166
FXUS63 KLOT 070544
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1244 AM CDT SUN JUN 7 2026
KEY MESSAGES
- ISOLATED TO WIDELY SCATTERED SHOWERS AND THUNDERSTORMS WILL
CONTINUE OVERNIGHT, MAINLY ALONG AND SOUTH OF A ROCHELLE TO
JOLIET AND LAFAYETTE, IN LINE. NO SEVERE WEATHER IS EXPECTED.
- WHILE THERE WILL BE DAILY SHOWER AND THUNDERSTORM CHANCES
THROUGH THE UPCOMING WEEK, EXPECT PLENTY OF DRY HOURS. OUTSIDE
OF THE CONVECTIVE CHANCES, IT WILL BE VERY WARM AND HUMID
(FOCUSED AWAY FROM THE LAKE UNTIL TUESDAY).
UPDATE
ISSUED AT 849 PM CDT SAT JUN 6 2026
NO SIGNIFICANT CHANGES TO THE GOING FORECAST THIS EVENING,
MAINLY MINOR TWEAKS TO ACCOUNT FOR VARIOUS BOUNDARIES (LAKE
BREEZE, OUTFLOW AND FRONTAL) AND THEIR IMPACTS ON POP COVERAGE
AND TEMPS.
EARLY EVENING SURFACE ANALYSIS DEPICTS A COMPOSITE FRONTAL/LAKE
BREEZE/OUTFLOW BOUNDARY STRETCHING ACROSS THE FORECAST AREA
ALONG A LINE FROM ROUGHLY CLINTON, IA TO SOUTH OF ROCHELLE, THEN
SOUTHEAST THROUGH NORTHEAST LIVINGSTON COUNTY EVENTUALLY TO THE
LAFAYETTE, IN VICINITY. WHILE LITTLE/NO MID TO UPPER LEVEL
FORCING IS PRESENT, RAP MESOANALYSIS INDICATES ~2000 J/KG OF
MLCAPE REMAINS ALONG/SOUTH OF THE AFOREMENTIONED BOUNDARY(IES)
IN OUR WARM/HUMID SUMMER-LIKE AIR MASS. WEAK LOW-LEVEL
CONVERGENCE AND MODEST SOUTHWEST FLOW (10-15 KT IN THE 925-850
MB LAYER) FEEDING INTO THE STALLED BAROCLINIC ZONE CONTINUES TO
PRODUCE ISOLATED TO WIDELY-SCATTERED SHOWERS AND THUNDERSTORMS
ACROSS THE SOUTHWEST HALF OR SO OF THE CWA AT MID- EVENING.
WHILE MID-LEVEL SHORT WAVE RIDGING IS PROGGED TO CONTINUE TO
BUILD OVERHEAD OVERNIGHT, AND LOW-LEVEL INSTABILITY WILL
DECREASE DIURNALLY, WEAK SHORT WAVE ENERGY WRAPPING NORTHWARD
AROUND THE EASTERN PERIPHERY OF THE UPPER LEVEL LOW CENTERED
OVER THE SOUTHERN PLAINS IS EXPECTED TO MAINTAIN THIS SOUTHWEST
LOW-LEVEL FLOW OVERNIGHT WHICH SHOULD ALLOW ISOLATED CONVECTION
TO CONTINUE ALONG/SOUTH OF THE COMPOSITE BOUNDARY. THIS WILL
PERSIST INTO SUNDAY AS WELL, AS THE MID-LEVEL SHORT WAVE NUDGES
THE MID-LEVEL RIDGE EAST AND NORTHEAST OF THE FORECAST AREA AND
DIURNAL INSTABILITY AGAIN INCREASES.
