660
FXUS63 KLOT 091737
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1237 PM CDT TUE JUN 9 2026
KEY MESSAGES
- TODAY THROUGH THURSDAY WILL BE HOT AND HUMID WITH PEAK HEAT
INDICES IN THE 90S TO LOCALLY 100. THE HOTTEST CONDITIONS ARE
FAVORED ON WEDNESDAY INCLUDING UP TO THE LAKE MICHIGAN
SHORELINE.
- OUTSIDE ISOLATED SHOWERS THIS AFTERNOON, SEVERAL ROUNDS OF
SEVERE THUNDERSTORMS MAY OCCUR IN THE GENERAL REGION TUESDAY
NIGHT THROUGH THURSDAY. THURSDAY CONTINUES TO LOOK LIKE THE
MOST CONCERNING DAY FOR SEVERE WEATHER LOCALLY.
- FRIDAY AND SATURDAY WILL BE DRY AND NOTICEABLY COOLER. A
GENERALLY COOL AND AT TIMES WET PATTERN WILL DEVELOP NEXT
WEEK.
DISCUSSION
ISSUED AT 312 AM CDT TUE JUN 9 2026
NEAR TERM / TODAY:
THE CENTER OF THE UPPER-LEVEL WAVE RESPONSIBLE FOR WAVES OF
SHOWERS AND THUNDERSTORMS THE PAST FEW DAYS IS NOW DRIFTING
NORTHEASTWARD AWAY FROM OUR AREA. SUBTLE VORTICITY MAXIMA
ROTATING AROUND THE PERIMETER OF THE UPPER-LEVEL LOW INTERACTING
WITH THE VERY MOIST AIRMASS (PWATS NEAR 2" AND FREEZING LEVELS
ABOVE 15KFT, PER THE 00Z DVN RAOB) CONTINUE TO SUPPORT REGIONS
OF ISOLATED TO SCATTERED SHOWERS IN THE GENERAL REGION. MOSTLY
CLOUDY SKIES ENVELOP MUCH OF THE LOCAL AREA EARLY THIS MORNING,
WHICH IS LEADING TO TEMPERATURES HOLDING STEADY IN THE LOWER
70S.
AFTER DAYBREAK, THE STRONG SUN ANGLE WILL FACILITATE EFFICIENT
MIXING THROUGH THE CLOUD LAYER LEADING TO A TRANSITION FROM
MOSTLY TO PARTLY CLOUDY SKIES. GIVEN THE WARM START TO THE DAY,
TEMPERATURES WILL ROCKET INTO THE MID TO UPPER 80S WITH PERHAPS
A FEW LOCAL 90 DEGREE READINGS NOT OUT OF QUESTION. WHILE MID-
LEVEL HEIGHT TENDENCIES WILL BE NEUTRAL (INDICATIVE OF LITTLE TO
NO LARGE-SCALE VERTICAL MOTION) THROUGH THE DAY, THE WARM AND
MOIST BOUNDARY LAYER WILL NEVERTHELESS SUPPORT POTENTIAL
ISOLATED SHOWER DEVELOPMENT (PERHAPS AN AFTERNOON STORM)
THROUGHOUT THE DAY.
TONIGHT:
OVER THE NEXT 24 HOURS, AGGREGATE TROUGHING ACROSS THE WESTERN
UNITED STATES WILL SHIFT EASTWARD ESTABLISHING EXPANSIVE
SOUTHWESTERLY LOW- TO UPPER-LEVEL FLOW FROM THE CENTRAL PLAINS
TOWARD THE UPPER MISSISSIPPI RIVER VALLEY. SUCH BROAD
SOUTHWESTERLY FLOW WILL ADVECT AN EXPANSIVE EML PLUME EASTWARD
INTO THE MIDDLE MISSISSIPPI RIVER VALLEY ATOP A SIMILARLY-
EXPANSIVE REGION OF LOW-LEVEL MOISTURE ACROSS THE CENTRAL
UNITED STATES. THE NET RESULT WILL BE THE DEVELOPMENT OF A
LARGE RESERVOIR OF INSTABILITY AHEAD OF THE AGGREGATE UPPER-
LEVEL TROUGHING. OVER THE NEXT FEW DAYS, EMBEDDED SHORTWAVES
MOVING AROUND THE PERIMETER OF THE BROADER LONG-WAVE TROUGHING
INTERACTING WITH THE RESERVOIR OF INSTABILITY WILL SUPPORT
PERIODIC EPISODES OF SEVERE THUNDERSTORMS ACROSS THE MIDWEST.
