307
FXUS63 KLOT 071055
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
555 AM CDT SUN JUN 7 2026
KEY MESSAGES
- SHOWERS AND STORMS ARE EXPECTED TODAY WITH THE HIGHEST
COVERAGE SOUTHWEST OF A LINE FROM ROCKFORD TO JOLIET TO
RENSSELAER, AND THEN AREAWIDE ON MONDAY.
- THE STRONGEST STORMS TODAY AND TOMORROW WILL BE CAPABLE OF
PRODUCING LOCALIZED FLASH FLOODING AND WIND DAMAGE.
- HEAT AND HUMIDITY WILL BUILD TUESDAY, WEDNESDAY, AND POSSIBLY
INTO THURSDAY WITH PEAK HEAT INDICES IN THE MID TO UPPER 90S.
- THERE IS A LOW (20%) CHANCE FOR THUNDERSTORMS TUESDAY AND
WEDNESDAY FOLLOWED BY A THREAT FOR SEVERE WEATHER ON THURSDAY.
DISCUSSION
ISSUED AT 248 AM CDT SUN JUN 7 2026
EARLY MORNING WATER VAPOR IMAGERY DEPICTS SHORT-WAVELENGTH
UPPER-LEVEL RIDGING ACROSS THE MIDWEST BETWEEN AGGREGATE
TROUGHING OVER THE PACIFIC NORTHWEST AND NORTHEASTERN UNITED
STATES. A BROAD UPPER-LEVEL LOW IS SLOWLY LIFTING NORTHEASTWARD
FROM THE SOUTHERN PLAINS TOWARD THE MIDDLE MISSISSIPPI RIVER
VALLEY TOWARD THE CENTER OF THE RIDGE. CLOSER TO THE GROUND, AN
ELONGATED STATIONARY FRONT IS PRESENT FROM THE NORTHERN PLAINS
THROUGH THE LOWER GREAT LAKES. THE POSITION OF THE FRONT MIRRORS
THE SHAPE OF LAKE MICHIGAN ACROSS NORTH CENTRAL ILLINOIS AND
NORTHWESTERN INDIANA THANKS TO ONSHORE FLOW FORCED BY A SURFACE
HIGH PRESSURE SYSTEM CENTERED OVER LAKE SUPERIOR.
OVER THE NEXT 24 HOURS, THE AFOREMENTIONED SURFACE HIGH
PRESSURE SYSTEM WILL MEANDER EASTWARD INTO SOUTHERN ONTARIO
LEADING TO A EAST-SOUTHEASTERLY WIND DIRECTION ACROSS THE GREAT
LAKES. THE STATIONARY FRONT WILL HENCE REMAIN MORE OR LESS IN
THE SAME PLACE TODAY, STRETCHING FROM NEAR ROCKFORD TO JOLIET TO
RENSSELAER. SOUTHWEST OF THE FRONT, CONTINUED MUGGY CONDITIONS
(DEW POINTS IN THE LOWER 70S) WILL FACILITATE EASY-TO-ACHIEVE
CONVECTIVE TEMPERATURES AROUND 80 DEGREES ALTOGETHER FORCING A
DIURNAL FLARE IN AFTERNOON SHOWERS AND THUNDERSTORMS. POOR LAPSE
RATES (NEAR 6 K/KM) TIED TO TROPICAL-LIKE MOISTURE (PWATS NEAR
2 INCHES) AMIDST MEAGER SHEAR IN THE CONVECTIVE LAYER (AROUND
25KT) WILL PROMOTE SLOW-MOVING SPATIALLY-SMALL CELLS CAPABLE OF
TORRENTIAL DOWNPOURS AND WET MICROBURSTS. MORE SPECIFICALLY, THE
STRONGEST STORMS WILL BE CAPABLE OF PRODUCING RAIN RATES WILL
EXCEED OF 2 INCHES PER HOUR, LOCALIZED FLASH FLOODING, AND
HIGHLY LOCALIZED WIND DAMAGE. MEANWHILE, IT IS SHAPING UP TO BE
A FAIRLY PLEASANT AND DRY DAY NORTHEAST OF THE FRONT (INCLUDING
ACROSS MUCH OF THE CHICAGO METROPOLITAN AREA) WITH RELATIVELY
LOWER HUMIDITY VALUES AND HIGHS IN THE MID 80S (UPPER 60S TO
LOWER 70S LAKESIDE).
