231
FXUS63 KLOT 210004
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
704 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.
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 /00Z TAFS THROUGH 06Z WEDNESDAY/
ISSUED AT 636 PM CDT MON JUL 20 2026
KEY MESSAGES FOR THE 00Z TAF PERIOD (UPDATED AT 700 PM CDT):
* OCCASIONAL MVFR VSBYS CONTINUE DUE TO WILDFIRE SMOKE
* A PERIOD OF THUNDERSTORMS REMAINS POSSIBLE LATE THIS EVENING
AND OVERNIGHT
WHETHER OR NOT WE WILL SEE NEW DEVELOPMENT ALONG THE COLD FRONT
TO OUR NORTH IN THE WAKE OF EARLIER ROUNDS OF ACTIVITY,
INCLUDING THE LIGHT BAND OF SHOWERS AT 00Z TAF TIME, REMAINS
THE BIG QUESTION FOR THE EVENING AND OVERNIGHT PERIOD. THE TWO
FORECAST MODELS THAT SEEM TO CURRENTLY HAVE THE BEST HANDLE ON
THE ONGOING TRENDS BOTH SUGGEST A GAP WILL CONTINUE TO EXIST
BETWEEN THE THUNDERSTORM CLUSTERS TO OUR WEST AND NORTH, WITH
THE NORTHERN ACTIVITY ACROSS WI TRACKING MORE SOUTHEAST AND OUT
ACROSS THE LAKE. THIS IDEA FITS WITH HOW THESE STORMS CURRENTLY
APPEAR TO BE DEVELOPING...AND ALSO WHERE THEY ARE NOT
DEVELOPING...BASED ON THE OVERALL PATTERN OF ATMOSPHERIC SUPPORT
FROM VERTICAL MOISTURE AND WIND PROFILES BOTH LOCALLY AND
UPSTREAM.
STILL AM NOT CONFIDENT ENOUGH TO COMPLETELY RULE OUT TSRA
CHANCES AS THE FRONT APPROACHES LATER TONIGHT WITH A WARM AND
HUMID SURFACE AIRMASS AHEAD OF IT. BUT ELECTED TO CUT BACK FROM
A TEMPO TO A PROB30 AND DELAY THE POTENTIAL ARRIVAL TIME BY A
COUPLE HOURS WHILE ALSO DROPPING THE RESIDUAL SHRA IN THE WAKE
OF THE STORMS. AGAIN, THIS MOVEMENT TOWARD A LESS ACTIVE
OVERNIGHT PERIOD IS BASED ON THE OVERALL LACK OF WIDESPREAD
ACTIVITY CURRENTLY TO OUR NORTH WHERE ALL THE NECESSARY
INGREDIENTS ALREADY APPEAR TO BE IN PLACE BUT AREN'T HAVING MUCH
EFFECT AT THE MOMENT.
LENNING
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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