484
FXUS63 KLOT 090923
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
423 AM CDT SUN AUG 9 2026
KEY MESSAGES
- TWO WINDOWS FOR STORMS EXIST TODAY: ONE FROM AROUND MIDDAY
THROUGH THIS AFTERNOON, AND THE OTHER FROM THE LATE AFTERNOON
THROUGH TONIGHT. THE EXACT COVERAGE OF STORMS WITH BOTH ROUNDS
REMAINS SOMEWHAT UNCERTAIN.
- ANY STORMS IN OUR AREA TODAY WILL HAVE THE POTENTIAL TO BE
SEVERE. THERE IS ALSO A POTENTIAL FOR FLASH FLOODING,
PARTICULARLY WITH THE SECOND ROUND OF STORMS.
- ADDITIONAL PERIODS OF STORMS ARE EXPECTED MONDAY THROUGH MID-
WEEK. SOME OF THESE STORMS COULD BE SEVERE, ESPECIALLY LATE
MONDAY AFTERNOON OR MONDAY NIGHT.
DISCUSSION
ISSUED AT 423 AM CDT SUN AUG 9 2026
A PROLONGED, CONVECTIVELY-ACTIVE PERIOD IS EXPECTED ACROSS THE
MIDWEST THROUGH MUCH OF THIS WEEK AS A MUGGY AND UNSTABLE AIR
MASS STUBBORNLY HOVERS OVER THE REGION OVER THE NEXT SEVERAL
DAYS. THAT SAID, CONFIDENCE IN FORECAST SPECIFICS REGARDING THE
THUNDERSTORM POTENTIAL FOR ANY GIVEN DAY DURING THIS PERIOD IS
INHERENTLY LOW GIVEN THE NATURE OF THIS SUMMERTIME AIR MASS, THE
INVOLVEMENT OF SUBTLE FORCING MECHANISMS, AND THE INFLUENCE OF
ONE CONVECTIVE CYCLE ON THE NEXT AND THE SUBSEQUENT DOMINO
EFFECTS THAT FOLLOW.
FIRST THING'S FIRST, THOUGH. CLEAR SKIES AND CALM/LIGHT WINDS
HAVE ALLOW FOR SOME FOG DEVELOP IN OUR AREA EARLY THIS MORNING,
MAINLY FOCUSED OUTSIDE OF THE CHICAGO AND ROCKFORD METRO AREA.
THUS FAR, IT APPEARS THAT ANY DENSER FOG HAS REMAINED PATCHY
BASED ON AREA WEBCAMS, BUT WE'LL CONTINUE TO MONITOR THE
POTENTIAL NEED FOR A TARGETED DENSE FOG ADVISORY AS THE MORNING
GOES ALONG.
ANYWAYS, CIRCLING BACK TO TODAY'S THUNDERSTORM POTENTIAL...
THERE STILL APPEAR TO BE TWO POTENTIAL WINDOWS FOR THUNDERSTORMS
IN OUR AREA TODAY. THE FIRST WINDOW WILL BE FROM AROUND MIDDAY
THROUGH THIS AFTERNOON AND WILL BE TIED TO THE CONVECTION THAT
IS ONGOING TO OUR WEST AT THIS EARLY HOUR IN IOWA AND EASTERN
SOUTH DAKOTA. THERE WAS CONCERN EARLIER THAT THE STORMS EASTERN
SOUTH DAKOTA COULD GROW UPSCALE INTO A MATURE, WELL-ORGANIZED
MCS THAT WOULD PLOW THROUGH OUR AREA LATER TODAY. WHILE SUCH A
SCENARIO ISN'T QUITE OUT OF THE EQUATION JUST YET, THE
EXTENSIVE, MESSY NATURE OF THE CONVECTION ONGOING ACROSS IOWA
DOES LEND DOUBT TO THAT SCENARIO BEING REALIZED. HOWEVER, SOME
LOOSELY-ORGANIZED CONGLOMERATE OF THE ONGOING IOWA AND SOUTH
DAKOTA STORMS AND/OR ANY NEW CONVECTION THAT SPROUTS BETWEEN OR
