542
FXUS63 KLOT 240519
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1219 AM CDT FRI JUL 24 2026
KEY MESSAGES
- HEAT AND HUMIDITY WILL RETURN TO THE REGION SUNDAY AND
CONTINUE INTO MONDAY. THE MAGNITUDE OF HEAT MAY REQUIRE HEAT
HEADLINES AT SOME POINT.
- THERE IS CURRENTLY A 20-40% CHANCE FOR THUNDERSTORMS ON BOTH
SUNDAY AND MONDAY. SEVERE THUNDERSTORMS WITH DESTRUCTIVE WINDS
AND FLASH FLOODING MAY OCCUR ON BOTH DAYS IN THE GREAT LAKES
REGION, BUT WHETHER SUCH A THREAT WILL MATERIALIZE HERE
LOCALLY IS UNCERTAIN AT THIS TIME.
DISCUSSION
ISSUED AT 252 PM CDT THU JUL 23 2026
THE SEPTEMBER-LIKE AIR MASS THAT HAS SETTLED INTO THE REGION
WILL STICK AROUND FOR YET ANOTHER DAY TOMORROW. A THIRD
CONSECUTIVE DAY OF AIR MASS WARMING PAIRED WITH MODEST RETURN
FLOW ON THE BACKSIDE OF A DEPARTING ~1022 MB SURFACE HIGH WILL
LIKELY ALLOW FOR AT LEAST A FEW LOW 80S AIR TEMPERATURE
READINGS TO BE OBSERVED TOMORROW AFTERNOON AMIDST A MIX OF
SUNSHINE AND CLOUDS, WITH UPPER 70S HIGH TEMPERATURES EXPECTED
OTHERWISE. DEW POINTS WILL ALSO INCREASE FROM WHAT THEY WERE
TODAY, BUT HUMIDITY LEVELS SHOULD NEVERTHELESS STILL REMAIN IN
A COMFORTABLE RANGE TOMORROW.
A COUPLE OF SHORTWAVE TROUGHS WILL TRACK EAST-SOUTHEASTWARD
TONIGHT INTO TOMORROW FROM THE GREAT PLAINS TOWARDS THE
MISSISSIPPI AND OHIO RIVER VALLEYS AND WILL BE ACCOMPANIED BY
RAIN IN SOME AREAS. THE NORTHERNMOST OF THESE WAVES WILL PASS
OVER OR TRACK VERY NEAR OUR CWA AND WILL LIKELY INDUCE ENOUGH
SATURATION IN THE MIDDLE AND UPPER LEVELS OF THE TROPOSPHERE TO
SUPPORT PRECIPITATION IN THE ASSOCIATED CLOUD LAYER OVER OR VERY
NEAR OUR SOUTHERN COUNTIES. HOWEVER, DESCENDING HYDROMETEORS
WILL HAVE TO WORK THROUGH A ROBUST DRY SUB-CLOUD LAYER
(INITIALLY OVER 10000 FT DEEP), AND THIS MAY PROVE TO BE
DIFFICULT TO OVERCOME IN THE ABSENCE OF STRONGER FORCING ALOFT.
THUS, WHILE SOME SPRINKLES COULD BE OBSERVED IN SOME OF OUR
SOUTHERNMOST LOCALES DURING THE DAYTIME TOMORROW, MEASURABLE
PRECIPITATION APPEARS UNLIKELY TO OCCUR.
AFTER THIS SHORTWAVE DISTURBANCE DEPARTS, A PLUME OF MEAGER
INSTABILITY WILL LIFT NORTHEASTWARD INTO THE REGION FRIDAY NIGHT
INTO SATURDAY MORNING. WHILE LAPSE RATES WILL REMAIN
UNIMPRESSIVE DURING THIS TIME FRAME, INCREASING LOW-LEVEL
MOISTURE MAY NEVERTHELESS ALLOW FOR SOME SHOWER ACTIVITY TO
SPROUT WITHIN THE ASSOCIATED WING OF WARM AIR ADVECTION/ISENTROPIC
ASCENT -- PRIMARILY ACROSS OUR SOUTHERN COUNTIES AND POINTS
FARTHER TO THE SOUTH. OPTED TO INTRODUCE SLIGHT CHANCE POPS TO
THE GRIDDED FORECAST DATABASE ACROSS THE SOUTHERN HALF OR SO OF
OUR FORECAST AREA FOR THE OVERNIGHT FRIDAY INTO SATURDAY
MORNING TIME FRAME TO ACCOUNT FOR THIS POSSIBILITY. IF ANY CELLS
ASSOCIATED WITH THIS ACTIVITY MANAGE TO GROW TALL ENOUGH, THEN
A FEW ISOLATED LIGHTNING STRIKES COULD ALSO OCCUR. OTHERWISE,
CONDITIONS SHOULD DRY OUT FOR SATURDAY AFTERNOON AS THE
ASSOCIATED FORCING PROGRESSES EASTWARD AND STRENGTHENING CAPPING
QUASHES ANY ATTEMPTS FROM SURFACE-BASED AIR PARCELS TO FREELY
CONVECT WITHIN AN INCREASINGLY MOIST/HUMID AIR MASS.