MEANWHILE, OUTSIDE THE CONVECTIVE EPISODES, THE COMBINATION OF
SEASONABLY WARM TEMPERATURES AND THE RESIDENT HUMID AIRMASS WILL
LEAD TO HOT CONDITIONS.
TONIGHT, THE EASTERN EDGE OF THE EML PLUME WILL APPROACH THE
LOWER GREAT LAKES. BEING ON THE NORTHEASTERN EDGE OF THE EML
PLUME IS OFTEN FRAUGHT WITH DANGER AS ANY SUBTLE WAVE RIDING
ATOP THE ELEVATED FRONTAL BOUNDARY OR UNEXPECTED MOISTENING AT
THE BASE OF THE EML CAN SUPPORT NOCTURNAL SEVERE THUNDERSTORMS.
GUIDANCE REMAINS MIXED AS TO WHETHER ANY SUCH WAVE OR ENOUGH
MID-LEVEL MOISTENING WILL BE ABLE TO ACTIVATE THE NORTHEASTWARD-
MOVING EML PLUME, WITH PERHAPS A BETTER SIGNAL NORTHWEST OF OUR
AREA. NEVERTHELESS, MUCAPE IN EXCESS OF 3000 J/KG, CONVECTIVE-
LAYER SHEAR IN EXCESS OF 30KT, AND PWATS IN EXCESS OF 2 INCHES
WOULD SUPPORT THREATS FOR DAMAGING WINDS, DAMAGING HAIL, AND
FLASH FLOODING SHOULD CONVECTION DEVELOP IN OUR AREA TONIGHT.
ALL THINGS CONSIDERED, WILL MAINTAIN LOW-END CHANCE (30 TO 40%)
POPS ACROSS THE AREA TONIGHT. THE SPC LEVEL 1 THREAT AREA
REMAINS APPROPRIATE.
OUTSIDE THE THREAT FOR THUNDERSTORMS TONIGHT, THE HIGH-
MOISTURE AIRMASS WILL MAINTAIN SEASONABLY WARM TEMPERATURES WITH
OVERNIGHT LOWS GENERALLY IN THE 70S.
WEDNESDAY:
ANY THUNDERSTORMS THAT DEVELOP OVERNIGHT SHOULD SHIFT EASTWARD
BY OR JUST AFTER DAYBREAK AS CAPPING STRENGTHENS BENEATH THE
NORTHEASTWARD-MOVING EML PLUME. THE WARM START TO THE DAY WILL
ACT AS A LAUNCH PAD FOR TEMPERATURES TO SPRING INTO THE UPPER
80S TO LOWER 90S ACROSS THE REGION BY EARLY AFTERNOON. HEAT
INDEX VALUES MAY APPROACH OR LOCALLY EXCEED 100 DEGREES WHERE
TEMPERATURES AND DEW POINTS ARE HIGHEST. WHILE LOCAL HEAT
ADVISORY CRITERIA IS 105F, CONDITIONS ON WEDNESDAY WILL BE THE
WARMEST WE HAVE EXPERIENCED SO FAR THIS YEAR SO HEAT SAFETY TIPS
SHOULD BE PRACTICED.
ATTENTION THEN TURNS TO THE NEXT THREAT WINDOW FOR SEVERE
WEATHER. AT THIS POINT, AM SEEING TWO POTENTIAL WINDOWS FOR
SEVERE STORMS DURING THE DAY: THE FIRST IN THE AFTERNOON (2 TO
6 PM) AND ANOTHER IN THE EVENING (6 PM TO 12 AM).
FOR THE FIRST TIME WINDOW, A SUBTLE SIGNAL EXISTS IN BOTH CAM
AND GLOBAL GUIDANCE FOR A CONVECTIVELY-INVIGORATED SHORTWAVE OR
MCV TO DEVELOP IN THE CENTRAL PLAINS TONIGHT AND THEN LIFT
NORTHEASTWARD TOWARD THE EASTERN IOWA/SOUTHERN
WISCONSIN/NORTHERN ILLINOIS REGION DURING THE AFTERNOON HOURS.
