059
FXUS63 KLOT 150623
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
123 AM CDT SAT AUG 15 2026
KEY MESSAGES
- THERE IS A THREAT FOR SIGNIFICANT FLASH FLOODING TONIGHT
PRIMARILY NEAR AND SOUTH OF INTERSTATE 80. RAINFALL AMOUNTS
IN THIS AREA COULD EXCEED 3-4 INCHES IN PLACES.
- ADDITIONAL PERIOD OF SHOWERS AND THUNDERSTORMS SATURDAY NIGHT
INTO SUNDAY WITH A COLD FRONT.
- A BRIEF BREAK IN THE STORMY PATTERN IS EXPECTED MONDAY INTO
TUESDAY BEFORE ANOTHER STORM SYSTEM MOVES THROUGH TOWARDS
MIDWEEK.
DISCUSSION
ISSUED AT 123 AM CDT SAT AUG 15 2026
A SHORTWAVE TROUGH IS PIVOTING ACROSS EASTERN IA AND NORTHERN
MO AND WILL EVENTUALLY TRAVERSE ACROSS NORTHERN IL AND NORTHWEST
IN LATER TONIGHT INTO SATURDAY MORNING. AHEAD OF THE WAVE,
ISOLATED TO WIDELY SCATTERED SHOWERS AND SPRINKLES CONTINUE TO
FESTER OVER IL AND IN BUT WITH THE VERY LIMITED FORCING AND
INSTABILITY THEIR INTENSITY IS MEAGER TO SAY THE LEAST. CLOSER
TO THE SHORTWAVE, HOWEVER, AN AXIS OF THUNDERSTORMS IS
DEVELOPING NEAR THE IA-MO BORDER ALONG A REMNANT OUTFLOW
BOUNDARY FROM LAST NIGHT'S STORMS. THESE STORMS ARE EXPECTED TO
BECOME MORE WIDESPREAD IN COVERAGE AND SPREAD EAST ACROSS NORTH-
CENTRAL IL AND NORTHWEST IN THROUGH THE NIGHT AND WILL LINGER
INTO SATURDAY MORNING. GIVEN THE NEAR RECORD PWATS (AROUND 2.5
INCHES) IN CONJUNCTION WITH MODEST INSTABILITY, A DEVELOPING
LOW- LEVEL JET, AND THE AFOREMENTIONED WAVE, CONDITIONS ARE
FAVORABLE FOR TORRENTIAL RAINFALL (RAIN RATES OF 2+ IN/HR) TO
OCCUR WITH THESE STORMS. WHILE MOST OF NORTHERN IL AND NORTHWEST
IN IS EXPECTED TO SEE SHOWERS AND STORMS TONIGHT, A LOCALIZED
AXIS IS EXPECTED TO SEE THE HIGHEST RAINFALL AMOUNTS. AT THIS
TIME, THE AXIS OF HEAVIEST RAINFALL LOOKS TO BE SETTING UP NEAR
AND SOUTH OF A PERU, IL TO RENSSELAER, IN LINE BUT AS STORM
COVERAGE EXPANDS CANNOT RULE OUT THIS AXIS SHIFTING A HAIR
NORTHWARD TOWARDS I-80. REGARDLESS, RAINFALL AMOUNTS WITHIN THE
HEAVIEST AXIS LOOK TO BE IN EXCESS OF 3- 4 INCHES WHICH GIVEN
THE SATURATED SOILS AND ELEVATED RIVER LEVELS FROM PREVIOUS DAYS
OF RAIN COULD LEAD TO SIGNIFICANT FLASH FLOODING. FOR THIS
REASON A HIGHER-END FLOOD WATCH REMAINS IN EFFECT FOR AREAS
SOUTH OF I-80 THROUGH 10 AM CDT SATURDAY TO HIGHLIGHT THIS
THREAT.
OUTSIDE OF THIS HEAVIER RAIN AXIS, HEAVY DOWNPOURS ARE STILL
EXPECTED WITH THE SHOWERS AND STORMS TONIGHT BUT WITH THE LOWER
LIKELIHOOD OF TRAINING CONVECTION THE FLOOD THREAT LOOKS TO BE
MORE LOCALIZED TO POOR DRAINAGE AND LOWER-LYING AREAS FOR THOSE
NORTH OF I-80. NEVERTHELESS, A FLOOD WATCH REMAINS IN EFFECT FOR
OUR IL COUNTIES BETWEEN I-88 AND I-80 THROUGH 10 AM CDT.
ADDITIONALLY, RESENT MESOANALYSIS DOES SHOW AROUND 30-35 KTS OF
EFFECTIVE SHEAR OVERHEAD WHICH MAY SUPPORT A FEW STORMS BECOMING
STRONGER. WHILE THE OVERALL THREAT FOR WIDESPREAD SEVERE
WEATHER LOOKS LOW DUE TO THE POOR LAPSE RATES AND MODEST
INSTABILITY PRESENT, LOCALLY GUSTY WINDS UPWARDS OF 40-45 MPH
CANNOT BE RULED OUT WITH THE STRONGER STORMS TONIGHT.
AS WE HEAD INTO THIS AFTERNOON, THE AFOREMENTIONED SHORTWAVE
WILL EXIT THE AREA AND ALLOW ANY LINGERING SHOWERS AND
THUNDERSTORMS TO DIMINISH IN COVERAGE AND PUSH EAST OF THE AREA.
