509
FXUS63 KLOT 271721
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1221 PM CDT FRI JUN 27 2025
KEY MESSAGES
- ISOLATED TO WIDELY SCATTERED THUNDERSTORMS EXPECTED THIS
AFTERNOON AND EVENING, MAINLY EAST OF I-55/57. GUSTY
DOWNBURST WINDS A THREAT WITH THE STRONGEST STORMS.
- AFTER A BIT OF A REPRIEVE FROM HEAT AND HUMIDITY SATURDAY
(ESPECIALLY NEAR THE LAKE), ANOTHER HOT AND HUMID DAY IS
EXPECTED SUNDAY.
- ADDITIONAL THREATS FOR MAINLY AFTERNOON/EVENING STORMS SUNDAY
AND MONDAY.
MESOSCALE
ISSUED AT 1042 AM CDT FRI JUN 27 2025
WE REMAIN ON THE NORTHWEST PERIPHERY OF A SYNOPTIC RIDGE
CENTERED OVER THE SOUTHEASTERN CONUS FOR YET ANOTHER DAY WITH
THE SAME JUICY AIR MASS (CHARACTERIZED BY LOW-MID 70S SURFACE
DEW POINTS) IN PLACE THAT SUPPORTED ISOLATED TO SCATTERED
CONVECTION IN OUR AREA THE PAST COUPLE OF DAYS. A MID-MORNING
ANALYSIS OF SURFACE OBSERVATIONS AND SATELLITE IMAGERY REVEALS A
COUPLE OF KEY METEOROLOGICAL FEATURES OF NOTE: NAMELY, A
WASHED-OUT OUTFLOW BOUNDARY THAT BISECTS OUR CWA FROM SOUTHWEST
TO NORTHEAST, A TRAILING TRUE COLD FRONTAL BOUNDARY NEAR THE
MISSISSIPPI RIVER, A SUBTLE AND COMPACT MCV ENTERING OUR
SOUTHWESTERN CWA, AND ANOTHER CONVECTIVELY-ENHANCED DISTURBANCE
OVER CENTRAL MISSOURI. THE FORMER BOUNDARY AND DISTURBANCE WILL
BE THE KEY PLAYERS FOR OUR SHOWER AND THUNDERSTORM CHANCES
THROUGH MID-AFTERNOON, WHILE THE LATTER BOUNDARY AND
DISTURBANCE WILL BE OF RELEVANCE FOR OUR SHOWER AND THUNDERSTORM
CHANCES DURING THE LATE AFTERNOON AND EVENING.
FOR THE LATE MORNING THROUGH MID-AFTERNOON TIME FRAME, THE
VISIBLE PRESENCE OF CLUMPY CUMULUS FIELDS AHEAD OF THE OUTFLOW
BOUNDARY AND MCV COUPLED WITH THE 12Z CAM SUITE LARGELY COMING
IN IN FAVOR OF CONVECTIVE INITIATION OCCURRING IN OUR
SOUTHEASTERN CWA IN THE NEXT COUPLE OF HOURS HAS INCREASED OUR
CONFIDENCE IN SCATTERED SHOWERS AND AT LEAST ISOLATED
THUNDERSTORMS OCCURRING IN AREAS EAST OF I-55 DURING THIS TIME
FRAME. SUBPAR MID-LEVEL LAPSE RATES AND LIMITED SURFACE
CONFLUENCE NEAR THE OUTFLOW BOUNDARY DO RAISE QUESTIONS AS TO
WHETHER THE THUNDERSTORM THREAT HERE WILL BE ANYTHING MORE THAN
ISOLATED AND BRIEF, BUT WITH DIURNAL HEATING EXPECTED TO
FURTHER DESTABILIZE THE ALREADY MODESTLY UNSTABLE AIR MASS AHEAD
OF THE RESIDUAL OUTFLOW BOUNDARY AND MCV, THUNDERSTORM COVERAGE
AND OVERALL LIKELIHOOD IS EXPECTED TO INCREASE WITH TIME AND
EASTWARD EXTENT.
