083
FXUS63 KLOT 170601
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
101 AM CDT SUN MAY 17 2026
KEY MESSAGES
- A BETTER CHANCE FOR SHOWERS AND STORMS THIS EVENING-OVERNIGHT,
ESPECIALLY WITH WESTWARD EXTENT, AND THEN A FEW SHOWERS AND
STORMS MAY LINGER PAST DAYBREAK SUNDAY, MAINLY NORTH OF I-88.
- EXPECT MORE WIDESPREAD SHOWERS AND AT LEAST SCATTERED STORMS
AT TIMES MONDAY-TUESDAY, SOME OF WHICH MAY BE SEVERE.
- SUMMER-LIKE WARMTH AND HUMIDITY ALONG WITH FREQUENTLY GUSTY
SOUTH TO SOUTHWEST WINDS WILL CONTINUE THROUGH EARLY NEXT
WORKWEEK. COOLER CONDITIONS THEN RETURN MIDWEEK.
DISCUSSION
ISSUED AT 208 PM CDT SAT MAY 16 2026
THROUGH TONIGHT:
EARLY AFTERNOON VISIBLE SATELLITE IMAGERY TRENDS HAVE CAST SOME
DOUBT ON CONVECTIVE INITIATION (CI) PRIOR TO SUNSET OVER
NORTHERN ILLINOIS NORTH OF I-80. THERE'S A FEW AXES OF CLUMPIER
(BUT STILL MOSTLY FLAT) CUMULUS GROWTH, ONE OVER FAR NORTHERN
IL, AND THE OTHER JUST NORTH OF THE I-80 CORRIDOR. TO THE SOUTH,
THICK CIRRUS DEBRIS IS GREATLY CURTAILING INSOLATION AND
RESULTING DESTABILIZATION NORTH OF ONGOING SHOWERS AND STORMS
OVER CENTRAL IL AND IN.
RECENT KDVN RADAR LOOPS SHOW A DIFFUSE REMNANT BOUNDARY LIFTING
NORTHWARD OVER FAR WESTERN IL, COINCIDENT WITH THE AREA OF CU
GROWTH. DEW POINTS HAVE TICKED UP SLIGHTLY IN THIS CORRIDOR
(LOW-MID 60S) AS WELL. IN AN OVERALL SUBSIDENT REGIME, IT
REMAINS POSSIBLE/PROBABLE THAT CONVECTIVE COVERAGE, IF ANY, IS
SPARSE/ISOLATED. THAT SAID, NORTH OF I-80 AND NEAR/WEST OF I-39
IS LOOKING TO BE THE MAIN AREA TO WATCH UNTIL SUNSET FOR T-STORM
DEVELOPMENT. AS NOTED IN THE PREVIOUS UPDATE, *IF* A FEW STORMS
OCCUR, THE STRONGEST WOULD BE CAPABLE OF PRODUCING LOCALIZED
DOWNBURST WIND DAMAGE.
WHILE LARGE SCALE FORCING WILL REMAIN MODEST AT BEST TONIGHT,
THERE HAS BEEN RUN TO RUN CONSISTENCY IN SHORT-RANGE GUIDANCE IN
(LIKELY CONVECTIVELY MODULATED) 700 TO 500 MB IMPULSES LIFTING
NORTHEAST ACROSS THE MID MS VALLEY. PARTICULARLY IF CONVECTIVE
COVERAGE REMAINS AT A MINIMUM INTO/THROUGH THIS EVENING, AN
UNTAPPED MUCAPE RESERVOIR POSSIBLY UPWARDS OF 1K J/KG MAY BE IN
PLACE. THE MID-LEVEL SHORT-WAVE FORCING NOW APPEARS SUFFICIENT
FOR FAIRLY WIDESPREAD SHOWERS (50-70% POPS) AND SCATTERED
EMBEDDED STORMS FOCUSED NEAR/WEST OF THE FOX VALLEY DOWN INTO
WEST CENTRAL IL. DECREASING MID-LEVEL LAPSE RATES, MARGINAL
EFFECTIVE BULK SHEAR, AND AN UNFAVORABLE DIURNAL TIMING WILL
LIKELY LIMIT THE SEVERE THREAT. HOWEVER, WE CAN'T COMPLETELY
RULE OUT A STRONG TO SEVERE STORM OR TWO (LOCALIZED WIND DAMAGE
AND PERHAPS ISOLATED LARGE HAIL).
