232
FXUS63 KLOT 270535
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1235 AM CDT FRI JUN 27 2025
KEY MESSAGES
- CHANCES OF SHOWERS AND T-STORMS WILL CONTINUE AT TIMES TONIGHT
INTO FRIDAY.
- AFTER A BIT OF A REPRIEVE FROM HEAT AND HUMIDITY SATURDAY
(ESPECIALLY NEAR THE LAKE), ANOTHER HOT AND HUMID DAY IS
EXPECTED SUNDAY.
UPDATE
ISSUED AT 924 PM CDT THU JUN 26 2025
AFTER A BUSY EVENING WITH GUSTY TO LOCALLY DAMAGING
THUNDERSTORMS OVER NORTHEASTERN IL AND NORTHWESTERN IN,
ATTENTION TURNS TO THE LINE OF SHOWERS AND STORMS NOW
APPROACHING THE MISSISSIPPI RIVER. WATER VAPOR IMAGERY DEPICTS
THE PARENT UPPER-LEVEL SHORT INITIALLY RESPONSIBLE FOR
INITIATING THUNDERSTORMS ACROSS IOWA AND MINNESOTA EARLIER THIS
AFTERNOON NOW LIFTING EAST-NORTHEASTWARD TOWARD LAKE SUPERIOR.
WITH THE FORCING SO FAR REMOVED FROM THE LINE OF STORMS, ANY
RENEWED DEVELOPMENT INTO ILLINOIS WILL BE DEPENDENT ON SLABWISE
LIFTING ATOP THE COLD POOL. RECENT RADAR TRENDS FROM KDVN
DEPICTING THE LEADING EDGE OF THE COLD POOL RACING AHEAD OF THE
CONVECTIVE CELLS, IMPLYING THE SLOPE OF THE COLD POOL AND
ASSOCIATED STRENGTH OF FORCING ALONG THE LEADING EDGE IS
DECREASING. SUCH AN EVOLUTION IS NOT AT ALL SURPRISING GIVEN A
LACK OF STRONG LOW-LEVEL SHEAR AHEAD OF THE LINE OF STORMS (THE 00Z
DVN RAOB SAMPLED AROUND 20KT OF 0-3KM SHEAR, WHICH IS HARDLY
ENOUGH TO BALANCE A SUMMERTIME COLD POOL). TAKEN ALTOGETHER, THE
EXPECTATION IS FOR THE GUST FRONT TO CONTINUE MOVING AHEAD OF
THE LINE OF STORMS, LEADING TO A GRADUAL DECAY OF THE OVERALL
SYSTEM AS IT MOVES EASTWARD INTO NORTHERN ILLINOIS.
GIVEN THERE IS STILL SOME 800 TO 1000 J/KG OF DCAPE AND 2000
J/KG OF MUCAPE AHEAD OF THE COLD POOL, IT WILL TAKE SOME TIME
FOR THE ENTIRE SYSTEM TO FULLY DECAY. AS A RESULT, STILL EXPECT
AT LEAST A WIND SHIFT WITH GUSTY WEST WINDS FOLLOWED BY
SCATTERED SHOWERS AND STORMS TO MAKE IT TO I-39, AND PERHAPS AS
FAR EAST AS THE FOX VALLEY. CHANCES THAT THUNDERSTORMS HOLD
TOGETHER AS FAR EAST AS CHICAGO SEEM PRETTY LOW (20% OR LESS).
TAKEN TOGETHER, NO ADDITIONAL SEVERE WEATHER IS EXPECTED
TONIGHT.
UPDATED PRODUCTS WILL BE SENT SOON.