MEANWHILE, DRY MID-LEVEL AIR (LIKELY MUCH DRIER THAN WHAT WAS
SAMPLED IN THE 12Z DVN RAOB THIS MORNING, PER HRRR FORECAST
SOUNDINGS) BETWEEN THE OUTFLOW BOUNDARY AND TRUE COLD FRONT WILL
LIKELY PROHIBIT THE DEVELOPMENT OF ANY CONVECTION OF NOTE NEAR
THE COLD FRONT AS IT TRACKS EASTWARD ACROSS OUR FORECAST AREA
TODAY. THE EXCEPTION TO THIS COULD AGAIN BE IN SOUTHEASTERN
PORTIONS OF OUR FORECAST AREA AS THE ARRIVAL OF THE COLD FRONT
THERE LATER THIS AFTERNOON AND EVENING WILL COINCIDE WITH THE
ARRIVAL OF THE AFOREMENTIONED CENTRAL MISSOURI DISTURBANCE.
WITH DEEP-LAYER SHEAR LIKELY TO REMAIN AT AROUND 20 KTS OR LESS
AND MLCAPE LIKELY CLIMBING INTO THE 2000-2500 J/KG RANGE IN OUR
SOUTHEASTERN CWA, ANY THUNDERSTORMS THAT DEVELOP TODAY SHOULD
HAVE A SIMILAR PULSE-LIKE CHARACTER TO THE STORMS THAT WE'VE
SEEN THE PAST COUPLE OF DAYS. THEREFORE, STRONG TO LOCALLY
SEVERE DOWNBURST WINDS WILL LIKELY OCCUR WITH THE MOST ROBUST
CONVECTION THAT DEVELOPS TODAY, WITH LIGHTNING AND BRIEFLY
TORRENTIAL DOWNPOURS ALSO EXPECTED TO BE HAZARDS. AGAIN, THE
THREAT FOR ISOLATED TO SCATTERED SHOWERS AND STORMS TODAY
APPEARS TO BE CONFINED TO AREAS NEAR AND EAST OF I-55, BUT MORE
SO IN AREAS NEAR AND EAST OF I-57 WITH THE LIKELIHOOD OF
ISOLATED STRONG TO MARGINALLY SEVERE THUNDERSTORMS INCREASING
WITH EASTWARD EXTENT INTO NORTHERN INDIANA.
OGOREK
DISCUSSION
ISSUED AT 319 AM CDT FRI JUN 27 2025
THROUGH SATURDAY:
OUTFLOW FROM EARLIER CONVECTION ACROSS IOWA IS PRESSING EAST OF
THE I-57 EARLY THIS MORNING. WHILE ALMOST ALL OF THE EARLIER
SHOWER AND THUNDERSTORM ACTIVITY HAS DIMINISHED LOCALLY, A
TONGUE OF ENHANCED MID-LEVEL MOISTURE IS CURRENTLY DRIFTING EAST
OF THE MISSISSIPPI RIVER. ALONG THE EASTERN FLANKS OF THIS
CORRIDOR, SCATTERED ELEVATED CONVECTION WILL BE POSSIBLE AS
SEVERAL LOW-AMPLITUDE IMPULSES RIPPLE NORTHEASTWARD. WILL HOLD
ONTO SOME CHANCES FOR SHOWERS/STORMS THROUGH THE MORNING HOURS
AS THIS MID-LEVEL MOIST AXIS AND ASSOCIATED VORTICITY MAXIMA
SCOOT EASTWARD.
