522
FXUS63 KLOT 132326
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
626 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 /00Z TAFS THROUGH 06Z THURSDAY/
ISSUED AT 626 PM CDT TUE OCT 13 2026
KEY AVIATION MESSAGES FOR THE CURRENT TAF PERIOD:
- SHOWERS AND SCATTERED THUNDERSTORMS EXPECTED THIS EVENING AND
THROUGH THE OVERNIGHT.
- PREVAILING MVFR CIGS ARE EXPECTED TOMORROW.
WESTERLY WINDS CONTINUE TO DIMINISH UNDER VFR CLOUDS PRESENTLY.
ISOLATED TO SCATTERED SHOWERS AND STORMS ARE ONGOING IN EASTERN
IOWA. THIS ACTIVITY IS EXPECTED TO CONTINUE TO MOVE EASTWARD
THIS EVENING AND THROUGH THE OVERNIGHT. THERE IS LOWER
CONFIDENCE IN COVERAGE OF STORMS AS IT MOVES IN PRIOR TO
MIDNIGHT. HOWEVER, NO CHANGES WERE MADE TO THE TIMING OF THE
PROB30/TEMPOS AS COVERAGE IS EXPECTED TO EXPAND AROUND AND AFTER
MIDNIGHT AS BETTER FORCING MOVING IN. THERE IS MODERATE
CONFIDENCE IN SHOWERS AND STORMS CONTINUING THROUGH AROUND
DAYBREAK. THERE IS A SLIGHT CHANCE FOR LINGERING LIGHT
SHOWERS/DRIZZLE TO FESTER THROUGH 12Z, BUT GENERALLY MOST
SHOWERS SHOULD BE SINKING SOUTH BY THEN WITH ANY THUNDER
ACTIVITY DIMINISHING. AN MVFR STRATUS DECK IS EXPECTED TO
DEVELOP IN THE WAKE OF THE PRECIPITATION WITH NORTHEAST WINDS
BETWEEN 10 TO 15 KNOTS. ITS POSSIBLE THAT CIGS BELOW 2000 FT
LIFT FOR A BRIEF WINDOW TO 2500-3000 FT IN THE AFTERNOON. BUT
WITH LOWER CONFIDENCE IN THE TIMING OF HIGHER CIGS AS WELL AS
GUIDANCE KEEPING MVFR CIGS THROUGH 00Z, OPTED TO PREVAIL MVFR
CIGS AROUND 2000 FEET THROUGH THE END OF THE TAF.
DK
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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