578
FXUS63 KLOT 140710
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
210 AM CDT WED OCT 14 2026
KEY MESSAGES
- TODAY WILL START OUT DRAB WITH MOSTLY CLOUDY SKIES. A FEW
SHOWERS OR AREAS OF DRIZZLE CANNOT BE RULED OUT THROUGH THE
AFTERNOON.
- A FALL STORM SYSTEM WILL MOVE THROUGH THE AREA THURSDAY AND
FRIDAY BRINGING PERIODS OF RAIN SHOWERS AND GUSTY
NORTHWESTERLY WINDS (THE LATTER PRIMARILY ON FRIDAY).
- FROSTY AND LOCALLY FREEZING CONDITIONS ARE FAVORED AWAY FROM
LAKE MICHIGAN FRIDAY NIGHT INTO SATURDAY.
- AFTER THE BRIEF PERIOD OF CHILLY WEATHER, THERE WILL BE A
WARMING TREND THIS WEEKEND INTO EARLY NEXT WEEK.
DISCUSSION
ISSUED AT 210 AM CDT WED OCT 14 2026
THOUGH TONIGHT:
EARLY MORNING GOES-19 WATER VAPOR IMAGERY DEPICTS A (NEARLY
CUT-OFF) UPPER-LEVEL TROUGH PROPAGATING ATOP THE FOUR CORNERS
REGION. SEVERAL CLUSTERS OF SHOWERS AND THUNDERSTORMS ARE
ONGOING AHEAD OF THE TROUGH ASSOCIATED WITH SEVERAL UPPER-
LEVEL VORTICITY MAXIMA PROPAGATING ATOP AN ELONGATED BAROCLINIC
ZONE DRAPED FROM THE SOUTHERN PLAINS THROUGH THE LOWER GREAT
LAKES. LOCALLY, HAVE BEEN MONITORING SCATTERED STORMS ACROSS THE
AREA THOUGH RELATIVELY MEAGER INSTABILITY IS MAINTAINING A
RELATIVELY GENERIC QUALITY INTENSITY IN SPITE OF AN OTHERWISE
FAVORABLE SHEAR PROFILE FOR ORGANIZED CONVECTION. MEANWHILE, A
SPRAWLING 1020MB+ SURFACE HIGH PRESSURE SYSTEM IS BUILDING INTO
THE NORTHERN PLAINS, AHEAD OF WHICH AN EXPANSIVE REGION OF LOW-
LEVEL STRATUS IS OOZING SOUTHWARD THROUGH THE UPPER MIDWEST.
AFTER DAYBREAK, THE AFOREMENTIONED SURFACE HIGH PRESSURE SYSTEM
WILL SHIFT EASTWARD TOWARD THE UPPER GREAT LAKES LEADING TO AN
INCREASE IN NORTHEASTERLY FLOW ACROSS NORTHERN ILLINOIS AND
NORTHWESTERN INDIANA. AS A RESULT, THE LOW-LEVEL BAROCLINIC ZONE
IN WHICH SHOWERS AND THUNDERSTORMS ARE ONGOING WILL SHIFT
SOUTHWARD WITH TIME. LOW-LEVEL ONSHORE FLOW WITHIN A MARGINALLY
UNSTABLE LAKE EFFECT REGIME BENEATH A STOUT LOW-LEVEL INVERSION
WILL REINFORCE LOW-LEVEL STRATUS THROUGH THE MORNING AND EARLY
AFTERNOON HOURS, LEADING TO A GRAY START TO THE DAY. CANNOT RULE
OUT A FEW INSTANCES OF SPRINKLES OR DRIZZLE NEAR LAKE MICHIGAN
OR NEAR US-24 (CLOSER TO THE LOW-LEVEL BAROCLINIC ZONE), SO WILL
MAINTAIN LOW-END POPS (10-20% CHANCES) GENERALLY EAST OF I-39
AND SOUTH OF I-80 THROUGH THE DAY. THE HIGH TEMPERATURE FORECAST
WILL HINGE ENTIRELY ON WHETHER OR NOT STRATUS IS ABLE TO CLEAR
BY EARLY THIS AFTERNOON, WITH HIGH RES GUIDANCE PROVIDING AN
AFFIRMATIVE "NO." AS SUCH GUIDANCE CAN SOMETIMES BE TOO
AGGRESSIVE WITH STRATUS, WILL TAKE THE MIDDLE GROUND AND ADVERTISE
HIGHS IN THE LOW TO MID 60S NORTH OF I-80 AND UPPER 60S TO
AROUND 70 SOUTH OF I-80 KEEPING IN MIND ACTUAL VALUES MAY VERIFY PLUS
OR MINUS A FEW DEGREES OF OUR FORECAST.
