985
FXUS63 KLOT 101740
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1240 PM CDT MON AUG 10 2026
KEY MESSAGES
- ADDITIONAL PERIODS OF STORMS ARE EXPECTED AT TIMES THROUGH
MID-WEEK. SOME OF THESE STORMS COULD BE SEVERE AND LEAD TO
ADDITIONAL FLOODING.
DISCUSSION
ISSUED AT 300 AM CDT MON AUG 10 2026
FORECAST REMAINS COMPLEX THROUGH MID-WEEK, AS A NEARLY
STATIONARY FRONTAL BOUNDARY LINGERS ACROSS THE FORECAST AREA
BENEATH AN ACTIVE WEST-NORTHWEST FLOW PATTERN ALOFT. PERIODIC
SHOWER AND THUNDERSTORM CHANCES WILL PERSIST WITH SOMEWHAT LOW
CONFIDENCE IN TIMING AND COVERAGE, ULTIMATELY MODULATED BY
INDIVIDUAL SHORT WAVES AND DAILY DIURNAL HEATING AND INSTABILITY
TRENDS. EPISODES OF SEVERE WEATHER AND LOCALLY HEAVY RAINFALL
REMAIN POSSIBLE.
IN THE NEAR-TERM, LATEST SURFACE ANALYSIS DEPICTS A NEARLY
STATIONARY FRONTAL BOUNDARY STRETCHING FROM AN AREA OF LOW
PRESSURE OVER WESTERN KS NORTHEAST INTO WESTERN IA, THEN EAST
ALONG ROUGHLY THE I-80 CORRIDOR ACROSS NORTHERN IL/NORTHWEST IN.
A VERY WARM/HUMID AIRMASS IS IN PLACE ALONG/SOUTH OF THE
BOUNDARY, CHARACTERIZED BY TEMPS IN THE UPPER 70/AROUND 80 AND
DEW POINTS IN THE MID-70S AT THIS LATE NIGHT HOUR. ALOFT,
SEASONABLY FAST WEST-NORTHWEST FLOW WAS IN PLACE ACROSS THE
REGION, SUPPLYING A TRACK FOR A SERIES OF MID-LEVEL SHORT WAVE
DISTURBANCES OF VARYING AMPLITUDE. ONE SUCH WAVE IS CURRENTLY
TRACKING FROM IA INTO NORTHERN IL, SUPPORTING A SOUTHWESTERLY 35
KT LOW-LEVEL JET ATOP THE LOW-LEVEL FRONTAL ZONE INTO NORTHEAST
IL/NORTHWEST IN. SEVERAL CLUSTERS OF STRONG THUNDERSTORMS HAD
DEVELOPED IN THE ENHANCED WARM/MOIST ADVECTION REGIME ASSOCIATED
WITH THIS JET LAST EVENING, WITH A SMALL MCS REMAINING ACROSS
OUR SOUTHERN TIER OF CWA COUNTIES AS OF 2 AM ON THE NOSE OF THE
JET IN THE VICINITY OF THE SURFACE FRONTAL BOUNDARY. GIVEN
ML/MUCAPE VALUES IN THE 3000-3500 J/KG RANGE, 35-40 KTS OF
EFFECTIVE SHEAR AND PRECIPITABLE WATER VALUES NEAR 2 INCHES,
SEVERE WEATHER AND LOCALLY HEAVY RAINFALL REMAIN A CONCERN WITH
THESE STORMS FOR THE NEXT HOUR OR SO, BEFORE THEY EVENTUALLY
SLIDE SOUTHEAST OF THE AREA TOWARD/JUST AFTER DAYBREAK AS THE
LOW-LEVEL JET GRADUALLY VEERS MORE WESTERLY AND WEAKENS WITH THE
PASSAGE OF THE MID-LEVEL WAVE.
ONCE THESE STORMS EXIT THE AREA, THERE SHOULD BE A BIT OF A
LULL IN CONVECTION IN THE WAKE OF THE DEPARTING SHORT WAVE AND
DURING OUR DIURNAL INSTABILITY MINIMUM. CAN'T COMPLETELY RULE
OUT SOME ISOLATED ELEVATED SHOWER OR THUNDERSTORM DEVELOPMENT
HOWEVER, DUE TO THE PRESENCE OF THE FRONT/BAROCLINIC BOUNDARY
AND WEAKER BUT STILL PERSISTENT WARM/MOIST ADVECTION. CHANCES
SHOULD INCREASE AGAIN AT LEAST A BIT TOWARD MIDDAY AND INTO THIS
AFTERNOON HOWEVER, AS ANOTHER WEAK WAVE OR MCV (CURRENTLY
APPROACHING THE OMAHA VICINITY) TRACKS EAST DURING A MORE
FAVORABLE DIURNAL TIME. CAM GUIDANCE LOOSELY DEPICTS THIS,
THOUGH DIFFERENCES IN COVERAGE AND TIMING DETAILS ARE EVIDENT.
