306
FXUS63 KLOT 170914
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
414 AM CDT THU APR 17 2025
KEY MESSAGES
- THERE IS LOWER THAN AVERAGE CONFIDENCE IN THE FORECAST FOR THE
DAYLIGHT HOURS TODAY OWING TO UNCERTAINTY IN THE COVERAGE (IF
ANY) OF SHOWERS AND STORMS.
- ADDITIONAL SHOWERS AND STORMS MAY TRACK NEAR AND NORTH OF
I-88 TONIGHT WITH A THREAT FOR HAIL AND GUSTY WINDS (20 TO 40%
CHANCE).
- FRIDAY WILL OFFER AN EARLY TASTE OF SUMMER-LIKE WARMTH WITH
HIGHS NEAR 80F.
- SHOWERS AND STORMS MAY DEVELOP FRIDAY EVENING, ESPECIALLY
ALONG AND SOUTH OF I-55. A FEW STORMS MAY BE SEVERE WITH
DAMAGING WINDS AND HAIL.
- PERIODS OF SHOWERS AND PERHAPS SOME THUNDERSTORMS ARE FORECAST
ON SUNDAY WITH WIDESPREAD RAIN AND SOME STORMS SUNDAY NIGHT. A
HIGHLY CONDITIONAL SEVERE THUNDERSTORM THREAT EXISTS FOR
MAINLY FAR SOUTHERN PORTIONS OF THE FORECAST LATE SUNDAY
AFTERNOON AND EVENING.
DISCUSSION
ISSUED AT 414 AM CDT THU APR 17 2025
THROUGH FRIDAY NIGHT:
EARLY MORNING GOES-19 WATER VAPOR IMAGERY DEPICTS A DEEPENING
UPPER-LEVEL LONGWAVE TROUGH OVER THE WESTERN CONUS WHILE A LOW-
AMPLITUDE UPPER-LEVEL RIDGE SITS OVER THE SOUTHEASTERN QUADRANT
OF THE CONUS. IN BETWEEN THESE FEATURES RESIDES A SHARPENING
BAROCLINIC ZONE CO-LOCATED WITH AN ENERGETIC SOUTHWESTERLY
MID/UPPER-LEVEL JET. LOWER IN THE ATMOSPHERE, A STRONG 50+ KT
SOUTHWESTERLY LOW-LEVEL JET REMAINS CENTERED OVER CENTRAL KANSAS
AND OKLAHOMA AND IS FUNNELING A FEED OF RICH THETA-E TOWARDS
THE MID-MISSISSIPPI RIVER VALLEY. AS THE NOSE OF THE LOW-LEVEL
JET AND THE ASSOCIATED ZONE OF FOCUSED WARM AIR-ADVECTION AND
ISENTROPIC ASCENT PROGRESS NORTHEASTWARD, CONVECTION WILL
CONTINUE TO BLOSSOM NEAR THE MISSISSIPPI RIVER AS DAYBREAK
APPROACHES AND WILL THEN GRADUALLY TRICKLE EASTWARD TOWARDS OUR
FORECAST AREA.
