053
FXUS63 KLOT 110637
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
137 AM CDT TUE AUG 11 2026
KEY MESSAGES
- SCATTERED THUNDERSTORMS MAY DEVELOP OVER NORTHERN ILLINOIS
DURING THE PRE-DAWN HOURS. ISOLATED INSTANCES OF LARGE HAIL
AND DAMAGING WIND AS WELL AS LOCALIZED FLOODING ARE POSSIBLE
WITH THESE STORMS.
- POSSIBLE LINE/COMPLEX OF SEVERE THUNDERSTORMS MID/LATE TUESDAY
MORNING INTO EARLY TUESDAY AFTERNOON. SEVERE WIND GUSTS TO 80
MPH POSSIBLE, ALONG WITH HEAVY RAIN AND LOCALIZED FLOODING.
- CONTINUED THUNDERSTORM CHANCES THROUGH THE END OF THE WEEK.
MESOSCALE
ISSUED AT 1026 PM CDT MON AUG 10 2026
THROUGH SUNRISE:
IN THE WAKE OF THIS EVENING'S STORMS, WE HAVE TURNED OUR FOCUS
TO A COMPACT MID-LEVEL WAVE OVER NORTH-CENTRAL IOWA AND ITS
POTENTIAL INTERACTION WITH A LOW-LEVEL FRONT EXTENDING ESE
ACROSS EASTERN IOWA INTO NORTHERN ILLINOIS. RECENT SURFACE
ANALYSIS INDICATES THAT THE DIFFUSE WARM FRONT ALIGNS ROUGHLY
FROM AROUND DIXON TO JUST SOUTH OF JOLIET TO NORTHERN JASPER
COUNTY, AND IS SLOWLY DRIFTING NORTHWARD.
ISOLATED CONVECTION HAS ALREADY DEVELOPED OVER PORTIONS OF
EASTERN IOWA IN RESPONSE TO WEAK LOW-LEVEL ISENTROPIC ASCENT ON
THE NORTHERN PERIPHERY OF A MODEST LOW-LEVEL JET. AS THE JET
VEERS THROUGH THE NIGHT, THE FOCUS FOR ISENTROPIC ASCENT IS
EXPECTED TO SHIFT TOWARD NORTHERN ILLINOIS. MEANWHILE, THE
INCOMING WAVE OVER IOWA WILL CROSS NORTHERN ILLINOIS OVERNIGHT
AND PROVIDE BROADER SUPPORT.
WHILE SOME LOW-LEVEL CAPPING REMAINS IN THE WAKE OF THE EVENING
WAVE, STEEPENING MID-LEVEL LAPSE RATES AND SEASONABLY STRONG
EFFECTIVE SHEAR (FOR BOTH SURFACE AND ELEVATED CELLS) WILL
SUPPORT POTENTIAL RAPID GROWTH OF MOSTLY ELEVATED SUPERCELLS AND
MULTICELL CLUSTERS NEAR AND NORTH OF THE WARM FRONT. CONFIDENCE
REMAINS LOW, BUT ANY STORM COULD BECOME SEVERE WITH LARGE HAIL
(ESPECIALLY WITH ELEVATED LEFT SPLITTING SUPERCELLS), INSTANCES
OF DAMAGING WIND (PARTICULARLY WITH MULTICELL CLUSTERS), AND A
NON-ZERO TORNADO RISK (FOR ANY CELLS ROOTED ON THE WARM FRONT).
ADDITIONALLY, PROPAGATION VECTORS PARALLEL TO THE FRONT AND
LOW-LEVEL FLOW ROUGHLY PERPENDICULAR TO THE FRONT MAY LEAD TO
TRAINING THUNDERSTORMS ALONG A NW TO SE CORRIDOR (UNLESS A
DEEPER COLD POOL PUSHES SOUTHWESTWARD WITH TIME). HAVE CONTINUED
TO ASSESS THE NEED FOR A FLASH FLOOD WATCH FOR MUCH OF
NORTHEAST ILLINOIS, BUT THE LOWER CONFIDENCE IN COVERAGE AND
LOCATION PRECLUDES A WATCH AT THIS TIME. HOWEVER, IF STORM
COVERAGE IS BEGINNING TO APPEAR MORE WIDESPREAD WITHIN THE NEXT
SEVERAL HOURS, A TARGETED WATCH WILL BE NEEDED.