WITH THE PASSAGE OF THE AFOREMENTIONED OUTFLOW THIS MORNING,
CONVERGENCE ALONG AN INCOMING COLD FRONT THIS AFTERNOON DOESN'T
LOOK PARTICULARLY SIGNIFICANT, WITH THE SURFACE WIND FIELD
FORECAST TO HOMOGENIZE SOMEWHAT WITH MIXING. ADDITIONALLY,
SOUNDINGS SHOW CONSIDERABLE DRYING IN THE 800-500 MB LAYER
OCCURRING THROUGH THE DAY WEST OF ABOUT I-55, ALONG WITH
GENERALLY NEBULOUS/WEAK FORCING MECHANISMS IN THE REGION. AS A
RESULT, WHILE AREAS ROUGHLY ALONG AND EAST OF A LA SALLE TO
WAUKEGAN LINE WILL BECOME MODERATELY UNSTABLE AND UNCAPPED THIS
AFTERNOON, SHOWER/STORM COVERAGE LATER TODAY REMAINS A BIT
UNCERTAIN. THE HESITANCY FOR HIGH RESOLUTION GUIDANCE TO CONVECT
SUGGESTS THAT DRY AIR ENTRAINMENT INTO INCIPIENT UPDRAFTS MAY
PLAY A ROLE IN CURTAILING COVERAGE, PARTICULARLY THE FARTHER
WEST ACROSS THE CWA YOU GO. WITH BETTER MID-LEVEL MOISTURE IN
PLACE SOUTH AND EAST OF ABOUT I-57, AND GLOBAL GUIDANCE
GENERALLY PRODUCING PRECIPITATION, CONTINUE TO HOLD ONTO
"CHANCE" POPS IN THIS REGION DURING THE AFTERNOON. LIMITED DEEP
LAYER SHEAR SUGGESTS PULSE/"AIRMASS" CONVECTION AND A POTENTIAL
FOR ISOLATED STRONG DOWNBURSTS WITH 30+ C SURFACE-700 MB THETA-E
DEFICITS IN PLACE.
ANY LINGERING CONVECTION WILL DIMINISH THIS EVENING, WITH THE
COLD FRONT PRESSING THROUGH THE REST OF THE CWA. SURFACE HIGH
PRESSURE WILL DRIFT ACROSS THE REGION ON SATURDAY, WHICH WILL
RESULT IN A BRIEF REPRIEVE FROM THE MID/UPPER 70S DEWPOINTS.
WEAK GRADIENT FLOW WILL ALLOW A LAKE BREEZE TO PUSH INLAND
THROUGH THE LATE MORNING AND AFTERNOON, HOLDING TEMPERATURES
ACROSS IMMEDIATE LAKESIDE LOCALES IN THE MID 70S.
CARLAW
SATURDAY NIGHT THROUGH THURSDAY:
HIGH PRESSURE WILL SCOOT EAST SATURDAY NIGHT, WITH SOUTHERLY
RETURN FLOW GRADUALLY RE-ESTABLISHING ACROSS THE REGION. THE
EASTERN TERMINUS OF A ROBUST ELEVATED MIXED LAYER IS FORECAST TO
BUILD ACROSS WESTERN IOWA AND NORTHERN WISCONSIN, WITH ROBUST
CONVECTIVE DEVELOPMENT POSSIBLE IN THE VICINITY OF A WARM FRONT
SATURDAY AFTERNOON/EVENING ACROSS CENTRAL MINNESOTA. EXTENDED
HIGH-RES GUIDANCE INDICATES A PROPENSITY FOR CONVECTION TO GROW
UPSCALE INTO AN MCS INTO SATURDAY NIGHT. CONVECTIVE INHIBITION
WILL LIKELY BE QUITE HIGH LOCALLY SATURDAY NIGHT, WITH A
SIGNIFICANT MUCAPE GRADIENT FORECAST OFF TO OUR NORTH AND WEST.
