916
FXUS63 KLOT 201751
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1251 PM 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.
UPDATE
ISSUED AT 1115 AM CDT MON JUL 20 2026
SMALL MCS OVER CONTINUES TO TRACK SOUTHWARD ACROSS EASTERN IA
AND FAR NORTHWEST IL LATE THIS MORNING, STRADDLING A SHARP
WEST-EAST INSTABILITY GRADIENT. THE THUNDERSTORM ACTIVITY HAS
BEEN CONFINED TO THE WESTERN FLANKS OF THE MCS CLOSER TO THE
RESERVOIR OF INSTABILITY. CONVECTION HAS LARGELY MAINTAINED ITS
INTENSITY THIS MORNING, DESPITE THE WEAKENING LOW LEVEL JET.
AIR MASS TO ITS SOUTH IS DESTABILIZING AND GIVEN THE SUFFICIENT
SHEAR AND THE PRESENCE OF A MODEST COLD POOL, SEEMS PLAUSIBLE
THAT THIS MCS COULD PERSIST FOR AT LEAST A COUPLE/FEW MORE
HOURS.
SOME OF THE STRATIFORM RAIN ON THE EASTERN SIDE OF THE MCS IS
LIKELY TO BRUSH AREAS NEAR/WEST OF I-39 WITH THICK CIRRUS
BLOWOFF RESULTING IN SEVERAL HOURS OF OVERCAST SKIES FOR AREAS
FURTHER EAST. GIVEN THE RAIN WEST AND CLOUD COVER EAST, OPTED TO
SHAVE A COUPLE DEGREES OFF OF FORECAST HIGH TEMPS FOR TODAY.
WITH THE INSTABILITY AXIS STILL WEST OF THE MISSISSIPPI RIVER,
THE THREAT OF ANY THUNDER IN OUR CWA PRIOR TO THIS EVENING IS
VERY, VERY LOW, SO REMOVED THUNDER FROM THIS AFTERNOON'S
FORECAST.
THE COLD POOL ISN'T PARTICULARLY STRONG AND ITS FOOTPRINT IS
FAIRLY SMALL, SO IT WILL CERTAINLY DELAY DESTABILIZATION, BUT
PROBABLY NOT COMPLETELY PREVENT IT. AXIS OF 70F+ DEWPOINTS
QUICKLY SPREADING NORTHEAST AND EAST AHEAD OF THE APPROACHING
FRONT WITH JUST A SMALL CARVE OUT OF COOLER/STABLE AIR NEAR AND
IN THE IMMEDIATE WAKE OF THE MCS. BY THE TIME THE PRE-FRONTAL
AXIS OF INSTABILITY FLOPS EAST/SOUTHEAST INTO OUR CWA THIS
EVENING, ANTICIPATE SOME MODEST CONVECTIVE INHIBITION FOR
BOUNDARY LAYER BASED PARCELS, HOWEVER, MOST MODELS SUPPORT AN
AXIS OF 2000+ J/KG OF MUCAPE MOVING INTO THE AREA.
IT SEEMS REASONABLE THAT INITIALLY SURFACE BASED SEVERE
CONVECTION THAT DEVELOPS ALONG THE BOUNDARY TO OUR NORTHWEST
ACROSS WESTERN WI INTO NORTHERN IA, MAY PERSIST AND MOVE
SOUTHEAST INTO NORTHERN IL LATER THIS EVENING, WHILE PROBABLY
BECOMING ROOTED ABOVE THE BOUNDARY LAYER. STRENGTHENING SYNOPTIC
ASCENT IN ADVANCE OF THE STRONG SHORTWAVE TROUGH AND ASSOCIATED
WITH A STRONG 120KT UPPER LEVEL JET STREAK THAT IS PROGGED TO
NOSE INTO THE WESTERN GREAT LAKES THIS EVENING SEEMS LIKE IT
COULD SUPPORT CONVECTION PERSISTING LATE INTO THE EVENING, EVEN
AS IT BECOMES ROOTED ABOVE THE BOUNDARY LAYER. GIVEN THE
MAGNITUDE OF SHEAR AND INSTABILITY, SEEMS AS THOUGH THERE WILL
BE SOME SEVERE THREAT WITH THIS ACTIVITY, POTENTIALLY LATE INTO
THE EVENING.
WHILE THERE REMAINS SOME SPREAD IN THE OUTCOMES AMONG AVAILABLE
CAM GUIDANCE, THERE IS MORE OF A SIGNAL FOR CONVECTION IN OUR
CWA LATER THIS EVENING WITH THE MORNING'S RUNS. STILL UNCLEAR
HOW WIDESPREAD THE CONVECTION AND SUBSEQUENT SEVERE THREAT WILL
BE, BUT SOME THREAT CERTAINLY STILL EXISTS TONIGHT. LOCALLY
DAMAGING WINDS AND PERHAPS SOME LARGE HAIL APPEAR TO BE THE MAIN
THREATS. CONVECTION MAY BE PROGRESSIVE ENOUGH TO PREVENT A
SIGNIFICANT OR WIDESPREAD FLASH FLOOD THREAT, BUT GIVEN THE HIGH
PWATS, STORMS WILL BE CAPABLE OF PRODUCING TORRENTIAL DOWNPOURS,
SO EVEN A BIT OF TRAINING COULD LEAD TO SOME LOCALIZED FLASH
FLOODING.
- IZZI
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 /18Z TAFS THROUGH 00Z WEDNESDAY/
ISSUED AT 1241 PM CDT MON JUL 20 2026
KEY MESSAGES FOR THE 18Z TAF PERIOD:
* 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 MOST
TERMINALS THIS EVENING, THOUGH WE ONLY HAVE MEDIUM CONFIDENCE IN
TIMING. CURRENT TAFS HAVE SHIFTED FROM PROB30S TO TEMPOS AND WE
HAVE PEGGED 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 TEMPO 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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