KLUBER
DISCUSSION
ISSUED AT 217 PM CDT MON AUG 10 2026
THE PRIMARY FORECAST CHALLENGE REMAINS THUNDERSTORM TIMING AND
STRENGTH THROUGH MIDWEEK WITH A COMPLEX OF SEVERE THUNDERSTORMS
POSSIBLE MID/LATE TUESDAY MORNING INTO EARLY TUESDAY AFTERNOON.
A VERY MOIST AIRMASS IS IN PLACE WITH DEWPOINTS IN THE MID/UPPER
70S WITH A FEW LOCATIONS TAGGING 80. ISOLATED THUNDERSTORMS HAVE
PERSISTED ACROSS EASTERN IA AND FAR NORTHWEST IL THE PAST FEW
HOURS BUT HAVE BEEN SLOW TO STRENGTHEN. HOWEVER, THE EXPECTATION
IS FOR THIS ACTIVITY TO CONTINUE MOVING EAST AND TO SLOWLY
INCREASE IN COVERAGE AND INTENSITY. AS IT TAPS INTO THE HIGH
INSTABILITY IN PLACE, SOME OF THESE STORMS MAY BECOME SEVERE
ACROSS NORTHERN IL AND FAR NORTHWEST IN AND PERSIST THROUGH MID
EVENING. IN ADDITION TO THE SEVERE THREAT, TORRENTIAL RAIN AND
LOCALIZED FLOODING WILL ALSO BE POSSIBLE THOUGH THERE REMAINS
SOME UNCERTAINTY FOR HOW WIDESPREAD ANY FLOODING MAY BECOME.
CONSIDERATION WAS GIVEN FOR A FLOOD WATCH BUT HAVE OPTED TO HOLD
OFF FOR NOW. MUCH OF THE GUIDANCE HAS TRENDED DRIER FOR THE
LATE EVENING AND OVERNIGHT HOURS TONIGHT AND HAVE FOLLOWED THIS
TREND WITH THIS FORECAST THOUGH SOME SHOWERS AND ISOLATED
THUNDERSTORMS MAY LINGER.
FOCUS THEN SHIFTS TO A RATHER CONSISTENT FEATURE IN MOST OF THE
MODELS FOR A COMPLEX OF SEVERE THUNDERSTORMS TO DEVELOP OVER
NORTHEAST IA EARLY TUESDAY MORNING AND RACE SOUTHEAST ACROSS THE
LOCAL AREA FROM MID MORNING TUESDAY THROUGH EARLY TUESDAY
AFTERNOON. SOME OF THE CAM SOLUTIONS ARE QUITE CONCERNING WITH A
LINE OF SEVERE THUNDERSTORMS MOVING ACROSS A LARGE PART OF THE
CWA. THE UPDATED SPC DAY 2 OUTLOOK HAS INCLUDED A LEVEL 3 OF 5
SEVERE THREAT FOR MOST OF THE AREA AND GIVEN ALL OF THESE TRENDS
HAVE MENTIONED WIND GUSTS TO 80 MPH POSSIBLE AND IF THESE STORM
MATURE AS SHOWN ON SOME OF THE CAMS, POCKETS OF HIGHER GUSTS
MAY MATERIALIZE. BASED ON THESE TRENDS, HAVE ALSO INCLUDED
SEVERE MENTION TO THE GRIDS AND ZONE FORECAST. ONCE THESE
STORMS EXIT TO THE EAST, THERE SHOULD BE A LULL IN THE
PRECIPITATION CHANCES FROM MID/LATE TUESDAY AFTERNOON THROUGH
AT LEAST THE EARLY OVERNIGHT HOURS WEDNESDAY MORNING.
THERE IS ANOTHER WAVE THAT MAY MOVE ACROSS THE REGION
WEDNESDAY MORNING WITH ANOTHER POTENTIAL SEVERE THUNDERSTORM
COMPLEX NEAR OR OVER THE LOCAL AREA. QUITE A BIT OF UNCERTAINTY
FOR THIS TIME PERIOD, BUT WILL NEED TO BE MONITORED CLOSELY. IN
ADDITION, ALL OF THESE PERIODS OF HEAVY/TORRENTIAL RAIN WILL
ALLOW EACH FOLLOWING WAVE/COMPLEX TO POTENTIALLY PRODUCE
FLOODING MORE QUICKLY AND OVER LARGER AREAS.
