509
FXUS63 KLOT 200648
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
148 AM CDT MON JUL 20 2026
KEY MESSAGES
- THERE REMAINS A THREAT FOR SEVERE WEATHER TODAY, BUT CURRENT
THINKING IS MUCH OF OUR AREA MAY BE MISSED.
- A SERIES OF COLD FRONTS WILL LEAD TO COOLER TEMPERATURES BY
MIDWEEK.
DISCUSSION
ISSUED AT 148 AM CDT MON JUL 20 2026
TODAY AND TONIGHT:
EARLY MORNING WATER VAPOR IMAGERY DEPICTS A PAIR OF UPPER-
LEVEL SHORT-WAVELENGTH TROUGHS ALONG THE US/CANADIAN BORDER WITH
THE LEADING WAVE MOVING INTO SOUTHERN MANITOBA AND THE OTHER
CROSSING INTO SOUTHERN ALBERTA. THE LEADING WAVE IS ANCHORED BY
A SEASONABLY STRONG 998 SURFACE LOW PRESSURE SYSTEM MOVING INTO
WESTERN ONTARIO, AND IS SUPPORTING A BROAD LOW-LEVEL JET ACROSS
THE UPPER MISSISSIPPI RIVER VALLEY AS CONFIRMED BY SOME 30-40KT
OF FLOW SAMPLED BY THE FSD VWP EARLY THIS MORNING. MEANWHILE, A
SURFACE HIGH PRESSURE SYSTEM IS CENTERED DIRECTLY OVER THE LOWER
GREAT LAKES EARLY THIS MORNING LEADING TO NEARLY CALM WINDS AND
CLEAR SKIES. WITH SURFACE TEMPERATURES DROPPING TOWARD THE
LOWER 50S (LOCALLY UPPER 50S) EARLY THIS MORNING, HAVE BEEN
NOTING AREAS OF PATCHY FOG PARTICULARLY NEAR LAKE MICHIGAN AND
ACROSS THE KANKAKEE RIVER VALLEY. IT IS OTHERWISE A QUIET
MORNING ACROSS OUR AREA.
ALL EYES ARE ON A CLUSTER OF STORMS MOVING INTO WESTERN
MINNESOTA AT PRESS TIME. PER RAP-MESOANALYZED FIELDS, THE
CLUSTER OF STORMS IS LOCATED RIGHT ON THE EASTERN EDGE OF AN EML
PLUME CENTERED ON THE NORTHERN US (00Z ARB RAOB SAMPLED 800 TO
500MB LAPSE RATES OF AROUND 8 K/KM) AND NARROW SURFACE-BASED
INSTABILITY PLUME THAT ARCS FROM THE SOUTHERN US NORTHWARD ALONG
THE SOUTH DAKOTA AND MINNESOTA BORDER. AS WESTERLY MID-LEVEL
FLOW ON THE SOUTHERN SIDE OF BOTH UPPER-LEVEL WAVES CONTINUES TO
ADVECT THE LAPSE RATE PLUME EASTWARD AND SOUTHWESTERLY LOW-
LEVEL FLOW FACILITATES LOW-LEVEL WARM AIR ADVECTION INTO THE
UPPER MISSISSIPPI RIVER VALLEY, WOULD HAVE TO THINK THAT THE
ONGOING CLUSTER OF STORMS WILL INTENSIFY AND/OR NEW STORMS WILL
DEVELOP NEAR THE MISSISSIPPI RIVER IN THE COMING HOURS. THE
RESULTING COMPLEX OF STORMS SHOULD THEN DIVE SOUTHWARD ALONG THE
INSTABILITY AXIS ALIGNED WITH OR JUST WEST OF THE MISSISSIPPI
RIVER THROUGH THE MORNING REACHING NORTHERN IOWA TOWARD DAYBREAK
AND POSSIBLY NORTHEASTERN MISSOURI BY EARLY AFTERNOON (LARGELY
MISSING OUR AREA).
