352
FXUS63 KLOT 180527
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1227 AM CDT SAT APR 18 2026
KEY MESSAGES
- SHOWERS AND ISOLATED THUNDERSTORMS OVERNIGHT.
- WINDY SATURDAY WITH COLDER WEATHER OVER THE WEEKEND INTO
EARLY NEXT WEEK.
- FROST/FREEZE CONDITIONS ARE EXPECTED MANY AREAS SUNDAY AND
ESPECIALLY MONDAY MORNINGS.
DISCUSSION
ISSUED AT 136 PM CDT FRI APR 17 2026
FOR NEAR TERM DETAILS ON THE CONVECTIVE THREATS THROUGH THIS
EVENING, SEE THE MESOSCALE DISCUSSION (AND/OR ADDITIONAL FUTURE
DISCUSSIONS) ABOVE. ADDITIONAL CONCERNS FOR TONIGHT WILL BE
CENTERED ON HEAVY RAINFALL AND LOCALIZED FLASH FLOODING.
PRECIPITABLE WATER VALUES STILL LIE AT THE UPPER ECHELON OF
TYPICALLY OBSERVED VALUES FOR MID APRIL, AND THIS COUPLED WITH
SOME ENHANCED FORCING SHOULD LEAD TO AREAS OF 1-1.5" RAINFALL
IN A RELATIVELY SHORT WINDOW OF TIME. WE CANNOT RULE OUT ANY
HIGHER OVERALL TOTALS (PUSHING 3"), GIVEN THAT WE HAVE SEVERAL
WINDOWS OF FORCING BOTH IN THE OPEN WARM SECTOR AND ALONG THE
COLD FRONT. MUCH OF THIS RAIN WILL GO IMMEDIATELY INTO RUNOFF.
IN ADDITION TO ANY URBAN LOCATIONS, IT IS HARD TO PINPOINT THE
MORE FAVORED AREAS IN THE WATCH AREA, HOWEVER THE MOST
SUSCEPTIBLE AREAS OVERLAPPING WITH HIGHER CONFIDENCE RAINFALL
WOULD BE IN THE ROCK RIVER BASIN, AND THEN EXTENDING EASTWARD
INTO THE FOX AND DES PLAINES RIVER BASINS ACROSS NORTHERN
ILLINOIS. A SECONDARY HEAVY RAIN AXIS MAY SETUP SOUTH, BUT IF WE
HAVE A FORWARD PROPAGATING SYSTEM, THAT MAY LIMIT THE DURATION
OF HEAVY PRECIPITATION.
A TASTE OF REALITY WILL RETURN TO THE LOWER GREAT LAKES REGION
BEHIND TONIGHT'S STRONG COLD FRONT. HIGH TEMPERATURES WILL
REACHED AT MIDNIGHT. WHILE SOME TEMPERATURE RECOVERIES WILL
OCCUR AS CLOUDS BREAK THROUGH THE MORNING, RATHER STOUT COLD AIR
ADVECTION THROUGH THE DAY WILL PREVENT TEMPERATURES FROM
PLATEAUING HIGHER THAN THE MID 40S TO LOW 50S AREA WIDE. NORMAL
HIGHS FOR MID APRIL ARE RIGHT AT 60. A STIFF NORTHWEST BREEZE
WILL MAKE IT FEEL EVEN LESS PLEASANT, WITH "WIND CHILL" READINGS
IN THE LOWER 40 IN MANY AREAS IN THE AFTERNOON. THIS WILL SET
THE STAGE FOR A COLD NIGHT SATURDAY NIGHT.
COLD ADVECTION GETS REINFORCED AS THE UPPER TROUGH AXIS WILL BE
SHIFTING OVERHEAD. THE CENTER OF THE SURFACE HIGH WILL BE OFF TO OUR
SOUTHWEST SATURDAY NIGHT, THUS WE WILL MAINTAIN A BIT OF A WIND
COMPONENT, HOWEVER THINGS LOOK TO DECOUPLE ENOUGH TO SUGGEST SOME
AREAS OF FROST.
