873
FXUS63 KLOT 151951
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
251 PM CDT FRI MAY 15 2026
KEY MESSAGES
- LOCALIZED DAMAGING WIND GUSTS POSSIBLE WITH A WEAKENING
CONVECTIVE COMPLEX LATE TONIGHT INTO EARLY SATURDAY.
- SOME ISOLATED STORM CHANCES EXIST SATURDAY THROUGH SUNDAY
MORNING, THOUGH MUCH OF THE TIME COULD END UP DRY.
- EXPECT MORE WIDESPREAD SHOWERS AND AT LEAST SCATTERED STORMS
AT TIMES MONDAY-TUESDAY, SOME OF WHICH MAY BE SEVERE.
- SUMMER-LIKE WARMTH AND HUMIDITY IS IN STORE THIS WEEKEND
THROUGH EARLY NEXT WORKWEEK.
DISCUSSION
ISSUED AT 251 PM CDT FRI MAY 15 2026
THROUGH TONIGHT:
INTO THIS EVENING, IT WILL BE BREEZY AND PLEASANT WITH
TEMPERATURES GRADUALLY FALLING FROM THE 70S INTO THE 60S.
OUR MAIN FOCUS TONIGHT IS THE LIKELIHOOD OF A WEAKENING MCS
(SHOWERS AND EMBEDDED STORMS) TO MOVE ACROSS THE AREA OVERNIGHT
TONIGHT, WITH GUSTY OUTFLOW ON ITS LEADING EDGE. THUNDERSTORMS
INITIATING BY EVENING FROM THE OMAHA AREA TO WESTERN WISCONSIN
WILL LIKELY EVOLVE INTO ONE OR MORE LINEAR CLUSTERS. GIVEN THE
DRY AND MIXED PROFILES TODAY, NOT EXPECTING ANY SURFACE BASED
INSTABILITY OVERNIGHT. ON THE OTHER HAND, A MUCAPE RESERVOIR OF
UP TO 1500-2000 J/KG WILL EXPAND ACROSS THE MS RIVER IN TANDEM
WITH A STOUT EML, WHICH MAY MAINTAIN SUFFICIENT ORGANIZATION IN
THE MCS (ALBEIT STILL ON AN OVERALL WEAKENING TREND DUE TO
UNFAVORABLE DIURNAL TIMING) TO YIELD SOME STRONG TO LOCALLY
DAMAGING WIND GUSTS ON THE LEADING EDGE OUTFLOW BOUNDARY. THE
BEST CHANCE FOR THIS APPEARS TO BE IN THE NORTHWEST 1/3 OR SO OF
THE CWA (IE. NEAR AND WEST OF A WAUKEGAN TO PERU IL LINE). A
RELATIVELY GREATER WIND THREAT MAY PRESENT ITSELF JUST NORTH OF
THE IL/WI STATE LINE DUE TO THE WEST-SOUTHWESTERLY FLOW
ORIENTATION ALOFT.
SINCE THE COMPLEX WILL BE ROOTED ABOVE THE BOUNDARY LAYER,
EFFECTIVE BULK SHEAR WILL BE FAIRLY MODEST. CAN'T COMPLETELY
RULE OUT ISOLATED LARGE HAIL IN ANY MORE ROBUST CORES BEHIND THE
OUTFLOW IF EFFECTIVE SHEAR ENDS UP A BIT STRONGER THAN
ANTICIPATED.
SATURDAY THROUGH FRIDAY:
BY SATURDAY MORNING, THE PRIMARY MCS FROM TONIGHT IS EXPECTED
TO MOVE EAST OF THE AREA, THOUGH A COMBINED OUTFLOW/COLD FRONTAL
BOUNDARY IS FORECAST TO BECOME NEARLY STATIONARY ACROSS PROBABLY
SOUTHERN PORTIONS OF THE FORECAST AREA (THOUGH THE EXACT
POSITION IS OF LOW CONFIDENCE FROM CURRENT GUIDANCE RUNS). A
TRAILING WEAKER CONVECTIVELY MODULATED SHORT-WAVE AND LINGERING
WARM AIR ADVECTION/ASCENT MAY KEEP SCATTERED SHOWERS AND
ISOLATED EMBEDDED THUNDERSTORMS GOING PAST DAYBREAK INTO OUR
SOUTHEAST 1/3 TO 1/2 OF THE CWA OR SO.
