN A LEVEL 1 OF 5
THREAT. SO, WHILE CONFIDENCE IN THE COVERAGE OF STORMS REMAINS
LOW INTO TUESDAY MORNING, THE METEOROLOGICAL ENVIRONMENT WILL BE
SUPPORTIVE OF A CONDITIONAL THREAT FOR STRONG STORMS.
OUTSIDE OF THE THREAT OF STORMS THROUGH TUESDAY MORNING,
TEMPERATURES AND HUMIDITY LEVELS WILL BE ON THE RISE THROUGH
MID-WEEK AS THE AIRMASS UNDER THE EXPANSIVE MID/UPPER-LEVEL
RIDGE CONTINUES TO WARM. WE ANTICIPATE HIGH TEMPERATURES IN THE
UPPER 80S MONDAY, THE LOW 90S TUESDAY AND THE LOW TO MID 90S
WEDNESDAY. IN SPITE OF US BEING PAST THE PEAK TIMING FOR
EVAPOTRANSPIRATION, LIMITED MIXING UNDER AN INVERSION CENTERED
NEAR 850 MB SHOULD KEEP DEW POINTS IN THE LOW TO MID 70S DURING
PEAK HEATING, PARTICULARLY ON TUESDAY AND WEDNESDAY, RESULTING
IN PEAK HEAT INDICES IN THE 100 TO 105 RANGE.
RELIEF FROM THE HEAT LOOKS PLAUSIBLE LATER IN THE WEEK AS A
BACKDOOR COLD FRONT SAGS SOUTHWARD INTO THE AREA. HOWEVER, THIS
LOOKS TO COME AT THE EXPENSE OF A PERIOD OF MORE ACTIVE WEATHER
(A PERIOD OR TWO OF THUNDERSTORMS, SOME POSSIBLY STRONG) AT THE
END OF THE WEEK. THE SPECIFICS SUCH AS THE TIMING OF THE FRONT
AND BEST POTENTIAL FOR THUNDERSTORMS REMAIN A BIT UNCLEAR AT
THIS POINT, BUT STORM CHANCES BEGIN TO RAMP UP ACROSS OUR AREA
LATE WEDNESDAY NIGHT INTO THURSDAY.
KJB
AVIATION /18Z TAFS THROUGH 00Z TUESDAY/
ISSUED AT 1238 PM CDT SUN AUG 30 2026
FORECAST CONCERNS INCLUDE...
CHANCE OF THUNDERSTORMS THIS AFTERNOON AND MONDAY MORNING.
GUSTY SOUTH/SOUTHWEST WINDS EARLY THIS AFTERNOON.
SCATTERED THUNDERSTORMS ARE CURRENTLY MOVING ALONG THE IL/WI
STATE LINE IN RESPONSE TO AN UPPER LEVEL WAVE APPROACHING THE
AREA. ADDITIONAL SHOWERS AND ISOLATED THUNDERSTORMS WILL BE
POSSIBLE ACROSS NORTHERN IL AND THE TERMINALS THROUGH LATE THIS
AFTERNOON, THOUGH THUNDER COVERAGE REMAINS UNCERTAIN. GIVEN THE
LATEST TRENDS, PROB THUNDER MENTION SEEMS REASONABLE FOR THE
CHICAGO TERMINALS WITH TEMPO MENTION AT RFD. THE OVERALL TREND
IN GUIDANCE IS FOR THIS ACTIVITY TO SLOWLY WEAKEN BY LATE
AFTERNOON/EARLY THIS EVENING, BUT LINGERING SHOWERS MAY PERSIST
INTO THIS EVENING.
THERE WILL BE TWO MORE TIME PERIODS WITH POTENTIAL ISOLATED
THUNDERSTORMS, THE FIRST AROUND/AFTER DAYBREAK MONDAY MORNING
AND THEN MONDAY AFTERNOON. CONFIDENCE FOR BOTH TIME PERIODS
REMAINS VERY LOW AND OPTED TO MAKE NO CHANGES TO THE FORECAST,
KEEPING CURRENT PROB THUNDER MENTION FOR MONDAY MORNING AND
KEEPING THE FORECAST DRY FOR MONDAY AFTERNOON.
SOUTH/SOUTHWEST WINDS WILL GUST INTO THE LOWER/MID 20KT RANGE
FOR A FEW MORE HOURS, THEN GUSTS ARE EXPECTED TO DIMINISH BY
MID AFTERNOON. WIND DIRECTIONS ARE EXPECTED TO BECOME SOUTH/
SOUTHEAST THIS EVENING, THEN TURN BACK TO SOUTH/SOUTHWEST
OVERNIGHT AND CONTINUE ON MONDAY. CMS
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 3 PM CDT THIS AFTERNOON FOR THE IL
NEARSHORE WATERS.
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