863
FXUS63 KLOT 291155
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
655 AM CDT SAT MAR 29 2025
KEY MESSAGES
- A COLD FRONT WILL MOVE SOUTH INTO FAR NORTHERN IL THIS
AFTERNOON, TURNING WINDS NORTHEAST AND MUCH COOLER TEMPS NEAR
LAKE MICHIGAN.
- SCATTERED SHOWERS TODAY/TONIGHT. CHANCE (20%) OF A
THUNDERSTORM TONIGHT.
- SEVERE STORMS SUNDAY WITH ALL SEVERE WEATHER MODES POSSIBLE.
- ACTIVE WEATHER PATTERN CONTINUES INTO NEXT WEEK WITH THE NEXT
BEST CHANCE FOR THUNDERSTORMS MIDWEEK.
DISCUSSION
ISSUED AT 245 AM CDT SAT MAR 29 2025
THROUGH SUNDAY:
PRIMARY FORECAST FOCUS IS FOR SEVERE THUNDERSTORMS ON SUNDAY.
SOUTHWEST WINDS ARE SLOWLY DIMINISHING EARLY THIS MORNING AND
THIS TREND WILL CONTINUE THROUGH DAYBREAK BUT GUSTS BACK INTO
THE 30 MPH RANGE ARE EXPECTED TODAY, ESPECIALLY FOR AREAS SOUTH
OF I-80. THE COLD FRONT THAT IS STILL EXPECTED TO MOVE SOUTH
ALONG THE LAKE MICHIGAN SHORE THIS AFTERNOON HAS PUSHED AS FAR
SOUTH AS MKE/RAC IN SOUTHEAST WI EARLY THIS MORNING. THE STRONG
SOUTHWEST WINDS ARE SO FAR KEEPING IT FROM MOVING FURTHER
SOUTH. SOME OF THE HIGH RES GUIDANCE DOES SHOW THE BOUNDARY
MAKING IT TO NEAR THE IL/WI STATE LINE THIS MORNING. HOWEVER,
THE OVERALL TRENDS IN GUIDANCE HAS BEEN TO SLOW THE FRONT'S PUSH
SOUTH THIS AFTERNOON, NOT MOVING IT AS FAR SOUTH AS PREVIOUSLY
SHOWN AND HAVE IT RETREATING BACK NORTH FASTER TONIGHT, PERHAPS
WITH SOUTHERLY WINDS ACROSS THE ENTIRE AREA BY DAYBREAK SUNDAY
MORNING. DESPITE ITS CURRENT LOCATION, HAVE OPTED TO MAKE NO
CHANGES TO THE PREVIOUS FORECAST THROUGH EARLY EVENING, BUT DID
LIFT IT BACK NORTH FASTER OVERNIGHT. WHEREVER THE FRONT MOVES,
TEMPS WILL TANK WITH 40S LIKELY CLOSER TO THE LAKE ALONG WITH
THE POTENTIAL FOR FOG. AHEAD OF THIS FRONT AND FOR THE REST OF
THE AREA, HIGHS LIKELY REACH THE UPPER 60S TO LOWER 70S.
PRECIPITATION CHANCES TODAY REMAIN UNCERTAIN. THERE ARE TWO
PERIODS AND AREAS THAT THE MODELS SEEM TO BE TRENDING TOWARD.
THE FIRST IS THIS MORNING AND GENERALLY SOUTH OF I-80 AND THEN
THE SECOND IS LATER THIS AFTERNOON/EARLY THIS EVENING, GENERALLY
NORTH OF I-80. BUT THERE WILL LIKELY BE MANY DRY HOURS ACROSS
THE ENTIRE AREA TODAY AND OPTED TO CAP POPS IN THE 30-40% RANGE.
INSTABILITY LOOKS LIMITED AT BEST AND ANY PRECIP THAT DOES
DEVELOP SHOULD BE MAINLY SHOWERS. THE DRIER TREND LOOKS TO
CONTINUE INTO TONIGHT WHICH MAY BE DRY ACROSS MUCH OF THE AREA
THROUGH THE EARLY OVERNIGHT HOURS AND ALSO REDUCED POPS DURING
THIS TIME PERIOD AS WELL.
