389
FXUS63 KLOT 151206
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
706 AM CDT SAT AUG 15 2026
KEY MESSAGES
- SHOWERS ARE EXPECTED AT TIMES THROUGH THIS EVENING WITH THE
GREATEST COVERAGE THIS MORNING.
- ANOTHER ROUND OF SHOWERS AND THUNDERSTORMS LIKELY LATE
TONIGHT INTO SUNDAY.
- 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 /12Z TAFS THROUGH 18Z SUNDAY/
ISSUED AT 705 AM CDT SAT AUG 15 2026
KEY AVIATION FORECAST MESSAGES:
- SCATTERED SHRA AND POCKETS OF DZ THIS MORNING.
- IFR TO LOW-END MVFR CIGS THIS MORNING (LIFR ALONG THE
LAKESHORE). MVFR PERSISTS THROUGH THE AFTERNOON.
- CLUSTER OF STORMS MAY MOVE ACROSS THE AREA AGAIN LATE TONIGHT
INTO EARLY SUNDAY AM (30-50% CHANCE).
WHILE THE CORRIDOR OF HEAVIEST RAINFALL REMAINED WELL SOUTH OF
THE TERMINALS OVERNIGHT THERE IS AN AXIS OF SCATTERED SHOWERS
AND POCKETS OF DRIZZLE THAT HAVE DEVELOPED ALONG THE I-88/80
CORRIDOR. THIS IS EXPECTED TO CONTINUE DRIFTING ACROSS THE AREA
THROUGH THE MORNING. WHILE THE LIGHTNING THREAT IS NOT ZERO IT
REMAINS LOW (<20%) WITH THIS ACTIVITY.
CEILINGS ARE EXPECTED TO CONTINUE TO DETERIORATE THIS MORNING
FROM MVFR TO IFR AT ALL TERMINALS. LIFR CIGS WILL LIKELY
CONTINUE ALONG THE LAKESHORE FOR AT LEAST A FEW HOURS ALONG THE
LAKESHORE. IT IS UNCLEAR HOW LONG IT WILL TAKE FOR IMPROVEMENT
TO OCCUR AND MAY NOT OCCUR UNTIL WINDS BEGIN TO TREND MORE SOUTH
TO SOUTHWEST THIS AFTERNOON. MVFR CIGS THEN LIKELY PERSIST
THROUGH THE AFTERNOON.
SPOTTY SHOWERS MAY PERSIST OR REDEVELOP LATE MORNING THROUGH
THE EVENING AT TIMES AND HAVE MAINTAINED A VCSH MENTION TO
ACCOUNT FOR THIS FOR NOW. THERE REMAINS A SIGNAL FOR SLIGHTLY
HIGHER COVERAGE OF SHOWERS (AND PERHAPS A FEW LIGHTNING STRIKES)
LATE AFTERNOON/EARLY EVENING AND HAVE MAINTAINED PROB30S FOR
SHRA TO ACCOUNT FOR THIS. ALSO CAN'T FULLY RULE OUT A LIGHTNING
STRIKE WITH THIS ACTIVITY (IF IT DEVELOPS).
LOOKING AHEAD TO THE OVERNIGHT INTO EARLY SUNDAY MORNING HOURS,
THERE REMAINS A SIGNAL FOR YET ANOTHER THUNDERSTORM COMPLEX TO
MOVE ACROSS THE AREA. HOWEVER, IT IS UNCLEAR HOW FAR NORTH THIS
WILL EXTEND. HAVE MAINTAINED AND EXTENDED IN TIME PROB30S FOR
TSRA TO ACCOUNT FOR THIS (~9-14Z AT ORD/MDW). IF CONFIDENCE IN
A FARTHER NORTH TRACK INCREASES THEN TEMPOS OR VCTS MENTION MAY
BE NEEDED.
WINDS WILL BE LIGHT EAST TO SOUTHEAST INITIALLY THIS MORNING
AROUND 5-10 KT THEN TRENDING SOUTH AND THEN SOUTH SOUTHWEST IN
THE AFTERNOON. IN THE WAKE OF ANY MORNING CONVECTION SUNDAY
WINDS WILL TURN WEST TO NORTHWEST AND BECOME INCREASINGLY GUSTY
THROUGH MIDDAY AROUND 15-20 KT.
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.
VISIT US AT WEATHER.GOV/CHICAGO
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page