JUST NORTH OF THEM WILL STILL LIKELY DRIFT TOWARDS OUR AREA,
WITH THE ASSOCIATED OUTFLOW LIKELY TO PRESS EASTWARD INTO
FORECAST AREA LATER TODAY. BY THE TIME THIS OUTFLOW ARRIVES HERE
AROUND THE EARLY AFTERNOON, CONVECTIVE INHIBITION TO 2000-3000
J/KG OF MLCAPE HERE WILL HAVE LARGELY BEEN ERODED, AND NEW
UPDRAFTS WILL BE ABLE TO GO UP ALONG IT UNINHIBITED. HOWEVER,
QUESTIONS STILL REMAIN REGARDING THE STRENGTH OF THE ATTENDANT
COLD POOL AND THE DEGREE OF CONVERGENCE ALONG THIS BOUNDARY, AS
THE RELATIVE LACK OF SYNOPTIC-SCALE FORCING SUPPORT THIS
AFTERNOON WILL NECESSITATE STRONGER LIFT AT THE SURFACE FOR
STORMS TO DEVELOP AND HARNESS THE FULL POTENTIAL OF THE
THERMODYNAMIC ENVIRONMENT IN PLACE. THE STORMS THAT DO END UP
PULSING HIGH ENOUGH THIS AFTERNOON WILL BE CAPABLE OF PRODUCING
LOCALIZED DAMAGING WINDS AND POSSIBLY A FEW INSTANCES OF 1+"
DIAMETER HAIL.
THE SECOND WINDOW FOR STORMS IN OUR AREA IS EXPECTED TO COME
LATE THIS AFTERNOON INTO TONIGHT AS A LOW-LEVEL JET RAMPS UP AND
A SHORTWAVE TROUGH PASSES BY TO OUR NORTH. NOTE THAT IT IS
POSSIBLE THAT THERE MAY NOT BE MUCH OF A BREAK BETWEEN THESE TWO
POTENTIAL STORM WINDOWS. THE OUTFLOW BOUNDARY FROM THE EARLIER
CONVECTION WILL LIKELY BE LAID OUT SOMEWHERE IN OR VERY NEAR OUR
FORECAST AREA BY THIS EVENING, AND INCREASING ISENTROPIC ASCENT
ATOP THIS BOUNDARY WILL LIKELY GENERATE NEW CONVECTION ALONG IT
DURING THIS SECOND THUNDERSTORM WINDOW AS LONG AS THE STORMS
FROM EARLIER IN THE DAY DON'T END UP BEING OVERLY ROBUST AND
EXTENSIVE IN COVERAGE. HOW MUCH INSTABILITY WILL BE AVAILABLE
FOR THESE LATER STORMS TO WORK WITH WILL DEPEND ON HOW STRONG
AND WIDESPREAD THE EARLIER STORMS WERE, BUT DEEP-LAYER SHEAR
LOOKS TO BE SUFFICIENTLY STRONG TO SUPPORT ROTATING UPDRAFTS
WITH ANY MATURE CONVECTION DURING THIS SECOND THUNDERSTORM
WINDOW. DAMAGING WINDS AND HAIL WILL THUS BE POSSIBLE WITH
THESE STORMS, AND A THREAT FOR TORNADOES ALSO COULDN'T BE RULED
OUT WITH ANY SUPERCELLS THAT DEVELOP NEAR THE OUTFLOW BOUNDARY
IF THE BOUNDARY LAYER ON THE COOL SIDE OF THE OUTFLOW BOUNDARY
MANAGES TO RE-DESTABILIZE IN TIME BEFORE NOCTURNAL
STABILIZATION STARTS TO SET IN. IF THE OUTFLOW BOUNDARY WERE TO
GET LAID OUT IN A NORTHWEST-SOUTHEAST ORIENTATION LIKE SOME
CAMS HAVE BEEN SHOWING, THEN THAT WOULD INCREASE THE LIKELIHOOD
OF STORMS TRAINING OVER THE SAME AREA. WITH THE MUGGY AIR MASS
BEING CONDUCIVE TO TORRENTIAL RAINFALL RATES, THIS WOULD RAISE
CONCERN FOR THE THREAT FOR FLASH FLOODING TONIGHT.
