412
FXUS63 KLOT 112321
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
621 PM CDT MON MAY 11 2026
KEY MESSAGES
- TUESDAY WILL BE WARM AND START DRY WITH SHOWERS AND PERHAPS A
THUNDERSTORM DURING THE AFTERNOON AND EVENING HOURS.
- COOLER CONDITIONS ARE EXPECTED ON WEDNESDAY BEFORE A LONGER-
LASTING WARM UP ARRIVES TO CLOSE THE WEEK.
- THE MAY 16 THROUGH 19 TIMEFRAME MAY FEATURE SEVERAL ROUNDS OF
SHOWERS AND STORMS IN THE GENERAL REGION.
DISCUSSION
ISSUED AT 138 PM CDT MON MAY 11 2026
A LARGE SURFACE HIGH PRESSURE SYSTEM CONTINUES TO SERVE AS THE
MAIN FACTOR OF INFLUENCE TODAY, AND IS LEADING TO SUNNY SKIES,
AN EAST TO NORTHEASTERLY BREEZE, AND COOL TEMPERATURES IN THE
UPPER 50S TO LOWER 60S.
TONIGHT, THE SURFACE HIGH WILL SHIFT EASTWARD CAUSING WINDS TO
GRADUALLY VEER SOUTHEASTERLY. A GRADIENT IN OVERNIGHT LOWS IS
EXPECTED WITH PARTLY CLOUDY SKIES HOLDING VALUES IN THE UPPER
30S TO LOWER 40S ACROSS ILLINOIS AND LARGELY CLEAR SKIES
ALLOWING FOR TEMPERATURES TO DROP INTO THE MID 30S ACROSS
NORTHWESTERN INDIANA. DO EXPECT AT LEAST PATCHY FOG TO DEVELOP
ACROSS NORTHWESTERN INDIANA OVERNIGHT, BUT WILL HOLD OFF ON A
FROST ADVISORY GIVEN THE EXPECTATION FOR TEMPERATURES TO REMAIN
ABOVE FREEZING.
TOMORROW, AN UPPER-LEVEL SHORTWAVE (CURRENTLY PROPAGATING ALONG
THE MONTANA, NORTH DAKOTA, AND SASKATCHEWAN BORDERS) WILL DIVE
SOUTHEASTWARD INTO THE GREAT LAKES. AHEAD OF THE WAVE,
SOUTHWESTERLY FLOW WILL INCREASE MARKEDLY LEADING TO BREEZY
SURFACE WINDS THROUGH THE AFTERNOON HOURS. WITH A VERY DRY START
TO THE DAY (DEW POINTS IN THE UPPER 20S), CONTINUE TO LEAN ON
THE MORE "MIX-Y" GUIDANCE WHICH ADVERTISES GUSTS PEAKING NEAR 40
MPH BY EARLY AFTERNOON. CONSEQUENTLY, A PLUME OF WARM
TEMPERATURES (850MB VALUES NEAR +12C) WILL ADVECT INTO THE
REGION VIA THE STRONG SOUTHWESTERLY FLOW, WHICH WITH THE DRY
PROFILE WILL SUPPORT HIGHS IN THE UPPER 70S TO LOWER 80S
AREAWIDE.
DURING THE AFTERNOON HOURS, GRADUALLY INCREASING DCVA AHEAD OF
THE APPROACHING TROUGH WILL SUPPORT AN AREA OF SOUTHEASTWARD-
MOVING SHOWERS AHEAD OF A SOUTHEASTWARD-MOVING COLD FRONT. WITH
THE RESIDUAL DRY AIRMASS, IT MAY TAKE TIME FOR TOP-DOWN
SATURATION TO ALLOW FOR RAINDROPS TO SURVIVE TO THE GROUND
THROUGH THE AFTERNOON HOURS. IN FACT, LOCAL ENHANCEMENTS TO THE
WIND FIELD MAY OCCUR AS EVAPORATION LEADS TO MORE EFFICIENT
DOWNWARD MIXING. WITH THAT SAID, SUSPECT THAT SATURATION WILL
FINALLY BE ARCHIVED WITH SOUTHEASTWARD EXTENT, SUPPORTING A
GRADUAL INCREASE AND BROADENING OF POPS THROUGH THE AFTERNOON
HOURS WITH TIME. WITH EFFECTIVE EQUILIBRIUM LEVELS EXPECTED TO
TERMINATE RIGHT AROUND MINUS 20C, CHANCES FOR THUNDER CONTINUE
TO LOOK ON THE LOWER END OF THE SPECTRUM AND AROUND 15 TO 20% AT
ANY GIVEN POINT.
WITH RESPECT TO THE THREAT FOR SEVERE WEATHER ALONG THE COLD
FRONT TOMORROW EVENING, AM NOT IMPRESSED WITH THE EXCEEDINGLY
MARGINAL THERMODYNAMICS (MUCAPE OF 100-200 J/KG) AND APPARENT
LINEAGE TO PRECEDING RAINFALL (TO MOISTEN THE LOW-LEVEL MOISTURE
PROFILE) TO TAKE ADVANTAGE OF WHAT WOULD OTHERWISE BE A
SUPPORTIVE FORCING/KINEMATIC REGIME. IN FACT, SUSPECT LITTLE TO
NO CONVECTION WILL BE SUSTAINED ALONG THE FRONT, FAVORING A DRY
EVENING AND OVERNIGHT PERIOD. SO, WILL WITHHOLD ANY MENTION OF
SEVERE WEATHER IN ANY OUTGOING PRODUCTS.