TONIGHT LOOKS QUIET. INCREASING UPPER-LEVEL CLOUD COVER AND
CONTINUED ONSHORE FLOW WILL HOLD OVERNIGHT LOWS GENERALLY IN THE
MID TO UPPER 50S, WARMEST NEAR LAKE MICHIGAN AND NEAR US-24.
THURSDAY INTO FRIDAY:
ENSEMBLE MODEL GUIDANCE REMAINS IN EXCELLENT AGREEMENT THAT THE
SOUTHWESTERN US TROUGH WILL EJECT NORTHEASTWARD AND PHASE WITH
A NORTHERN-STREAM TROUGH SCREAMING SOUTHEASTWARD OUT OF CANADA.
AM NOTING INCREASING AGREEMENT IN THE EXACT TRACK AND EVOLUTION
OF THE RESULTING SURFACE LOW, EMERGING FROM NEAR DODGE CITY, KS
THURSDAY MORNING TO KANSAS CITY, MISSOURI BY EARLY AFTERNOON,
PASSING DIRECTLY OVER OUR AREA THURSDAY EVENING, AND THEN
CONTINUING TOWARD SOUTHERN ONTARIO OVERNIGHT INTO FRIDAY.
AS THE SURFACE LOW APPROACHES ON THURSDAY, GRADUALLY INCREASING
LOW-LEVEL ISENTROPIC ASCENT WITHIN THE NORTHWARD-MOVING
BAROCLINIC ZONE MAY SUPPORT AREAS OF DRIZZLE AND RAIN SHOWERS AS
EARLY AS DAYBREAK BEFORE A HIGHER COVERAGE OF SHOWERS SLIDES
OVERHEAD DURING THE AFTERNOON AND EVENING HOURS. SUPPOSE THERE
MAY BE A THUNDERSTORM OR TWO AS WELL, PARTICULARLY THURSDAY
EVENING AS A NARROW INSTABILITY AXIS ATTEMPTS TO LIFT NORTHWARD
AHEAD OF A SOUTHEASTWARD-MOVING COLD FRONT. THE SEVERE WEATHER
THREAT CONTINUES TO LOOK VERY LOW FOR OUR AREA BOTH FROM A
CONCEPTUAL MODEL FRAMEWORK AS WELL AS FROM EXPLICIT OUTPUT (OF
NEARLY ZERO PROBABILITIES) FROM ML-BASED GUIDANCE. WITH OUR AREA
SMACK-DAB IN THE MIDDLE OF THE BAROCLINIC ZONE, AM ANTICIPATING
QUITE A GRADIENT IN HIGH TEMPERATURES ON THURSDAY. WILL
UNDERCUT NBM GUIDANCE AND FEATURE HIGHS IN THE UPPER 50S NEAR
AND NORTH OF I-88 AND LOWER 60S SOUTH OF I-80. TAKEN ALTOGETHER,
THURSDAY LOOKS FAIRLY DRAB.
