532
FXUS63 KLOT 100831
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
331 AM 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 CONTINUES TO BE FAVORED FOR
SCATTERED/WIDELY SCATTERED SHOWER COVERAGE OF SUCH ACTIVITY,
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 WITH THE MAIN HAZARDS OF 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.
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, DO THINK WEDNESDAY 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 90 ON
THURSDAY. THE INFLUENCE OF THE LAKE ON TEMPERATURES MAY BE MORE
MUTED BY THURSDAY OWING TO THE STRONGER SOUTHERLY WINDS.
THURSDAY EVENING 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 TO FRIDAY 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
TOWARD THE END OF NEXT WEEK. 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.
TAKING A STEP BACK, 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 /06Z TAFS THROUGH 12Z SUNDAY/
ISSUED AT 1220 AM CDT SAT MAY 10 2025
KEY MESSAGES:
- GUSTY NORTHEAST WIND SHIFT BEHIND BACKDOOR FRONT EXPECTED LATE
MORNING BETWEEN ~15-17Z.
LIGHT AND VARIABLE WINDS WILL SETTLE INTO A PREVAILING
SOUTHWESTERLY DIRECTION TOWARD DAYBREAK AND GRADUALLY VEER
NORTHWEST AHEAD OF AN APPROACHING BACKDOOR COLD FRONT. THE FRONT
IS EXPECTED TO MOVE ACROSS THE AREA BETWEEN ~15-17Z. EXPECT
SOME FINE TUNING TO THE TIMING OF THE GUSTY NORTHEAST WIND SHIFT
AS THE FRONT GETS CLOSER. WIND GUSTS IN THE MID-20 KT RANGE
WILL CONTINUE THROUGH THE AFTERNOON AND EARLY EVENING HOURS,
THEN GRADUALLY EASE OVERNIGHT.
PETR
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY FROM 10 AM THIS MORNING TO 7 AM CDT
SUNDAY FOR THE IL AND IN NEARSHORE WATERS.
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