079
FXUS63 KLOT 150558
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1258 AM CDT SAT AUG 15 2026
KEY MESSAGES
- THERE IS A THREAT FOR SIGNIFICANT FLASH FLOODING TONIGHT
PRIMARILY SOUTH OF INTERSTATE 80.
- THERE IS A TREND TOWARD LESS COVERAGE OF SHOWERS AND STORMS
SATURDAY NIGHT INTO SUNDAY MORNING, BUT NO GUARANTEES YET.
- A BRIEF BREAK IN THE STORMY PATTERN IS EXPECTED MONDAY INTO
TUESDAY BEFORE ANOTHER SERIES OF STORM SYSTEMS MOVE THROUGH
THE REGION DURING THE MIDDLE OF THE WEEK.
DISCUSSION
ISSUED AT 130 PM CDT FRI AUG 14 2026
THREAT FOR SIGNIFICANT FLASH FLOODING TONIGHT...
EARLY AFTERNOON SURFACE CHARTS DEPICT AN ELONGATED STATIONARY
FRONT EXTENDING FROM CENTRAL VIRGINIA ALONG THE OHIO RIVER
NORTHWESTWARD TOWARD KANSAS CITY, MISSOURI. A SERIES OF MID-
LEVEL PERTURBATIONS ARE RIDING ALONG AND NORTH AS THE FRONT AS
EVIDENT BY FESTERING AREAS OF SHOWERS AND THUNDERSTORMS FROM
OMAHA, NEBRASKA TO INDIANAPOLIS, INDIANA. THE WESTERN-MOST
PERTURBATION (NEAR OMAHA) IS THE STRONGEST IN THE REGION, AS
DEMONSTRATED BY BROAD ANTICYCLONIC UPPER-LEVEL VENTING DEPICTED IN
MID-LEVEL WATER VAPOR IMAGERY AS WELL AS A CLEAR CYCLONIC LOW-
LEVEL CIRCULATION (A "WARM-CORE" LOW) BEING SAMPLED BY BOTH
KOAX/KDMX WSR-88D RADARS.
THIS EVENING, THE OMAHA WARM-CORE LOW PRESSURE SYSTEM WILL
SHIFT EASTWARD AND ENCOUNTER AN INCREASINGLY UNSTABLE AIRMASS
(MUCAPE > 3000 J/KG) ACROSS SOUTHERN IOWA. RAPID THUNDERSTORM
DEVELOPMENT AND ASSOCIATED REGIONS OF LATENT HEAT RELEASE WILL
BE POISED TO INTENSIFY THE WARM CORE LOW WEST OF THE MISSISSIPPI
RIVER BY MIDNIGHT, LEADING TO AUGMENTED LOW-LEVEL MOISTURE
TRANSPORT NORTH OF THE STALLED FRONT AND INTO THE CIRCULATION.
INTENSE MOISTURE CONVERGENCE WILL LEAD TO UNUSUALLY HIGH
TROPICAL-LIKE MOISTURE VALUES WITH MEAN PWATS FORECASTED TO
APPROACH 2.5" (NEAR ALL-TIME RECORDS PER SOUNDING CLIMATOLOGY AT
ILX/DVN) AHEAD OF THE LOW. TAKEN ALTOGETHER, A CLUSTER OF
THUNDERSTORMS WITH INTENSE RAIN RATES (3 TO 5"/HR) IS EXPECTED
TO DEVELOP AND MOVE INTO NORTHERN ILLINOIS DURING THE PRE-DAWN
HOURS OF SATURDAY MORNING. (THIS PROCESS IS NOT UNLIKE HOW
TROPICAL SYSTEMS INTENSIFY AND PRODUCE INTENSE RAIN RATES).
WHILE THE CENTER OF THE WARM CORE LOW IS EXPECTED TO TRACK MORE
OR LESS ALONG THE I-88 OR I-80 CORRIDORS DURING THE MORNING
HOURS, THE WEST-TO-EAST ORIENTATION AXIS OF THE INSTABILITY AXIS
SOUTH OF THE CORE SHOULD PROMOTE THE HIGHEST COVERAGE OF
THUNDERSTORMS NEAR AND SOUTH OF I-80. THE THUNDERSTORMS ARE
EXPECTED TO REACH THE I-39 CORRIDOR SOMETIME IN THE 1 TO 3 AM
TIMEFRAME, AND THEN THE I-55 AND I-57 CORRIDORS SOMETIME IN THE
2 TO 5 AM TIMEFRAME, AND THEN NORTHWESTERN INDIANA AFTER 5 AM.
THE BACK EDGE OF THUNDERSTORMS WOULD THEN WORK EASTWARD THROUGH
THE AREA AFTER DAYBREAK, PERHAPS NOT CLEARING NORTHWESTERN
INDIANA UNTIL THE 10 AM TO 1 PM TIMEFRAME.