REGARDLESS OF HOW THE STORMS IN OUR AREA PLAY OUT TODAY AND
TONIGHT, TODAY'S MOIST AND UNSTABLE AIR MASS WILL NOT BUDGE MUCH
GOING INTO TOMORROW, SO CONDITIONS ON MONDAY WILL REMAIN
FAVORABLE FOR ADDITIONAL THUNDERSTORMS TO DEVELOP IN THE REGION
ONCE AGAIN. CONFIDENCE IN FORECAST SPECIFICS FOR MONDAY REMAINS
RELATIVELY LOW OWING TO THERE BEING SOME DEPENDENCE ON TONIGHT'S
CONVECTIVE FOOTPRINT, BUT BROADLY SPEAKING, MOST OF THE LATEST
CAM GUIDANCE KEEPS OUR AREA DEVOID OF THUNDERSTORM ACTIVITY
DURING THE DAYTIME HOURS TOMORROW DUE TO A COMBINATION OF
CAPPING AND A LACK OF LARGE-SCALE FORCING MECHANISMS OUTSIDE OF
A WEST-EAST-ORIENTED CORRIDOR OF FAIRLY WEAK MID-LEVEL WARM AIR
ADVECTION/ISENTROPIC ASCENT. THIS ASCENT MAY ACTUALLY HINDER
THE POTENTIAL FOR THUNDERSTORMS DURING THE DAYTIME MORE THAN IT
WILL HELP AS IT WILL LIKELY LEAD TO EXTENSIVE MID- TO HIGH-LEVEL
CLOUD COVER (AND POSSIBLY EVEN SOME HIGH-BASED SHOWERS) THAT
WILL FILTER SOLAR INSOLATION TO SOME DEGREE WHERE IT IS PRESENT
AND THUS DELAY DESTABILIZATION EFFORTS.
WHILE A STORMS COULDN'T BE RULED OUT TO DEVELOP EARLIER IN THE
DAY, THE MOST LIKELY SCENARIO AT THIS TIME FOR TOMORROW IS THAT
CONVECTIVE INITIATION HOLDS OFF UNTIL THE LATE AFTERNOON OR
EVENING, WHEN THE LOW-LEVEL JET TO OUR SOUTHWEST GETS GOING
AGAIN AND A SUBTLE MID-LEVEL DISTURBANCE IS PROGGED TO ARRIVE
FROM THE WEST. EXACTLY WHERE STORMS WILL INITIATE IS NOT YET
CLEAR AT THIS TIME (AND IT'S NOT YET A LOCK THAT OUR CWA WILL
SEE STORMS TOMORROW), BUT IT'S LIKELY THAT THEIR POINT OF
ORIGIN WILL BE SOMEWHERE ALONG THE AFOREMENTIONED BOUNDARY.
WHEREVER STORMS DO DEVELOP, STRONG TO LOCALLY EXTREME
INSTABILITY WILL BE SUPPORTIVE OF EXPLOSIVE UPDRAFTS, WHILE
LARGELY UNIDIRECTIONAL DEEP-LAYER SHEAR WILL BE ROBUST ENOUGH TO
PROMOTE SOME LEVEL OF THUNDERSTORM ORGANIZATION, INCLUDING
UPDRAFT ROTATION AND/OR BOWING SEGMENTS.
OGOREK
TUESDAY THROUGH FRIDAY:
THE NORTHWEST FLOW PATTERN ALOFT IS FORECAST TO REMAIN IN PLACE
THROUGH MUCH OF THE UPCOMING WEEK, WHICH WILL CONTINUE TO
SUPPORT PERIODS OF SHOWERS AND THUNDERSTORMS THROUGH AT LEAST
WEDNESDAY NIGHT. AS MENTIONED IN PREVIOUS DISCUSSIONS, THERE IS
THE CHANCE THAT AS REPEATED ROUNDS OF STORMS OCCUR FOR THE
EFFECTIVE FRONTAL ZONE TO SHIFT SOUTH OF NORTHERN IL AND
NORTHWEST IN BUT CONFIDENCE ON WHEN OR IF THIS ACTUALLY HAPPENS
REMAINS LOW. THEREFORE, OUR FORECAST WILL CONTINUE TO ADVERTISE
SHOWER AND THUNDERSTORM CHANCES THROUGH AT LEAST THE MIDDLE OF
NEXT WEEK. OUTSIDE OF THE RAIN, EXPECT SEASONABLE TEMPERATURES
TO PREVAIL WITH DAILY HIGHS IN THE 80S AND OVERNIGHT LOWS IN THE
60S.