NATURALLY, CONFIDENCE IN WHERE THE TRACK OF A WAVE ORIGINATING
FROM PRIOR THUNDERSTORMS IN THE PLAINS (LET ALONE WHETHER IT
WILL ACTUALLY DEVELOP) IS NATURALLY QUITE LOW. WITH THAT SAID,
THE ENVIRONMENT AHEAD OF ANY EARLY-DAY WAVE WILL BE MORE THAN
SUPPORTIVE OF SEVERE THUNDERSTORMS WITH MUCAPE > 5000 J/KG AND
EFFECTIVE SHEAR (ITSELF DRIVEN BY THE CONVECTIVE WAVE) OF 25 TO
30 KT. INITIAL SUPERCELLULAR DEVELOPMENT WOULD PROBABLY BE PRONE
TO GROWING UPSCALE INTO A FOWARD-PROPEGATING MCS WITH A THREAT
FOR DAMAGING WINDS. AT THIS POINT, WHAT SUBTLE SIGNAL THERE IS
FOR A LEAD WAVE FAVORS AREAS GENERALLY ALONG AND NORTH OF
INTERSTATE 88 AS BEING IN THE THREAT ZONE DURING THE FIRST TIME
WINDOW.
THE SECOND TIME WINDOW WILL BE DRIVEN BY A SYNOPTIC-SCALE
SHORTWAVE EMBEDDED IN THE AGGREGATE TROUGHING ALONG THE
US/CANADIAN BORDER. APPRECIABLE SYNOPTIC-SCALE ASCENT AHEAD OF
THE WAVE IN THE MIDWEST CHARACTERIZED BY 12-HOUR 500MB HEIGHT
FALLS ON THE ORDER OF 10M/HR WILL INDUCE THE DEVELOPMENT OF
THUNDERSTORMS ALONG A WARM FRONT STRETCHING ACROSS NORTHERN
WISCONSIN INTO CENTRAL MINNESOTA AND A SEPARATE REGION OF
THUNDERSTORMS ALONG A COLD FRONT STRETCHING INTO CENTRAL IOWA
DURING THE LATE AFTERNOON HOURS. CURRENT THINKING IS THAT
OBLIQUE ORIENTATIONS OF THE DEEP-LAYER SHEAR VECTOR TO THE COLD
FRONT WILL SUPPORT INITIAL SUPERCELLULAR DEVELOPMENT IN CENTRAL
IOWA IN THE LATE AFTERNOON BEFORE CONGLOMERATION INTO A SQUALL
LINE TOWARD THE MISSISSIPPI RIVER DURING THE EVENING HOURS
(MOVING INTO NORTHERN ILLINOIS AFTER 5 TO 6 PM).
WITH THE UPPER-LEVEL JET AND ASSOCIATED ACCESS TO DEEP-LAYER
SHEAR DISPLACED NORTHWEST OF OUR AREA, THE STRONGEST PORTION OF
ANY SQUALL LINE MAY TEND TO LIFT NORTHEASTWARD INTO WISCONSIN.
WITH THAT SAID, THE RESERVOIR OF INSTABILITY ACROSS OUR AREA AS
WELL AS INTENSIFYING LOW-LEVEL FLOW (925 TO 850MB FLOW NEAR
35-40KT) MAY MAINTAIN THE SOUTHEASTWARD SPILL OF AN OUTFLOW-
DOMINANT PORTION OF THE SQUALL LINE INTO NORTHERN ILLINOIS
THROUGH THE EVENING HOURS. WHILE LOCALLY DAMAGING WINDS WOULD BE
A THREAT, THE OBLIQUE ORIENTATION OF THE LOW-LEVEL JET TO THE
WEST-TO-EAST POSITIONING OF ANY OUTFLOW-DRIVEN PORTION OF THE
SQUALL LINE RAISES RED FLAGS FOR POTENTIAL TRAINING AND FLASH
FLOODING. ALSO, SHOULD CONVECTION OCCUR IN THE FIRST TIME WINDOW
AND LEAVE AN OUTFLOW BOUNDARY SOMEWHERE IN THE REGION TO
INTERSECT WITH THE SQUALL LINE DURING THE SECOND TIME WINDOW,
COULD EASILY ENVISION A CORRIDOR OF HEIGHTENED TORNADO
POTENTIAL SOMEWHERE IN THE REGION. OVERALL, CONFIDENCE IN THE
EVOLUTION OF CONVECTION ON WEDNESDAY IS LOW TO MEDIUM. THE SPC
LEVEL 2 TO 3 THREAT LEVEL ACROSS OUR AREA SEEMS APPROPRIATE,
ALBEIT WITH HIGHER CONFIDENCE IN IMPACTS TYPICAL OF LEVEL 3
AREAS OCCURRING PERHAPS IN IOWA OR WISCONSIN.