OVERALL IT LOOKS AS IF MOST OF THE AFTERNOON HOURS SATURDAY
SHOULD BE DRY FOR MOST, BUT FORECAST SOUNDINGS DO SHOW SOME
LINGERING MOISTURE IN THE PRESENCE OF WEAKLY UNSTABLE AIR WHICH
MAY SUPPORT SOME ISOLATED SHOWERS FESTERING ACROSS PARTS OF THE
AREA THROUGH SUNSET. WITH SOME BROAD SYNOPTIC ASCENT FORECAST TO
BE OVERHEAD SATURDAY, IT IS HARD TO PIN POINT ANY SPECIFIC
AREAS SHOWERS WILL BE FAVORED SO HAVE OPTED TO JUST KEEP ALL OF
NORTHERN IL AND NORTHWEST IN UNDER SOME 15% POPS FOR NOW.
OTHERWISE, EXPECT MOSTLY CLOUDY SKIES TO PREVAIL THROUGH THE DAY
THOUGH TEMPERATURES SHOULD STILL BE ABLE TO WARM INTO THE LOWER
TO MID-80S WITH CONTINUED WARM ADVECTION.
ANOTHER SHORTWAVE TROUGH IS EXPECTED TO PIVOT ACROSS THE
MISSISSIPPI RIVER VALLEY TONIGHT WITH A COLD FRONT IN TOW. THESE
FEATURES LOOK TO LEAD TO THE DEVELOPMENT OF ADDITIONAL SHOWERS
AND THUNDERSTORMS ACROSS NORTHERN IL AND NORTHWEST IN LATE THIS
EVENING INTO THE OVERNIGHT HOURS. INITIALLY THE COVERAGE OF
SHOWER/STORMS ALONG THE FRONT MAY BE MORE MUTED AS OUR AREA
RESIDES IN THE SUBSIDENCE BEHIND THIS AFTERNOON'S WAVE AND THE
NEW ONE TONIGHT, BUT COVERAGE SHOULD INCREASE OVERNIGHT AS THE
FRONT PROGRESSES SOUTHWARD. WITH THE HUMID AIR MASS STILL IN
PLACE IN COMBINATION WITH THE MODEST INSTABILITY AND FORCING,
THESE SHOWERS/STORMS WILL ONCE AGAIN BE CAPABLE OF LOCALLY HEAVY
TO TORRENTIAL DOWNPOURS. HOWEVER, SINCE THE FRONT SHOULD BE
RATHER PROGRESSIVE IT SEEMS THE THREAT FOR TRAINING STORMS AND
FLOODING SHOULD BE LOWER. FINALLY, THERE WILL ALSO BE ANOTHER
THREAT FOR LOCALLY GUSTY WINDS WITH THE STORMS TONIGHT THOUGH
THE OVERALL SEVERE THREAT DOES LOOK LOW.
THE COLD FRONT IS EXPECTED TO JUST ABOUT EXIT OUR AREA BY
SUNDAY MORNING WHICH WILL ALLOW DRIER AIR TO FILTER IN AND
FINALLY CONCLUDE THIS ACTIVE PATTERN. HOWEVER, THERE IS A CHANCE
THAT SOME ISOLATED SHOWERS OR STORMS MAY ATTEMPT TO DEVELOP
NEAR THE FRONT SUNDAY AFTERNOON SOUTH AND EAST OF I-57, BUT WITH
THE DRIER AIR AND CAPPING CONFIDENCE IS LOW ON SHOWERS/STORMS
ACTUALLY MATERIALIZING. THEREFORE, EXPECT MOST AREAS TO BE DRY
FOR SUNDAY AFTERNOON WITH TEMPERATURES STILL SEASONABLE IN THE
LOWER TO MID-80S. WINDS WILL BE OUT OF THE NORTHWEST WITH GUSTS
PEAKING AROUND 20 MPH DURING THE AFTERNOON.
DRY WEATHER WILL PERSIST THROUGH AT LEAST TUESDAY AFTERNOON AS
A SURFACE HIGH BUILDS INTO THE GREAT LAKES ON MONDAY. SO EXPECT
TEMPERATURES TO REMAIN SEASONABLE WITH HIGHS IN THE 80S BUT WITH
LOWER HUMIDITY AND COOLER OVERNIGHT LOWS IN THE 60S.
UNFORTUNATELY THE DRY WEATHER DOES NOT LOOK TO LAST LONG AS AN
AMPLIFIED TROUGH IS FORECAST TO DIVE INTO THE GREAT LAKES
TOWARDS THE MIDDLE OF THE WEEK AND BRING WITH IT MORE CHANCES
FOR SHOWERS AND THUNDERSTORMS. AS THINGS SIT RIGHT NOW, THE
HIGHER COVERAGE OF SHOWERS/STORMS LOOKS TO BE LATE TUESDAY NIGHT
INTO WEDNESDAY AS GUIDANCE SHOWS A COMPLEX MOVING THROUGH THE
AREA BUT EXACT TIMING IS STILL UNCERTAIN. THAT SAID, WILL NEED
TO MONITOR THIS PERIOD FOR THE POTENTIAL FOR A THREAT OF
STRONGER STORMS AND/OR HEAVY RAINFALL AS WELL.
ON THE BRIGHT SIDE, LONG RANGE ENSEMBLE GUIDANCE IS HINTING
THAT HIGH PRESSURE MAY MOVE IN BEHIND WEDNESDAY'S STORM SYSTEM
WHICH MAY KEEP THE BULK OF ANY ADDITIONAL STORMS SOUTH AND WEST
OF US FOR THE LATER HALF OF THE WEEK. OBVIOUSLY THIS IS LOWER
CONFIDENCE RIGHT NOW BUT AT LEAST SOMETHING TO POSSIBLY LOOK
FORWARD TO.
YACK
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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