OWING TO THE REPEATED ROUNDS OF THUNDERSTORMS THIS PAST WEEK,
SOILS ALONG AND SOUTH OF I-88 ARE SATURATED AND PRONE TO CAUSE
WIDESPREAD FLOODING WITH AS LITTLE AS ONE HALF TO ONE INCH OF
RAIN. EVEN WITH THE EXPECTATION FOR THE WARM-CORE LOW AND
ASSOCIATED REGION OF HEAVY RAIN TO BE SOMEWHAT PROGRESSIVE
TONIGHT (MOVING QUICKLY RATHER THAN STAYING OVER THE SAME EXACT
AREA), THE INTENSITY OF RAIN RATES SHOULD STILL NEVERTHELESS
LEAD TO A SWATH OF 3 TO 6 INCHES OF RAIN (LOCALLY HIGHER), AS
SUPPORTED BY 12Z HREF AND REFS 24-HOUR LPMM QPF. SUCH RAINFALL
OVER SATURATED SOILS WOULD LEAD TO WIDESPREAD SIGNIFICANT FLASH
FLOODING INCLUDING WIDESPREAD ROAD CLOSURES AND EVEN STRUCTURE
FLOODING. ACCORDINGLY, A RARE LEVEL 3 OUT OF 4 FLASH FLOOD
THREAT HAS BEEN ISSUED BY WPC FOR AREAS ALONG AND SOUTH OF I-80
(PRIMARILY ALONG AND SOUTH OF A LINE FROM MENDOTA, ILLINOIS TO
FOWLER, INDIANA).
A FLOOD WATCH FOR FLASH FLOODING HAS BEEN ISSUED ACROSS MUCH OF
NORTHERN ILLINOIS IN TWO SEGMENTS. THE FIRST SEGMENT IS ALONG
AND SOUTH OF I-80 AND FEATURES HEIGHTENED WORDING FOR
SIGNIFICANT FLASH FLOODING. THE SECOND SEGMENT IS ALONG THE I-88
CORRIDOR FOR SOMEWHAT LOWER CONFIDENCE FLASH FLOODING SHOULD
THE TRACK OF THE WARM CORE LOW AND ASSOCIATED REGION OF
THUNDERSTORMS TRACK FURTHER NORTH THAN CURRENTLY EXPECTED. BOTH
SEGMENTS WILL BE IN EFFECT FROM 10 PM THIS EVENING THROUGH 10 AM
TOMORROW.
NOT TO BE FORGOTTEN, CANNOT RULE OUT LOCALLY DAMAGING WINDS
ALONG THE LEADING EDGE OF THE THUNDERSTORM CLUSTER TONIGHT. EVEN
IF WINDS DO NOT TECHNICALLY MEET SEVERE CRITERIA (58 MPH), THE
SATURATED SOILS MAY ALLOW FOR TREES TO FALL EASIER THAN IN
TYPICAL CONDITIONS. AT THIS POINT, CURRENTLY SEE THE THREAT FOR
SEVERE WEATHER AS SECONDARY TO THE THREAT OF FLASH FLOODING.
SATURDAY AFTERNOON ONWARD:
IN THE WAKE OF THE WARM-CORE LOW, A FEW SHOWERS AND AREAS OF
DRIZZLE MAY LINGER AS LATE AS THE AFTERNOON. HOWEVER, CURRENT
THINKING IS THAT COVERAGE SHOULD MARKEDLY DECREASE DURING THE
LATE MORNING AND EARLY AFTERNOON HOURS. ATTENTION THEN TURNS
TOWARD THE NEXT UPPER-LEVEL WAVE AND AN ASSOCIATED COLD FRONT
DUE TO SWEEP ACROSS THE AREA LATE SATURDAY NIGHT INTO SUNDAY. AM
NOTING A TREND TOWARD LESS INSTABILITY AHEAD OF THE FRONT WHICH
MAY LIMIT THE COVERAGE OF SHOWERS AND STORMS ACROSS OUR AREA,
BUT IT REMAINS TO BE SEEN IF SUCH A TREND WILL CONTINUE. SO, WILL
MAINTAIN MID-RANGE CHANCE POPS (30% OR SO) ACROSS THE AREA
THROUGH SUNDAY MORNING.
