648
FXUS63 KLOT 270555
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1255 AM CDT SUN JUL 27 2025
KEY MESSAGES
- SCATTERED THUNDERSTORMS ARE LIKELY THIS EVENING MAINLY SOUTH
OF A PONTIAC TO VALPARAISO LINE. TORRENTIAL RAIN WITH THESE
STORMS COULD LEAD TO LOCALIZED FLOODING.
- DANGEROUS HEAT AND HUMIDITY MAY RETURN ON MONDAY.
- PERIODS OF THUNDERSTORMS RETURN MONDAY THROUGH WEDNESDAY, SOME
POSSIBLY STRONG TO SEVERE WITH TORRENTIAL RAIN WHICH COULD
LEAD TO FLASH FLOODING.
- DANGEROUS SWIMMING CONDITIONS AT LAKE MICHIGAN BEACHES
WEDNESDAY INTO THURSDAY.
DISCUSSION
ISSUED AT 235 PM CDT SAT JUL 26 2025
THROUGH SUNDAY NIGHT:
THE PRIMARY FORECAST CONCERN IS THUNDERSTORM COVERAGE/LOCATION
AND THE IMPACT TO THE CURRENT FLOOD WATCH. THE BULK OF
ADDITIONAL THUNDERSTORMS THIS AFTERNOON INTO THIS EVENING ARE
EXPECTED TO REMAIN SOUTH OF INTERSTATE 80 AND MAY END UP MAINLY
SOUTH OF THE KANKAKEE RIVER. CONFIDENCE IS INCREASING THAT ANY
HEAVY RAIN AND LOCALIZED FLASH FLOODING, IF ANY OCCURS, WILL BE
SOUTH OF THE CURRENT FLOOD WATCH AREA AND HAVE CANCELLED THE
WATCH. ITS POSSIBLE A NEW FLOOD WATCH MAY BE NEEDED FOR THE FAR
SOUTHERN CWA THIS EVENING, BUT CONFIDENCE IS TOO LOW FOR A NEW
WATCH AT THIS TIME. SCATTERED THUNDERSTORMS CONTINUE TO DEVELOP
ACROSS NORTHERN MO INTO WEST CENTRAL IL AND THIS ACTIVITY WILL
CONTINUE TO MOVE EAST/NORTHEAST THIS AFTERNOON INTO THIS
EVENING. IF THIS ACTIVITY WERE TO TRAIN OVER THE SAME AREAS,
THEN FLOODING WOULD BE THE CONCERN. CURRENT TRENDS SUGGEST THAT
IF THIS DOES MATERIALIZE, IT WOULD BE ACROSS THE FAR SOUTHERN
CWA, ACROSS CENTRAL IL AND CENTRAL IN.
MAIN SEVERE THREAT (LEVEL 1 OUT OF 5) WITH ANY STORMS THROUGH
THIS EVENING WILL BE LOCALLY DAMAGING WIND BUT ALL OF THESE
STORMS ARE ROTATING AND WITH THE VERY MOIST LOW LEVELS, THERE
REMAINS A LOW POTENTIAL FOR A POSSIBLE TORNADO. AGAIN THIS WOULD
BE SOUTH OF I-80 AND MORE LIKELY ACROSS THE SOUTHERN THIRD OR
SO OF THE CWA.
DEPENDING ON WHERE THESE THUNDERSTORMS TRACK LATER THIS EVENING,
THEY MAY CONTINUE INTO THE OVERNIGHT HOURS ACROSS THE FAR
SOUTHERN CWA, BUT THE OVERALL TREND SHOULD BE FOR THESE TO
GRADUALLY SHIFT SOUTHEAST AND EVENTUALLY OUT OF THE LOCAL AREA.
CONFIDENCE IS ALSO INCREASING THAT SUNDAY WILL NOW BE MAINLY DRY
FOR MOST OF THE AREA WITH LITTLE SUPPORT FOR THUNDERSTORM
DEVELOPMENT. IF ANYTHING DEVELOPS, THE BEST CHANCE WOULD BE
ACROSS THE FAR SOUTHERN CWA AND MAINTAINED SLIGHT CHANCE POPS
ACROSS THIS AREA BUT LATER FORECASTS MAY BE ABLE TO GO DRY FOR
THE ENTIRE AREA.
MUCH OF SUNDAY NIGHT IS EXPECTED TO BE DRY. HOWEVER, THERE IS A
CONSENSUS AMONG GUIDANCE FOR A POSSIBLE THUNDERSTORM COMPLEX
MOVING SOUTHEAST FROM MN/WI INTO NORTHEAST IA/NORTHWEST IL EARLY
MONDAY MORNING, PERHAPS AROUND DAYBREAK. LOW CONFIDENCE FOR THIS
POSSIBILITY, BUT OPTED TO INCLUDE LOW CHANCE POPS ACROSS THE FAR
NORTHWEST CWA FOR NOW AND TRENDS WILL NEED TO BE MONITORED WITH
LATER FORECASTS.
