808
FXUS63 KLOT 042341
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
641 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 /00Z TAFS THROUGH 06Z SATURDAY/
ISSUED AT 641 PM CDT THU JUN 4 2026
FORECAST CONCERNS INCLUDE...
CHANCE OF THUNDERSTORMS OVERNIGHT THROUGH FRIDAY AFTERNOON.
MVFR CIGS, POSSIBLE IFR CIGS, FRIDAY MORNING.
GUSTY SOUTHWEST WINDS FRIDAY.
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE EXPECTED TO
DEVELOP ACROSS NORTHWEST IL AND AT RFD IN THE PREDAWN HOURS AND
THEN MOVE EAST/NORTHEAST THROUGH THE MID MORNING HOURS FRIDAY.
THERE IS QUITE A BIT OF UNCERTAINTY FOR WHEN THIS ACTIVITY MAY
DEVELOP AND HOW FAR EAST IT WILL MOVE AND WHETHER IT MAY REACH
THE CHICAGO TERMINALS. OPTED TO INCLUDE VICINITY SHOWER MENTION
FOR THE CHICAGO TERMINALS FOR THIS POTENTIAL AND THEN MAINTAINED
TEMPO SHOWERS FOR THE MID/LATE MORNING. HOWEVER, SOME THUNDER
MENTION MAY BE NEEDED DURING THIS TIME BUT CONFIDENCE IS TOO
LOW. BEST CHANCE FOR THUNDER APPEARS TO BE IN THE EARLY
AFTERNOON AND CURRENT TEMPO MENTION SEEMS ON TRACK FOR NOW.
MVFR CIGS ARE EXPECTED TO DEVELOP ACROSS NORTHWEST IL BY
DAYBREAK AND MAY EXTEND AS FAR SOUTHEAST AS THE CHICAGO
TERMINALS BY LATE MORNING. CIGS MAY CONTINUE TO LOWER TO IFR
ACROSS NORTHWEST IL INCLUDING AT RFD THOUGH THERE REMAINS
UNCERTAINTY FOR HOW LOW CIGS MAY DROP. THESE LOWER CIGS ARE
EXPECTED TO SLOWLY LIFT FRIDAY AFTERNOON.
SOUTH/SOUTHWEST WINDS WILL GUST AS HIGH AS 20KT EARLY THIS
EVENING, THEN DIMINISH WITH SUNSET. SPEEDS MAY INCREASE BACK
INTO THE 10-15KT RANGE IN THE PREDAWN HOURS. GUSTS INTO THE MID
20KT RANGE ARE POSSIBLE FRIDAY MORNING BUT THESE HIGHER GUSTS
WILL LIKELY BE DEPENDENT ON PRECIP COVERAGE. MAINTAINED THESE
HIGHER GUSTS FOR NOW, BUT CHANGES WILL BE POSSIBLE. WINDS WILL
TREND MORE WEST/SOUTHWEST FRIDAY AFTERNOON WITH SOME GUSTS STILL
POSSIBLE. CMS
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...AIR QUALITY ALERT UNTIL MIDNIGHT CDT /1 AM EDT/ TONIGHT FOR
INZ001-INZ002-INZ010-INZ011-INZ019.
LM...SMALL CRAFT ADVISORY FROM 10 AM TO 7 PM CDT FRIDAY FOR THE IL
AND IN NEARSHORE WATERS.
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