BORCHARDT
DISCUSSION
ISSUED AT 249 PM CDT THU JUN 26 2025
ANOTHER DAY OF HOT AND HUMID CONDITIONS ACROSS THE AREA THIS
AFTERNOON. SOME ISOLATED SHOWERS AND THUNDERSTORMS HAVE BROUGHT
SOME TEMPORARY RELIEF TO A FEW PLACES THIS AFTERNOON, BUT THE
MAJORITY OF THE AREA IS EXPERIENCING ANOTHER DAY WITH
TEMPERATURES IN THE 90S AND HEAT INDEX READINGS NEAR OR JUST
ABOVE 100 DEGREES. ATMOSPHERE IS HOT, HUMID, AND UNCAPPED, WHICH
HAS ALLOWED FOR SOME "AIR MASS" CONVECTION TO POP THIS
AFTERNOON. THE THREAT OF THESE ISOLATED TO WIDELY SCATTERED
STORMS COULD LINGER THROUGH SUNSET, BUT UNLESS WE GET SOME
AMALGAMATION OF COLD POOLS TO FORCE ADDITIONAL STORMS, COVERAGE
SHOULD REMAIN PRETTY ISOLATED THROUGH SUNSET.
WATER VAPOR IMAGERY SHOWS A WELL DEFINED SHORTWAVE OVER THE
NORTHERN PLAINS MOVING GRADUALLY EAST TO THE UPPER MISSISSIPPI
VALLEY. MORE ORGANIZED CONVECTION HAS BEEN DEVELOPING IN
ASSOCIATION WITH THIS SHORTWAVE FROM SOUTHERN MN SOUTH INTO
CENTRAL IA. THIS CONVECTION IS EXPECTED TO CONTINUE TO SHIFT
GRADUALLY EASTWARD TOWARD THE MS RIVER THE REST OF THE
AFTERNOON. STRONGER SHEAR ASSOCIATED WITH THIS SHORTWAVE IS
NORTH OF OUR LATITUDE, SO DESPITE THE INSTABILITY, ANTICIPATE
THIS CONVECTION SHOULD FALL APART AFTER SUNSET AS IT CROSSES THE
MS RIVER INTO NORTHWEST IL. KEPT THE HIGHEST POPS LATER THIS
EVENING INTO THE EARLY OVERNIGHT OVER OUR NORTHWESTERN CWA, WITH
MUCH LOWER CHANCES FOR THIS ACTIVITY SURVIVING LONG ENOUGH TO
BRING ANY ORGANIZED RAIN CHANCES OVER OUR EASTERN CWA.
COMPOSITE OUTFLOW/WEAK SYNOPTIC FRONT IS EXPECTED TO MOVE ACROSS
OUR CWA TOMORROW. STRONGEST FORCING ASSOCIATED WITH THE
SHORTWAVE TROUGH IS EXPECTED TO PASS WELL NORTH OF THE AREA, BUT
WITH AIR MASS EXPECTED TO BECOME MODERATELY TO STRONGLY UNSTABLE
AND UNCAPPED IN ADVANCE OF THIS BOUNDARY TOMORROW. CERTAINLY
PLAUSIBLE THAT SCATTERED THUNDERSTORMS COULD DEVELOP AHEAD OF
THIS FRONT TOMORROW AFTERNOON, PARTICULARLY ACROSS NW IN AND OUR
EAST CENTRAL IL COUNTIES. SLIGHTLY DRIER AND MORE STABLE
CONDITIONS IN THE WAKE OF THE FRONT SHOULD RESULT DRY WEATHER
OVER OUR NORTHWEST CWA.
TRANSIENT SURFACE HIGH WILL MOVE ACROSS THE WESTERN GREAT LAKES
SATURDAY WITH LOWER DEWPOINTS MAKING THE STILL SEASONABLY WARM
TEMPERATURES MORE TOLERABLE. THE POSITION OF THE HIGH SHOULD
ALSO ALLOW FOR A PROMINENT LAKE BREEZE TO MOVE WELL INLAND
DURING THE AFTERNOON, PROVIDING FOR NATURE PROVIDED AC FOR AREAS
CLOSER TO THE LAKE.
