598
FXUS63 KLOT 132017
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
317 PM CDT TUE OCT 13 2026
KEY MESSAGES
- SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED LATE THIS
EVENING AND OVERNIGHT, ESPECIALLY SOUTH OF INTERSTATE 88. THE
STRONGEST STORMS MAY BE CAPABLE OF SMALL HAIL.
- ADDITIONAL SHOWERS AND A FEW THUNDERSTORMS WILL MOVE THROUGH
THE REGION ON THURSDAY.
- FRIDAY WILL FEATURE BLUSTERY NORTHWEST WINDS AND HIGHS IN THE
50S. AREAS OF FROST AND LOCALLY NEAR-FREEZING CONDITIONS ARE
FAVORED AWAY FROM LAKE MICHIGAN FRIDAY NIGHT.
- AFTER THE BRIEF PERIOD OF CHILLY WEATHER, THERE WILL BE A
WARMING TREND EARLY NEXT WEEK.
DISCUSSION
ISSUED AT 315 PM CDT TUE OCT 13 2026
TODAY WAS YET ANOTHER UNSEASONABLY WARM MID-OCTOBER DAY ACROSS
CHICAGOLAND. THE WEAK COLD FRONT THAT MOVED INTO THE AREA
EARLIER THIS MORNING HAS SINCE STALLED OUT SOUTH OF I-80 WHICH
HAS RESULTED IN A NOTABLE TEMPERATURE GRADIENT FROM NORTHWEST
(MID 70S) TO SOUTHEAST (UPPER 80S). A COUPLE OF AREAS OF
ALTOCUMULUS (ONE OVERHEAD AND ANOTHER CROSSING THE MISSISSIPPI
RIVER) ASSOCIATED WITH NARROW POCKETS OF MID-LEVEL MOISTURE HAVE
MANAGED TO PRODUCE ISOLATED SHOWERS/SPRINKLES. THINK THIS
ACTIVITY WILL REMAIN FAIRLY ISOLATED THROUGH THE EARLY EVENING
HOURS BUT CAN'T RULE OUT A FEW SHOWERS OR A RUMBLE OF THUNDER.
FOCUS CONTINUES TO BE ON THE POTENTIAL FOR SCATTERED SHOWERS
AND THUNDERSTORMS LATER THIS EVENING THROUGH THE OVERNIGHT
HOURS. MODEL GUIDANCE HAS REMAINED VARIED ON THE TIMING AND
PLACEMENT OF THE GREATEST COVERAGE OF SHOWERS, LIKELY OWING TO
DIFFERENCES IN THE HANDLING OF THE TIMING AND PLACEMENT OF
SUBTLE VORT LOBES AND AREAS OF DRIER AIR BETWEEN PLUMES OF
INCREASING MOISTURE. THIS IS ESPECIALLY EVIDENT IN REGIONAL
SATELLITE AND RADAR IMAGERY SHOWING LARGE GAPS BETWEEN ONGOING
CONVECTION AND AREAS OF ACCAS. NEVERTHELESS, THE PRESENCE OF
SUFFICIENT SYNOPTIC FORCING WITHIN THE RIGHT ENTRANCE OF THE
UPPER JET AND MOIST AIR LIFTING ATOP A STALLED SURFACE BOUNDARY
SUPPORT AN EVENTUAL INCREASE IN SHOWER AND STORM COVERAGE
OVERNIGHT, AND POTENTIALLY DEVELOPING AS EARLY AS 8-9 PM IF
SOME OF THE EARLIER HI-RES GUIDANCE VERIFIES. OVERALL WEAKER
MID-LEVEL LAPSE RATES SHOULD LIMIT STORM STRENGTH OVERALL EVEN
IN THE PRESENCE OF FAVORABLE SHEAR FOR HAIL. THUS, WILL CONTINUE
TO MESSAGE THE POTENTIAL FOR SMALL HAIL WITH THE STRONGEST
STORMS WITH THE SEVERE POTENTIAL REMAINING MAINLY SOUTHWEST OF
THE AREA.
THE THREAT OF LIGHTNING QUICKLY WANES TOWARD DAYBREAK WEDNESDAY
WITH SHOWER COVERAGE BEGINNING TO FOCUS SOUTH OF THE AREA.
HOWEVER, RESIDUAL LOW TO MID-LEVEL MOISTURE IN THE PRESENCE OF
WEAK ASCENT MAY SUPPORT LINGERING LIGHT RAIN OR DRIZZLE THROUGH
PART OF THE MORNING. EXPANDING HIGH PRESSURE ACROSS THE WESTERN
GREAT LAKES WILL EVENTUALLY SHIFT THIS SOUTH OF THE AREA TOWARD
MIDDAY, WITH DRY CONDITIONS FORECAST THROUGH THE REMAINDER OF
THE AFTERNOON AND EVENING HOURS. PERSISTENT NORTH TO
NORTHEASTERLY WINDS WILL BRING TEMPERATURES BACK TO MORE
SEASONABLE LEVELS WITH HIGHS IN THE 60S FOR MOST OF THE AREA AND
LOWER 70S WELL SOUTH OF I-80.
THIS BRIEF BREAK IN PRECIPITATION WILL BE FAIRLY SHORT LIVED AS
ENERGY EJECTING OFF THE ROCKIES WILL PHASE WITH A WAVE DIVING
SOUTHEAST TOWARD THE UPPER MIDWEST LATE WEDNESDAY NIGHT INTO
THURSDAY. AN ASSOCIATED DEVELOPING LOW PRESSURE SYSTEM WILL
MOVE ACROSS THE AREA BRINGING WIDESPREAD SHOWERS AND A CHANCE OF
THUNDERSTORMS ON THURSDAY.
PETR
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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