THE PATTERN IS NOW LOOKING QUITE ACTIVE INTO THIS WEEKEND,
THOUGH THERE REMAINS QUITE A BIT OF UNCERTAINTY FOR TIMING AND
LOCATION AS A SERIES OF HIGH PRESSURE SYSTEMS AND COLD FRONTS
MOVE ACROSS THE UPPER MIDWEST AND NORTHERN GREAT LAKES. HOW FAST
THESE MOVE, HOW FAR SOUTH THEY PUSH, ETC. WILL HAVE LARGE
IMPACTS ON WHEN THUNDERSTORMS WOULD BE MOST LIKELY ACROSS THE
LOCAL AREA. CMS
AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/
ISSUED AT 136 AM CDT TUE AUG 11 2026
KEY MESSAGES:
- SCATTERED SHOWERS AND PERHAPS A FEW STORMS MAY OCCUR NEAR THE
TERMINALS THROUGH EARLY THIS MORNING.
- AN ORGANIZED COMPLEX OF THUNDERSTORMS IS LIKELY TO IMPACT THE
TERMINALS BETWEEN MID-MORNING AND MID-AFTERNOON TODAY. SEVERE
WIND GUSTS IN EXCESS OF 50 KTS MAY OCCUR WITH THESE STORMS.
- SUB-VFR CEILINGS AND VISIBILITIES WILL BE OBSERVED AT TIMES
THROUGH THIS MORNING.
ISENTROPIC LIFT OVER A SURFACE BOUNDARY MAY CONTINUE TO GENERATE
SHOWERS AND POSSIBLY A FEW ADDITIONAL STORMS THROUGH EARLY THIS
MORNING. MUCH OF THIS ACTIVITY HAS FOCUSED NORTH AND EAST OF THE
TERMINALS THUS FAR, AND CONFIDENCE IS LOW THAT ANY NEW CELLS
THAT DEVELOP WILL AFFECT THE TERMINALS, BUT (AT LEAST FOR NOW)
OPTED TO MAINTAIN THE INHERITED PROB30 GROUPS FOR TSRA FOR LATER
TONIGHT/THIS MORNING AS A PRECAUTION.
THE TERMINALS WILL, HOWEVER, LIKELY BE AFFECTED BY A
THUNDERSTORM COMPLEX BETWEEN THE MID-MORNING AND MID-AFTERNOON
TODAY. CONFIDENCE IN THE PRECISE ARRIVAL TIME OF THESE STORMS
REMAINS SOMEWHAT LOW AT THIS TIME AS THE COMPLEX HAS YET TO
REALLY MATERIALIZE (AS OF THIS WRITING), AND MODEL GUIDANCE HAS
A POOR HANDLE ON WHAT'S GOING ON UPSTREAM OF OUR AREA, SO MADE
NO CHANGES TO THE INHERITED TEMPO GROUP TIMINGS. IF THIS COMPLEX
MATURES QUICKLY ENOUGH INTO AN ORGANIZED LINE OR BOW AND TAKES
A FAVORABLE TRACK ACROSS THE TERMINALS LIKE MANY HIGH-RESOLUTION
MODEL SOLUTIONS ARE SUGGESTING, THEN SEVERE WIND GUSTS IN
EXCESS (AND POTENTIALLY WELL IN EXCESS) OF 50 KTS MAY BE
OBSERVED AS THESE STORMS ROLL THROUGH.
LASTLY, THE PERSISTING ABUNDANCE OF LOW-LEVEL MOISTURE HAS
ALLOWED FOR MVFR STRATUS AND FOG/MIST TO DEVELOP ONCE AGAIN
TONIGHT. THE REDUCED VISIBILITIES COULD DIP BELOW MVFR AS THEY
PRIMARILY REMAIN AT RFD, GYY, AND DPA, BUT THE MVFR CEILINGS
WILL LIKELY CONTINUE TO AFFECT ALL OF OUR TAF SITES AT TIMES
THROUGH THIS MORNING. ANOTHER EPISODE OF FOG AND LOW CEILINGS
APPEARS POSSIBLE EARLY WEDNESDAY MORNING, AND THAT IS SOMETHING
THAT WILL NEED TO BE ASSESSED MORE CLOSELY FOR FORTHCOMING TAF
ISSUANCES.
OGOREK
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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