ASSUMING THIS OCCURS, AT LEAST SOME AIRMASS RECOVERY MAY TAKE
PLACE ACROSS EASTERN IOWA BEFORE NEW THUNDERSTORMS DEVELOP BY
MID-AFTERNOON NEAR THE INTERSECTION OF AN APPROACHING COLD
FRONT (ASSOCIATED WITH THE LEAD WAVE) AND THE RESIDUAL OUTFLOW
BOUNDARY FROM THE EARLY DAY MCS DRAPED ACROSS CENTRAL IOWA. SUCH
A RESULT WOULD SQUASH ANY OPPORTUNITY FOR THE SURFACE-BASED
INSTABILITY AXIS TO SHIFT INTO OUR AREA THIS AFTERNOON,
EFFECTIVELY ELIMINATING THE THREAT FOR SEVERE WEATHER IN OUR
AREA THROUGH THE EVENING HOURS. MEANWHILE, A SEPARATE REGIME OF
SUPERCELLS COULD MATERIALIZE CLOSER TO THE SURFACE CYCLONE IN
NORTHERN WISCONSIN AND UPPER MICHIGAN. THE NET RESULT WOULD BE A
LARGE GAP IN CONVECTIVE COVERAGE ACROSS SOUTHERN WISCONSIN AND
NORTHERN ILLINOIS THIS EVENING.
EVEN WITH MINIMAL COVERAGE OF STORMS THIS EVENING, COULD STILL
ENVISION A THREAT FOR A FEW THUNDERSTORMS OVERNIGHT AS THE
SECONDARY UPPER-LEVEL WAVES SLIDES OVERHEAD PERHAPS FAVORING THE
10 PM THROUGH 6 AM WINDOW. WITH INSTABILITY PROFILES LARGELY
BEING FORCED BY THE EASTERN EDGE OF A WORKED-OVER LAPSE RATE
PLUME (PERHAPS 1000-1500 J/KG OF MUCAPE) BUT OTHERWISE STELLAR
SHEAR PROFILES (EFFECTIVELY 45-55 KT IN THE ELEVATED CONVECTIVE
LAYER), WOULD STILL NEED TO WATCH FOR A STORM TO BECOME SEVERE
WITH A THREAT FOR DAMAGING WINDS OR DAMAGING HAIL. HOWEVER,
COVERAGE OF SEVERE WEATHER WOULD LARGELY BE CONSISTENT WITH A
LEVEL 1 OUT OF 5 THREAT LEVEL IN OUR AREA AND INDEED ON AN
ISOLATED BASIS. (OFTENTIMES, THE HRDPS PERFORMS WELL WITH
SUMMERTIME CONVECTIVE REGIMES AND HAS CONSISTENTLY SHOWN THIS
FORECAST OUTCOME FOR EVERY RUN).
NOW, IF THE CLUSTER OF STORMS IN WESTERN MINNESOTA CROAKS AND
NEW DEVELOPMENT IN WESTERN WISCONSIN IS KEPT TO A MINIMUM THIS
MORNING, THE SURFACE-BASED INSTABILITY AXIS WOULD HAVE A MUCH
BETTER OPPORTUNITY TO ARC NORTHEASTWARD INTO NORTHERN ILLINOIS
AND SOUTHERN WISCONSIN THIS EVENING. THUS WOULD SET THE STAGE
FOR A MORE CONCERNING SEVERE WEATHER SCENARIO LOCALLY WHERE THE
OVERLAP OF INTENSE ALMOST COOL-SEASON LIKE KINEMATICS WITH WARM-
SEASON INSTABILITY PROFILES WOULD SUPPORT EXPLOSIVE SUPERCELL
DEVELOPMENT AND SUBSEQUENT GROWTH INTO BOWING CLUSTERS OF STORMS
WITH A THREAT FOR ALL HAZARDS ACROSS OUR AREA. AT THIS POINT,
DO NOT THINK THIS SCENARIO IS PARTICULARLY LIKELY GIVEN TRENDS
IN WESTERN MINNESOTA (A SEVERE THUNDERSTORM WARNING WAS
RECENTLY ISSUED FOR THE CLUSTER CONFIRMING IT IS INTENSIFYING).
WHEN TAKEN ALTOGETHER, WILL CAUTIOUSLY ADVERTISE A LARGELY DRY
DAY WITH HIGHS IN THE MID 80S. THEN, WILL FEATURE MID-RANGE
CHANCE (40-50%) POPS DURING THE OVERNIGHT HOURS FOR ISOLATED TO
SCATTERED STORMS. NEEDLESS TO SAY, WILL BE WATCHING UPSTREAM
TRENDS CLOSELY IN CASE THE SHIP NEEDS TO TURN TO FEATURE HIGHER
CHANCES FOR STORMS LATER TODAY.
