857
FXUS63 KLOT 081108
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
608 AM CDT THU MAY 8 2025
KEY MESSAGES
- ISOLATED SHOWERS/THUNDERSTORMS THIS MORNING SOUTH/SOUTHEAST OF
CHICAGO.
- AREAS OF FROST LIKELY BY SUNRISE FRIDAY ALONG/NORTH OF THE
ILLINOIS AND KANKAKEE RIVER VALLEYS AND AWAY FROM THE CITY OF
CHICAGO.
- THIS WEEKEND WILL FEATURE MOSTLY SUNNY SKIES, LIKELY NO RAIN,
AND MILD TO POTENTIALLY UNSEASONABLY MILD TEMPERATURES
(ALTHOUGH IT WILL BE COOLER NEAR LAKE MICHIGAN).
DISCUSSION
ISSUED AT 350 AM CDT THU MAY 8 2025
THROUGH FRIDAY:
EARLY MORNING SURFACE ANALYSIS PLACES YESTERDAY'S STRONG COLD
FRONT SOUTH OF THE FORECAST AREA FROM CENTRAL IL INTO NORTHEAST
IN, WHILE STRONG 1030+ MB SURFACE HIGH PRESSURE WAS TO OUR
NORTH, CENTERED FROM ONTARIO INTO NORTHERN QUEBEC. THE WESTERN
GREAT LAKES REGION REMAINS IN COOL, BREEZY NORTHEAST FLOW ALONG
THE SOUTHERN PERIPHERY OF THE SURFACE HIGH. LOOKING ALOFT, A
POSITIVE-TILT MID-LEVEL SHORT WAVE WAS DIGGING SOUTHEAST ACROSS
THE GREAT LAKES REGION, AND WAS AIDING THE DEVELOPMENT OF A FEW
ISOLATED SHOWERS/THUNDERSTORMS ACROSS PARTS OF LOWER MI/NORTHERN
IN AT THIS HOUR. MODEL GUIDANCE SUGGESTS SOME OF THESE ISOLATED
SHOWERS AND STORMS MAY AFFECT PARTS OF OUR SOUTHEASTERN CWA
SOUTH OF ABOUT A PONTIAC TO VALPARAISO LINE THIS MORNING
(CURRENTLY AN ISOLATED TSRA ALONG THE PORTER/LA PORTE COUNTY
LINE SOUTHEAST OF KVPZ), AND HAVE ADDED SOME 20% POPS WITH
ISOLATED WORDING IN THESE AREAS PRIOR TO NOON. OTHERWISE, A
CONSIDERABLE AMOUNT OF LOW CLOUD COVER IS SPREADING SOUTHWEST
INTO THE AREA THIS MORNING AND WILL MAKE FOR PARTLY TO MOSTLY
CLOUDY SKIES BEFORE CLEARING DEVELOPS FROM THE NORTH/NORTHEAST
LATER THIS MORNING AND AFTERNOON. THOSE BREEZY NORTHEAST WINDS
WILL KEEP TEMPERATURES COOLER, ESPECIALLY ALONG/NEAR LAKE
MICHIGAN TODAY, WITH HIGHS EXPECTED TO RANGE FROM THE LOW 50S
NEAR THE SHORE TO AROUND 60 WELL INLAND ACROSS THE CHICAGO AREA.
FARTHER WEST AND SOUTH ACROSS THE FORECAST AREA MID TO UPPER
60S (PERHAPS EVEN A 70) ARE LIKELY TOWARD OUR WFO DVN/ILX
BORDERS.
THE SURFACE HIGH PRESSURE RIDGE TO OUR NORTH WILL CONTINUE TO
SETTLE ACROSS THE UPPER MIDWEST AND WESTERN GREAT LAKES REGION
TONIGHT, EVENTUALLY ALLOWING WINDS TO DIMINISH UNDER GENERALLY
CLEAR SKIES. THIS WILL ALLOW FOR GOOD RADIATIONAL COOLING
CONDITIONS, WITH TEMPERATURES EXPECTED TO FALL INTO THE MID-30S
IN PARTS OF INTERIOR NORTHERN IL/NORTHWEST IN. FROST DEVELOPMENT
IS THUS LIKELY ACROSS PARTS OF NORTHERN IL AND NORTHWEST IN
OVERNIGHT, ESPECIALLY NORTH OF THE ILLINOIS AND KANKAKEE RIVER
VALLEYS, BUT AWAY FROM THE HEART OF CHICAGO. ANTICIPATE THAT THE
DAY SHIFT WILL LIKELY NEED TO CONSIDER A FROST ADVISORY FOR
SOME OF THE AREA.