INTO SATURDAY AFTERNOON, SUBSIDENCE IN THE WAKE OF THE MORNING
SHORT-WAVE(S) ENTAIL NEBULOUS AT BEST FORCING MECHANISMS. HAVE
MAINTAINED SOME CHANCE POPS (30-50%) MAINLY SOUTH OF I-80,
WHERE A BIT BETTER POTENTIAL OF ADDITIONAL DIURNAL
SHOWERS/ISOLATED STORMS WOULD MORE LIKELY BE FOCUSED NEAR/SOUTH
OF THE STALLED BOUNDARY. POTENTIAL FOR LINGERING CLOUD COVER
AND OUTFLOW-DISTURBED WIND FIELD COULD LIMIT HIGH TEMPERATURES
SOMEWHAT, THOUGH CURRENT MODEL LOW-LEVEL THERMAL FIELDS SUGGEST
AFTERNOON HIGHS FROM NEAR/AROUND 80F EAST/FAR SOUTH TO THE LOW-
MID 80S FARTHER NORTH/WEST WOULD BE ATTAINABLE WITH SOME
AFTERNOON SUNSHINE. AS AN ADDITIONAL MINOR NOTE ON TEMPERATURES,
A WEAK COLD FRONT MAY SLIP INTO FAR NORTHERN ILLINOIS AND ENABLE
AN ONSHORE WIND SHIFT AND MORE QUICKLY COOLING TEMPS TOWARDS
SUNSET NEAR THE FAR NORTHEAST ILLINOIS SHORE.
FORCING MECHANISMS FOR ANY ADDITIONAL CONVECTION REMAIN
NEBULOUS SATURDAY NIGHT, AS FORECAST MID-LEVEL HEIGHT RISES CAST
UNCERTAINTY ON ANY AREAS OF FOCUS. A NORTHEASTWARD PROPAGATING
SHORT-WAVE MAY CONCEIVABLY SUPPORT ISOLATED TO PERHAPS WIDELY
SCATTERED SHOWERS AND STORMS (20-40% POPS/HIGHEST NEAR AND WEST
OF I-39) AS THE STALLED FRONT/OUTFLOW BOUNDARY LIFTS BACK NORTH
AS A WARM FRONT. A BROAD LEVEL 1 OF 5 SEVERE THREAT IN THE
CURRENT OUTLOOK MAY BE A BIT AGGRESSIVE FOR THE PROGGED SETUP,
(DECREASING MID-LEVEL LAPSE RATES, SUB MARGINAL EFFECTIVE BULK
SHEAR, AND AN AGAIN UNFAVORABLE DIURNAL TIMING).
MOST RECENT GUIDANCE CONTINUES TO INDICATE BREEZY (30-35 MPH
GUSTS) SOUTH WINDS WILL DEVELOP SUNDAY AFTERNOON, AFTER THE WARM
FRONT LIFTS NORTH OF THE AREA. WITH ANY MORNING SHOWERS/STORMS
(FAVORING NEAR/NORTH OF I-88) DEPARTING AND DECREASING CLOUD
COVER IN THE WARM SECTOR, HIGH TEMPERATURES IN THE MID-UPPER 80S
APPEAR LIKELY AT THIS DISTANCE. THE EXCEPTION MAY BE NEAR THE
LAKE COUNTY IL SHORE, AS A JUST EAST OF SOUTH COMPONENT TO THE
WINDS COULD CAP HIGHS IN THE 70S LATER IN THE DAY. BREEZY AND
MILD CONDITIONS LOOK TO PERSIST SUNDAY NIGHT, WITH LOWS
GENERALLY IN THE MID TO UPPER 60S.
