252
FXUS63 KLOT 041920
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
220 PM CDT THU JUN 4 2026
KEY MESSAGES
- TRENDING WARMER AND MORE HUMID WITH PERIODS OF SHOWERS AND
THUNDERSTORMS STARTING EARLY FRIDAY AND CONTINUING INTO NEXT
WEEK.
- LOW (LEVEL 1 OUT OF 5) SEVERE WEATHER THREAT FRIDAY PM ALONG
WITH A THREAT FOR LOCALLY HEAVY RAINFALL.
DISCUSSION
ISSUED AT 217 PM CDT THU JUN 4 2026
FOR FRIDAY AND SATURDAY THE MAIN FORECAST QUESTION IS SHOWER AND
THUNDERSTORM TRENDS, WITH GREATER EMPHASIS ON THE SHOWERS GIVEN THE
OVERALL MARGINAL LAPSE RATES AND LACK OF STRONG FORCING FOR
CONVECTION. CAM GUIDANCE NORMALLY WOULDN'T BE RELIED ON TOO
CLOSELY, BUT SEVERAL MODELS SHOW SIMILAR TRENDS AND ALIGN WITH THE
OVERALL CONCEPT OF HOW THINGS APPEAR LIKELY TO EVOLVE, SO ELECTED TO
FOLLOW A BLEND OF THOSE THAT APPEARED TO REFLECT THIS THINKING.
A CLUSTER OF SHOWERS WITH SOME EMBEDDED THUNDERSTORMS IS EXPECTED TO
MAKE ITS WAY INTO THE AREA FROM IOWA EARLY FRIDAY AHEAD OF A DIFFUSE
COLD FRONT AND WEAK SHORTWAVE ALOFT. THIS ACTIVITY SHOULD
OVERSPREAD THE AREA THROUGH THE MORNING INTO EARLY AFTERNOON AT
WHICH POINT SLIGHT RIDGING ALOFT AND MOVEMENT AWAY FROM THE
SUPPORTING SURFACE BOUNDARY MAY ALLOW FOR A DECREASE IN COVERAGE FOR
LATER IN THE AFTERNOON AND EVENING. THE EXCEPTION MAY BE IN THE
SOUTHERN HALF OF OUR FORECAST AREA WHERE AN OUTFLOW BOUNDARY FROM
THE EARLIER ACTIVITY COULD PROVIDE THE FOCUS FOR ADDITIONAL
DEVELOPMENT.
MOST LOCATIONS ON FRIDAY AND FRIDAY NIGHT DO NOT APPEAR POISED FOR A
COMPLETE WASHOUT, BUT GIVEN AN AXIS OF PWATS EXCEEDING 1.75" AND THE
EXPECTED SLOW MOTION OF THIS CLUSTER, SOME AREAS COULD SEE SOME
HEAVY RAINFALL. SPC ALSO HAS US IN A DAY TWO MARGINAL RISK BUT THIS
WOULD NOT APPEAR TO POSE A WIDESPREAD THREAT GIVEN THE
AFOREMENTIONED MARGINAL SUPPORT FOR CONVECTION OVERALL.
LATER FRIDAY NIGHT INTO SATURDAY THE MODEL GUIDANCE BEGINS TO
DIVERGE, BUT THE GENERAL IDEA STILL APPEARS TO KEEP THE BEST FOCUS
FOR CONTINUED SHOWERS IN SOUTHERN AND WESTERN PORTIONS OF THE
FORECAST AREA. THE EXCEPTION COULD BE ALONG A DEVELOPING LAKE
BREEZE THAT MIGHT BE ABLE TO TAP INTO THE MOIST AIRMASS AND SUPPORT
AN ADDITIONAL AREA OF SHOWERS SATURDAY AFTERNOON.
FOR SUNDAY INTO THE FIRST PART OF NEXT WEEK, MODEL GUIDANCE IS
SHOWING A NARROW MID TO UPPER LEVEL RIDGE BUILDING OVERHEAD, WITH A
STATIONARY FRONT AT THE SURFACE EXTENDING EAST FROM THE PLAINS INTO
THE OHIO VALLEY. THIS BOUNDARY, WHEREVER IT HAPPENS TO PARK, WOULD
APPEAR TO BE THE BEST FOCUS FOR ADDITIONAL SHOWER AND THUNDERSTORM
ACTIVITY, ESPECIALLY WITH SUPPORT FROM AFTERNOON HEATING AND
DEWPOINTS IN THE 60S TO OCCASIONALLY LOWER 70S.
LENNING
AVIATION /18Z TAFS THROUGH 00Z SATURDAY/
ISSUED AT 108 PM CDT THU JUN 4 2026
KEY AVIATION FORECAST MESSAGES:
- PERIODS OF SHRA AND TSRA RETURN FRIDAY
VFR AND DRY CONDITIONS ARE EXPECTED THROUGH TONIGHT FOR MOST OF
THE AREA. WINDS WILL BE BREEZY OUT OF THE SOUTHWEST WITH GUSTS
AROUND 20 KT THROUGH THIS AFTERNOON THEN EASE WITH SUNSET.
A CLUSTER OF SHOWERS AND ISOLATED EMBEDDED THUNDERSTORMS IS
EXPECTED TO APPROACH THE AREA INTO FRIDAY MORNING FROM IOWA. AN
INITIAL ARC OF SPOTTY SHOWERS MAY DEVELOP AHEAD OF THIS
FEATURE, REACHING RFD POTENTIALLY AS EARLY AS 9-10Z AND THE
CHICAGO AREA TERMINALS CLOSER TO 11-12Z WITH CEILINGS VERY
GRADUALLY DECREASING THROUGH THE MORNING TOWARD MVFR IN THEIR
WAKE. AS WE GET LATER INTO THE MORNING TOWARD MIDDAY SHOWER
COVERAGE IS EXPECTED TO INCREASE ALONG WITH THE POTENTIAL FOR
THUNDER. HAVE SHIFTED THE TS MENTION A BIT LATER, TO THE EARLY
TO MID AFTERNOON HOURS, FOR THE CHICAGO TERMINALS BASED ON A
SLOWER ARRIVAL OF SLIGHTLY MORE FAVORABLE INSTABILITY. HEAVY
DOWNPOURS (RAINFALL RATES >1"/HR) AND LOCALLY GUSTY WINDS ARE
THE PRIMARY CONCERNS WITH THESE STORMS IN ADDITION TO OCCASIONAL
LIGHTNING STRIKES. GUIDANCE CONTINUES TO TREND TOWARD THE
SHOWER AND THUNDERSTORM POTENTIAL FOCUSING MAINLY SOUTH OF I-80
INTO THE EVENING AND OVERNIGHT HOURS.
WINDS WILL QUICKLY INCREASE OUT OF THE SOUTHWEST AROUND 25 KTS
AHEAD OF THE STORMS FRIDAY MORNING THEN BECOME MORE VARIABLE
IN THEIR WAKE AND EASING INTO THE EVENING HOURS.
PETR
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...AIR QUALITY ALERT UNTIL MIDNIGHT CDT /1 AM EDT/ TONIGHT FOR
INZ001-INZ002-INZ010-INZ011-INZ019.
LM...NONE.
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