THERE REMAINS AGREEMENT THAT AN UNUSUALLY STRONG SURFACE HIGH
PRESSURE SYSTEM WILL QUICKLY BUILD INTO THE CENTRAL UNITED
STATES IN THE WAKE OF THE DEPARTING SURFACE LOW LEADING TO AN
IMPRESSIVE 40 TO 45 MB PRESSURE GRADIENT DIRECTLY OVER THE GREAT
LAKES ON FRIDAY. A SOMEWHAT BIFURCATED PRESSURE RISE COUPLET (A
CONSEQUENCE OF THE UPPER-LEVEL TROUGHS PHASING DIRECTLY
OVERHEAD) SUGGEST A ONE-TWO PUNCH TO WINDS ON THE BACKSIDE OF
THE SYSTEM WITH A PERIOD OF GUSTY NORTHWESTERLY WINDS OF 30 TO
35 MPH FRIDAY MORNING FOLLOWED BY A STRONGER PERIOD OF GUSTS OF
35 TO 40 MPH DURING THE AFTERNOON AND EVENING HOURS. GUSTS MAY
BE HIGHER (LOCALLY 45 MPH) ALONG THE LAKE AND PORTER INDIANA
SHORELINES OF LAKE MICHIGAN WHERE LAKE INSTABILITY WILL SUPPORT
DEEPER MIXING PROFILES.
TUMBLING COLUMN TEMPERATURES BY WAY OF EFFICIENT COLD-AIR
ADVECTION WILL SUPPORT A FLARE IN DIURNAL INSTABILITY
LEADING TO AN EXPANSIVE STRATUS DECK. WHILE ENSEMBLE MEAN
TEMPERATURES SUPPORT HIGHS IN THE LOW TO MID 50S, AM NOTING
QUITE A FEW INDIVIDUAL MEMBERS AND DETERMINISTIC COUNTERPARTS
SHOWING EXPLICIT UPPER 40 DEGREE HIGHS ACROSS NORTHWESTERN
ILLINOIS. WILL (ONCE AGAIN) UNDERCUT NBM GUIDANCE TO FEATURE
HIGHS IN THE LOWER 50S AS A HAPPY MEDIUM.
AS THE CORE OF THE NORTHERN-STREAM TROUGH SLIDES OVERHEAD (PEAK
DIURNAL INSTABILITY), CAN ENVISION ISOLATED TO SCATTERED
SHOWERS ACCOMPANIED BY LOCALLY GUSTIER WINDS MOVING THROUGH THE
AREA DURING THE AFTERNOON HOURS. COVERAGE OF GUSTY SHOWERS
SHOULD BE MAXIMIZED IN NORTHWESTERN INDIANA BY SUNSET WHERE
850MB TO MARINE AIRMASS TEMPERATURE DIFFERENTIALS OF 15 TO 20C
WITHIN THE CYCLONIC SHEAR SIDE OF THE UPPER-LEVEL TROUGH WILL
PUSH LAKE-INDUCED INSTABILITY TOWARD 500 J/KG. (IT'LL BE PRETTY
RAW OUT THERE ALONG NORTHWESTERN INDIANA COMMUNITIES).
FRIDAY NIGHT ONWARD:
LAKE EFFECT RAIN SHOWERS SHOULD END OVERNIGHT AS INVERSION
HEIGHTS CRASH ON THE BACKSIDE OF THE DEPARTING UPPER-LEVEL
TROUGH AND THE SURFACE HIGH PRESSURE SYSTEM SLIDES INTO THE
MIDDLE MISSISSIPPI RIVER VALLEY. WITH WEAKENING WINDS AND
CLEARING SKIES, OVERNIGHT LOWS WILL BE POISED TO BE THE COLDEST
OF THE AUTUMN SEASON SO FAR WITH WIDESPREAD READINGS IN THE LOW
TO MID 30S. THE EXCEPTION WILL BE NEAR LAKE MICHIGAN AND ALONG
THE I-65 CORRIDOR WHERE LOWS WILL BOTTOM OUT IN THE LOWER 40S
THANKS TO TO THE CONTINUED INFLUENCE OF LAKE MICHIGAN AND
LINGERING LAKE EFFECT STRATUS. ASSUMING NO MAJOR CHANGES TO THE
FORECAST, WILL HAVE TO CONSIDER FREEZE WATCHES FOR PORTIONS OF
THE AREA BEFORE TOO LONG.