THURSDAY:
AT THIS POINT, THE EXPECTATION IS FOR THE COLD FRONT ASSOCIATED
WITH THE WEDNESDAY CONVECTIVE EPISODE(S) TO STALL SOMEWHERE IN
THE SOUTHERN IOWA/NORTHERN ILLINOIS VICINITY BY MID-THURSDAY
MORNING. AS A RESULT, DO EXPECT ANOTHER HOT AND HUMID DAY ACROSS
THE AREA (ESPECIALLY SOUTH OF I-80) WITH HEAT INDICES IN THE
UPPER 90S TO LOCALLY 100. WE CONTINUE TO SEE A SIGNAL IN VARIOUS
MODEL GUIDANCE THAT AN MCS MAY DEVELOP IN THE PLAINS WEDNESDAY
EVENING AND RACE TOWARD NORTHERN ILLINOIS OUR SOUTHERN WISCONSIN
DURING THE MORNING (OR EARLY AFTERNOON?) HOURS WITH A THREAT
FOR DAMAGING WINDS, THOUGH CONFIDENCE IN THIS SCENARIO IS
NATURALLY VERY LOW. SHOULD THAT MCS OCCUR, IT WOULD ALL BUT
CERTAINLY MODULATE THE POSITIONING OF THE FRONT LEADING TO A
BUST IN TEMPERATURES ACROSS PORTIONS OF THE AREA.
DURING THE AFTERNOON HOURS, THE DOMINANT UPPER-LEVEL SHORTWAVE
IN THE BROADER UPPER-LEVEL TROUGH IN THE NORTHERN US WILL EJECT
EASTWARD INTO THE GREAT LAKES AND SUPPORT THE DEVELOPMENT OF A
SURFACE LOW TRACKING NEAR THE MISSISSIPPI RIVER DURING THE
EVENING. CONCEPTUALLY, THE PATTERN MATCHES ANALOGS FOR
SIGNIFICANT SEVERE WEATHER EVENTS IN OUR AREA AS THE STRONGEST
UPPER-LEVEL FORCING, LOW- TO DEEP-LAYER SHEAR, AND INSTABILITY
WILL OVERLAP DIRECTLY ACROSS THE LOWER GREAT LAKES.
AT THIS POINT, IT IS TOUGH TO HAVE CONFIDENCE IN THE EXACTLY
EVOLUTION OF THUNDERSTORMS GIVEN WE ARE STILL MORE THAN 48 HOURS
OUT, ESPECIALLY CONSIDERING THERE COULD BE COMPLICATING
THUNDERSTORMS IN THE MORNING. WITH ALL OF THAT SAID, DO WANT TO
HIGHLIGHT THAT THERE IS A SCENARIO WHERE MORNING THUNDERSTORMS
REINFORCE A WEST-TO-EAST ORIENTATION OF THE WARM FRONT BY LATE
AFTERNOON SOMEWHERE IN OUR AREA. SUCH A FRONTAL ORIENTATION
WOULD PROVIDE PROLONGED ACCESS TO AN OVERLAP OF STRONG
INSTABILITY (MUCAPE >3000 J/KG) AND LOW-LEVEL SHEAR (0-3 KM
SHEAR OF 30-35 KT WITH >300 J/KG OF 0-3KM SRH) FOR EASTWARD-
MOVING STORMS. THE NET RESULT WOULD LIKELY BE THE DEVELOPMENT OF
FOCUSED ZONE OF INTENSE THUNDERSTORMS WITH A THREAT FOR ALL
HAZARDS (TORNADOES, DESTRUCTIVE WINDS, DAMAGING HAIL, AND FLASH
FLOODING) OUR AREA. EVEN IF THE FRONT IS NOT ORIENTED IN SUCH A
FASHION ON THURSDAY, AN ALL-HAZARD SEVERE THREAT COULD STILL
EMERGE AS THE UPPER-LEVEL WAVES MOVES OVERHEAD.
THE SPC LEVEL 3 OF 5 THREAT LEVEL FOR THURSDAY IS VERY
APPROPRIATE ACROSS OUR AREA GIVEN THE SYNOPTIC-SCALE SET-UP.
READERS ARE ADVISED TO KEEP CLOSE TABS ON THE FORECAST.
FRIDAY ONWARD:
A BREAK IN THE HOT AND STORMY PATTERN IS EXPECTED FRIDAY AND
SATURDAY AS A SURFACE HIGH PRESSURE SYSTEM WORKS THROUGH THE
REGION. HIGHS ON FRIDAY SHOULD TOP OFF IN THE UPPER 70S (LOCALLY
80), AND LOWS FRIDAY NIGHT SHOULD FALL INTO THE LOWER 60S.