TONIGHT, COMPOSITE OUTFLOW FROM AFTERNOON CONVECTION AND A
SYNOPTIC TURN OF THE WINDS TO ADOPT A MORE SOUTHERLY COMPONENT
SHOULD ALLOW FOR THE FRONTAL BOUNDARY TO LIFT NORTHEASTWARD. AS
A RESULT, MUGGY CONDITIONS ARE POISED TO SPREAD ACROSS THE
REMAINDER OF THE AREA BY DAYBREAK MONDAY. THE CORE OF THE UPPER-
LEVEL LOW WILL THEN PASS OVERHEAD THROUGHOUT THE DAY, LEADING
TO ANOTHER DIURNAL FLARE OF SLOW-MOVING SHOWERS AND
THUNDERSTORMS. LIKE TODAY, POOR LAPSE RATES, HIGH COLUMN
MOISTURE VALUES, AND MEAGER SHEAR WILL PROMOTE TORRENTIAL
DOWNPOURS AND WET MICROBURSTS WITH THE THUNDERSTORMS TOMORROW.
IN OTHER WORDS, THERE WILL BE RENEWED THREAT FOR LOCALIZED
FLASH FLOODING AND WIND DAMAGE. SHOULD ANY SLOW-MOVING STORM
OVERLAP WITH AN URBAN AREA (ROCKFORD OR THE CHICAGO METROPOLITAN
AREA), FLASH FLOODING COULD BE LOCALLY SIGNIFICANT (FLOODED
ROADWAYS AND VIADUCTS). FINALLY, CANNOT RULE OUT A FEW FUNNEL
CLOUDS ON MONDAY AS THE CENTER OF THE UPPER-LEVEL LOW MOVES
DIRECTLY OVERHEAD. HIGHS ON MONDAY WILL BE IN THE UPPER 70S TO
LOWER 80S, WHICH WITH DEW POINTS IN THE LOW TO MID 70S WILL MAKE
IT FEEL MORE LIKE FLORIDA THAN THE MIDWEST. SHOWERS AND STORMS
MAY CONTINUE EVEN AFTER SUNSET UNTIL THE UPPER-LEVEL LOW FINALLY
PIVOTS AWAY FROM THE AREA BY DAYBREAK TUESDAY.
TUESDAY THROUGH THURSDAY:
IN THE WAKE OF THE UPPER-LEVEL LOW, ENSEMBLE GUIDANCE DEPICTS
THE REINFORCEMENT OF UPPER-LEVEL RIDGING IN THE MIDWEST AS
TROUGHING STRENGTHENS ACROSS THE PACIFIC NORTHWEST. THE NET
RESULT WILL BE WARMING TEMPERATURES LOCALLY TUESDAY AND
WEDNESDAY WITH HIGHS POISED TO RETURN TO THE UPPER 80S TO
LOCALLY 90 (PARTICULARLY ON WEDNESDAY). WHEN COMBINED WITH THE
(BY THIS POINT) STAGNANT AND HUMID AIRMASS, HEAT INDEX VALUES
WILL CLIMB INTO THE MID TO UPPER 90S BOTH DAYS. IT'LL BE THE
FIRST TASTE OF SUMMER-LIKE HEAT OF THE YEAR.
AT THIS POINT, OUR FORECAST FAVORS TUESDAY AND WEDNESDAY TO BE
DRY IN OUR LOCAL AREA LEADING TO LITTLE TO RELIEF FROM THE HEAT.
HOWEVER, PERIODIC UPPER-LEVEL SHORTWAVES SHEDDING FROM THE
AGGREGATE TROUGHING ACROSS THE WESTERN UNITED STATES MAY PROVIDE
JUST ENOUGH ASCENT TO BREAK THROUGH STRONG CAPPING AT THE BASE
OF AN EXPANSIVE EML PLUME ACROSS THE PLAINS. WHILE DEEP-LAYER
SHEAR WILL NOT BE PARTICULARLY STRONG INTO THE MIDWEST TUESDAY
AND WEDNESDAY, THE PRESENCE OF AN EXPANSIVE RESERVOIR OF
INSTABILITY (NEARLY DRY-ADIABATIC MID-LEVEL LAPSE RATES ATOP
SEASONABLY MOST LOW-LEVELS) AND NIGHTLY LOW-LEVEL JETS
(TERMINATING INTO THE MID-MISSISSIPPI RIVER VALLEY) DOES RAISE
CONCERN FOR ANY PLAINS CONVECTION TO GROW UPSCALE INTO EASTWARD-
MOVING MESOSCALE CONVECTIVE SYSTEMS (MCSS). IN OTHER WORDS, ANY
STORMS THAT DEVELOP UPSTREAM OF OUR AREA WOULD LIKELY CONTINUE
EASTWARD INTO OCEAN OF INSTABILITY. WITH HINTS OF SUCH A THREAT
DEPICTED IN A FEW MODEL SOLUTIONS (REFS IN PARTICULAR IS
BULLISH), WILL PLASTER LOW-END CHANCE (20%) POPS NEARLY
CONTINUOUSLY TUESDAY AND WEDNESDAY (THOUGH KEEP IN MIND THAT
EQUATES TO AN 80% CHANCE OF DRY CONDITIONS).
