818
FXUS63 KLOT 131835
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
135 PM CDT TUE OCT 13 2026
KEY MESSAGES
- TODAY WILL BE ANOTHER WARM DAY WITH HIGHS RANGING FROM THE
UPPER 70S (NORTH) TO MID 80S (SOUTH). A SPRINKLE OR TWO CANNOT
BE RULED OUT MAINLY THIS MORNING.
- SHOWERS AND THUNDERSTORMS WILL MOVE THROUGH THE REGION THIS
EVENING AND TONIGHT ESPECIALLY NEAR AND SOUTH OF INTERSTATE 88
NO SEVERE WEATHER IS EXPECTED AT THIS TIME.
- ADDITIONAL SHOWERS AND A FEW THUNDERSTORMS WILL MOVE THROUGH
THE REGION ON THURSDAY TIED TO A FALL STORM SYSTEM.
- FRIDAY WILL FEATURE BLUSTERY NORTHWEST WINDS AND HIGHS IN THE
50S. 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 208 AM CDT TUE OCT 13 2026
THOUGH TONIGHT:
A RECENT HAND SURFACE ANALYSIS REVEALED A 1003MB SURFACE LOW
PRESSURE SYSTEM CENTERED OVER SOUTHERN WISCONSIN. A SHARP COLD
FRONT EXTENDS SOUTHWESTWARD THROUGH CENTRAL IOWA AND INTO THE
CENTRAL PLAINS TOWARD A SECONDARY SURFACE LOW CENTERED NEAR THE
COLORADO AND KANSAS BORDER. IN THE WARM SECTOR OF THE GREAT
LAKES CYCLONE, IT IS AN UNSEASONABLY WARM NIGHT WITH CURRENT
TEMPERATURES AT PRESS TIME IN THE MID 70S (SOME 10 DEGREES
WARMER THAN TYPICAL HIGH TEMPERATURES THIS TIME OF YEAR). A
STRONG LOW-LEVEL JET (50-55KT AT ABOUT 3000 FEET AGL PER THE
KLOT VWP) IS MAINTAINING A FEW SOUTHWESTERLY SURFACE GUSTS OF 15
TO 20 MPH EARLY THIS MORNING, AS WELL (THE CHICAGO CRIB IS
GUSTING TO NEARLY 40 MPH). TAKING A STEP BACK, THE LARGE-SCALE
PATTERN IS BEING DRIVEN BY A STRONG PACIFIC TROUGH DIGGING
TOWARD THE FOUR CORNERS REGION, LEADING TO QUASI-ZONAL FLOW
ACROSS THE CENTRAL AND EASTERN UNITED STATES. OVER THE NEXT 72
HOURS, THE LOCAL WEATHER WILL BE INFLUENCED BY THE TROUGH AS IT
EVOLVES EASTWARD WITH TIME.
BASED ON THE CURRENT LOCATION AND SPEED OF THE COLD FRONT, IT
SHOULD MOVE ACROSS OUR LOCAL AREA JUST AFTER DAYBREAK. LOW-LEVEL
COLD AIR ADVECTION DOESN'T LOOK PARTICULARLY NOTEWORTHY IN OUR
AREA BEHIND THE FRONT, A CONSEQUENCE OF A LOW-LEVEL PRESSURE COL
DEVELOPING BETWEEN THE DEPARTING LOW PRESSURE SYSTEM TOWARD THE
NORTHEASTERN US AND THE SURFACE PRESSURE FALLS IN THE PLAINS.
IN FACT, THE FRONT MAY VERY WELL STALL SOMEWHERE NEAR US-24 BY
EARLY AFTERNOON, TRANSITIONING INTO MORE OF A STATIONARY FRONT
AHEAD OF THE TROUGH MOVING THROUGH THE SOUTHWESTERN UNITED
STATES. NEVERTHELESS, TODAY IS STILL SHAPING UP TO BE ANOTHER
UNSEASONABLY WARM DAY WITH HIGHS IN THE UPPER 70S NEAR THE
WISCONSIN STATE LINE, AROUND 80 NEAR THE I-88 AND I-80
CORRIDORS, AND MID TO LOCALLY UPPER 80S IN CLOSER PROXIMITY TO
THE FRONTAL BOUNDARY NEAR US-24. WILL HAVE TO WATCH FOR A
SPRINKLE OR TWO FROM MID-MORNING TO EARLY AFTERNOON NEAR THE
FRONT AS A PLUME OF MODESTLY STEEP MID-LEVEL LAPSE RATES (AROUND
7 K/KM PER THE 00Z OAX RAOB) COINCIDENT WITH A POCKET OF MID-
LEVEL MOISTURE (AREA OF ACCAS CURRENTLY OVER EASTERN NEBRASKA
AND WESTERN IOWA) SLIDES THROUGH NORTHERN ILLINOIS. GIVEN A
RESIDUAL POCKET OF DRY LOW-LEVEL AIR ACROSS THE AREA (NOTABLY
BELOW 700 MB, SEE THE 00Z DVN RAOB), WILL KEEP THE CHANCE OF
MEASURABLE PRECIPITATION IN THE 5 TO 10% RANGE, AGAIN LARGELY
SOUTH OF I-80.