GOING FORECAST HAS THIS SCENARIO HANDLED FAIRLY WELL, THUS
OTHER THAN SOME TWEAKS TO POPS/TEMPS THIS EVENING THROUGH THE
OVERNIGHT HOURS BASED ON THE LOCATION OF THE COMPOSITE
BOUNDARIES, HAVE NOT MADE SIGNIFICANT CHANGES (THOUGH DID WARM
OVERNIGHT MINS SOUTH OF THE BOUNDARY WHERE TEMPS WILL LIKELY
REMAIN NEAR 70 DEGREES).
RATZER
DISCUSSION
ISSUED AT 307 PM CDT SAT JUN 6 2026
THROUGH SUNDAY NIGHT:
GOES VISIBLE SATELLITE IMAGERY THIS AFTERNOON SHOWS SEVERAL
REGIONS OF AGITATED CUMULUS IN AND NEAR OUR FORECAST AREA. THE
MOST CONGESTED CUMULUS HAS GENERALLY BEEN FOCUSED NEAR THE LAKE
BREEZE AND ALONG A SOMEWHAT DIFFUSE REMNANT OUTFLOW BOUNDARY
FROM LAST NIGHT'S CONVECTION THAT HAS BEEN LAID OUT ACROSS OUR
FAR SOUTHERN COUNTIES AND INTO CENTRAL INDIANA, BUT DEEPER
CUMULUS GROWTH HAS ALSO BEEN NOTED WITHIN A COUPLE OF LOW-LEVEL
CONFLUENCE/CONVERGENCE ZONES ACROSS THE NORTHERN HALF OF OUR
FORECAST AREA. SYNOPTIC-SCALE FORCING REMAINS FAIRLY NEBULOUS
AND PRETTY MUCH LIMITED TO VERY MODEST ISENTROPIC UPGLIDE, BUT
WITHIN MOIST AND UNSTABLE SUMMERTIME AIR MASSES LIKE THE ONE IN
PLACE TODAY, IT TYPICALLY DOES NOT TAKE MUCH FOR CONVECTION TO
GET GOING, AND THAT HAS BEEN THE CASE TODAY. THAT SAID, THE
RELATIVE LACK OF LARGE-SCALE ASCENT HAS KEPT CONVECTIVE COVERAGE
ISOLATED TO WIDELY SCATTERED THUS FAR, AND THAT SHOULD LARGELY
CONTINUE TO REMAIN THE CASE THROUGH THIS EVENING.
ACROSS OUR SOUTHERN COUNTIES, RAP OBJECTIVE MESOANALYSIS
DEPICTS 2000-2500 J/KG OF MLCAPE AMIDST 15-25 KTS OR SO OF DEEP-
LAYER SHEAR. THIS ENVIRONMENT WAS JUST FAVORABLE ENOUGH TO
YIELD SEVERE DOWNBURST WINDS AND SMALL HAIL IN BENTON COUNTY, IN
WITH A TALL STORM THAT BRIEFLY PULSED UP THERE A LITTLE WHILE
AGO, AND WOULD NOT BE SURPRISED TO SEE ANOTHER INSTANCE OR TWO
OF LOCALIZED DAMAGING WINDS AND HAIL UP TO QUARTER SIZE WITH ANY
CONVECTIVE UPDRAFT CORES THAT MANAGE TO PULSE UP TOWARDS THE
~13 KM AGL EQUILIBRIUM LEVELS SOUTH OF I-80. FARTHER NORTH, A
MORE PRONOUNCED WARM NOSE AT AROUND 600 MB MAY INHIBIT
CONVECTIVE GROWTH TO A GREATER DEGREE IN THE ABSENCE OF
STRONGER FORCING FOR ASCENT, MAKING IT LESS LIKELY FOR CELLS TO
GROW TALL ENOUGH TO PRODUCE SEVERE WINDS AND HAIL THERE, IN
ADDITION TO REDUCING THE OVERALL LIKELIHOOD OF LIGHTNING.