THE HOT AND HUMID PATTERN LOOKS TO BREAK DOWN ON THURSDAY AS A
STOUT UPPER-LEVEL SHORTWAVE "KICKS" THE AGGREGATE PACIFIC
TROUGHING AND AND ASSOCIATED COLD FRONT EASTWARD TOWARD THE
MIDWEST. WHILE THE STRONGEST UPPER-LEVEL FLOW LOOKS LIKE IT WILL
BE DISPLACED BEHIND THE COLD FRONT, SEASONABLY STRONG LOW-LEVEL
FLOW AHEAD OF THE FRONT (925-700 MB FLOW INCREASING FROM 30 TO
50 KT) WITHIN A STRONGLY UNSTABLE AIRMASS (MUCAPE > 3000 J/KG)
DOES RAISE CONCERN FOR AN EASTWARD-MOVING SQUALL LINE WITH A
THREAT FOR DESTRUCTIVE WINDS IN THE GENERAL REGION. TEMPERATURES
AND HEAT INDICES ON THURSDAY WILL DEPEND ON THE ULTIMATE
ARRIVAL TIMING OF THE FRONT (OUR CURRENT FORECAST HAS IT
ARRIVING DURING THE EVENING MEANING DAYTIME HOURS MAY BE HOT AND
HUMID ONCE AGAIN).
BORCHARDT
AVIATION /12Z TAFS THROUGH 18Z MONDAY/
ISSUED AT 555 AM CDT SUN JUN 7 2026
MAIN CONCERNS:
- POTENTIAL FOR TS INTO RFD AREA AND THE FAR WESTERN CHICAGO
METRO LATER THIS AFTERNOON INTO THIS EVENING.
- LOW CHANCE FOR TS LATE THIS EVENING THROUGH EARLY MONDAY, WITH
A HIGHER CHANCE BY LATE MONDAY MORNING-MIDDAY.
EXPECTATIONS ARE FOR PRIMARILY QUIET CONDITIONS AT THE MAIN
CHICAGO AREA TERMINALS THROUGH TONIGHT/EARLY MONDAY. RFD AREA
CONTINUES TO HAVE THE HIGHEST CHANCE FOR TS, WHERE A PROB30 WAS
MAINTAINED. STILL MAY NEED TO CONSIDER A PROB30 FOR DPA WITH
LATER ISSUANCES, INFORMED BY SATELLITE TRENDS THIS AFTERNOON.
FOR ORD, MDW, AND GYY, THE MOST LIKELY SCENARIO IS THAT THE
STABLE MARINE LAYER CONDITIONS PREVENT TS INTO THE VICINITY
THROUGH THIS EVENING. TS COVERAGE DOES LOOK HIGH ENOUGH THIS
AFTERNOON-MID EVENING SOUTH AND WEST OF CHICAGO FOR PROLONGED
AIR SPACE IMPACTS. WHILE SHRA/TS MAY APPROACH AT TIMES
TONIGHT/EARLY MONDAY, THE NEXT BEST CHANCE APPEARS TO BE BY LATE
MONDAY MORNING (PROB30 MENTION AT ORD AND MDW).
EASTERLY WINDS AROUND 10 KT TODAY WILL ONLY GRADUALLY DIMINISH
TONIGHT/SUNDAY NIGHT. DIRECTION SHOULD FAVOR EAST-SOUTHEAST
AFTER DAYBREAK MONDAY. OUTSIDE OF SHRA/TS, EXPECT VFR
CONDITIONS UNTIL POSSIBLE PATCHY MVFR CIGS MONDAY MORNING.
CASTRO
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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