BY SUNDAY MORNING, LOW PRESSURE WILL BE OVER EASTERN IA AND WILL
LIKELY TRACK ACROSS FAR NORTHERN IL/SOUTHEAST WI DURING THE
AFTERNOON AND THEN INTO SOUTHERN LOWER MI BY SUNDAY EVENING, A
FREQUENTLY FAVORABLE TRACK FOR SEVERE WEATHER FOR THE LOCAL
AREA. THE CONCERN HERE IS WHETHER ANY SHOWER/THUNDERSTORM
ACTIVITY CAN DEVELOP EARLY ENOUGH TO LIMIT INSTABILITY THIS FAR
NORTH. IN THE EVENT THIS OCCURS, THE GREATEST AREA OF CONCERN
FOR SEVERE WEATHER COULD BE THE FAR SOUTHEAST CWA. HOWEVER, THE
ECMWF HAS BEEN VERY CONSISTENT SHOWING STORMS DEVELOPING BY LATE
MORNING AND RACING ACROSS MUCH OF THE CWA THROUGH MID/LATE
AFTERNOON AND ACTUALLY SHOWS TEMPS IN THE MID/UPPER 70S JUST
AHEAD OF THE STORMS, AS DOES THE CANADIAN. THE NAMNEST ALSO IS
FAIRLY DRY SUNDAY MORNING, PRIOR TO THUNDERSTORMS DEVELOPING BY
LATE MORNING. WHILE ALL SEVERE WEATHER MODES ARE POSSIBLE, THE
PROXIMITY OF THE SURFACE LOW MAY LEAD TO A HIGHER TORNADO THREAT
ACROSS NORTHERN IL. STILL 36+ HOURS AWAY AND TRENDS WILL NEED
TO BE CLOSELY MONITORED, BUT SEVERE WEATHER FOR MUCH OF THE AREA
IS STILL ON TRACK, ALONG WITH NO CHANGES FROM THE PREVIOUS SPC
DAY3 OUTLOOK TO THE NEW DAY2 OUTLOOK. HEAVY RAIN WILL ALSO BE
POSSIBLE WITH THESE STORMS WHICH MAY LEAD TO MINOR FLOODING
CONCERNS, BUT THE OVERALL FAST SPEED OF THE STORMS SHOULD LIMIT
ANY FLOODING. CMS
SUNDAY NIGHT THROUGH FRIDAY:
THUNDERSTORMS WILL BE ON THEIR WAY OUT OF THE AREA HEADING INTO
SUNDAY NIGHT. WRAP AROUND PRECIPITATION ON THE BACK SIDE OF THE
DEPARTING SURFACE LOW MAY LEAD TO LIGHT RAIN AND SNOW DRIFTING
INTO THE AREA OVERNIGHT INTO MONDAY MORNING. WHILE TEMPERATURES
ARE FORECAST TO DROP INTO THE 30S, WARM ANTECEDENT CONDITIONS
SHOULD LIMIT ANY SLUSHY COATINGS TO MAINLY COLDER ELEVATED
SURFACES. IT IS ALSO POSSIBLE THE MAJORITY OF THIS PRECIPITATION
ENDS MORE QUICKLY THAN CURRENTLY FORECAST. STRONG COLD AIR
ADVECTION AND ONSHORE FLOW BEHIND SUNDAY'S WEATHER SYSTEM WILL
HOLD DAYTIME HIGH TEMPERATURES ON MONDAY TO THE UPPER 30S ALONG
THE LAKESHORE TO MID 40S FURTHER INLAND.
BEYOND THE WEEKEND, THE WEATHER PATTERN REMAINS ACTIVE WITH
ANOTHER STRONG LOW PRESSURE SYSTEM FORECAST TO LIFT ACROSS THE
REGION MIDWEEK WHICH COULD BRING ANOTHER ROUND OF THUNDERSTORMS
(SOME POSSIBLY SEVERE?). OUT AHEAD OF THIS FEATURE, WARM
ADVECTIVE SHOWERS COULD DEVELOP AS EARLY AS TUESDAY EVENING, AND
MAY EVEN MIX WITH SNOW TOWARD THE WI/IL STATELINE. TIMING
DIFFERENCES REMAIN WITH WEDNESDAY'S SHOWER/THUNDERSTORM
POTENTIAL. A FASTER ONSET MAY LIMIT OUR OVERALL SEVERE WEATHER
POTENTIAL IF STORMS ROLL THROUGH DURING THE MORNING HOURS, WHILE
A SLOWER ONSET WOULD ALLOW MORE TIME FOR DESTABILIZATION INTO
THE AFTERNOON, SUPPORTING A GREATER SEVERE WEATHER THREAT. AT
THIS RANGE GUIDANCE HAS TRENDED TOWARD MORE MORNING CONVECTION,
BUT THIS CAN CERTAINLY CHANGE GIVEN HOW FAR OUT IT IS. WILL
CONTINUE TO HONE IN ON THIS POTENTIAL OVER THE COMING DAYS.
