466
FXUS63 KLOT 101716
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1216 PM CDT SAT MAY 10 2025
KEY MESSAGES
- A SHARP LAKE-ENHANCED COLD FRONT WILL BRING GUSTY WINDS AND
FALLING TEMPERATURES (MOST RAPID TEMP DROP AND STRONGEST
WINDS ALONG THE LAKESHORE) TODAY INTO THIS EVENING.
- ASIDE FROM THE COOL-DOWN TODAY, GENERALLY WELL ABOVE NORMAL
TEMPERATURES ARE IN STORE THROUGH THE WORK WEEK, WITH HIGHS
APPROACHING 90F ON THURSDAY FOR SOME AREAS.
- THERE WILL BE SHOWERS AND THUNDERSTORMS AT TIMES MONDAY
THROUGH THURSDAY, THOUGH MANY HOURS WILL ALSO BE DRY.
DISCUSSION
ISSUED AT 330 AM CDT SAT MAY 10 2025
THROUGH TONIGHT:
THERE ARE NO BIG CHANGES IN FORECAST THINKING FOR THE LAKE-
ENHANCED COLD FRONT POISED TO SURGE INLAND FROM THE LAKE AND
SPREAD WEST/SOUTHWESTWARD THE REST OF THE AFTERNOON. THE FRONT
IS CURRENTLY LOCATED UP ACROSS NORTHERN WISCONSIN NEAR THE DOOR
PENINSULA AND IS EXPECTED TO ENTER FAR NORTHEAST ILLINOIS DURING
THE 9 AM HOUR AND PROGRESS STEADILY SOUTHWESTWARD FROM THERE.
UNFORTUNATELY FOR LAKESIDE LOCATIONS, THERE WILL ONLY BE A
FLEETING PERIOD OF WARMTH THIS MORNING BEFORE THE FRONT CHARGES
IN. IN FACT, WE HAVE DOWNTOWN CHICAGO FORECAST TO REACH AROUND
70F/LOWER 70S AT 10AM AND THEN CRASH INTO THE LOWER-MID 50S
WITHIN AN HOUR!
WELL INLAND OF THE LAKE, TEMPERATURES WILL REACH THE MID 70S TO
LOWER 80S, WARMEST SOUTHWEST, BEFORE STARTING TO TUMBLE. IT DOES
APPEAR THAT FAR INLAND SECTIONS OF NORTHERN ILLINOIS SHOULD SEE
A BIT OF A LAG IN MUCH OF A TEMPERATURE DROP UNTIL AN EASTERLY
WIND SHIFT LATE IN THE DAY. OTHERWISE, FOR INTERIOR CHICAGO
SUBURBS, THE HIGHS IN THE 70S WILL OCCUR IN THE EARLY AFTERNOON,
AND THEN STEADILY FALL FROM THERE.
NORTH-NORTHEASTERLY WINDS WILL GUST UP TO 25-35 MPH BEHIND
FRONTAL PASSAGE, STRONGEST ALONG THE LAKESHORE, DUE TO 3-HOUR
PRESSURE RISES OF ABOUT 3-4 MB, FAIRLY STOUT FOR MAY. BRIEF
GUSTS INTO THE 35-40 MPH RANGE CAN'T BE RULED OUT IMMEDIATELY
BEHIND THE FRONT RIGHT ON THE LAKEFRONT. A REINFORCING SURGE OF
COOL AIR IN THE LATE AFTERNOON AND EARLY EVENING WILL PROBABLY
BRING A BRIEF UPTICK IN THE WINDS WITHIN RANGE OF THE LAKE (IF
THEY EASE A BIT DURING THE EARLY AFTERNOON). THESE WINDS WILL OF
COURSE MAKE THE FALLING TEMPS EVEN CHILLIER, APPARENT TEMPS IN
THE 40S NEAR THE LAKE PRIOR TO SUNSET! DON'T FORGET TO BRING
EXTRA LAYERS IF YOU WILL BE OUT AND ABOUT LATER TODAY INTO THIS
EVENING.
TONIGHT WILL BE FAIRLY CHILLY AS WELL WITH OVERNIGHT LOWS IN
THE UPPER 30S NEAR WISCONSIN TO LOWER-MID 40S ELSEWHERE AS WINDS
QUICKLY EASE IN THE LATE EVENING AND OVERNIGHT. SUPPOSE THERE
COULD BE SOME PATCHY FROST WHERE TEMPERATURES ARE COLDEST,
THOUGH IT DOESN'T LOOK LIKE A REPEAT OF LAST NIGHT (A CONTINUED
EAST TO NORTHEASTERLY BREEZE SHOULD WORK AGAINST TEMPERATURES AT
GRASS LEVEL FALLING BELOW FREEZING).