ENSEMBLE GUIDANCE THAN DEPICTS THE DEVELOPMENT OF EXPANSIVE
TROUGHING ACROSS THE NORTHERN UNITED STATES NEXT WEEK. WHILE THE
MAIN RESERVOIR OF HOT AND HUMID AIR WOULD GET SHUNTED WELL
SOUTH OF OUR AREA, A PARADE OF SHORTWAVES MAY LEAD TO PERIODIC
OPPORTUNITIES FOR SHOWERS AND THUNDERSTORMS ACROSS OUR REGION
THROUGH NEXT WEEK.
BORCHARDT
AVIATION /18Z TAFS THROUGH 00Z THURSDAY/
ISSUED AT 1230 PM CDT TUE JUN 9 2026
KEY AVIATION MESSAGES FOR THE CURRENT TAF PERIOD:
- LINGERING MVFR CIGS THIS AFTERNOON
- LESS THAN 20 PERCENT CHANCE FOR SHOWERS THIS AFTERNOON, BEST
CHANCES AROUND AND SOUTH OF KGYY
- WINDS TURN TO THE NORTHEAST THIS EVENING BEHIND A LAKE BREEZE
- A CHANCE FOR SHOWERS AND STORMS WITH REDUCED CIGS AND VIS
AROUND DAYBREAK
- ANOTHER CHANCE FOR STORMS AREAWIDE TOMORROW AFTERNOON, SOME
MAY BE STRONG TO SEVERE
WINDS REMAIN OUT OF THE SOUTHWEST AROUND 10 KNOTS WITH
OCCASIONAL GUSTS UNDER 20 KNOTS. SCT/BKN CLOUDS ABOVE 2000 FEET
REMAIN OVER NORTHERN ILLINOIS AND NORTHWEST INDIANA. CLOUD COVER
SHOULD SCATTER OUT THIS AFTERNOON, BUT WITH LOWER CONFIDENCE IN
THE EXACT TIMING, IT WAS DECIDED TO MAINTAIN A TEMPO FOR MVFR
CIGS THROUGH 21Z. THERE IS A WEAK DISTURBANCE OVER WEST-CENTRAL
ILLINOIS THAT IS CLOSELY BEING MONITORED. AS IT MOVES
NORTHEASTWARD, THERE IS A CHANCE FOR SOME SHOWERS WITH IT, BUT
THE EXPECTATION IS FOR THESE TO REMAIN AROUND AND SOUTH OF
KGYY. SO WHILE THE TAFS FOR THE TERMINALS ARE DRY FOR THE
AFTERNOON, COVERAGE OF SHOWERS WILL BE MONITORED IN CASE A AMD
IS NEEDED.
AS A WEAK LATE BREEZE DEVELOPS LATER TODAY, WINDS ARE EXPECTED
TO SHIFT TO THE EAST AFTER 00Z. AS THE STRENGTH OF THE WINDS
DIMINISHES AFTER SUNSET, MODELS ARE SUGGESTING SOME FOG MAY
DEVELOP OVER LAKE MICHIGAN. SOME 6SM BR MIGHT BE POSSIBLE
OVERNIGHT, BUT IMPACTS SHOULD BE MINIMAL, ESPECIALLY WITH THE
CHANCES FOR SHOWERS AND STORMS.
TOWARD DAYBREAK, THE NEXT DISTURBANCE IS EXPECTED TO PASS OVER
NORTHERN ILLINOIS PROVIDING A 30 TO 40 PERCENT CHANCE FOR
SHOWERS AND STORMS. REDUCED VIS AND CIGS CAN BE EXPECTED WITH
THE STRONGEST EMBEDDED CELLS. WINDS WILL TURN TO THE SOUTHWEST
BEHIND THE RAINS TOMORROW MORNING WITH GUSTS 20 TO 25 KNOTS.
LASTLY, YET ANOTHER LINE OF SHOWERS AND STORMS IS EXPECTED
TOMORROW AFTERNOON. NAM/HRRR MODELS ARE SHOWING A MID AFTERNOON
ARRIVAL, WHEREAS RAP/HRDRPS SHOWS A MUCH LATER ARRIVAL (POSSIBLY
OUTSIDE THE CURRENT TAF WINDOW). WHILE THERE IS A LOT OF
UNCERTAINTY ON THE TIMING OF THE LINE, IT IS LOOKS LIKE THIS
LINE COULD HAVE STRONG TO POTENTIALLY SEVERE STORMS WITH IT.
DK
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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