THIS EVENING AND TONIGHT, THE DOMINANT PACIFIC UPPER-LEVEL
TROUGH WILL PROPAGATE TOWARD THE FOUR CORNERS REGION
ESTABLISHING SOUTHWESTERLY LOW- TO MID-LEVEL FLOW FROM THE
SOUTHERN PLAINS TOWARD THE LOWER GREAT LAKES. THE TIGHTENING
LOW-LEVEL BAROCLINIC ZONE ACROSS THE MIDDLE MISSISSIPPI RIVER
VALLEY (PARTIALLY FORCED BY A BUILDING SURFACE HIGH IN THE
NORTHERN PLAINS) BENEATH A PARADE OF UPPER-LEVEL SHORTWAVES WILL
SUPPORT THE DEVELOPMENT OF SEVERAL CLUSTERS OF SHOWERS AND
THUNDERSTORMS. THE CURRENT EXPECTATION IS FOR THE MOST ROBUST
ACTIVITY TO REMAIN TIED TO THE HIGHEST-QUALITY LOW-LEVEL
MOISTURE NEAR AND SOUTH OF THE FRONT GENERALLY FROM CENTRAL
KANSAS TO CENTRAL ILLINOIS, THROUGH STILL DO EXPECT A HEALTHY
COVERAGE OF SHOWERS AND STORMS AS FAR NORTH AS THE I-88 CORRIDOR
FROM THE EVENING THROUGH THE OVERNIGHT HOURS. RELATIVELY HIGH
FREEZING LEVELS (NEAR 14,500 FT AGL) AND MODEST/SKINNY CAPE
PROFILES TO LIMIT UPDRAFT INTENSITY (WEAK LAPSE-RATES) SHOULD
OTHERWISE OFFSET A FAVORABLE KINEMATIC/SHEAR PROFILE FOR HAIL.
AND WHILE THE UPPER-LEVEL FLOW DOES LOOK EXTREMELY UNBALANCED,
ANY SYNOPTIC-SCALE GRAVITY WAVE FORMATION SHOULD TEND TO BE
OFFSET WELL NORTH OF THE INSTABILITY AXIS LIKELY MITIGATING A
GWAC/DAMAGING WIND THREAT. AS A RESULT, CURRENT EXPECTATIONS ARE
FOR THE THUNDERSTORMS TONIGHT TO BE FAIRLY GENERIC WITH THE
COMMON THREATS OF DOWNPOURS, OCCASIONAL LIGHTNING STRIKES, AND
PEA TO DIME SIZE HAIL. COVERAGE OF ACTIVITY SHOULD WANE MARKEDLY
BY DAYBREAK WEDNESDAY.
WEDNESDAY INTO WEDNESDAY NIGHT:
ON WEDNESDAY, THE NORTHERN PLAINS HIGH PRESSURE SYSTEM WILL
SLIDE EASTWARD BENEATH RISING MID-LEVEL HEIGHTS AS THE PACIFIC
TROUGH MOVES TOWARD THE CENTRAL ROCKY MOUNTAINS. AN INCREASE IN
EAST-NORTHEASTERLY FLOW ON THE SOUTHERN SIDE OF THE SURFACE
HIGH PRESSURE SYSTEM WILL SHUNT THE LOW-LEVEL BAROCLINIC ZONE
SOUTHWARD. TRAPPED LOW-LEVEL MOISTURE BENEATH A PERSISTENT
INVERSION AS WELL AS A STEADY STREAM OF HIGH CLOUDS FROM
CONVECTION TO OUR SOUTH WILL MAINTAIN CLOUDY SKIES THROUGHOUT
THE DAY. IN FACT, WOULD NOT BE SURPRISED TO SEE SOME AREAS OF
DRIZZLE PARTICULARLY IN THE MORNING BEFORE DRY AIR ADVECTION
ALLOWS FOR THE LOW-LEVEL MOISTURE DEPTH TO SHRINK THROUGH THE
AFTERNOON HOURS. TAKEN ALTOGETHER, OPTED TO UNDERCUT NBM
TEMPERATURES FOR WEDNESDAY AND INSTEAD ADVERTISE HIGHS IN THE
LOW TO MID 60S TO PERHAPS AROUND 70 NEAR THE US-24 CORRIDOR.