THE INITIAL SPITS OF PRECIPITATION MAY BEGIN TO MAKE IT INTO
OUR SOUTHWESTERN CWA AROUND SUNRISE, THOUGH THE MAIN AXIS OF
CONVECTION DOESN'T LOOK TO ARRIVE UNTIL THE LATE MORNING OR
EARLY AFTERNOON. SOME UNCERTAINTY REMAINS REGARDING JUST HOW
WIDESPREAD PRECIPITATION COVERAGE WILL BE HERE LOCALLY, THOUGH,
AS THE FORCING MECHANISMS DRIVING IT WILL WEAKEN WITH TIME, AND
IT APPEARS THAT THIS ACTIVITY WILL ALSO OUTPACE THE BETTER
MOISTURE AND INSTABILITY TO OUR WEST/SOUTHWEST. IN SPITE OF
THIS, MOST HI-RES MODEL GUIDANCE REMAINS QUITE BULLISH ON
SHOWERS PERSISTING IN SOME CAPACITY ACROSS OUR FORECAST AREA
DURING THE DAYTIME TODAY, SO HAVE POPS PEAKING IN THE 50-60%
RANGE AT MOST LOCATIONS. A FEW EMBEDDED THUNDERSTORMS MAY ALSO
OCCUR LATE THIS MORNING/EARLY THIS AFTERNOON BEFORE THIS SHOWER
ACTIVITY DECAYS. THE CHANCES FOR LIGHTNING OCCURRING NEAR ANY
PARTICULAR LOCATION APPEAR TO BE GREATEST ACROSS OUR WESTERN
COUNTIES, THOUGH WITH THE MEAGER DEGREE OF INSTABILITY THAT
CONVECTION WILL HAVE TO WORK WITH, OPTED TO CAP THUNDER
PROBABILITIES IN THE SLIGHT CHANCE CATEGORY.
DUE TO THE INCREASED LIKELIHOOD OF RAIN OCCURRING AND THE
ASSOCIATED CLOUD COVER BEING MORE EXPANSIVE AND PERSISTING
LONGER, THERE IS NOW AN INCREASED LIKELIHOOD OF TEMPERATURES
REMAINING IN THE 50S THROUGH A GOOD CHUNK OF THE DAY. HOWEVER,
THERE SHOULD STILL BE ENOUGH DRY TIME FOR HIGH TEMPERATURES TO
AT LEAST REACH THE LOW-MID 60S TODAY, ESPECIALLY WITH THE
BREEZY SOUTHERLY WINDS THAT WILL BE IN PLACE TODAY. IF RAIN
COVERAGE ENDS UP BEING LESS WIDESPREAD THAT EXPECTED, THEN
WOULDN'T BE SURPRISED IF SOME LOCATIONS MADE A RUN FOR 70
DEGREES THIS AFTERNOON, BUT THIS SCENARIO DOES NOT APPEAR
PARTICULARLY LIKELY AT THIS TIME.
GUSTS IN EXCESS OF 30 MPH ARE EXPECTED TO OCCUR DURING THE
DAYTIME TODAY DURING ANY TIME PERIODS WHEN STEADY RAIN ISN'T
SUPPRESSING MIXING HEIGHTS. AS THE LOW-LEVEL JET RESTRENGTHENS
GOING INTO THIS EVENING, THERE MAY BE A BRIEF PERIOD OF TIME
WHEN GUSTS CLOSER TO 40 MPH MAY BE OBSERVED, BUT AGAIN, WHETHER
THIS ENDS UP MATERIALIZING WILL BE INFLUENCED BY THE STABILIZING
EFFECTS OF THE RAIN. THE REINVIGORATING LOW-LEVEL JET COULD
ALSO CAUSE AN UPTICK IN SHOWER COVERAGE ACROSS NORTHERN PORTIONS
OF OUR FORECAST AREA LATE THIS AFTERNOON/EARLY THIS EVENING
BEFORE INCREASING CONVECTIVE INHIBITION CAUSES ALL SHOWER
ACTIVITY TO CEASE BY LATE EVENING. IT'S POSSIBLE THAT AN
ISOLATED STORM OR TWO COULD DEVELOP DURING THIS CONVECTIVE
UPTICK, SO HAVE SLIGHT CHANCE THUNDER PROBABILITIES CONTINUING
ACROSS OUR NORTHERN COUNTIES THROUGH MID-EVENING.
