051
FXUS63 KLOT 180847
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
347 AM CDT MON MAY 18 2026
KEY MESSAGES
- A FEW ADDITIONAL ROUNDS OF SHOWERS AND THUNDERSTORMS TODAY AND
TUESDAY, SOME OF WHICH COULD BE STRONG TO SEVERE MAINLY DURING
THE AFTERNOON HOURS.
- SUMMER-LIKE WARMTH AND BREEZY WINDS AT TIMES WILL PREVAIL
THROUGH TUESDAY, THEN COOLER TEMPERATURES RETURN FOR THE
MIDDLE OF THE WEEK.
- MILDER WEATHER RETURNS HEADING INTO THE WEEKEND, THOUGH WITH
AT LEAST INTERMITTENT SHOWER/THUNDERSTORM POTENTIAL.
DISCUSSION
ISSUED AT 347 AM CDT MON MAY 18 2026
REGIONAL RADAR MOSAIC SHOWS A LINEAR MCS MOVING ACROSS THE
MISSISSIPPI RIVER INTO WESTERN WI/IL EARLY THIS MORNING. THERE
HAS BEEN A NOTABLE WEAKENING TREND TO THE CONVECTION OVER THE
PAST FEW HOURS AS THE COMPLEX PROPAGATES INTO A REGION OF
DECREASING DEEP- LAYER SHEAR AND LOW-LEVEL INSTABILITY, THOUGH
STORMS SHOULD CONTINUE TO SPREAD EASTWARD THIS MORNING ALONG A
COMPOSITE OUTFLOW BOUNDARY AT THE LEADING EDGE OF THE
CONVECTION. IN FACT, RECENT RADAR TRENDS INDICATE A FEW NEW
CELLS DEVELOPING AHEAD OF THE LINE NEAR THE QUAD CITIES, PERHAPS
AIDED BY ENHANCED ASCENT ASSOCIATED WITH ONE OR MORE AN
APPARENT MCVS NEAR THE IA/IL/MO BORDER. GUSTY WINDS OF 30-40 MPH
WITH THE OUTFLOW AND SOME SMALL HAIL ARE POSSIBLE WITH THESE
STORMS EARLY THIS MORNING, THOUGH THE OVERALL THREAT OF
ORGANIZED SEVERE WEATHER APPEARS LOW FOR THE NEXT SEVERAL HOURS.
LATER THIS MORNING HOWEVER, DIURNAL WARMING AND ASSOCIATED
DESTABILIZATION ALONG THE EAST/SOUTHEAST PERIPHERY OF THE
COMPLEX REMNANTS AND OUTFLOW BOUNDARY MAY SUPPORT RENEWED
DEVELOPMENT/STRENGTHENING OF CONVECTION WITH MORE OF A SEVERE
THREAT INTO THIS AFTERNOON. THOUGH DEPENDING ON HOW FAR THE
OUTFLOW BOUNDARY MAKES IT THIS MORNING, THIS WOULD LIKELY BE
ACROSS THE SOUTH/FAR EAST PORTIONS OF THE FORECAST AREA. FARTHER
NORTH/NORTHWEST, LINGERING STRATIFORM RAIN AND CLOUD COVER THIS
MORNING LOOKS TO LIMIT DESTABILIZATION AND RECENT CAM TRENDS
HAVE BEEN CONSISTENTLY DRY THERE DURING THE DAY/EVENING.
FARTHER TO THE WEST, EARLY MORNING GOES VAPOR IMAGERY INDICATES
ANOTHER MID-LEVEL SHORT WAVE ROUNDING THE BASE OF A WESTERN
CONUS LONG-WAVE TROUGH. WIDESPREAD STRONG CONVECTION IS PROGGED
TO DEVELOP LATE THIS AFTERNOON AND EVENING ACROSS KS/NE/IA ONCE
AGAIN IN RESPONSE, EVENTUALLY GROWING UPSCALE INTO ANOTHER
EASTWARD- PROPAGATING LINEAR MCS. SIMILARLY TO THIS MORNING, CAM
RUNS CONTINUE TO DEPICT A SIMILAR WEAKENING OF THIS SYSTEM AS
IT REACHES THE MISSISSIPPI RIVER AND SPREADS INTO WI/IL EARLY
TUESDAY MORNING WITH ASSOCIATED RELATIVELY LOW SEVERE POTENTIAL.
THE LINGERING MCS COLD POOL FOOTPRINT AND RESIDUAL CLOUDINESS
WILL LIKELY DELAY DESTABILIZATION INTO MIDDAY TUESDAY, THOUGH
ADDITIONAL STORM DEVELOPMENT APPEARS POSSIBLE ACROSS THE
SOUTHEAST HALF OF THE FORECAST AREA TUESDAY AFTERNOON/EVENING AS
THE COLD FRONT FINALLY PUSHES THROUGH THE FORECAST AREA.
STRONGER MID-LEVEL FLOW ON THE SOUTHEASTERN PERIPHERY OF THE
AFOREMENTIONED SHORT WAVE WILL LIKELY SUPPORT ENOUGH STORM
ORGANIZATION FOR A HAIL/WIND THREAT DURING THIS TIME.