WEDNESDAY NIGHT INTO THURSDAY NIGHT:
WEDNESDAY NIGHT INTO THURSDAY, ENSEMBLE MODEL GUIDANCE IS IN
FAIR AGREEMENT THAT THE TROUGH IN THE CENTRAL PLAINS WILL PHASE
WITH A NORTHERN-STREAM TROUGH DIVING SOUTHEASTWARD OUT OF
CANADA. EVEN WITH THE USUAL VARIANCE IN EXACTLY HOW THE SYSTEMS
PHASE, THERE REMAINS A PERSISTENT SIGNAL FOR DISORGANIZED
PRESSURE FALLS IN THE PLAINS TO MERGE INTO A COHERENT SURFACE
LOW WHICH WOULD BE POISED TO RAPIDLY DEEPEN WHILE LIFTING
NORTHEASTWARD CLOSE TO OR DIRECTLY OVER OUR AREA ON A PATH
TOWARD SOUTHEASTERN CANADA. TAKEN TOGETHER, DO EXPECT PERIODS OF
SHOWERS AND A FEW THUNDERSTORMS FOCUSED ON THURSDAY AS THE
SURFACE LOW MOVES THROUGH THE AREA, WHICH IS REFLECTED IN NBM
POPS OF 80 TO 90% AREAWIDE. DID OPT TO AGAIN UNDERCUT NBM
HIGHS PARTICULARLY WITH NORTHWARD EXTENT TO BE CLOSER ALIGNED TO
ENSEMBLE MEANS, THOUGH WILL NOTE THERE COULD BE A FAIRLY TIGHT
GRADIENT LOCALLY AS THE WARM SECTOR ATTEMPTS TO LIFT ALONG THE
I-57 CORRIDOR. NEVERTHELESS, WILL ADVERTISE HIGHS IN THE UPPER
50S NEAR THE WISCONSIN STATE LINE TO THE MID 60S SOUTH OF I-80.
FINALLY, AM NOT SEEING ANY OBVIOUS WARNING SIGNS FOR SEVERE
THUNDERSTORMS LOCALLY WITH THE CYCLONE, BUT IT'S STILL A BIT TO
EARLY TO SAY FOR SURE GIVEN THE AFOREMENTIONED VARIANCE IN
PHASING WITHIN THE ENSEMBLE ENVELOPE.
FRIDAY ONWARD:
AS THE SURFACE LOW PULLS AWAY (AND DEEPENS TOWARD 990 MB IN
SOUTHERN ONTARIO), THE ARRIVAL OF A STRONG (NEARLY 1040 MB)
SURFACE HIGH PRESSURE SYSTEM INTO THE CENTRAL PLAINS WILL SET
THE STAGE FOR AN IMPRESSIVE PRESSURE GRADIENT ACROSS THE GREAT
LAKES. ACCORDINGLY, DO EXPECT A WINDY DAY ON FRIDAY WITH EARLY
BUFKIT MIXING PROFILES SUPPORTING FREQUENT GUSTS OF 30 TO 40
MPH. SUCH STRONG WINDS WILL FACILITATE AGGRESSIVE LOW-LEVEL COLD
AIR ADVECTION IN THE WAKE OF THE CYCLONE WITH MEAN 850MB
TEMPERATURES PLUMMETING 10 TO 15 DEGREES C IN 24 HOURS (TO NEAR
OR BELOW 0C). TAKEN TOGETHER, FRIDAY WILL FEEL EVERY BIT LIKE
OCTOBER WITH HIGHS IN THE 50S, BLUSTERY NORTHWEST WINDS, AND
SHOWERS OF LEAVES (NOT WATER) FLYING THROUGH THE AIR. WITH THAT
SAID, A NOTABLE TEMPERATURE DIFFERENCE BETWEEN LAKE MICHIGAN
WATER AND THE FALL AIRMASS WILL SUPPORT LAKE EFFECT RAIN SHOWERS
MAINLY EAST OF GARY.