BY SUNDAY, A MUCH MORE JULY-LIKE AIR MASS WILL BECOME ESTABLISHED
ACROSS THE REGION WITH AIR TEMPERATURES BUILDING INTO THE UPPER
80S AND 90S AND EVAPOTRANSPIRATIONALLY-SUPPLEMENTED DEW POINTS
CLIMBING SOLIDLY INTO THE 70S (AND POSSIBLY EVEN NEAR 80F IN
SPOTS) AS AN UPPER-LEVEL RIDGE STRENGTHENS AND EXPANDS ACROSS
THE CENTRAL THIRD OF THE CONUS. HEAT INDICES IN OUR AREA ARE
THUS LIKELY TO ECLIPSE THE CENTURY MARK AND COULD POTENTIALLY
RISE HIGH ENOUGH TO WARRANT HEAT HEADLINES FOR AT LEAST PART OF
OUR FORECAST AREA ON SUNDAY AND POSSIBLY AGAIN ON MONDAY AS WELL.
THIS MUGGY AIR MASS WILL ALSO BE PRIMED FOR THUNDERSTORM
ACTIVITY. PARTICULARLY, THE CONSISTENT MODEL SIGNAL FOR MULTIPLE
SHORTWAVES NAVIGATING AROUND THE TOP OF THE AFOREMENTIONED
RIDGE AND DIVING INTO THE MOIST AND STRONGLY UNSTABLE AIR MASS
PRESENT ACROSS THE UPPER MIDWEST/GREAT LAKES AMIDST STRONG
NORTHWESTERLY FLOW DOES RAISE CONCERN FOR ONE OR MORE SEVERE TO
POTENTIALLY DESTRUCTIVE CONVECTIVE COMPLEXES TRACKING THROUGH
THE REGION ON SUNDAY AND/OR MONDAY. ADDITIONALLY, WITH
PRECIPITABLE WATER VALUES PROGGED TO APPROACH AND EVEN EXCEED
2", TORRENTIAL RAINFALL WILL ACCOMPANY ANY STORMS THAT DEVELOP
AND COULD RESULT IN FLASH FLOODING WHEREVER STORMS PERSIST FOR
A SUFFICIENTLY LONG PERIOD OF TIME. WITH THIS POTENTIAL
THUNDERSTORM TIME WINDOW STILL BEING 3-4 DAYS OUT, IT REMAINS
PRACTICALLY IMPOSSIBLE TO PINPOINT PRECISELY WHERE AND WHEN
SUCH THREATS MAY MATERIALIZE IN THE REGION, AND IT'S ENTIRELY
WITHIN THE REALM OF POSSIBILITY AT THIS POINT FOR THIS
THUNDERSTORM ACTIVITY TO AVOID OUR AREA ALTOGETHER (THOUGH THIS
ISN'T A SCENARIO THAT WE'D BET ON BASED ON THE LOOK OF THIS
FORTHCOMING WEATHER PATTERN). THE MAIN MESSAGE AT THIS POINT IN
TIME IS THAT CONDITIONS WILL BE FAVORABLE FOR MULTIPLE ROUNDS OF
SEVERE THUNDERSTORMS SOMEWHERE IN THE GENERAL REGION ON SUNDAY
AND ON MONDAY, BUT SPECIFIC DETAILS REGARDING THIS SEVERE
THUNDERSTORM POTENTIAL REMAIN HIGHLY UNCERTAIN AT THIS TIME.
FORECAST CONFIDENCE FROM TUESDAY ONWARD ALSO REMAINS RELATIVELY
LOW, IN PART DUE TO THE UNCERTAINTIES WITH WHAT WILL HAPPEN IN
THE PRECEDING DAYS. ENSEMBLE GUIDANCE GENERALLY FAVORS MIDWEEK
CONDITIONS THAT AREN'T AS HOT AND HUMID COMPARED TO SUNDAY AND
MONDAY, AND THIS OUTCOME WOULD BE LIKELY TO COME TO FRUITION IF
EXTENSIVE THUNDERSTORM ACTIVITY MATERIALIZES ON SUNDAY AND/OR
MONDAY AND SHUNTS THE MUGGIEST AIR WELL TO OUR SOUTH AND/OR
EAST.
OGOREK
AVIATION /06Z TAFS THROUGH 12Z SATURDAY/
ISSUED AT 1219 AM CDT FRI JUL 24 2026
MAIN ITEM OF NOTE:
- SOMEWHAT UNCERTAIN WIND DIRECTIONS AT ORD AND MDW, ESPECIALLY
THIS AFTERNOON.
WHILE IT WILL BE ANOTHER VFR PERIOD WITH NO SIGNIFICANT
CONCERNS, THE WIND FORECAST IS A BIT TRICKY AT THE NEAR LAKE
TERMINALS. FOLLOWING LIGHT/VRB TO CALM WINDS THROUGH THE PRE-
DAWN HOURS AREA-WIDE, WIND DIRECTION AT ORD AND MDW SHOULD
INITIALLY FAVOR SOUTHEAST BY THE MID TO LATE MORNING. AS A LAKE
BREEZE BOUNDARY SHARPENS UP THIS AFTERNOON, WINDS TO THE WEST OF
THE BOUNDARY SHOULD VEER TO SOUTH-SOUTHWEST. GIVEN TYPICALLY
WEAK LAKE BREEZES IN LATE JULY, CURRENT THINKING IS THAT THE
BOUNDARY WILL REMAIN EAST OF MDW AND ESPECIALLY ORD (HIGHER
CONFIDENCE THERE), WITH VRB WINDS AT GYY. ASIDE FROM THE
UNCERTAINTY NEAR THE LAKE, EXPECT LIGHT TO MODERATE SOUTH-
SOUTHWEST WINDS INLAND, DIMINISHING WITH SUNSET THIS EVENING.
CASTRO
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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