QUICKLY RISING SURFACE PRESSURE IN THE WAKE OF THE COLD FRONT
WILL FACILITATE THE EFFICIENT ADVECTION OF COOL AIR IN THE WAKE
OF THE FRONT TUESDAY NIGHT INTO WEDNESDAY. A TRAILING SHORTWAVE
ARRIVING IN THE MORNING HOURS MAY ACTUALLY BOLSTER COLD AIR
ADVECTION THROUGH THE DAY. FALLING 850MB TEMPERATURES TOWARD 0C
WILL SET THE STAGE FOR STEEP LOW-LEVEL LAPSE RATES LEADING TO AN
EXPANSIVE STRATOCUMULUS DECK BY MID-MORNING. IN FACT, WOULD NOT
BE SURPRISED IN THE LEAST TO SEE SPRINKLES OR A FEW SHOWERS
THROUGHOUT THE DAY (HAVE MANUALLY INTRODUCED "SILENT" 10 POPS
FOR NOW). WHEN TAKEN ALTOGETHER, WEDNESDAY IS SHAPING UP TO FEEL
A BIT MORE LIKE FALL THAN SPRING.
TOWARD THE END OF THE WEEK, THE UPPER-LEVEL PATTERN WILL
UNDERGO A TRANSITION FROM PREDOMINANT TOUGHING TO QUASI-ZONAL
FLOW ALONG THE US-CANADIAN BORDER. AS A RESULT, THE MUCH-
ANTICIPATED TRANSITION TOWARD WARMER WEATHER REMAINS ON TRACK TO
ARRIVE BY THIS WEEKEND. WILL ALSO NOTE AN ENSEMBLE SIGNAL FOR
ROUNDS OF SHOWERS AND STORMS IN THE GENERAL REGION IN THE MAY
16-19 TIMEFRAME.
BORCHARDT
AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/
ISSUED AT 621 PM CDT MON MAY 11 2026
FORECAST CONCERNS FOR THE TERMINALS...
- GUSTY SOUTHWEST WINDS ON TUESDAY WITH PEAK GUSTS IN THE 30-35
KT RANGE.
- PERIOD OF SHOWERS TUESDAY AFTERNOON AND EVENING WHICH MAY
RESULT IN LOCALLY HIGHER WIND GUSTS. AN ISOLATED THUNDERSTORM
(15-20% CHANCE) MAY OCCUR AS WELL.
A SURFACE HIGH CONTINUES TO MEANDER ACROSS THE WESTERN GREAT
LAKES THIS EVENING WHICH WILL MAINTAIN GENERALLY TRANQUIL
WEATHER THROUGH TONIGHT. THE BREEZY NORTHEAST WINDS WILL
CONTINUE TO SUBSIDE THIS EVENING WITH LIGHT (5-10 KT) WINDS
OVERNIGHT. THOUGH, DIRECTIONS WILL BE VEERING INTO A SOUTHEAST
DIRECTION BEFORE EVENTUALLY SETTLING INTO A SOUTHWEST DIRECTION
TUESDAY MORNING.
HEADING INTO TUESDAY, THE UPPER DISTURBANCE (CURRENTLY OVER THE
ND-CANADIAN BORDER) WILL BEGIN TO PIVOT INTO THE GREAT LAKES
WHICH WILL PUSH A COLD FRONT THROUGH NORTHERN IL AND NORTHWEST
IN. AHEAD OF THIS FRONT SOUTHWESTERLY WINDS ARE EXPECTED TO
INCREASE WITH GUSTS INITIALLY AROUND 25-30 KTS BUT THEY WILL
PEAK IN THE 30-35 KT RANGE TUESDAY AFTERNOON. AS THE FRONT
ARRIVES, A BAND OF SHOWERS IS EXPECTED TO DEVELOP AND SWEEP
ACROSS THE AREA TUESDAY AFTERNOON INTO THE EVENING HOURS. WHILE
OVERALL MOISTURE AND INSTABILITY CONTINUE TO LOOK LIMITED IN
RECENT FORECAST SOUNDINGS, THERE IS STILL A 15-20% CHANCE FOR
AN ISOLATED THUNDERSTORM TO DEVELOP TUESDAY AFTERNOON.
REGARDLESS, THE STOUT WINDS ALOFT AND DRY-SUBCLOUD LAYER MAY
RESULT IN LOCALLY HIGHER GUSTS (UPWARDS OF 40 KTS) WITH ANY
SHOWERS.
SHOWERS ARE EXPECTED TO TAPER BY 02-03Z AT THE TERMINALS TUESDAY
EVENING WITH DRY CONDITIONS EXPECTED TO CLOSE OUT THE TAF
PERIOD. WHILE WINDS WILL BE DECREASING BEHIND THE FRONT TUESDAY
EVENING, A FEW 20-25 KT GUSTS MAY LINGER THROUGH 06Z. OTHERWISE,
VFR CONDITIONS ARE EXPECTED TO PREVAIL THROUGH THE ENTIRE
FORECAST PERIOD.
YACK
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY FROM 9 AM TUESDAY TO 7 PM CDT WEDNESDAY
FOR THE IL NEARSHORE WATERS.
SMALL CRAFT ADVISORY UNTIL 10 PM CDT THIS EVENING FOR THE IN
NEARSHORE WATERS.
SMALL CRAFT ADVISORY FROM 9 AM TUESDAY TO 1 AM CDT THURSDAY
FOR THE IN NEARSHORE WATERS.
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