TUESDAY ONWARD:
HRRR-SMOKE OUTPUT SHOWS ANOTHER PLUME OF WILDFIRE SMOKE MOVING
INTO THE REGION TUESDAY MORNING BEHIND THE FRONTAL PASSAGE, BUT
LARGELY ALOFT WHICH SHOULD LEAD TO AN OPAQUE LOOK TO THE SKY. IT
WILL BE AN INITIALLY WARM START TO THE DAY AS STRAGGLING DEW
POINTS IN THE UPPER 60S TO LOWER 70S ACT AS A SPRINGBOARD FOR
TEMPERATURES TO RISE TOWARD THE LOWER 80S BY LATE MORNING. 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. NORTHWESTERLY WINDS WILL
INCREASE AND GUST IN THE 20 TO 25 MPH RANGE DURING THE
AFTERNOON, CAUSING TEMPERATURES TO EFFECTIVELY STAGNATE.
TUESDAY NIGHT, A SEASONABLY STRONG SURFACE HIGH PRESSURE SYSTEM
WILL BUILD INTO THE NORTHERN UNITED STATES. WITH OUR AREA
REMAINING ON THE CYCLONIC SHEAR SIDE OF UPPER-LEVEL CYCLONIC
FLOW, CAN ENVISION POCKETS OF LOW- AND MID-LEVEL CLOUDS
MEANDERING THROUGH THE AREA. IF CLOUDS WERE TO CLEAR,
TEMPERATURES OVERNIGHT COULD DROP FAIRLY QUICKLY WITH MORE
AGGRESSIVE GUIDANCE SUGGESTING LOWS NORTH OF I-88 MAKING A RUN
FOR THE UPPER 40S. WILL GO WITH A MORE CONSERVATIVE FORECAST FOR
NOW AND FEATURE LOWS GENERALLY IN THE MID 50S NORTH TO LOWER
60S SOUTH.
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. AM NOTING A MUTED
SIGNAL FOR A CONVECTIVE EVENT SOMETIME IN THE JULY 27-29
TIMEFRAME IN THE GENERAL REGION, WHICH WOULD POSE THE NEXT
CHANCE OF MEANINGFUL RAINFALL.
BORCHARDT
AVIATION /06Z TAFS THROUGH 12Z TUESDAY/
ISSUED AT 1245 AM CDT MON JUL 20 2026
KEY MESSAGES FOR THE 06Z TAF PERIOD:
* 4-6SM VSBYS OVERNIGHT DUE TO WILDFIRE SMOKE
* LOW CONFIDENCE POTENTIAL FOR THUNDERSTORMS MONDAY, ESPECIALLY
DURING THE EVENING AND EARLY OVERNIGHT
MVFR TO LOW VFR VSBYS ARE FOUND AROUND THE AREA DUE TO WILDFIRE
SMOKE. EXACT TRENDS ARE NOT CLEAR AND IN THE TAFS, VSBYS OUT
THE GATE WERE LARGELY BASED ON OBS. HOWEVER, GRADUAL
IMPROVEMENTS ARE EXPECTED TOWARD DAWN WITH SOLIDLY VFR
ANTICIPATED FOR THE DAYTIME.
MUCH UNCERTAINTY REMAINS REGARDING THUNDERSTORM TRENDS FOR
MONDAY. A DECAYING CLUSTER IS EXPECTED TO DIVE SOUTHWARD THROUGH
WI THIS AFTERNOON. THIS MAY HOLD TOGETHER LONG ENOUGH TO BRING
A FEW SHOWERS AND EMBEDDED THUNDERSTORMS TO THE TERMINALS AS
EARLY AS MID-AFTERNOON, BUT BEST GUESS IS THAT THE AREA REMAINS
LARGELY DRY THROUGH THE AFTERNOON. RFD HAS THE SEEMINGLY
GREATEST CHANCE AT SEEING ANY PRECIP DURING THE AFTERNOON HOURS.
AT THIS TIME, CHANCES SEEMED TOO LOW TO WARRANT INCLUDING IN
THE TAFS, BUT LOOK FOR A POSSIBLE MENTION IN FUTURE ITERATIONS,
PARTICULARLY AT RFD.
CHANCES INCREASE FOR THE EVENING AND EARLY OVERNIGHT, ALTHOUGH
COVERAGE IS AGAIN UNCERTAIN AND MAY REMAIN LARGELY WEST OF THE
TERMINALS. HOWEVER, SHOULD THUNDERSTORMS MOVE OVER, THEY COULD
OFFER PERIODS OF STRONG WINDS, VERY HEAVY RAIN, AND LOWERED
VSBYS. WINDOW OF GREATEST OPPORTUNITY IS MID-EVENING THROUGH THE
MIDDLE OF THE OVERNIGHT, BUT A LARGE MAJORITY OF THAT TIMEFRAME
WILL BE DRY AND VFR.
DOOM
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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