CASTRO
SUNDAY THROUGH SATURDAY:
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 LINGERING MORNING SHOWERS/STORMS
(FAVORING NEAR/NORTH OF I-88) DEPARTING AND DECREASING CLOUD
COVER IN THE WARM SECTOR, HIGH TEMPERATURES IN THE MID TO
LOCALLY UPPER 80S APPEAR LIKELY. THE NOTABLE EXCEPTION TO THIS
WILL BE NEAR THE LAKE COUNTY IL SHORE (AND PART OF THE DAY ALONG
THE COOK CO. SHORE), AS A JUST EAST OF SOUTH COMPONENT TO THE
WINDS WILL MAKE FOR NOTABLY COOLER CONDITIONS (60S TO 70S0
UNTIL FLOW TURNS SOUTH-SOUTHWESTERLY SUNDAY EVENING. 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 CONTINUES 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 /06Z TAFS THROUGH 12Z MONDAY/
ISSUED AT 101 AM CDT SUN MAY 17 2026
AVIATION FORECAST CONCERNS FOR THE 06Z TAFS:
- PERIOD OF SHRA/POSSIBLE TSRA PREDAWN INTO MID-MORNING,
HIGHEST CHANCES AT RFD.
- WINDS GENERALLY SSE THROUGH THIS MORNING, THEN SOUTH WITH
GUSTS 25-30 KTS THIS AFTERNOON. WINDS STAY BREEZY TONIGHT.
- WINDS MAY TURN MORE E OR EVEN NE FOR A TIME THIS MORNING NEAR
LAKE MICHIGAN (ORD/MDW/GYY), THOUGH WITH LOW CONFIDENCE.
A WEAK COLD FRONT STRETCHES FROM NORTHERN LOWER MI, SOUTHWEST
ACROSS SOUTHERN WI AND IA TO AN AREA OF LOW PRESSURE IN
SOUTHEAST CO EARLY THIS MORNING. CONSIDERABLE THUNDERSTORM
ACTIVITY WAS OCCURRING ALONG/SOUTH OF THE FRONT ACROSS SOUTHERN
IA AND NORTHERN MO, WITH A CONVECTIVELY-ENHANCED MID-LEVEL
CIRCULATION (MCV) NOTED OVER NORTHEAST MO. THIS MCV IS EXPECT TO
TRACK SLOWLY NORTHEAST THROUGH THE PREDAWN HOURS, EVENTUALLY
SPREADING AN AREA OF RAIN/EMBEDDED TSRA INTO PARTS OF NORTHERN
IL/SOUTHERN WI. CURRENT CAM GUIDANCE SUGGESTS THE GREATEST
PRECIPITATION COVERAGE WOULD BE WEST/NORTHWEST OF THE CHICAGO
TERMINALS (RFD MORE LIKELY IMPACTED), THOUGH THE EASTERN
PERIPHERY MAY SWEEP ACROSS THE CHICAGO AREA TOWARD/AFTER
DAYBREAK. FARTHER TO THE NORTHWEST, THERE IS ALSO SCATTERED TSRA
ACROSS SOUTHWEST WI AT THIS TIME, THOUGH THIS IS EXPECTED TO
REMAIN NORTH/NORTHWEST OF RFD AT THIS TIME. HAVE MAINTAINED SOME
SHRA/VCSH MENTION AFTER 10Z, WITH PROB30 FOR TSRA AT ALL SITES
BUT GYY (MAY REMAIN SOUTHEAST OF MAIN TS THREAT AREA) IN THE
13-16Z TIMEFRAME. UNCERTAIN EXTENT OF COVERAGE OF TSRA AT THIS
TIME, THOUGH COULD FORESEE NEEDING A TEMPO ESPECIALLY FOR RFD.
WILL CONTINUE TO MONITOR. PRECIPITATION THREAT SHOULD END BY
MID-LATE MORNING AS THE MCV MOVES OFF TO THE NORTHEAST OF THE
REGION.
IN THE WAKE OF THE MORNING SHRA/TS, A WARM FRONT WILL DEVELOP
NORTH ACROSS THE AREA ALLOWING SOUTH-SOUTHEAST WINDS THIS
MORNING TO BECOME QUITE BREEZY FROM THE SOUTH THIS AFTERNOON.
GUSTS 25-30 KTS APPEAR LIKELY BY MID-LATE AFTERNOON, POSSIBLY A
BIT HIGHER. BREEZY SOUTH FLOW WILL PERSIST OVERNIGHT AT WELL,
WITH SUSTAINED SPEEDS LIKELY ABOVE 10 KTS AND AT LEAST
OCCASIONAL GUSTS AROUND/ABOVE 20 KT POSSIBLE.
ONE CAVEAT TO WINDS THIS MORNING - THE COLD FRONT OVER NORTHERN
LAKE MICHIGAN IS PUSHING SOUTH OVER THE COOL LAKE WATERS, AND
MAY MAKE IT INTO THE CHICAGO TERMINALS EARLY THIS MORNING (AFTER
10-11Z AT CURRENT SPEED OF THE FRONT) BEFORE STALLING OVER THE
AREA. FAIRLY CONFIDENT THIS WILL RESULT IN A PERIOD OF WINDS IN
THE SOUTHEAST TO NORTHEAST QUADRANTS FROM NEAR DAYBREAK UNTIL
LATER IN THE MORNING. DETAILS OF THE EXACT DIRECTION IS LESS
CERTAIN WITH QUITE A BIT OF SPREAD IN MODEL GUIDANCE.
RATZER
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
VISIT US AT WEATHER.GOV/CHICAGO
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page