THERE REMAINS ENSEMBLE AGREEMENT THAT THE SURFACE HIGH WILL
SLIDE DIRECTLY OVER THE GREAT LAKES FRIDAY NIGHT INTO SATURDAY
MORNING SETTING THE STAGE FOR IDEAL RADIATIONAL COOLING AND THE
COLDEST NIGHT OF THE AUTUMN SEASON SO FAR. ASSUMING NO MAJOR
CHANGES IN FORECAST GUIDANCE, WOULD EXPECT AREAS OF FROST AND
EVEN LOCALLY FREEZING TEMPERATURES ACROSS THE REGION RIGHT IN
LINE WITH CLIMATOLOGY (THE FIRST FREEZING TEMPERATURES AWAY FROM
LAKE MICHIGAN TYPICALLY OCCUR IN THE OCTOBER 11 TO 20
TIMEFRAME).
THEREAFTER, ENSEMBLE GUIDANCE ADVERTISES THE SURFACE HIGH
STALLING OVER THE ATLANTIC SEABOARD AND THE NORTHWARD-SHIFT OF
THE DOMINANT UPPER-LEVEL JET INTO CANADA SUPPORTING GRADUALLY
RISING TEMPERATURES INTO NEXT WEEK.
BORCHARDT
AVIATION /18Z TAFS THROUGH 00Z THURSDAY/
ISSUED AT 135 PM CDT TUE OCT 13 2026
KEY MESSAGES:
- SHOWERS AND SCATTERED THUNDERSTORMS ARE LIKELY TO AFFECT THE
TERMINALS TONIGHT.
- A PERIOD OF MVFR CEILINGS IS LIKELY TOMORROW.
STRENGTHENING WARM AIR ADVECTION/ISENTROPIC ASCENT WILL LEAD TO
AN INCREASE IN SHOWER AND THUNDERSTORM COVERAGE ACROSS THE AREA
THIS EVENING. UNCERTAINTY REMAINS REGARDING THE EXACT ONSET
TIME OF THE SHOWER AND THUNDERSTORM ACTIVITY AND HOW LONG IT
WILL PERSIST NEAR ANY ONE TAF SITE. IN GENERAL, THE CHANCES FOR
LIGHTNING ARE GREATER AT THE CHICAGO METRO TERMINALS THAN THEY
ARE AT RFD, WHERE THE 18Z TAF WAS RECONFIGURED TO CONTAIN TWO
PROB30 GROUPS WITH TSRA FOR TWO POTENTIAL DISCRETE WAVES OF
SHOWERS AND STORMS. AT THE CHICAGO METRO TERMINALS, IT'S
POSSIBLE THAT THIS ACTIVITY MAY ALSO END UP BREAKING DOWN INTO
ONE OR TWO DISTINCT WAVES, BUT IT ALSO REMAINS POSSIBLE THAT
THERE COULD JUST BE ONE LONGER, DRAWN-OUT PERIOD WITH SHOWERS
AND STORMS IN THE VICINITY OF THE TERMINALS INSTEAD. OPTED TO
MAINTAIN AN EXTENDED PERIOD OF TSRA/VCTS IN THE TAFS THERE FOR
THAT REASON, AND WILL LET THIS TIMING BE REFINED AS MODEL AND
OBSERVATIONAL TRENDS BECOME CLEARER. THERE IS ALSO SOME CHANCE
FOR SCATTERED SHOWERS TO PERSIST WELL INTO THE MORNING AT/NEAR
THE CHICAGO METRO TERMINALS TOMORROW IF TONIGHT'S CONVECTIVE
FOOTPRINT ENDS UP BEING SMALLER THAN EXPECTED. HOWEVER, THIS IS
PRESENTLY NOT THE MOST LIKELY OUTCOME, SO THE TAFS DO NOT
CONTAIN ANY FORMAL PRECIPITATION MENTIONS BEYOND 11Z AT THIS
TIME.
MVFR STRATUS IS EXPECTED TO DEVELOP OVER THE AREA SOMETIME LATE
TONIGHT OR TOMORROW MORNING. PERSISTENT NORTHEASTERLY ONSHORE
FLOW WILL LIKELY MAINTAIN THIS STRATUS DECK THROUGH THE
REMAINDER OF THIS TAF PERIOD, THOUGH THERE IS SOME CHANCE THAT
CLOUD BASES COULD LIFT ABOVE 3000 FT AGL PRIOR TO THE END OF THE
TAF PERIOD, ESPECIALLY AT RFD. IF THIS STRATUS DECK GROWS THICK
ENOUGH, THEN COULDN'T RULE OUT PATCHY DRIZZLE OR A FINE MIST
DEVELOPING SOMEWHERE, BUT THE ODDS OF THIS OCCURRING AT ANY
PARTICULAR TAF SITE REMAIN FAIRLY LOW (10-15% CHANCE) AT THIS
TIME.
OGOREK
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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