805
FXUS63 KLOT 201942
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
242 PM CDT MON JUL 20 2026
KEY MESSAGES
- THERE REMAINS A THREAT FOR SEVERE WEATHER THIS EVENING, BUT
SOME AREAS MAY GET MISSED BY THUNDERSTORMS ENTIRELY.
- A SERIES OF COLD FRONTS WILL LEAD TO COOLER TEMPERATURES BY
MIDWEEK.
MESOSCALE
ISSUED AT 236 PM CDT MON JUL 20 2026
MCS CONTINUES TO PUSH SOUTHWARD ACROSS WESTERN IL WITH EXTENSIVE
CLOUD COVER ACROSS OUR CWA AND EVEN SOME LIGHT RAIN OVER ABOUT THE
SOUTHWEST HALF OF OUR CWA. SKIES ARE QUICKLY CLEARING IN THE WAKE
OF THIS MCS ACROSS SOUTHWEST WI AND EASTERN IA, WITH THAT CLEARING
LINE LIKELY TO REACH OUR NORTHWEST CWA BY AROUND 20Z. NEARLY FULL
SUNSHINE BEHIND THE MCS SHOULD ALLOW FOR SOME HEATING AND
RECOVERY OF THE BOUNDARY LAYER, BUT CURRENTLY SATELLITE IMAGERY
WOULD CERTAINLY SUGGEST STRONG MLCINH IS IN PLACE GIVEN THE
COMPLETE ABSENCE OF ANY CLOUDINESS.
THE BAND OF CONVECTION HAS DEVELOPED OVER SOUTHERN MN IN AN AREA
OF TRANSVERSE WAVE CLOUDS IN THE WAKE OF THE MORNING MCS,
SUGGESTING THAT THOSE STORMS ARE ELEVATED. ALONG THE WESTERN FLANK
OF THAT REMNANT COLD POOL BOUNDARY LAYER DESTABILIZATION IS QUITE
EVIDENT IN VISIBLE SATELLITE IMAGERY WITH SOME CUMULUS DEVELOPING
IN AN AXIS OF STRONG CONVERGENCE/CONFLUENCE. CONCEPTUALLY, IT
WOULD MAKE SENSE THAT THE PORTION OF THE LINE OF CONVECTION ALONG
THE MN/IA BORDER NEARER TO THAT CONFLUENCE AXIS WOULD BE MORE
LIKELY TO THRIVE/EXPLODE THAN THE PORTION OF THE LINE FARTHER EAST
HEADING INTO THE REMNANT COLD POOL.
RECENT TRENDS IN THE WARN OF FORECAST SYSTEM (WOFS) GUIDANCE HAS
BEEN FOR MORE INTENSE CONVECTION TOWARD EARLY EVENING TO BE
PROGRESSIVELY FARTHER WEST. THIS COULD BE AN INDICATION THAT THE
INFLUENCE OF THE STABLE COLD POOL BEING BETTER RESOLVED BY THE
MODEL.
NOT FAR BEHIND THIS INITIAL BAND OF CURRENTLY ELEVATED
CONVECTION, A CUMULUS FIELD IS DEVELOPING ALONG THE ACTUAL COLD
FRONT IN MN INTO WI. THIS AREA SEEMS PRONE TO INTENSE CONVECTIVE
INITIATION LATER THIS AFTERNOON AS LARGE SCALE FORCING ARRIVES.
THE BIG QUESTION IS HOW FAR SOUTHWEST THAT CONVECTION DEVELOPS.
ULTIMATELY THE CONVECTION SHOULD FOLLOW THE FRONT INTO NORTHERN IL
THIS EVENING, BUT CAN'T COMPLETELY RULE OUT A SCENARIO WHERE WE
GET GAPPED BETWEEN THE STORMS OVER IA AND THE STORMS OVER WI.
ASSUMING STORMS GET INTO NORTHERN IL AND NORTHWEST IN, WHICH SEEMS
LIKE ABOUT A 60% CHANCE AT THIS POINT, THEN SEVERE WEATHER WOULD
CERTAINLY BE A CONCERN GIVEN THE STRONG SHEAR. EVEN WITH STORMS
LIKELY ROOTED ABOUT THE BOUNDARY LAYER AS THEY MOVE ACROSS OUR
CWA, SIGNIFICANT ELEVATED INSTABILITY AND STRONG EFFECTIVE SHEAR
WOULD SUPPORT A SEVERE THREAT.
-IZZI
DISCUSSION
ISSUED AT 236 PM CDT MON JUL 20 2026
TUESDAY...
RRFS AND HRRR BOTH HAVE A SIGNAL FOR ADDITIONAL SMOKE CONCENTRATIONS
BACK BEHIND THE LEADING COLD FRONT TONIGHT, BUT THERE IS A MUTED
SIGNAL FOR ANY VISIBILITY REDUCTIONS. OUTSIDE OF THIS, A
STRENGTHENING UPPER JET AND COLDER TEMPERATURES ALOFT WILL PROMOTE
CUMULUS DEVELOPMENT DURING THE AFTERNOON. A SECONDARY AND MORE
NOTEWORTHY FRONT WILL SWEEP SOUTHWARD ACROSS THE GREAT LAKES DURING
THE AFTERNOON HOURS POSSIBLY ACCOMPANIED BY LOW-TOPPED SHOWERS AND
SPRINKLES, BUT NOT BEFORE TEMPERATURES RECOVER BACK TO THE LOW TO
MID 80S. NORTHWESTERLY WINDS WILL INCREASE AND GUST IN THE 20 TO 25
MPH RANGE DURING THE AFTERNOON. THE SURFACE HIGH, QUITE STRONG FOR
MID JULY, WILL STRENGTHEN FURTHER TUESDAY NIGHT AND DIP SOUTH ACROSS
THE UPPER MIDWEST. A SHARP UPPER TROUGH WILL PASS OVER THE GREAT
LAKES AND PUSH A NOTABLY COOLER AND DRIER AIRMASS INTO THE LOWER
GREAT LAKES REGION OVERNIGHT INTO WEDNESDAY. THERE IS A LIMITED QPF
FOOTPRINT ON SEVERAL GUIDANCE SOURCES, AND CLOUD DEPTHS MAY GET JUST
TALL ENOUGH FOR SOME SPRINKLES OR LOW TOPPED SHOWERS LATER IN THE
DAY INTO THE EVENING, HIGHEST CONFIDENCE INTO NW INDIANA. THIS WILL
SET THE STAGE FOR SOME SEASONABLY COMFORTABLE OVERNIGHT LOWS (IN THE
50S) FOR MANY AREAS OUTSIDE THE URBAN CORE.