REINFORCED NORTHWEST FLOW ON THE BACKSIDE OF THE UPPER TROUGH WILL
MAINTAIN A SIMILAR AIRMASS ON SUNDAY AND PROVIDE A CARBON COPY DAY
FROM SATURDAY. WITH HIGH PRESSURE NEARBY SUNDAY NIGHT, A WIDESPREAD
FROST APPEARS INCREASINGLY LIKELY, WITH SOME AREA IN OUTLYING AREAS
HEADING FOR A POTENTIAL HARD FREEZE.
UPPER HEIGHTS RECOVER NICELY AND WARM ADVECTION ON THE BACK SIDE FOR
THE DEPARTING SURFACE HIGH WILL ENCOURAGE TEMPERATURES TO REBOUND
BACK ABOVE NORMAL THROUGH MID WEEK WITH GENERALLY DRY
CONDITIONS. THERE WILL BE PERIODS OF ONSHORE FLOW KEEPING COOL
READINGS NEAR THE SHORE.
KMD
AVIATION /06Z TAFS THROUGH 12Z SUNDAY/
ISSUED AT 1227 AM CDT SAT APR 18 2026
FORECAST CONCERNS INCLUDE...
LOW MVFR, POSSIBLE IFR, CIGS OVERNIGHT INTO SATURDAY MORNING.
STRONG/GUSTY NORTHWEST WINDS SATURDAY.
SCATTERED SHOWERS OVERNIGHT.
SCATTERED SHOWERS WILL CONTINUE FOR A FEW MORE HOURS OVER THE
TERMINALS WITH SHOWERS EXTENDING THROUGH DAYBREAK JUST SOUTHEAST
OF THE TERMINALS. THERE IS A SMALL CHANCE FOR THUNDER OVER THE
NEXT HOUR OR SO, BUT ANY ADDITIONAL THUNDER POTENTIAL IS
EXPECTED TO REMAIN SOUTHEAST OF THE TERMINALS.
LOW MVFR CIGS AND PATCHY IFR CIGS HAVE DEVELOPED ACROSS
NORTHWEST IL AND SOUTHERN WI ALONG AND BEHIND AN APPROACHING
COLD FRONT. THESE LOWER CIGS ARE EXPECTED TO SPREAD EAST ACROSS
THE REST OF THE AREA OVERNIGHT. ONLY MEDIUM CONFIDENCE FOR CIG
TRENDS, BUT PREVAILING LOW MVFR CIGS LOOK ON TRACK FOR AT LEAST
A FEW HOURS. CIGS WILL LIKELY BE SLOWLY LIFTING INTO LOW VFR
AFTER DAYBREAK WITH CIGS POSSIBLY SCATTERING OUT DURING THE
AFTERNOON AND MOST LIKELY BY SATURDAY EVENING.
SOUTHWEST WINDS GUSTING INTO THE LOWER 20KT RANGE WILL SHIFT TO
THE WEST/NORTHWEST BEHIND THE COLD FRONT OVERNIGHT WITH GUSTS
INTO THE MID 20KT RANGE. GUSTS WILL INCREASE FURTHER, PERHAPS
INTO THE 30KT RANGE MID/LATE SATURDAY MORNING. SPEEDS AND GUSTS
WILL DIMINISH QUICKLY WITH SUNSET SATURDAY EVENING AND TURN TO
THE SOUTHWEST. CMS
LOT WATCHES/WARNINGS/ADVISORIES
IL...FLOOD WATCH UNTIL 5 AM CDT SATURDAY FOR ILZ003-ILZ004-ILZ005-
ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019-ILZ020-
ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-ILZ104-ILZ105-
ILZ106-ILZ107-ILZ108.
IN...FLOOD WATCH UNTIL 5 AM CDT /6 AM EDT/ SATURDAY FOR INZ001-
INZ002-INZ010-INZ011-INZ019.
LM...SMALL CRAFT ADVISORY UNTIL 10 PM CDT SATURDAY FOR THE IL AND
IN NEARSHORE WATERS.
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