FOLLOWING THE COLD FRONT, SURFACE HIGH PRESSURE IS PROGGED TO
BUILD EAST INTO THE WESTERN GREAT LAKES REGION WEDNESDAY AND
THURSDAY. DRY, BUT BREEZY AND COOLER WEATHER IS EXPECTED BOTH
DAYS, WITH TEMPS MAINLY IN THE 60S, BUT ONLY IN THE 50S NEAR
LAKE MICHIGAN WITH NORTHEAST-EAST FLOW OFF THE LAKE. NIGHTTIME
LOWS IN THE 40S ARE EXPECTED. THE HIGH THEN DRIFTS OFF TO THE
EAST THURSDAY NIGHT, WITH THE UPPER LEVEL PATTERN FAVORING A
SERIES OF MID-LEVEL DISTURBANCES TRACKING THROUGH THE AREA
FRIDAY INTO THE WEEKEND. THIS WILL SUPPORT MILDER TEMPERATURES,
BUT ALSO SOME OCCASIONAL SHOWER/THUNDERSTORM CHANCES INTO THE
HOLIDAY WEEKEND.
RATZER
AVIATION /06Z TAFS THROUGH 12Z TUESDAY/
ISSUED AT 100 AM CDT MON MAY 18 2026
FORECAST CONCERNS FOR THE TERMINALS...
- LINE OF SHOWERS AND EMBEDDED THUNDERSTORMS TO MOVE THROUGH
NORTHERN IL AND NORTHWEST IN LATE TONIGHT INTO MONDAY MORNING.
A FEW STORMS COULD BE STRONG WITH A THREAT FOR LOCALLY GUSTY
WINDS.
- BREEZY SOUTH-SOUTHWEST WINDS MONDAY AFTERNOON WITH GUSTS
AROUND 25 KTS.
- ANOTHER PERIOD OF SHOWERS AND POSSIBLE STORMS LATE MONDAY
NIGHT INTO TUESDAY MORNING.
LATEST RADAR IMAGERY CONTINUES TO SHOW A LINE OF SHOWERS AND
THUNDERSTORMS STRETCHING FROM MN TO KS THAT IS RACING TOWARDS
NORTHERN IL AND EVENTUALLY NORTHWEST IN. ARRIVAL TIME OF THIS
LINE CONTINUE TO BE AROUND 09Z AT RFD AND BETWEEN 10-12Z FOR THE
CHICAGO AREA TERMINALS. WHILE LIGHTNING TRENDS WITHIN THE LINE
SEGMENT HEADING TOWARDS THE TERMINALS HAS BEEN DECREASING,
RECENT AMDAR SOUNDING OUT OF MDW CONTINUE TO SHOW STEEP MID-
LEVEL LAPSE RATES (AROUND 7-8 C/KM) WHICH COULD STILL SUPPORT AN
OCCASIONAL LIGHTNING STRIKE AS THE LINE MOVES THROUGH.
ADDITIONALLY, A FEW STRONGER SHOWERS/STORMS ARE POSSIBLE AND
COULD RESULT IN LOCALIZED GUSTY WINDS AND MAYBE SOME SMALL HAIL.
ONCE THE LINE OF SHOWERS/STORMS ARRIVES, IT SHOULD MOVE THROUGH
WITHIN 3-4 HOURS AT EACH SITE. HOWEVER, WITH THE EXPECTED
ARRIVAL TIME AROUND DAYBREAK THERE CONTINUES TO BE A CHANCE THAT
SOME RENEWED DEVELOPMENT COULD OCCUR WITHIN THE LINE AS IT
TRAVERSES THE AREA, ESPECIALLY SOUTH OF I-80. IF THIS OCCURS AS
GUIDANCE SUGGESTS THEN SHOWER/STORM ACTIVITY COULD PERSIST
THROUGH THE MORNING BEFORE THINGS FULLY EXIT THE AREA. IT WAS
FOR THIS REASON THAT THE LONG PROB30 WAS MAINTAINED, BUT
HOPEFULLY WE CAN REFINE THIS WINDOW AS THE LINE ARRIVES.
AFTER THE LINE EXITS THE AREA AROUND MIDDAY, BREEZY SOUTH-
SOUTHWEST WINDS WILL DEVELOP AND PERSIST THROUGH THE AFTERNOON.
GUSTS DURING THIS PERIOD LOOK TO GENERALLY BE AROUND 25 KTS BUT
LOCALLY HIGHER GUSTS (UPWARDS OF 30KTS) ARE POSSIBLE. WHILE
THERE IS STILL A NON-ZERO CHANCE (15-20%) FOR ADDITIONAL SHOWER
AND/OR THUNDERSTORMS TO DEVELOP THIS AFTERNOON, LATEST GUIDANCE
TRENDS HAVE CONTINUED TO BACK OFF ON THIS SCENARIO GIVEN THAT
THE BETTER FORCING FOR STORMS WILL BE CENTERED TO OUR WEST IN
IA. THAT SAID, ANOTHER ROUND OF SHOWERS AND THUNDERSTORMS IS
EXPECTED TO DEVELOP IN IA THIS AFTERNOON AND MOVE INTO NORTHERN
IL AND NORTHWEST IN LATE MONDAY NIGHT INTO TUESDAY MORNING.
THOUGH, THE COVERAGE OF THESE STORMS INTO OUR AREA LOOKS MUCH
MORE LIMITED (ESPECIALLY THE THUNDER COVERAGE) SO HAVE OPTED TO
INTRODUCE A PROB30 FOR SHRA IN THE 30-HOUR TAFS FOR NOW.
OTHERWISE, EXPECT VFR CONDITIONS TO PREVAIL THROUGH THE PERIOD.
YACK
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 4 AM CDT EARLY THIS MORNING FOR THE
IL AND IN NEARSHORE WATERS.
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