THAT HIGH WILL SCOOT OFF THE EAST OF THE REGION SUNDAY WITH
SOUTHERLY WINDS LIKELY TO DRAG THE HEAT AND HUMIDITY BACK NORTH
INTO THE AREA. HIGHS ON SUNDAY SHOULD TOP OUT IN THE LOW-MID 90S
WITH HEAT INDICES AGAIN NEAR TO JUST OVER 100 DEGREES. SOUTHERN
FLANKS OF ANOTHER SHORTWAVE TROUGH PASSING NORTH OF THE AREA
SUNDAY SHOULD LEAD TO INCREASING CHANCES OF SHOWERS AND STORMS
LATER SUNDAY AFTERNOON INTO SUNDAY EVENING. STRONGER SHEAR AND
BETTER THREAT FOR ORGANIZED CONVECTION SHOULD REMAIN TO OUR
NORTH, BUT THE AIR SHOULD BE VERY MOIST AND MODERATELY TO
STRONGLY UNSTABLE AGAIN SUNDAY AFTERNOON, SO IF CONVECTION MAKES
IT INTO THE AREA, WET MICROBURSTS AND TORRENTIAL DOWNPOURS
WOULD BE A THREAT.
LONGWAVE TROUGH IS PROGGED TO DIG INTO THE GREAT LAKES REGION
EARLY NEXT WEEK WITH MUCH MORE COMFORTABLE HUMIDITY, ESPECIALLY
BY TUESDAY AND WEDNESDAY. TEMPS WILL REMAIN SEASONABLY WARM
AWAY FROM THE LAKE, BUT NOT AS HOT AS MANY OF THE DAYS WE'VE
EXPERIENCED RECENTLY.
- IZZI
AVIATION /06Z TAFS THROUGH 12Z SATURDAY/
ISSUED AT 1235 AM CDT FRI JUN 27 2025
MAIN CONCERNS:
- SHRA/TSRA NEAR RFD FOR A FEW HOURS EARLY THIS MORNING.
- WIND SHIFT TO WEST-NORTHWEST STILL PROBABLE AT THE CHICAGO
AREA TERMINALS EARLY THIS MORNING.
- SMALL TSRA CHANCE (~15-25%) NEAR THE CHICAGO AREA TERMINALS IN
THE AFTERNOON, WITH HIGHER CHANCES OFF TO THE SOUTHEAST.
SHOWERS AND ISOLATED T-STORMS BEHIND AN OUTFLOW BOUNDARY MAY
RESULT IN SOME IN CLOUD LIGHTNING NEAR RFD FOR A FEW HOURS.
FARTHER EAST, A FEW VFR SHRA WILL BE POSSIBLE BEHIND THE
BOUNDARY. INCLUDED TEMPO MENTION FOR A BRIEF WEST-NORTHWEST WIND
SHIFT.
MVFR CIGS ARE LIKELY TO SPREAD INTO NORTH CENTRAL IL AFTER
DAYBREAK, INCLUDING AT RFD, THOUGH THESE CIGS MAY NOT MAKE IT
INTO THE CHICAGO AREA BEFORE SCATTERING AND/OR LIFTING OF CLOUD
BASES.
WINDS WILL VEER TO BREEZY WEST-SOUTHWEST AHEAD OF A COLD
FRONT LATE THIS MORNING. THE 240-260 DEG WIND DIRECTION SHOULD
SERVE TO LIMIT THE COVERAGE OF CONVECTIVE DEVELOPMENT AHEAD OF
THE FRONT NEAR THE TAF SITES, BUT STILL CAN'T RULE OUT TS NEAR
THE CHICAGO AREA TERMINALS. GYY AND MDW HAVE A LOW BUT
RELATIVELY HIGHER CHANCE THAN ORD AND DPA. WE'LL CONTINUE TO
ASSESS THE TS POTENTIAL FOR SUBSEQUENT UPDATES. WINDS WILL
LIKELY SHIFT TO NORTHWEST BEHIND THE FRONT EARLY THIS EVENING,
WITH A LOW CHANCE FOR A SHIFT TO NORTHEAST.
CASTRO
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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