A SURFACE HIGH PRESSURE SYSTEM WILL MOVE INTO THE GREAT LAKES
IN THE WAKE OF THE FRONT AND FACILITATE A MUCH-NEEDED BREAK FROM
THIS INCREDIBLY STORMY PATTERN. MONDAY AND AT LEAST THE FIRST
HALF OF TUESDAY LOOK COMPLETELY DRY BEFORE A SERIES OF STORM
SYSTEMS MOVE THROUGH THE GENERAL REGION BY MIDWEEK.
BORCHARDT
AVIATION /06Z TAFS THROUGH 12Z SUNDAY/
ISSUED AT 1258 AM CDT SAT AUG 15 2026
KEY AVIATION FORECAST MESSAGES:
- SHRA LIKELY THIS MORNING. LOWER CONFIDENCE IN NORTHWARD EXTENT
OF TS COVERAGE.
- SEVERAL HOUR PERIOD OF IFR CIGS LIKELY THIS MORNING THROUGH
MIDDAY, MVFR THEN PERSISTS THROUGH THE AFTERNOON.
- ANOTHER ROUND OF SHRA/TS MAY ARRIVE LATE TONIGHT INTO EARLY
SUNDAY AM (30% CHANCE).
THE CORRIDOR OF HEAVY RAIN AND THUNDERSTORMS REMAINS WELL
SOUTHWEST OF THE TERMINALS AT THIS HOUR. CONFIDENCE IN THE
NORTHWARD EXTENT OF THE GREATER SHOWER AND TS COVERAGE REMAINS
ON THE LOWER SIDE BUT IN GENERAL CONTINUES TO FAVOR AREAS SOUTH
OF I-80. THERE CONTINUES TO BE SOME GUIDANCE AS FAR NORTH AS THE
I-88 CORRIDOR, HOWEVER, AND HAVE ACCORDINGLY MAINTAINED
PREVAILING SHRA AND A VCTS MENTION WITH THIS UPDATE THIS MORNING.
DID MOVE UP THE TIME BY AN HOUR TO ACCOUNT FOR THE POTENTIAL FOR
SLIGHTLY EARLIER DEVELOPMENT AHEAD OF THE MAIN SYSTEM. SHOWERS
COULD THEN LINGER THROUGH MID TO LATE MORNING BEFORE THE SYSTEM
FULLY EXITS TO THE EAST.
CEILINGS WILL STEADILY DECREASE WITH TIME EARLY THIS MORNING
WITH WIDESPREAD LOW-END MVFR TO IFR CIGS LIKELY BY DAYBREAK
ACROSS THE AREA. GUIDANCE REMAINS CONSISTENT IN IFR CIGS
REMAINING IN PLACE THROUGH THE MORNING HOURS BEFORE GRADUALLY
LIFTING TO MVFR IN THE AFTERNOON AND POSSIBLY BRIEFLY VFR IN THE
EVENING BEFORE LOWERING AGAIN WITH OUR NEXT DISTURBANCE LATE
TONIGHT INTO SUNDAY AM.
WINDS WILL GRADUALLY TREND EAST AND THEN SOUTHEAST THROUGH THE
OVERNIGHT HOURS AHEAD OF THE INCREASING COVERAGE OF SHRA AND
POTENTIAL TS. IN THE WAKE OF ANY CONVECTION WINDS WILL TREND
SOUTHWEST IN THE AFTERNOON THROUGH THE REMAINDER OF THE PERIOD.
PETR
LOT WATCHES/WARNINGS/ADVISORIES
IL...FLOOD WATCH UNTIL 10 AM CDT THIS MORNING FOR ILZ008-ILZ010-
ILZ011-ILZ012-ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-
ILZ033-ILZ039-ILZ103-ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.
IN...FLOOD WATCH UNTIL 10 AM CDT /11 AM EDT/ THIS MORNING FOR
INZ001-INZ002-INZ010-INZ011-INZ019.
LM...NONE.
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