THE SURFACE RIDGE SETTLES ACROSS THE AREA ON FRIDAY, WITH
RIDGING DEVELOPING ALOFT. LIGHTER WINDS AND AMPLE SUNSHINE WILL
ALLOW FOR CONTINUED MODERATION IN TEMPERATURES, WITH HIGHS
GENERALLY 65-70 AWAY FROM THE LIGHTER, BUT STILL ONSHORE WINDS
OFF OF THE LAKE WHERE HIGHS IN THE 50S/LOWER 60S ARE EXPECTED.
RATZER
FRIDAY NIGHT THROUGH WEDNESDAY:
FRIDAY EVENING, AN UPPER LOW SWINGING ACROSS THE EASTERN GREAT
LAKES WILL EJECT TO THE EAST ALLOWING FOR THE WARM UPPER RIDGE
NORTH OF THE PLAINS TO SPREAD DEEPER OVER THE MIDWEST WHICH
WILL BRING UNSEASONABLY MILD CONDITIONS OVER THE WEEKEND. THERE
REMAINS UNCERTAINTY IN TEMPERATURE TRENDS THIS WEEKEND. THE NBM
CONTINUES TO RUN A BIT WARMER THAN MOST GUIDANCE OWING TO AN
ANOMALOUSLY WARM CMC MODEL/ENSEMBLE SUITE, SO STUCK WITH THE
PATTERN OF THE PAST FEW DAYS IN BRINGING TEMPERATURES DOWN A
COUPLE OF DEGREES FROM THE NBM'S INITIALIZATION. ANOTHER BIG
QUESTION THIS WEEKEND IS THE TIMING OF A BACKDOOR COLD FRONT ON
SATURDAY AND ITS INFLUENCE ON THE REST OF THE WEEKEND. JUST
ABOUT ALL MEDIUM-RANGE GUIDANCE IS ON BOARD WITH THIS FRONT
MOVING ACROSS THE AREA DURING THE DAY AND QUICKLY COOLING
CONDITIONS IN ITS WAKE. THE FRONT WILL SPREAD AWAY FROM THE LAKE
AND ACROSS THE CHICAGO METRO AREA SOMETIME IN THE AFTERNOON AND
ACROSS OUTLYING AREAS CLOSER TO LATE AFTERNOON/EVENING.
HOWEVER, THERE ARE DISCREPANCIES IN THE TIMING OF THIS FRONT,
ONLY ON THE ORDER OF A COUPLE OF HOURS BUT, GIVEN THE TIME OF
DAY, THOSE COUPLE OF HOURS WILL MAKE BIG DIFFERENCE IN
TEMPERATURE TRENDS DURING THE DAY. THE EURO IS THE EARLIEST
AMONG GUIDANCE AND BRINGS THE FRONT INLAND DURING THE EARLIER
PART OF THE AFTERNOON BEFORE THE METRO CAN TAKE FULL ADVANTAGE
OF DIURNAL HEATING. THE NAM IS THE LATEST BRINGING THE FRONT
THROUGH A BIT LATER IN THE AFTERNOON. ACCORDINGLY, THE EURO IS
SIGNIFICANTLY COOLER IN THE CITY AND AROUND THE INTERIOR CHICAGO
METRO FOR DAYTIME HIGHS THAN THE NAM. FINER DETAILS SHOULD COME
INTO FOCUS SOON AS MORE GUIDANCE BECOMES AVAILABLE, BUT AS OF
NOW TEMPERATURES LOOK TO REACH THE MIDDLE AND UPPER 70S ACROSS A
MAJORITY OF OUR CWA WHILE AREAS CLOSER TO THE LAKE WILL LIKELY
MAX OUT IN THE 60S BEFORE QUICKLY FALLING INTO THE 50S NEAR THE
LAKE DURING THE AFTERNOON BEHIND THE FRONT.
