037
FXUS63 KLOT 100631
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
131 AM CDT MON AUG 10 2026
KEY MESSAGES
- RENEWED THUNDERSTORM DEVELOPMENT IS EXPECTED OVER PORTIONS OF
THE AREA LATE THIS EVENING AND OVERNIGHT, SOME OF WHICH COULD
BE STRONG TO SEVERE.
- TRAINING OF HEAVY THUNDERSTORMS (LOCALIZED 2"/HR+ RAIN RATES)
OVER THE SAME AREAS LATE THIS EVENING AND OVERNIGHT MAY LEAD TO
FLASH FLOODING.
- ADDITIONAL PERIODS OF STORMS ARE EXPECTED MONDAY THROUGH MID-
WEEK. SOME OF THESE STORMS COULD BE SEVERE, ESPECIALLY LATE
MONDAY AFTERNOON OR MONDAY NIGHT AND LEAD TO ADDITIONAL
FLOODING.
UPDATE
ISSUED AT 700 PM CDT SUN AUG 9 2026
- FLASH FLOOD WATCH ISSUED FOR MUCH OF NORTHEAST IL AND
NORTHWEST IN LATE THIS EVENING THROUGH EARLY MONDAY AM.
CONCERNS ARE INCREASING THAT A CORRIDOR OF TRAINING HEAVY
THUNDERSTORMS (CAPABLE OF RAINFALL RATES IN EXCESS OF 2 INCHES
PER HOUR) WILL SET UP SOMEWHERE OVER NORTHEAST ILLINOIS INTO
NORTHWEST INDIANA LATE THIS EVENING THROUGH THE OVERNIGHT HOURS.
THE COMBINATION OF SEVERAL FACTORS HAVE LED US TO ISSUE A FLASH
FLOOD WATCH FOR PORTIONS OF NORTHEAST ILLINOIS AND NORTHWEST
INDIANA, INCLUDING: HIGH PWATS UPWARDS OF 2", THE NOSE OF A
STRENGTHENING LOW-LEVEL JET ORIENTED INTO THE AREA ATOP A STALLED
SURFACE BOUNDARY, AND SATURATED SOILS FROM THE FIRST ROUND OF
STORMS OVER PORTIONS OF THE CHICAGO METRO. THIS WATCH IS IN
EFFECT FROM 9 PM CDT THIS EVENING THROUGH 7 AM CDT MONDAY.
THOSE THAT LIVE IN ESPECIALLY FLOOD PRONE AREAS SHOULD MONITOR
TRENDS CLOSELY THROUGH THIS EVENING AND HAVE MULTIPLE METHODS TO
RECEIVE WARNING INFORMATION THAT WILL WAKE YOU UP.
NOT TO BE OVERSHADOWED, THE SEVERE THREAT WILL CONTINUE
OVERNIGHT, WITH THE PRIMARY THREAT BEING DAMAGING WIND GUSTS.
LARGE HAIL WILL BE POSSIBLE WITH THE STRONGEST STORMS. WE WILL
ALSO BE MONITORING A NON-ZERO TORNADO THREAT WITH ANY STORMS THAT
DEVELOP ALONG AND SOUTH OF THE STALLED SURFACE FRONT.
PETR
DISCUSSION
ISSUED AT 132 PM CDT SUN AUG 9 2026
WE HAVE BEEN ABLE TO DESTABILIZE AHEAD OF THE MORNING LINE OF
CONVECTION AS A NORTHWARD MOVING WARM FRONT HAS MADE STEADY
NORTHWARD PROGRESS. 3000 J/KG OF MLCAPE IS MOSTLY UNCAPPED AT
THIS POINT, AND THERE IS A NARROW RIBBON OF ENHANCED DCAPE
NOSING INTO THE CHICAGO AREA. THE STRONGER LEAD SHORTWAVE IS
LARGELY MOVING THROUGH HERE OVER THE NEXT FEW HOURS, AND THIS
WILL KEEP A MARGINAL SEVERE THUNDERSTORM RISK IN PLACE THROUGH
MID AFTERNOON. THE MAIN CONCERN WOULD BE THESE TRANSIENT
DOWNBURST SIGNATURES IN THE MORE MATURE DEVELOPED LINE OF
STORMS ALONG WITH A FEW INSTANCES OF HAIL. THE ORIENTATION THESE
STORMS ARE TAKING WILL ALSO LEAD TO VARYING WATER LEVELS NEAR
THE SHORE IN WAKE OF THESE STORMS, SO THE SEA WILL REMAIN
HAZARDOUS EVEN AFTER THE STORMS PASS THIS AFTERNOON.