KMD
WEDNESDAY THROUGH SUNDAY...
WEDNESDAY ONWARD, DEEP CYCLONIC UPPER-LEVEL FLOW WILL ONLY GRADUALLY
SHIFT EASTWARD AS A SURFACE HIGH PRESSURE SYSTEM MEANDERS THROUGH
THE UPPER MISSISSIPPI RIVER VALLEY. THE NET RESULT SHOULD BE A
PERIOD OF PLEASANT CONDITIONS WITH NO PRECIPITATION, HIGHS IN THE
UPPER 70S TO AROUND 80, AND OVERNIGHT LOWS IN THE UPPER 50S TO
AROUND 60. CHOPPY WAVES WILL MAKE SWIMMING HAZARDOUS ON LAKE
MICHIGAN BEACHES WEDNESDAY AND PERHAPS INTO EARLY THURSDAY.
ENSEMBLE GUIDANCE DEPICTS THE REDEVELOPMENT OF AN EXPANSIVE UPPER-
LEVEL RIDGE ACROSS THE CENTRAL UNITED STATES TOWARD NEXT WEEKEND
WHICH WOULD ENCOURAGE TEMPERATURES LOCALLY TO CLIMB BACK INTO THE
UPPER 80S TO PERHAPS LOWER 90S. THERE IS ONE RIPPLE IN THE MONSOONAL
MOISTURE THAT SHOULD BE ABLE TO PROGRESS TOWARD THE OHIO VALLEY ON
FRIDAY, BUT MOST GUIDANCE SENDS ANY PRECIPITATION WITH THIS WAVE
WELL SOUTH OF THE LOCAL AREA. THERE IS STILL A SIGNAL FOR A
CONVECTIVE EVENT SOMETIME IN THE JULY 27-29 TIMEFRAME IN THE GENERAL
REGION WITH NORTHWEST FLOW IN PLACE ON THE NORTHEAST FRINGES OF THE
STRONG UPPER RIDGE. THIS WOULD POSE THE NEXT CHANCE OF MEANINGFUL
RAINFALL SHOULD THIS SYSTEM MOVE TOWARD OUR LATITUDE.
BORCHARDT/KMD
AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/
ISSUED AT 1241 PM CDT MON JUL 20 2026
KEY MESSAGES FOR THE 18Z TAF PERIOD (UPDATE AT 236 PM CDT):
* OCCASIONAL MVFR VSBYS THIS MORNING DUE TO WILDFIRE SMOKE
* A PERIOD OF THUNDERSTORMS THIS EVENING AND OVERNIGHT
THE COMPLEX OF THUNDERSTORMS WEST OF THE TERMINALS WILL CONTINUE
TO TREK SOUTHEASTWARD. A STEADY OVERCAST SKY WITH A FEW
SPRINKLES WILL OCCUR FROM KDPA WESTWARD. WINDS WILL BECOME A
BIT GUSTY FROM THE SOUTHWEST BEHIND THIS COMPLEX. THESE WINDS
WILL HELP MIX OUT SOME OF THE WILDFIRE SMOKE AND HAZE FOR A
PERIOD LATER THIS AFTERNOON AND EVENING.
CONFIDENCE HAS INCREASED IN A PERIOD OF THUNDERSTORMS FOR MANY
AREAS THIS EVENING, THOUGH WE ONLY HAVE MEDIUM CONFIDENCE IN
DIRECT IMPACTS TO THE CHICAGO TERMINALS, AS THERE IS A PLAY
WHERE STORMS PASS BY TO THE NORTH AND ALSO THE SOUTHWEST. THE
HIGHEST CONFIDENCE PERIOD OF TS ON STATION IN THE 3Z-7Z WINDOW,
THOUGH TRENDS WILL NEED TO BE MONITORED. GUSTY WINDS WILL
ACCOMPANY THE LEADING EDGE OF STORMS, AND NOT LIKELY DURING THE
ENTIRE PERIOD.
A COLD FRONT WILL SHIFT INTO NE IL LATE TONIGHT, AND WILL BRING
SOME ADDITIONAL SMOKE AND HAZE, THOUGH CURRENT VISIBILITY PROGS
SUGGEST NO WORSE THAN MVFR. WINDS WILL ALSO SHIFT TO W AND THEN
NW INTO WEDNESDAY.
KMD
LOT WATCHES/WARNINGS/ADVISORIES
IL...AIR QUALITY ALERT UNTIL MIDNIGHT CDT TONIGHT FOR ILZ003-ILZ004-
ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019-
ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-ILZ104-
ILZ105-ILZ106-ILZ107-ILZ108.
IN...AIR QUALITY ALERT UNTIL MIDNIGHT CDT /1 AM EDT/ TONIGHT FOR
INZ001-INZ002-INZ010-INZ011-INZ019.
LM...NONE.
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