THEREAFTER, ENSEMBLE GUIDANCE ADVERTISES THE SURFACE HIGH
STALLING OVER THE ATLANTIC SEABOARD AND THE NORTHWARD RETREAT
OF THE DOMINANT UPPER-LEVEL JET INTO CANADA SUPPORTING GRADUALLY
RISING TEMPERATURES AND GENERALLY DRY WEATHER INTO NEXT WEEK.
ENSEMBLE METEOGRAMS OF QPF FROM ALL ENSEMBLE SUITES DEPICT A
TRANSITION TOWARD A SOMEWHAT SHOWERY PATTERN WITH SEASONABLE
TEMPERATURES DURING THE THE THE LAST 5 TO 10 DAYS OF THE MONTH.
BORCHARDT
AVIATION /06Z TAFS THROUGH 12Z THURSDAY/
ISSUED AT 1249 AM CDT WED OCT 14 2026
FORECAST CONCERNS FOR THE TERMINALS...
- SCATTERED SHOWERS AND THUNDERSTORMS WILL LINGER AT THE CHICAGO
AREA TERMINALS AND POINTS SOUTH THROUGH 10-11Z.
- MVFR CEILINGS WILL DEVELOP LATE TONIGHT AND PERSIST THROUGH AT
LEAST WEDNESDAY EVENING, ESPECIALLY AT THE CHICAGO AREA
TERMINALS.
- NON-ZERO CHANCE (15-20%) FOR A PERIOD OF LIGHT RAIN/DRIZZLE
WEDNESDAY MORNING AT THE CHICAGO TERMINALS WHICH WOULD RESULT
IN IFR CEILINGS AND/OR VISIBILITIES.
SCATTERED SHOWERS AND THUNDERSTORMS CONTINUE TO FESTER ALONG A
COLD FRONT STRETCHING FROM SOUTHERN MI TO CENTRAL MO. LOCALLY,
THE FAVORED AXIS OF SHOWERS/STORMS IS EXPECTED TO KEEP SHIFTING
SOUTHWARD THROUGH THE NIGHT BEFORE EXITING THE AREA BETWEEN
10-11Z. IN THE MEANTIME, EXPECT SOME SHOWERS AND OCCASIONAL
LIGHTNING TO LINGER IN AND AROUND THE CHICAGO AREA TERMINALS
THROUGH 08Z WITH GENERALLY DRY CONDITIONS EXPECTED AT RFD.
IN THE WAKE OF THE RAIN, CEILINGS SHOULD GRADUALLY LOWER TO MVFR
WITH BASES GENERALLY AROUND 2000-2500 FT WHERE THEY ARE
FORECAST TO REMAIN THROUGH THE REST OF THE TAF PERIOD. THAT
SAID, THERE IS A CHANCE (15-20%) FOR A PERIOD OF LIGHT RAIN AND
DRIZZLE TO DEVELOP AT THE CHICAGO AREA TERMINALS AND POINTS
SOUTH WEDNESDAY MORNING AS LOW-LEVEL MOISTURE POOLS BENEATH A
BUILDING INVERSION. GIVEN THAT COVERAGE OF DRIZZLE IS STILL
UNCERTAIN, HAVE OPTED TO INTRODUCE 3-4 HOUR PROB30S IN THE
CHICAGO TERMINALS' TAFS TO HIGHLIGHT THIS POTENTIAL. IF DRIZZLE
DOES MATERIALIZE THEN IFR CEILINGS AND/OR VISIBILITIES WOULD
ALSO ACCOMPANY THE DRIZZLE.
AS FOR WINDS, EXPECT WIND DIRECTIONS TO BECOME MORE
NORTHEASTERLY TONIGHT AS RAIN ENDS WITH SPEEDS AROUND 5 KTS
BEFORE INCREASING TO AROUND 10 KTS WEDNESDAY MORNING. THESE
NORTHEAST WINDS WILL PERSIST THROUGH WEDNESDAY EVENING BEFORE
DIRECTIONS TURN MORE EAST-SOUTHEAST AFTER MIDNIGHT WEDNESDAY
NIGHT.
YACK
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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