AS FAR AS THE REST OF THE DAY IS CONCERNED FARTHER SOUTH, THE
BATTLE WILL BE BETWEEN THE ARRIVING MID LEVEL SHORTWAVE SLIDING
THROUGH THE AREA VERSUS SOME CAPPING REINFORCEMENT FROM LOWER
LEVEL WARM ADVECTION AND ANVIL SHIELDING FROM ONGOING
CONVECTION. COLDER TEMPERATURES ALOFT ARE FOCUSED NORTH OF
I-80. THEREFORE, WITH AN UNCAPPED ENVIRONMENT, EXPECT SOME
ISOLATED TO WIDELY SCATTERED STORMS FARTHER SOUTH GIVEN THAT
FORCING IS MORE MUTED. THE SIGNAL THEN CONTINUES FOR A BIT OF A
LULL IN ACTIVITY AS SHORTWAVE FORCING TEMPORARILY EASES, AND
CAPPING WILL GET REINFORCED VIA AN UPTICK IN WARM AIR ADVECTION
AFTER THAT WE WILL HAVE TO TAKE A LOOK AND SEE WHERE THE SURFACE
WARM FRONT WILL SET UP THIS EVENING. THE PATTERN TONIGHT HAS
SOME SIMILARITY TO A MADDOX FLASH FLOOD SETUP, WITH A LOW
AMPLITUDE SHORTWAVE, UPPER JET TO THE NORTH, AND A SUBSTANTIAL
LOW LEVEL JET PROGGED. HOW MUCH OF MESOHIGH INFLUENCE IS A BIT
MORE VAGUE IN THE LATEST GUIDANCE. PMM/LPMM GUIDANCE (FROM 0Z/
6Z) HAD SOME HEFTY RAIN TOTALS ( 4-7" IN THE REGION). THE SIGNAL
IS A LITTLE MORE MUTED IN LATEST GUIDANCE, AT LEAST ON THE
FOOTPRINT OF THE HEAVY RAINFALL, BUT THE FLASH FLOOD POTENTIAL
THIS EVENING IS STILL ELEVATED. THE WARM FRONT HAS MOVED INTO
THE CHICAGO METRO AREA, AND IT SEEMS LIKE THAT IS WHERE IT WILL
REMAIN INTO THE EVENING HOURS. FORECAST SOUNDINGS DO STILL
SUGGEST, IN SPITE OF SOME DISAGREEMENTS IN LOW LEVEL JET
STRENGTH AND ORIENTATION WITH RESPECT TO THE WARM FRONT, A
PERIOD THIS EVENING INTO THE EARLY OVERNIGHT WHERE SLOW STORM
MOTIONS WOULD BE FAVORED VERY STRONG LIFT (LOWER LEVEL MOISTURE
CONVERGENCE), EVEN IF NOT QUITE AS LONG LIVED AS CONSIDERED
BEFORE. THE MOST CONCERNING TIME FRAME STILL LOOKS TO BE IN THE
MID EVENING THROUGH EARLY OVERNIGHT ACROSS THE CHICAGO AREA
BEFORE THE LOW LEVEL JET VEERS MORE TO WESTERLY. AS THIS OCCURS
THE AREA OF CONCERN WOULD SHIFT TO EAST CENTRAL IL (KANKAKEE
AREA) AND INTO NW INDIANA. THERE IS STILL CONSIDERABLE
UNCERTAINTY HERE ON COVERAGE, BUT THE SIGNS ARE THERE TO
CONTINUE THIS MESSAGE TONIGHT.