ADDITIONAL SYSTEMS ARE FORECAST TO MOVE ACROSS THE BROADER
REGION LATE WEEK INTO THE WEEKEND WHICH COULD BRING ADDITIONAL
RAIN CHANCES.
PETR
AVIATION /12Z TAFS THROUGH 18Z SUNDAY/
ISSUED AT 655 AM CDT SAT MAR 29 2025
KEY MESSAGES:
- SPOTTY SHOWERS (VCSH) POSSIBLE THROUGH MUCH OF THE PERIOD,
WITH SLIGHTLY BETTER POTENTIAL LATE AFTERNOON/EARLY EVENING.
- LOW CONFIDENCE IN NE WIND SHIFT REACHING ORD/MDW TODAY.
- PERIOD OF IFR CONDITIONS POSSIBLE NEAR AND BEHIND BACKDOOR
FRONT THIS EVENING, EXPANDING ACROSS ALL SITES OVERNIGHT.
- 30% CHANCE OF TSRA DEVELOPING LATE SUNDAY AM, WITH BETTER
POTENTIAL IN THE AFTERNOON.
AT LEAST SPOTTY VFR SHOWERS/SPRINKLES COULD BE WITHIN THE
VICINITY OF THE TERMINALS THROUGH MUCH OF THE TAF PERIOD. FOR
NOW HANDLE THIS WITH PREVAILING VCSH, WITH THE BEST SIGNAL FOR
GREATER COVERAGE OF SHOWERS BEING LATE AFTERNOON INTO EARLY
EVENING, CURRENTLY HANDLED BY TEMPO -SHRA. IT IS POSSIBLE
ADDITIONAL TEMPOS WILL BE NEEDED, POTENTIALLY AS EARLY AS THIS
MORNING BASED ON LATEST RADAR TRENDS.
CONFIDENCE IN THE TIMING AND OCCURRENCE OF A NORTHEAST WIND
SHIFT AT THE TERMINALS LATER TODAY REMAINS LOW, WITH A MAJORITY
OF HI-RES GUIDANCE KEEPING IT JUST NORTH OF ORD. WITH THAT
SAID, GUIDANCE TENDS TO NOT BE FAR ENOUGH SOUTH WITH THESE
BACKDOOR FRONTS. RATHER THAN MAKING BIG CHANGES TO THE INHERITED
TAFS, OPTED TO SHIFT THE TIMING A BIT LATER (0Z) AND WILL
CONTINUE TO MONITOR UPSTREAM OBSERVATIONS THROUGH THE DAY.
WHERE THE AFOREMENTIONED BACKDOOR FRONT ENDS UP WILL PLAY A
ROLE IN CIG/VSBY TRENDS THIS EVENING. CURRENTLY IFR CONDITIONS
ARE FAVORED NEAR AND NORTH OF THE BOUNDARY AND THEN GRADUALLY
EXPAND ACROSS THE REST OF THE TERMINALS OVERNIGHT. CAN'T RULE
OUT PATCHY DRIZZLE AND MVFR VSBY REDUCTIONS DURING THIS TIME,
BUT HAVE OPTED TO MAINTAIN VFR VCSH FOR NOW.
WE CONTINUE TO MONITOR THE POTENTIAL FOR SEVERE WEATHER ON
SUNDAY. ONE SCENARIO THAT COULD IMPACT THE AFTERNOON SEVERE
WEATHER POTENTIAL IS WHETHER MORNING STORMS DEVELOP AND LIMIT
THE AMOUNT OF DESTABILIZATION THAT OCCURS. DUE TO THIS SCENARIO
BEING A POSSIBILITY, OPTED TO INTRODUCE A PROB30 FOR -TSRA FROM
15-18Z AT ORD/MDW WHILE NOTING THE BETTER POTENTIAL FOR STORMS
WILL EXIST BEYOND THE CURRENT 30-HR TAF PERIOD.
PETR
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 10 AM CDT THIS MORNING FOR THE IL
NEARSHORE WATERS.
SMALL CRAFT ADVISORY UNTIL 4 PM CDT THIS AFTERNOON FOR THE IN
NEARSHORE WATERS.
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