A LITTLE BIT OF LOW LEVEL MOISTURE LOOKS TO ACCOMPANY THE
FRONT. PROFILES REMAIN LARGELY DRY AND FORCING DOESN'T LOOK
OVERLY IMPRESSIVE EITHER. HOWEVER, THERE MAY BE JUST ENOUGH
MOISTURE IN PLACE TO STIR UP SOME HIGH-BASED CAPE AND POSSIBLY A
COUPLE OF CONVECTIVE SHOWERS OR LIGHT THUNDERSTORMS. MAYBE A
COUPLE OF DOZEN OF THE 80 INDIVIDUAL GEFS AND EPS MEMBERS
RESOLVE QPF ON SATURDAY, SO THE FORECAST WAS KEPT DRY FOR NOW,
BUT SOME SLIGHT CHANCES MIGHT HAVE TO BE INTRODUCED IN THE NEAR
FUTURE.
THERE ARE ALSO DISAGREEMENTS IN THE DEGREE OF COOLING WE'LL SEE
BEHIND THE FRONT. THE EURO AND NAM ARE MUCH MORE AGGRESSIVE
WITH THE COLD ADVECTION THAN THE GFS, AND THIS WILL HAVE
IMPLICATIONS ON TEMPERATURE TRENDS FOR SUNDAY. SO CONFIDENCE IS
A BIT LOWER FOR SUNDAY, BUT TEMPERATURES ONCE AGAIN ARE FORECAST
TO REACH THE MIDDLE AND UPPER 70S, POSSIBLY CLOSE TO 80 IN OUR
FAR SOUTH AND WEST. EXPECT ANOTHER DAY IN THE 60S AROUND THE
LAKESHORE ON SUNDAY. A CORRIDOR OF ADDED CLOUD COVER WILL
PROBABLY ACCOMPANY THE FRONT ON SATURDAY, BUT OTHERWISE EXPECT
LOTS OF SUN OVER THE WEEKEND, ESPECIALLY ON SUNDAY.
A SUBTROPICAL UPPER LOW MEANDERING ABOUT THE ARKLATEX AND
TENNESSEE VALLEY REGIONS WILL KEEP THE POLAR JET CONFINED TO
OVER THE CANADIAN PROVINCES EARLY NEXT WEEK KEEPING THE WARM AIR
PUMPING INTO THE REGION. THERE IS MUCH LESS CERTAINTY IN EXACT
TEMPERATURES NEXT WEEK WITH QUITE A BIT OF SPREAD AMONG MODELS,
ALTHOUGH WE SHOULD CONTINUE TO GENERALLY TREND WARMER THROUGH
THE WEEK. BUT 80S ARE LOOKING LIKELY IN OUR CWA FOR AT LEAST A
COUPLE OF DAYS NEXT WEEK WITH MIDDLE AND UPPER 80S EVEN POSSIBLE
CLOSER TO MIDWEEK. SCATTERED SHOWER AND THUNDERSTORM CHANCES
WILL RETURN NEXT WEEK AS THAT UPPER LOW ADVECTS SOME LAYER
MOISTURE INTO THE REGION AMONG A FEW TRANSIENT WAVES HERE AND
THERE. THE HIGHEST CHANCES THROUGH THE MIDDLE OF NEXT WEEK WILL
COME ON TUESDAY AS THE LOW EJECTS ACROSS THE OHIO VALLEY.
DOOM
AVIATION /12Z TAFS THROUGH 18Z FRIDAY/
ISSUED AT 608 AM CDT THU MAY 8 2025
THE MAIN AVIATION WEATHER CONCERNS FOR THE 12Z TAF PERIOD
INCLUDE:
* INTERMITTENT MVFR CIGS THIS MORNING AT THE CHICAGOLAND SITES
MVFR CIGS WILL INTERMITTENTLY FILL IN OVER THE CHICAGOLAND
SITES THIS MORNING THROUGH AS LATE AS 14 OR 15Z BEFORE GOING VFR
FOR THE REMAINDER OF THE PERIOD. MEANWHILE, NE WINDS WILL GUST
TO AROUND OR JUST OVER 20 KT FOR THE BETTER PART OF TODAY BEFORE
SUBSIDING TO UNDER 10 KT FOR THE EVENING AND REMAINING AS SUCH
THROUGH FRIDAY MORNING.
DOOM
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 4 AM CDT FRIDAY FOR THE IL AND IN
NEARSHORE WATERS.
VISIT US AT WEATHER.GOV/CHICAGO
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page