WITH THE EXPECTATION THAT SUNDAY WILL BE DRY WITH AT LEAST
PARTLY CLOUDY SKIES BY AFTERNOON, HIGH TEMPS IN THE UPPER 80S TO
AROUND 90 LOOK ON TRACK. DEWPOINTS GENERALLY IN THE MID 70S,
PERHAPS A LITTLE HIGHER IN THE RURAL AREAS, MAYBE SLIGHTLY LOWER
IN THE URBAN AREAS. THIS WOULD YIELD PEAK HEAT INDICES GENERALLY
IN THE 95 TO 100 RANGE AND NOT PLANNING ANY HEAT HEADLINES FOR
SUNDAY.
FINALLY, WITH THE LIGHT WINDS, VERY MOIST LOW LEVELS AND A WEAK
FRONTAL BOUNDARY SAGGING INTO THE NORTHERN CWA, FOG WILL BE A
CONCERN OVERNIGHT INTO EARLY SUNDAY MORNING AND HAVE ADDED FOG
TO THE FORECAST FOR THE NORTH AND NORTHWEST CWA. SOME DENSE FOG
IS POSSIBLE BUT CONFIDENCE IS TOO LOW TO MENTION DENSE FOG FOR
NOW. CMS
MONDAY THROUGH SATURDAY:
EARLY MONDAY, A LOW AMPLITUDE UPPER WAVE WILL TRACK NEARBY
AROUND THE NORTHERN PERIPHERY OF THE UPPER HIGH CENTERED OVER
THE GULF COAST. AT THE SURFACE, A COUNTERPART COLD FRONT IS
EXPECTED TO GET HUNG UP TO OUR NORTH WHILE THE REST OF THE WAVE
COMES AND GOES THROUGH THE MORNING. THE DEPARTING UPPER WAVE
WILL STEAL A LOT OF LAYER MOISTURE AWAY FROM THE REGION
FOLLOWING THE MORNING. SOME CONVECTION MAY LINGER FROM SUNDAY
NIGHT WHILE THESE FEATURES REMAIN MORE CONGEALED. FOR MORE ON
THE PRECIP CHANCES THROUGH EARLY MONDAY, SEE THE SHORT TERM
DISCUSSION ABOVE. PLENTIFUL MOISTURE WILL REMAIN AT THE SURFACE
LEADING TO A HIGHLY UNSTABLE AND LARGELY UNCAPPED MIDDAY
AIRMASS. CONCEPTUALLY, THIS COULD LEAD TO INSTANCES OF FREE
CONVECTION DURING THE DAY, ALTHOUGH FEW PIECES OF GUIDANCE
RESOLVE ANY PRECIP ON MONDAY BEYOND THE MORNING LIKELY DUE TO A
LACK OF FORCING MECHANISMS. SO THE FORECAST WAS KEPT DRY MONDAY
AFTERNOON/EVENING FOR THE TIME BEING.
FOLLOWING WHAT WILL LIKELY BE AN UNCOMFORTABLY WARM SUNDAY,
EVEN MORE SWELTERING HEAT IS EXPECTED ON MONDAY, ALTHOUGH THERE
ARE UNCERTAINTIES. THE FOOTPRINT OF THE UPPER HIGH WILL EXPAND
ACROSS MUCH OF THE PLAINS AND MIDWEST LATE SUNDAY INTO MONDAY
KEEPING THE HOT AIRMASS PUMPING INTO THE REGION. HIGHS MONDAY
AFTERNOON ARE EXPECTED TO BE IN THE LOWER TO MIDDLE 90S,
INCLUDING ALONG THE LAKESHORE. WHEN COUPLED WITH DEWPOINTS
FORECAST IN THE UPPER 70S TO NEAR 80 DEGREES, WE COULD BE
LOOKING AT AFTERNOON HEAT INDICES BETWEEN 105 AND 110, POSSIBLY
EVEN NEARING 115 IN SPOTS. IT'S NOT WELL UNDERSTOOD YET HOW
MORNING CONVECTION AND LINGERING CLOUD COVER WILL INFLUENCE
DAYTIME HEATING, AND ANY ACTIVITY THAT BREWS LATER IN THE DAY
WOULD ALSO PLAY A ROLE. BUT FOR NOW, IT LOOKS AS THOUGH WE'RE
HEADED FOR HEAT HEADLINES TO KICK OFF THE WORK WEEK.
EVEN MORE UNCERTAINTIES LOOM FOR TUESDAY AS THAT COLD FRONT IS
EXPECTED TO MOVE ACROSS THE CWA SOMETIME TUESDAY-TUESDAY NIGHT.