CASTRO/BORCHARDT
SUNDAY THROUGH FRIDAY NIGHT:
THERE WERE AGAIN NO BIG CHANGES IN FORECAST THINKING FROM
MOTHER'S DAY THROUGH THE UPCOMING WORK WEEK.
WITH UPPER-LEVEL RIDGING BUILDING INTO THE GREAT LAKES NORTH OF
A CUT-OFF LOW PRESSURE SYSTEM MEANDERING ALONG THE GULF COAST,
THE BRIEF COOLDOWN TODAY WILL BE SHORT-LIVED, SETTING THE TABLE
FOR A SPECTACULAR MOTHER'S DAY. COMPLETELY SUNNY SKIES IN
TANDEM WITH LITTLE TO NO ADVECTION (THANKS TO FLOW AT OR BELOW
20KT THROUGH THE ENTIRE DEPTH OF THE TROPOSPHERE) WILL
EFFECTIVELY "BAKE" TEMPERATURES BACK INTO THE MID TO UPPER 70S.
THE EXCEPTION WILL BE ALONG THE LAKE MICHGIAN SHORELINE, WHERE
EASTERLY WINDS OF 5 TO 15 MPH WILL LEAD TO A LAKE SHADOW
EFFECTIVELY KEEPING TEMPERATURES IN THE UPPER 50S (LAKESIDE) TO
MID 60S (NEAR I-294).
MONDAY INTO TUESDAY, A PACIFIC TROUGH WILL DIVE INTO THE
NORTHWESTERN UNITED STATES AND ENCOURAGE THE AFOREMENTIONED CUT-
OFF LOW PRESSURE SYSTEM ALONG THE GULF COAST TO LIFT EAST-
NORTHEASTWARD TOWARD THE OHIO RIVER VALLEY. THE SPEED AT WHICH
THIS HAPPENS REMAINS SOMEWHAT UNCERTAIN, GIVEN SPREAD IN
ENSEMBLE MODEL GUIDANCE. IN GENERAL, THE ECMWF/EPS HAS BEEN THE
FASTEST IN THIS PROCESS OVER THE PAST FEW MODEL CYCLES.
REGARDLESS, THE TREND SHOULD BE A GRADUAL INCREASE IN HUMIDITY
LEVELS EARLY NEXT WEEK WITH CORRESPONDING INCREASES IN CHANCES
FOR SHOWERS AND THUNDERSTORMS. MONDAY AFTERNOON, SCATTERED SLOW
MOVING PULSE TYPE SHOWERS AND THUNDERSTORMS APPEAR MOST FAVORED
SOUTH OF I-80 (30-50% POPS), WITH ~20% POPS UP TO ROUGHLY THE
I-88 CORRIDOR. CONVECTION SHOULD SLOSH NORTHWARD MONDAY EVENING
IN A WEAKENING STATE WITH POPS IN THE 20-30% RANGE.
AT THIS POINT, TUESDAY REMAINS FAVORED FOR SCATTERED/WIDELY
SCATTERED SHOWER COVERAGE AWAY FROM THE LAKE, WARRANTING 30 TO
50% POPS. THAT SAID, UNINSPIRING LAPSE RATES AROUND 6 K/KM AND A
DEARTH OF FLOW WITHIN THE CONVECTIVE LAYER POINT TOWARD
QUINTESSENTIAL SLOW-GROWING SPRINGTIME ISOLATED "POP-UP"
THUNDERSTORMS. THE MAIN THUNDERSTORM HAZARDS MONDAY AND TUESDAY
WILL BE OCCASIONAL LIGHTNING STRIKES AND DOWNPOURS. HIGHS BOTH
MONDAY AND TUESDAY WILL BE WELL ABOVE AVERAGE AND IN THE UPPER 70S
TO LOWER 80S, SAVE FOR SHORELINE LOCATIONS (WHERE EAST TO
SOUTHEASTERLY FLOW WILL CONTINUE TO SERVE AS AN EFFICIENT COOL
DRAFT TO ABOUT I-294). OVERNIGHT LOWS WILL ALSO BE UNSEASONABLY
WARM AND IN THE LOWER 60S AWAY FROM THE LAKESHORE.