YACK
AVIATION /06Z TAFS THROUGH 12Z MONDAY/
ISSUED AT 1251 AM CDT SUN AUG 9 2026
AVIATION FORECAST CONCERNS FOR THE 06Z TAFS:
- PATCHY FOG/LOW STRATUS POSSIBLE THROUGH DAYBREAK.
- AT LEAST TWO ROUNDS OF TSRA POSSIBLE, SOME STRONG TO SEVERE,
FROM LATE THIS MORNING THROUGH TONIGHT. CONFIDENCE IN DETAILS
BELOW DO DECREASE BEYOND THIS AFTERNOON.
LATE EVENING SURFACE ANALYSIS DEPICTS LOW PRESSURE IN THE
VICINITY OF NORTHEAST CO/NE PANHANDLE REGION, WITH A WARM FRONT
EXTENDING EAST TO NEAR THE IA/MO BORDER AND INTO DOWNSTATE
IL/IN. THIS WARM FRONT IS FORECAST TO LIFT NORTH ACROSS IA AND
INTO NORTHERN IL/IN LATER TODAY, AS LOW-LEVEL SOUTHERLY FLOW
STRENGTHENS IN ASSOCIATION WITH AN APPROACHING MID-LEVEL
DISTURBANCE. THIS WILL BRING A WARM, MOIST AND UNSTABLE AIR MASS
ACROSS THE TERMINALS, SETTING THE STAGE FOR AT LEAST A COUPLE OF
ROUNDS OF STRONG THUNDERSTORMS FROM LATER THIS MORNING THROUGH
TONIGHT.
CURRENTLY, A SMALL CLUSTER OF THUNDERSTORMS HAS DEVELOPED ALONG
THE ND/SD BORDER AHEAD OF THE AFOREMENTIONED MID-LEVEL WAVE.
THIS CLUSTER IS EXPECTED TO TRACK SOUTHEAST INTO SOUTHERN MN BY
DAYBREAK, EVENTUALLY EXPANDING ON THE NOSE OF THE SOUTHWESTERLY
LOW-LEVEL JET INTO SOUTHERN WI/NORTHERN IL LATE THIS MORNING
INTO THIS AFTERNOON (BASICALLY SCENARIO 2 FROM OUR PREVIOUS 00Z
DISCUSSION). COVERAGE IS ANTICIPATED TO BE HIGH ENOUGH TO PUSH
AN OUTFLOW BOUNDARY THROUGH THE TERMINALS THIS AFTERNOON
(POTENTIALLY WITH GUSTY WINDS ON THE LEADING EDGE OF THE
STORMS), BUT THIS SHOULD BE ABLE TO RETURN NORTH (PERHAPS AS A
COMPOSITE WITH THE SYNOPTIC WARM FRONTAL BOUNDARY) LATER IN THE
DAY/EVENING. THIS BOUNDARY WOULD THEN LIKELY SERVE AS THE FOCUS
FOR ADDITIONAL THUNDERSTORM REDEVELOPMENT AS THE LOW-LEVEL JET
IMPINGES ON THE OUTFLOW/WARM FRONTAL BOUNDARY OVER THE AREA THIS
EVENING, ESPECIALLY ACROSS THE CHICAGO TERMINALS. THESE STORMS
COULD POTENTIALLY LINGER OVER/NEAR THE TERMINALS IN SOME FASHION
PAST MIDNIGHT BEFORE EVENTUALLY SLIDING OFF TO THE
SOUTH/SOUTHEAST AS THE COLD POOL EXPANDS AND THE LOW-LEVEL JET
VEERS MORE WESTERLY. IT'S IMPORTANT TO NOTE THAT CONFIDENCE IN
THE DETAILS IN THIS SCENARIO DECREASE CONSIDERABLY BEYOND THE
AFTERNOON HOURS.
PROVIDED STORMS DO SHIFT SOUTH/SOUTHEAST OF THE TERMINALS LATE
TONIGHT, A PERIOD OF LIGHT/VARIABLE WINDS APPEARS LIKELY ALONG
WITH SOME POTENTIAL FOR MVFR CONDITIONS TO LINGER THROUGH
DAYBREAK MONDAY.
RATZER
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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