THE FORCING DURING THE DAY ON MONDAY IS NOT AS CLEAR AND
CONFIDENCE ON STORM EVOLUTION ON MONDAY IS SOMEWHAT LOW. THE
WARM FRONT WILL BRIEFLY SHIFT SOUTH (OR TO SOUTHERN PORTIONS OF
OUR AREA) DURING THE MORNING HOURS, HOWEVER THE LOW LEVEL FLOW
WILL TURN BACK AROUND TO THE SOUTHWEST. ANY WEAK RIPPLES IN THE
FLOW ALOFT THOUGH COULD A TRIGGER A STORM OR TWO DURING THE
AFTERNOON. DEEPER FORCING MAY NOT ARRIVE UNTIL THE EVENING WITH
A VERY WARM. MOIST AND UNSTABLE AIR MASS IN PLACE COUPLED WITH
STRONG DEEP LAYER SHEAR. THIS ENVIRONMENT WOULD SUPPORT ALL
HAZARDS INITIALLY AND ALSO EVENTUALLY BOWING/LINE STRUCTURES.
ANOTHER FLASH FLOOD THREAT WOULD BE IN PLACE, ESPECIALLY WITH
ANOTHER UPTICK IN THE LOW LEVEL JET MONDAY EVENING. WE WILL HAVE
TO WATCH WHERE THE WARM/STATIONARY FRONT LAYS OUT TOMORROW, WITH
HIGH UNCERTAINTY ON THAT.
UNFORTUNATELY THE PATTERN LOOKS FAIRLY ACTIVE WITH A WARM/MOIST
AIRMASS IN PLACE AND A ENDLESS STREAM OF SHORTWAVES MOVING THROUGH
IN NORTHWEST FLOW UPON A LINGERING FRONTAL BOUNDARY TUESDAY AND
WEDNESDAY. A MORE DYNAMIC SYSTEM WILL MOVE THROUGH EASTERN CANADA
LATER IN THE WEEK, AND THIS WILL HELP TO MOVE THE FRONTAL BOUNDARY
FARTHER SOUTH. THIS WILL TAKE THE STORM TRACK WITH IT, AND ALSO LEAD
TO COOLER ONSHORE FLOW IN THIS SYSTEM'S WAKE THURSDAY AND FRIDAY.
KMD
AVIATION /06Z TAFS THROUGH 12Z TUESDAY/
ISSUED AT 131 AM CDT MON AUG 10 2026
KEY MESSAGES:
- SCATTERED SHOWERS AND POSSIBLY A FEW STORMS WILL CONTINUE
NEAR THE TERMINALS OVERNIGHT.
- THERE IS A POTENTIAL FOR MVFR (OR LOWER) CEILINGS AND/OR
VISIBILITIES THROUGH THIS MORNING.
- ADDITIONAL WAVES OF SHOWERS AND STORMS ARE POSSIBLE AT AND
NEAR THE TERMINALS TODAY, BUT A HIGH DEGREE OF UNCERTAINTY
REMAINS REGARDING THE TIMING AND COVERAGE OF THIS ACTIVITY.
THE WORST OF TONIGHT'S THUNDERSTORM ACTIVITY HAS PUSHED EAST AND
SOUTH OF THE TERMINALS, BUT SCATTERED SHOWERS WILL CONTINUE TO
FESTER NEAR THE TERMINALS FOR AT LEAST A FEW MORE HOURS TONIGHT.
A FEW ADDITIONAL STORMS MAY DEVELOP, BUT THEIR COVERAGE SHOULD
BE MORE ISOLATED AND THEY SHOULD BE LESS INTENSE THAN THE
EARLIER STORMS.
PATCHY MVFR CEILINGS HAVE DEVELOPED IN THE WAKE OF THE EARLIER
THUNDERSTORM ACTIVITY, AND THE EXPECTATION IS FOR THE FOOTPRINT
OF THESE LOWER CEILINGS TO EXPAND LATER OVERNIGHT AND PAST
DAYBREAK. SOME SITES COULD HOLD ONTO MVFR CEILINGS WELL INTO
THIS AFTERNOON, BUT CONFIDENCE IN CEILING TRENDS IS LOW ON THE
WHOLE. ADDITIONALLY, FOG MAY ALSO DEVELOP OVERNIGHT AS A RESULT
OF THE EXCESS LOW-LEVEL MOISTURE IN THE AREA. THE GREATEST
SIGNAL FOR VISIBILITY REDUCTIONS ACROSS THE LATEST AVAILABLE
FORECAST GUIDANCE SUGGESTS THAT RFD IS THE MOST LIKELY OF OUR
TAF SITES TO BE AFFECTED BY THIS, BUT OBSERVATIONAL TRENDS WILL
NEED TO BE MONITORED CLOSELY.