ADDITIONAL DEVELOPMENT ALSO APPEARS POSSIBLE LATER THIS EVENING,
AS THE NOCTURNAL LOW-LEVEL JET MODESTLY INCREASES ATOP THE
FRONTAL ZONE. THERE DOES APPEAR TO BE A SOMEWHAT CONSISTENT
SIGNAL HOWEVER, AMONGST BOTH CAM AND GLOBAL GUIDANCE, FOR AN MCS
TO DEVELOP OVER NE/SD LATER TONIGHT WHICH WOULD APPROACH THE
FORECAST AREA AROUND/AFTER DAYBREAK TUESDAY. THIS SUPPORTS THE
HIGHEST POPS (60-70%) DURING TUESDAY, AND HAVE LIMITED OTHER
MENTIONS TO JUST CHANCE (20-40%) LATER TODAY AND TONIGHT. GIVEN
OTHERWISE SIMILAR INSTABILITY/SHEAR AND MOISTURE PARAMETERS, WE
REMAIN IN SPC/WPC SLIGHT RISKS FOR SEVERE WEATHER AND EXCESSIVE
RAINFALL DURING THESE PERIODS.
NO SIGNIFICANT CHANGE IN THE PATTERN IS EVIDENT INTO MID-WEEK
(WEDNESDAY, POSSIBLY THURSDAY), THOUGH CONFIDENCE GRADUALLY
DECREASES BASED ON IMPACTS OF ANY PRECEDING CONVECTIVE/MCS
OUTFLOW IMPACTS. GLOBAL ENSEMBLES CONTINUE TO SHOW A SIGNAL FOR
OUR FRONTAL BOUNDARY TO SHIFT A LITTLE FARTHER SOUTH THURSDAY
NIGHT AND FRIDAY, WHICH MAY DECREASE OUR SHOWER/THUNDERSTORM
POTENTIAL BRIEFLY LATE IN THE WEEK, THOUGH THIS SIGNAL IS WEAKER
THAN EARLIER RUNS AND THERE ARE INDICATIONS THAT THE FRONT MAY
LIFT BACK INTO THE AREA NEXT WEEKEND. THUS, IT APPEARS THAT OUR
SEASONABLY WARM/HUMID AND PERIODICALLY STORMY PATTERN MAY
PERSIST FOR MUCH OF THE FORECAST PERIOD.
RATZER
AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/
ISSUED AT 1240 PM CDT MON AUG 10 2026
FORECAST CONCERNS INCLUDE...
CHANCE OF THUNDERSTORMS THIS AFTERNOON INTO THIS EVENING.
POSSIBLE LINE OF SEVERE THUNDERSTORMS MID/LATE TUESDAY MORNING.
POSSIBLE MVFR CIGS OVERNIGHT/TUESDAY MORNING.
MVFR CIGS WILL BE POSSIBLE THROUGH MID AFTERNOON, ESPECIALLY
JUST SOUTH OF THE TERMINALS. MOST OF THIS CLOUD COVER IS
EXPECTED TO LIFT TO LOW VFR BY MID/LATE AFTERNOON. MVFR CIGS MAY
REDEVELOP OVERNIGHT AND CONTINUE INTO TUESDAY MORNING THOUGH
CONFIDENCE IS LOW AND MAINTAINED SCATTERED MENTION FOR NOW.
THERE WILL BE A CHANCE OF THUNDERSTORMS FROM MID AFTERNOON
THROUGH MID/LATE THIS EVENING, PRIMARILY ACROSS NORTHEAST IL AND
THE TERMINALS. OVERALL CONFIDENCE IS SLOWLY DECREASING FOR BOTH
COVERAGE AND DURATION OF POSSIBLE THUNDERSTORMS THOUGH THE BEST
TIMING APPEARS TO BE 22Z TO 03Z AND CURRENT TEMPO MENTION SEEMS
TO MATCH UP WITH THIS POTENTIAL. THERE MAY BE A FEW LINGERING
SHOWERS OR AN ISOLATED THUNDERSTORM LATER THIS EVENING INTO THE
OVERNIGHT HOURS, BUT CONFIDENCE IS LOW AND LOW ENOUGH TO REMOVE
PREVIOUS PROB MENTION.
MUCH OF THE MODEL GUIDANCE IS IN AGREEMENT WITH A COMPLEX OF
THUNDERSTORMS DEVELOPING ACROSS NORTHEAST IA EARLY TUESDAY
MORNING AND RACING SOUTHEAST ACROSS NORTHERN IL AND THE
TERMINALS IN THE MID/LATE MORNING AND ACROSS NORTHWEST IL BY
EARLY TUESDAY AFTERNOON. WHILE THERE IS STILL SOME UNCERTAINTY
FOR THE STRENGTH, LOCATION AND MOVEMENT OF THIS EXPECTED LINE
OF STORMS, CONFIDENCE IS SLOWLY INCREASING AND TEMPO MENTION
SEEMS REASONABLE AT THIS TIME. THIS LINE OF THUNDERSTORMS WILL
MOST LIKELY BE SEVERE AND GUSTS TO 50KT IN THE TEMPO ALSO SEEM
REASONABLE BASED ON CURRENT TRENDS. OVERALL DURATION OF THUNDER
MAY END UP ONLY BEING 1-2 HOURS AT ANY ONE LOCATION. CMS
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
VISIT US AT WEATHER.GOV/CHICAGO
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page