LASTLY, COULD NOT ENTIRELY RULE OUT A FUNNEL CLOUD OR EVEN A
LANDSPOUT OCCURRING SOMEWHERE AS SLOW-MOVING CELLS DEVELOP
ALONG SURFACE BOUNDARIES IN THIS MOIST AND UNSTABLE AIR MASS.
THE LATEST RAP MESOANALYSIS DEPICTS NON-ZERO NON-SUPERCELL
TORNADO PARAMETER VALUES IN A FEW SPOTS, WHICH SUPPORTS THIS
THINKING.
A SLIGHT ENHANCEMENT TO THE LOW-LEVEL JET THIS EVENING MAY
ALLOW FOR DISORGANIZED CONVECTION TO FESTER ACROSS OUR SOUTHERN
COUNTIES FOR AT LEAST A FEW HOURS AFTER SUNSET, AND POSSIBLY
WELL INTO THE NIGHT. THIS CONVECTION SHOULD EVENTUALLY DIMINISH
IN COVERAGE, THOUGH, AS THE ATTENDANT INSTABILITY RESERVOIR
BECOMES INCREASINGLY DEPLETED WITH TIME TONIGHT. THE RESULTING
LULL IN CONVECTIVE ACTIVITY SHOULD PERSIST THROUGH AT LEAST
MID-MORNING TOMORROW BEFORE LARGE-SCALE FORCING INCREASES
TOWARD MIDDAY AS A CLOSED-OFF UPPER-LEVEL LOW PRESENTLY LOCATED
OVER THE SOUTHERN PLAINS LIFTS NORTHWARD TOWARD OUR LATITUDE AND
BECOMES SHEARED-OUT AS IT DOES SO. DESPITE THE WEAKENING NATURE
OF THE FORCING ASSOCIATED WITH THIS DISTURBANCE, THE PERSISTING
RICH LOW-LEVEL MOISTURE (SURFACE DEW POINTS UP TO AROUND 70F)
AND DIURNAL DESTABILIZATION AS SURFACE AIR TEMPERATURES WARM
INTO THE 80S WILL SUPPORT ANOTHER EPISODE OF CONVECTION IN OUR
FORECAST AREA INTO THE AFTERNOON HOURS. THIS TIME AROUND,
CONVECTIVE COVERAGE LOOKS TO BE GREATEST ACROSS THE SOUTHWESTERN
HALF OR SO OF OUR CWA. MINIMAL DEEP-LAYER SHEAR WILL ALSO
ENCOURAGE TOMORROW'S CONVECTION TO HAVE A PULSE-LIKE CHARACTER.
ENOUGH INSTABILITY WILL BE PRESENT TO SUPPORT A GUSTY WIND AND
SMALL HAIL THREAT WITH THE STRONGEST UPDRAFTS THAT PULSE UP,
BUT SUBPAR LAPSE RATES AND DCAPE SHOULD KEEP STORMS SUB-SEVERE.
OGOREK
MONDAY THROUGH FRIDAY:
THE AFOREMENTIONED WEAKENING MID-UPPER LOW/SHORT-WAVE WILL
CONTINUE TO SHEAR OUT SUNDAY NIGHT INTO MONDAY AS IT ENCOUNTERS
ROBUST RIDGING CENTERED OVER THE EASTERN LAKES BY THEN.
NONETHELESS, WEAKLY CAPPED TROPICS- LIKE AIRMASS SHOULD SUPPORT
FAIRLY WIDESPREAD SHOWERS AND AT LEAST SCATTERED STORMS
DEVELOPING AS EARLY AS MIDDAY MONDAY (UNLESS DEBRIS CLOUDINESS
PROVES TOO DETRIMENTAL TO SUFFICIENT DESTABILIZATION).
SOUTHEASTERLY SYNOPTIC FLOW AND LAKE BREEZE REINFORCEMENT WILL
KEEP IL SHORELINE LOCATIONS IN THE 70S ON MONDAY, WHILE THE REST
OF THE AREA REACHES THE LOW- MID 80S.