WEDNESDAY INTO EARLY THURSDAY, UPPER-LEVEL HEIGHT RISES AHEAD
OF THE PACIFIC TROUGH MOVING INTO THE SOUTHWESTERN UNITED STATES
WILL EFFECTIVELY SQUASH THE UPPER-LEVEL LOW WHILE LIFTING
INTO THE GREAT LAKES. AS A RESULT, WEDNESDAY AFTERNOON MAY ONLY
HAVE ISOLATED SHOWERS AND THUNDERSTORMS AND AT LEAST THE FIRST
HALF OF THURSDAY SHOULD BE LARGELY DRY. INCREASING HUMIDITY
LEVELS, AN INCREASINGLY SOUTHERLY COMPONENT TO THE WIND, AND WARM
OVERNIGHT LOW TEMPERATURES WILL SET THE STAGE FOR THE WARMEST AIR
THUS FAR THIS SPRING TO SURGE INTO THE REGION. HIGHS ON WEDNESDAY
WILL BE POISED TO CLIMB INTO THE LOW TO MID 80S, FOLLOWED BY
PERHAPS UPPER 80S TO NEAR/AROUND 90F ON THURSDAY. THE INFLUENCE
OF THE LAKE ON TEMPERATURES MAY BE MORE MUTED BY THURSDAY OWING TO
THE STRONGER SOUTHERLY WINDS.
THURSDAY PM INTO FRIDAY, THE UPPER-LEVEL TROUGH WILL FINALLY
EJECT INTO THE MIDWEST. CONSIDERING WARM TEMPERATURES, BUILDING
HUMIDITY LEVELS, THE EASTWARD-ADVECTION OF AM EML PLUME, AND
INCREASING DEEP-LAYER FLOW AHEAD OF THE TROUGH, THE THURSDAY
AFTERNOON AND EVENING TIMEFRAME WILL NEED TO BE WATCHED FOR SEVERE
WEATHER SOMEWHERE WITHIN THE BROAD MIDWEST TO GREAT LAKES REGION.
INDEED, AI/ML GUIDANCE ALREADY HIGHLIGHTS A BROAD REGION ACROSS
THE CENTRAL US AS HAVING A THREAT FOR SEVERE WEATHER. WE'LL GET
INTO MORE DETAILS AS WE GET CLOSER AND CAN ACCORDINGLY ASSESS
WHETHER OR NOT A THREAT WILL MATERIALIZE LOCALLY. HOWEVER, CAN'T
RESIST MENTIONING THAT THE USUAL ISSUES WITH CAPPING AT THE BASE
OF THE EML AS WELL AS THE TIMING OF THE FORCING ALREADY LOOK TO BE
PLAYERS THAT MAY GOVERN WHETHER OR NOT WE SEE STORMS. IF THE COLD
FRONT PASSAGE IS ROBUST ENOUGH WITH THE LATE WEEK SYSTEM, FRIDAY
COULD END UP MAINLY DRY, FOLLOWED BY A DRY AND COOLER START OF
NEXT WEEKEND (AT THE LEAST).
LOOKING OUT DEEPER INTO MAY, ENSEMBLE MODEL GUIDANCE FAVORS A
PATTERN CHARACTERIZED BY WESTERN-US TROUGHING PREVAILING THROUGH
THE LAST FEW WEEKS OF THE MONTH. SUCH A PATTERN WOULD TYPICALLY
FAVOR NEAR TO ABOVE AVERAGE TEMPERATURES AND REGULAR OPPORTUNITIES
FOR SHOWERS AND STORMS IN THE GREAT LAKES. SO, THE ONGOING PERIOD
OF DRY WEATHER (HOWEVER COMFORTABLE TEMPERATURE-WISE) DOES HAVE
AN END IN SIGHT.
BORCHARDT/CASTRO
AVIATION /18Z TAFS THROUGH 00Z MONDAY/
ISSUED AT 1216 PM CDT SAT MAY 10 2025
FORECAST CONCERN FOR THE TERMINALS...
- BREEZY (20-25 KT) NORTHEAST WINDS THIS AFTERNOON.
A LAKE ENHANCED COLD FRONT CONTINUES TO SURGE ACROSS NORTHEAST
IL AND NORTHWEST IN RESULTING A SHARP NORTHEAST WIND SHIFT AND
INCREASE IN WINDS IN THE FRONT'S WAKE. WHILE THERE HAVE BEEN
PERIODS OF 30 KT GUSTS IMMEDIATELY BEHIND THE FRONT, MOST GUSTS
HAVE GENERALLY BEEN IN THE 20-25 KT AND THEY SHOULD REMAIN AS
SUCH THROUGH THE AFTERNOON. GUSTS WILL GRADUALLY TAPER THIS
EVENING BEFORE FULLY SUBSIDING BETWEEN 03Z AND 05Z TONIGHT, THUS
WINDS IN THE 8-12 KT RANGE CAN BE EXPECTED OVERNIGHT THROUGH
SATURDAY WITH DIRECTIONS BECOMING MORE EASTERLY SATURDAY
MORNING. OTHERWISE, EXPECT MOSTLY CLEAR SKIES TO PREVAIL THROUGH
THE PERIOD.
YACK
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 7 AM CDT SUNDAY FOR THE IL AND IN
NEARSHORE WATERS.
VISIT US AT WEATHER.GOV/CHICAGO
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