AS A RESULT, ANY MCS SHOULD WEAKEN NOTABLY WITH TIME THROUGH THE
NIGHT. HOWEVER, WITH 850-300 MB THICKNESSES AND FORWARD-
PROPAGATING CORFIDI VECTORS ORIENTED SOUTH TO SOUTHEAST, IF A
WELL DEVELOPED, SEVERE MCS MANAGES TO MATERIALIZE UPSTREAM, IT
WOULDN'T BE TOTALLY OUT OF THE QUESTION FOR AN OUTFLOW AND
WEAKENING SHOWERS/STORMS TO MAKE A RUN INTO THE NORTHERN HALF OF
THE CWA INTO EARLY SUNDAY MORNING GIVEN THE SOMEWHAT CLOSE
PROXIMITY OF INITIAL MCS DEVELOPMENT. THIS REMAINS A LOWER
LIKELIHOOD OUTCOME AT THIS POINT, HOWEVER.
HEAT/HUMIDITY LOOKS TO INCREASE ON SUNDAY AS SOUTHWESTERLY
BREEZES KICK IN WITH HIGHS PUSHING BACK INTO THE LOW TO PERHAPS
MID 90S. DEWPOINT TRENDS DURING THE AFTERNOON ARE A BIT
UNCERTAIN, AS FORECAST SOUNDINGS DEPICT SIGNIFICANT DRYING IN
THE 850-700 MB LAYER WHICH COULD FACILITATE DOWNWARD MIXING IN
THE AFTERNOON, PARTICULARLY NORTH OF I-80. ADDITIONALLY, THERE
IS A POTENTIAL FOR SOUTHEASTERLY WINDS TO DEVELOP NEAR THE LAKE
IN THE AFTERNOON WHICH COULD OFFER ADDITIONAL COOLING TO
IMMEDIATE LAKESHORE LOCALES, PARTICULARLY INTO LAKE COUNTY,
IL. CURRENT FORECAST SHOWS PEAK HEAT INDICES NEAR AND LOCALLY
ABOVE 100 DEGREES, BUT THE ABOVE-MENTIONED ITEMS RESULT IN SOME
UNCERTAINTY. ISOLATED TO WIDELY SCATTERED THUNDERSTORMS ARE
POSSIBLE ON SUNDAY AFTERNOON WITH THE STRONGEST STORMS ONCE
AGAIN POSING A DOWNBURST WIND THREAT.
A NOTABLE TROUGH WILL SEND ANOTHER COLD FRONT SLICING THROUGH
THE REGION ON MONDAY WITH ADDITIONAL SHOWER AND THUNDERSTORM
CHANCES. THE FRONT LOOKS TO SCOUR THE WORST OF THE HEAT AND
HUMIDITY OUT FOR A BIT, WITH MORE SEASONABLE TEMPERATURES
TUESDAY AND WEDNESDAY ALONG WITH LOWER HUMIDITY. SOUTHWEST
RETURN FLOW WILL BEING TO PUMP HIGHER DEWPOINT AIR BACK INTO THE
REGION TOWARDS THE END OF NEXT WEEK.
CARLAW
AVIATION /18Z TAFS THROUGH 00Z SUNDAY/
ISSUED AT 1221 PM CDT FRI JUN 27 2025
PERIOD OF SOME MVFR CIGS EXPECTED DURING THE EARLY-MID
AFTERNOON BEFORE CIGS LIKELY SCATTER OUT AND LIFT LATER THIS
AFTERNOON. OTHERWISE, WITH SHOWERS AND THUNDERSTORMS LIKELY TO
REMAIN WELL SOUTH AND EAST OF THE TERMINALS, LOOK FOR VFR
CONDITIONS THROUGH THE REMAINDER OF THE TAF CYCLE.
GUSTY WESTERLY WINDS TODAY WILL DIMINISH THIS EVENING AND BECOME
LIGHT AND VARIABLE TONIGHT INTO SATURDAY MORNING. WINDS WILL
BECOME LIGHT EASTERLY SATURDAY MORNING WITH A LAKE BREEZE LIKELY
TO RESULT IN A MODEST BUMP UP IN THE WINDS TO AROUND 10KT AT ORD
AND MDW SATURDAY AFTERNOON
- IZZI
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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