THUNDERSTORM CHANCES THEN RETURN MONDAY AND TUESDAY, AS A
CENTRAL PLAINS SURFACE LOW PRESSURE SLOWLY LIFTS NORTHEAST
THROUGH THE NORTHERN GREAT LAKES AND EVENTUALLY TRAILS A COLD
FRONT THROUGH THE FORECAST AREA. AHEAD OF THE COLD FRONT, THE
FORECAST AREA WILL RESIDE IN BREEZY WARM SOUTHERLY FLOW,
CHARACTERIZED BY DAYTIME TEMPERATURES IN THE 80S AND INCREASING
LOW-LEVEL MOISTURE RETURN (SURFACE DEW POINTS POTENTIALLY UPPER
60S-TO NEAR 70F) FROM THE WESTERN GULF. RESULTING INSTABILITY,
COMBINED WITH MID-LEVEL FLOW NEAR 40 KTS WOULD POTENTIALLY
SUPPORT STRONG/SEVERE THUNDERSTORMS (AS WELL AS SOME THREAT FOR
FLOODING GIVEN HIGH COLUMN MOISTURE), THOUGH FORCING MECHANISMS
REMAIN UNCLEAR WITHIN THE BROAD WARM SECTOR MAKING CONVECTIVE
TIMING/EVOLUTION OF LOW CONFIDENCE AT THIS DISTANCE. MONDAY'S
OVERALL MESSY LOOK ALSO LENDS UNCERTAINTY TO HOW MUCH
INSTABILITY CAN BE REALIZED AT PEAK HEATING, PARTICULARLY IF
MORNING ACTIVITY ENDS UP FAIRLY WIDESPREAD.
ON TUESDAY, IN THE WAKE OF PROBABLE CONTINUED OVERNIGHT/EARLY
DAY CONVECTION, THE AFOREMENTIONED COLD FRONT WILL APPROACH.
IT'S NOT UNCOMMON IN THESE SETUPS FOR RENEWED STORMS AND ANY
ASSOCIATED STRONG TO SEVERE THREAT AHEAD OF THE FRONT TO FOCUS
PRIMARILY NEAR/SOUTHEAST OF I-55, THOUGH TIME WILL TELL IN THIS
REGARD. FOR THE MONDAY-TUESDAY PERIOD, SPC DAYS 4-5 OUTLOOKS
CONTINUE TO EXTEND SEVERE PROBABILITIES INTO OUR AREA, WHICH
APPEAR REASONABLE. QUIET AND COOLER CONDITIONS ARE THEN
EXPECTED BY MID-WEEK, AS SURFACE HIGH PRESSURE BUILDS ACROSS
THE REGION IN THE WAKE OF THE TUESDAY COLD FRONTAL PASSAGE.
CASTRO/RATZER
AVIATION /18Z TAFS THROUGH 00Z SUNDAY/
ISSUED AT 1213 PM CDT FRI MAY 15 2026
GUSTY S/SSW WINDS (OCCASIONALLY UP TO 30 KTS) WILL CONTINUE THIS
AFTERNOON BEFORE EASING THIS EVENING. WIND DIRECTIONS MAY TREND
MORE TOWARDS 170 AT THE CHICAGO-AREA TERMINALS THIS EVENING.
A THUNDERSTORM COMPLEX WILL LIKELY TRACK OUT OF IOWA LATE THIS
EVENING AND OVERNIGHT. THIS SHOULD GRADUALLY WEAKEN WITH
EASTWARD EXTENT, BUT HAS THE POTENTIAL TO PRODUCE A PERIOD OF
STRONG WIND GUSTS--PARTICULARLY INVOF RFD. HAVE CONVERTED THE
PROB30 AT RFD TO A TEMPO GROUP GIVEN HIGHER CONFIDENCE IN TIMING
AND THUNDERSTORM COVERAGE. AT THE CHICAGO-AREA TERMINALS,
CONFIDENCE IS A BIT LOWER, WITH AN INCREASED POTENTIAL FOR
OUTFLOW TO WORK ITS WAY AHEAD OF THUNDERSTORMS LEADING TO A
GRADUAL WEAKENING TREND. SUSPECT WE WILL NEED TO CONVERT TO
TEMPOS EVENTUALLY AS TIMING CONFIDENCE INCREASES.
IN THE WAKE OF CONVECTION, WINDS COULD TURN SELY FOR A PERIOD
BEFORE TURNING SW THROUGH SATURDAY MORNING. THE CHANCE FOR
ADDITIONAL THUNDERSTORMS SATURDAY AFTERNOON IS TOO LOW FOR A
MENTION IN THE CURRENT EXTENDED ORD/MDW TAFS.
CARLAW
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 7 PM CDT THIS EVENING FOR THE IL
AND IN NEARSHORE WATERS.
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