LOOKING AHEAD AT THE REST OF NEXT WORKWEEK, THERE HAVE BEEN SOME
GUIDANCE MEMBERS WITH SUFFICIENTLY STRONG MID-LEVEL RIDGING AND
LOW-LEVEL THERMAL RIDGING POKING INTO THE GREAT LAKES REGION FOR
A FEW DAYS OF VERY WARM (LOCALLY HOT) AND HUMID CONDITIONS. WITH
THAT SAID, THE MORE LIKELY SCENARIO IS OUR AREA BEING ON THE
PRECARIOUS NORTHWESTERN PERIPHERY OF RIDGING CENTERED NEAR THE
EAST COAST. THIS SHOULD ENTAIL LESS CAPPING AND A CONTINUATION
OF SHOWER AND THUNDERSTORM CHANCES. BY LATER IN THE WEEK
(THURSDAY OR THEREABOUTS), SEASONABLY STRONG TROUGHING FROM THE
NORTH CENTRAL US TO CENTRAL CANADA COULD PLAUSIBLY YIELD A
PATTERN SUPPORTIVE OF ORGANIZED STRONG TO SEVERE CONVECTION INTO
THE REGION.
NOTE THAT THE NBM DEPICTED TEMPERATURES CENTERED TUESDAY THROUGH
FRIDAY (MOST NOTABLY ON WEDNESDAY AND THURSDAY) ARE WELL
OUTSIDE OF THE ENSEMBLE SPECTRUM DUE TO LIKELY SPURIOUS UPWARD
BIAS CORRECTION. THUS WE WILL WITHHOLD FROM ANY HEAT MESSAGING
LOCALLY. IT LOOKS TO BE VERY WARM AND HUMID, BUT NOT HAZARDOUSLY
SO, PER THE CURRENT GLOBAL ENSEMBLE GUIDANCE CONSENSUS.
CASTRO
AVIATION /06Z TAFS THROUGH 12Z MONDAY/
ISSUED AT 1244 AM CDT SUN JUN 7 2026
MAIN CONCERN:
- POTENTIAL FOR TS INTO RFD AREA AND THE FAR WESTERN CHICAGO
METRO LATER THIS AFTERNOON INTO THIS EVENING. ADDITIONAL
SHRA/TS MAY APPROACH THE TERMINALS TOWARDS DAYBREAK TUESDAY.
CONDITIONS AT THE MAIN CHICAGO AREA TERMINALS WILL LIKELY BE
PRIMARILY QUIET THROUGH MOST OF THE CURRENT TAF PERIOD. RFD AREA
STILL HAS THE HIGHEST CHANCE FOR TS, WHERE A PROB30 WAS MAINTAINED.
MAY NEED TO CONSIDER A PROB30 FOR DPA WITH LATER ISSUANCES. FOR
ORD, MDW, AND GYY, THE MOST LIKELY SCENARIO IS THAT THE MORE
STABLE MARINE LAYER CONDITIONS PREVENT TS INTO THE VICINITY. TS
COVERAGE DOES LOOK HIGH ENOUGH THIS AFTERNOON-EARLY EVENING
WEST AND SOUTHWEST OF CHICAGO FOR PROLONGED AIR SPACE IMPACTS.
THE NEXT CHANCE FOR TS LOOKS TO BE TOWARDS AND BEYOND THE
CURRENT ORD AND MDW 30-HOUR TAF PERIOD, WITH NO MENTION IN THIS
ISSUANCE.
LIGHT EASTERLY WINDS OVERNIGHT/EARLY THIS MORNING WILL INCREASE
TO AROUND 10 KT BY THE MID TO LATE MORNING WITH SPEEDS ONLY
GRADUALLY DIMINISHING TONIGHT/SUNDAY NIGHT. OUTSIDE OF SHRA/TS,
EXPECT VFR CONDITIONS.
CASTRO
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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