MODEL CAMPS HAVE DIFFERING OPINIONS ON THE TIMING OF FROPA AND
THE MAGNITUDE OF COOLING IN ITS WAKE. GENERALLY, TUESDAY SHOULD
BE ANOTHER COOKER AROUND THE AREA WITH AFTERNOON HEAT INDICES
AGAIN NEARING OR EXCEEDING 100 DEGREES. A LAKE BREEZE LOOKS TO
MOVE ONSHORE WHICH WOULD KEEP COMMUNITIES NEAR AND DOWNWIND OF
THE LAKE NOTICEABLY COOLER, BUT A COUPLE PIECES OF GUIDANCE DO
SUGGEST OFFSHORE FLOW THROUGHOUT THE DAY UNTIL THAT FRONT DROPS
THROUGH WHICH WOULD OFFER LITTLE TO NO RELIEF NEAR THE LAKE. THE
FRONT MEANDERING ABOUT THE AREA WILL PROVIDE LOW CHANCES FOR
SCATTERED SHOWERS AND STORMS ON TUESDAY.
TUESDAY NIGHT INTO WEDNESDAY, THE UPPER HIGH WILL BREAK AND
GIVE WAY TO A LARGE UPPER TROUGH SWINGING ACROSS THE GREAT LAKES
AND ANOTHER UPPER HIGH FORMING OVER THE HIGH PLAINS. THIS WILL
ALLOW FOR MORE COMFORTABLE TEMPERATURES ON WEDNESDAY WITH HIGHS
FORECAST IN THE LOWER AND MIDDLE 80S. WITH THE RELATIVELY MOIST
ZONAL FLOW AND AMBIENT FORCING AROUND THE NEARBY JET, THERE IS A
SIGNAL FOR A WAVE OR TWO OF PRECIP TO MOVE THROUGH THE REGION
TUESDAY NIGHT THROUGH WEDNESDAY. SURFACE HIGH PRESSURE SITUATING
OVER THE GREAT LAKES WILL KEEP THE MORE TEMPERATE CONDITIONS
AROUND DURING THE BACK HALF OF THE WEEK WITH THE HIGH LOOKING TO
STEER MOST PRECIP SYSTEMS AWAY FROM THE LOCAL AREA.
DOOM
INCREASING NORTH/NORTHEAST WINDS WEDNESDAY AFTERNOON INTO
WEDNESDAY NIGHT, POSSIBLY GUSTING TO 30 MPH WILL LEAD TO HIGH
WAVES AND DANGEROUS SWIMMING CONDITIONS AT LAKE MICHIGAN
BEACHES. THESE NORTHERLY WINDS MAY CONTINUE THROUGH FRIDAY
LEADING TO UNCERTAINTY FOR WHEN THE DANGEROUS SWIMMING
CONDITIONS MAY END. CMS
AVIATION /06Z TAFS THROUGH 12Z MONDAY/
ISSUED AT 1245 AM CDT SUN JUL 27 2025
KEY MESSAGES:
- SPOTTY SHOWERS THROUGH THE OVERNIGHT, ESPECIALLY NEAR MDW AND
GYY
- PERIOD OF IFR TO MVFR VSBYS AT RFD/DPA OVERNIGHT, WITH SOME
POTENTIAL AT ORD/MDW/GYY
- EAST WIND SHIFT BEHIND A LAKE BREEZE LATE SUNDAY MORNING.
A WEAK MID LEVEL TROUGH APPROACHING THE AREA IS GENERATING SOME
ISOLATED TO SCATTERED SHOWERS ALONG THE INTERSTATE 80 CORRIDOR
EARLY TONIGHT. THESE WILL PROBABLY CONTINUE THROUGH MUCH OF THE
OVERNIGHT AND MAY AFFECT GYY AND POSSIBLY SKIRT MDW. OTHERWISE,
GUIDANCE IS SHOWING THAT IFR/MVFR CONDITIONS WILL TRY AND
DEVELOP YET TONIGHT AND PERSIST A FEW HOURS AFTER SUNRISE.
SUSPECT THAT THE EXTENT OF THIS IS OVERDONE AND HAVE THE BEST
CONFIDENCE IN AT LEAST MVFR VSBY REDUCTION AT RFD AND POSSIBLY
DPA. MAINTAINED THE MVFR AND TEMPO IFR FROM THE PREVIOUS TAF
ISSUANCE FOR NOW AND WILL CONTINUE TO MONITOR AND REFINE AS
NECESSARY.
A LIGHT WIND REGIME WILL CONTINUE OVERNIGHT WITH A STEADIER EAST
TO SOUTHEAST WIND EXPECTED LATER THIS MORNING THROUGH THE
AFTERNOON. WINDS WILL DIMINISH AFTER SUNSET AND WILL NEED TO
MONITOR FOR POSSIBLE MVFR/IFR ONCE AGAIN WITH A VERY MOIST
AIRMASS STILL IN PLACE.
MDB
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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