ADDITIONAL SHOWERS AND THUNDERSTORMS MAY DEVELOP IN THE AREA
LATER TODAY, BUT THE EXACT TIMING AND COVERAGE OF THIS POTENTIAL
ACTIVITY REMAINS HIGHLY UNCERTAIN. OPTED TO INTRODUCE TWO PROB30
GROUPS INTO THE TAFS TO HIGHLIGHT THE TIME WINDOWS WHEN
CONVECTION IS MOST LIKELY TO AFFECT THE TERMINALS. THE FIRST
WINDOW IS TIED TO A CONVECTIVELY-ENHANCED DISTURBANCE THAT MAY
EMANATE FROM THE CENTRAL PLAINS TONIGHT AND REACH OUR AREA
TOWARDS MIDDAY/THE EARLY AFTERNOON. IT IS NOT YET CLEAR HOW
WELL-DEFINED THIS DISTURBANCE WILL BE, WHETHER WE'LL STILL BE
CAPPED FOR STRONGER SURFACE-BASED THUNDERSTORMS TO DEVELOP
AS IT ARRIVES, AND WHETHER THE AXIS THAT THE POTENTIAL
THUNDERSTORM MAY FOCUS ALONG WILL REMAIN SOUTH OF THE TERMINALS,
SO OPTED TO CARRY -SHRA IN THIS PROB30 GROUP FOR NOW AS JUST
SEEING SOME SCATTERED HIGH-BASED SHOWERS IS ALSO VERY MUCH A
POSSIBILITY DURING THIS TIME WINDOW. THE SECOND WINDOW IS TIED
TO ANOTHER UPPER-LEVEL DISTURBANCE THAT IS PROGGED TO ARRIVE
SOMETIME LATE THIS AFTERNOON OR EVENING. THUNDERSTORMS,
INCLUDING STRONG TO SEVERE THUNDERSTORMS WITH STRONG WINDS AND
HAIL, APPEAR TO BE MORE LIKELY TO OCCUR DURING THIS TIME WINDOW
COMPARED TO EARLIER, BUT EXACTLY WHERE AND WHEN THEY WILL
DEVELOP REMAINS UNCERTAIN. ALL IN ALL, A LOT OF UNCERTAINTY
REMAINS REGARDING THE THUNDERSTORM POTENTIAL FOR LATER TODAY,
AND ADDITIONAL CHANGES TO THE TAFS WILL LIKELY BE NEEDED AS
OBSERVATIONAL TRENDS BECOME CLEARER.
LASTLY, CONFIDENCE IN WIND DIRECTION TRENDS FOR TODAY IS ALSO
FAIRLY LOW, LARGELY AS A RESULT OF THE THUNDERSTORM-RELATED
UNCERTAINTIES. OUTSIDE OF ANY THUNDERSTORM INFLUENCE THOUGH,
SURFACE FLOW SHOULD REMAIN AT OR UNDER 10 KTS THROUGH THE TAF
PERIOD WITH A GENERALLY EASTERLY OR NORTHEASTERLY DIRECTION
FAVORED AT ORD, MDW, AND GYY FROM AROUND MIDDAY THROUGH TONIGHT
AS A RESULT OF A WEAK LAKE BREEZE/ONSHORE FLOW.
OGOREK
LOT WATCHES/WARNINGS/ADVISORIES
IL...FLOOD WATCH UNTIL 7 AM CDT THIS MORNING FOR ILZ003-ILZ004-
ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019-
ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-ILZ104-
ILZ105-ILZ106-ILZ107-ILZ108.
IN...FLOOD WATCH UNTIL 7 AM CDT /8 AM EDT/ THIS MORNING FOR INZ001-
INZ002-INZ010-INZ011-INZ019.
LM...NONE.
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