THURSDAY NIGHT SHOULD BE MILD AND BREEZY AS A WARM FRONT TRACKS
NORTHWARD ACROSS THE REGION. WE'LL NEED TO KEEP AN EYE ON HOW
CONVECTION ACROSS IOWA AND SOUTHERN MINNESOTA EVOLVES OVER THE
COURSE OF THE EVENING AS THE STRONG KINEMATIC FIELDS AND
INCREASING DEGREE OF ELEVATED INSTABILITY COULD SUPPORT THESE
STORMS MAINTAINING STRONG TO SEVERE INTENSITY WITH A HAIL AND/OR
WIND THREAT AS THEY TRACK TOWARDS OUR LONGITUDE, PARTICULARLY
IF THEY END UP ORGANIZING INTO A COMPACT FORWARD-PROPAGATING
MCS LIKE THE HRRR HAS SHOWN IN ITS PAST COUPLE OF EXTENDED
RUNS. WHILE IT APPEARS THAT MOST OF THIS OVERNIGHT CONVECTION
WILL EITHER DECAY OR REMAIN TO OUR NORTH, THERE REMAINS ENOUGH
OF A CHANCE FOR STORMS TO AFFECT LOCATIONS SOUTH OF THE
ILLINOIS-WISCONSIN STATE LINE TO WARRANT MAINTAINING SLIGHT
CHANCE AND CHANCE POPS FOR LOCATIONS ROUGHLY NEAR AND NORTH OF
I-88 THROUGH EARLY FRIDAY MORNING.
ON FRIDAY, THE SPINE OF AN ELONGATED EML PLUME WILL POSITION
ITSELF SQUARELY OVER OUR FORECAST AREA. IN THE ABSENCE OF ANY
NOTABLE LARGE-SCALE ASCENT, VERY STRONG CAPPING AT THE BASE OF
THIS EML WILL PREVENT ANY CONVECTION FROM DEVELOPING IN THE AREA
DURING THE DAYTIME HOURS. BREEZY SOUTHWESTERLY WINDS, FILTERED
SUNSHINE THROUGH AN EXPANSIVE CIRRUS CANOPY, AND DEEP BOUNDARY
LAYER MIXING WILL ALL CONTRIBUTE TOWARD PROPELLING TEMPERATURES
INTO THE UPPER 70S TO LOW-MID 80S AREA-WIDE FRIDAY AFTERNOON
PRIOR TO THE ARRIVAL OF A COLD FRONT FROM THE WEST.
GRADUALLY INCREASING LARGE-SCALE ASCENT OVER THE COURSE OF THE
AFTERNOON WILL START TO CHEW AWAY AT THE AFOREMENTIONED CAP, AND
BY MID-EVENING, IT APPEARS ENOUGH LOW-LEVEL MOISTENING/WEAKENING
OF THE CAP WILL HAVE OCCURRED FOR CONVECTION TO START BUBBLING
ALONG AND JUST BEHIND THE COLD FRONT. BY THIS TIME, THE FRONT
WILL LIKELY HAVE TRACKED INTO THE SOUTHEASTERN HALF OF OUR
FORECAST AREA, AND FOR THIS REASON, STILL THINK THAT THE HIGHEST
CONVECTIVE COVERAGE FRIDAY NIGHT SHOULD BE NEAR AND EAST OF
I-55, WHERE OUR FORECAST POPS ARE IN THE CATEGORICAL RANGE.
THERMODYNAMIC AND KINEMATIC PROFILES WILL BE SUPPORTIVE OF
STRONG TO SEVERE THUNDERSTORMS DEVELOPING ACROSS THE FRONTAL
ZONE, THOUGH IT APPEARS THAT MOST CONVECTION THAT DEVELOPS WILL
EITHER FORM ATOP THE EML'S BASE OR QUICKLY BECOME UNDERCUT BY
THE COLD FRONT. THE ELEVATED NATURE OF THE CONVECTION AND
PROGGED FRONT-PARALLEL STORM MOTIONS, PLUS UNCERTAINTIES
REGARDING LINGERING INHIBITION AND HOW QUICKLY STORMS WILL BE
ABLE TO INTENSIFY DO RAISE QUESTIONS ABOUT THE EXTENT TO WHICH
STORMS WILL BE ABLE TO FULLY HARNESS THE PARAMETER SPACE THAT
WILL BE IN PLACE. THAT SAID, ANY ROBUST CONVECTION THAT MANAGES
TO DEVELOP SHOULD POSSESS A THREAT FOR LARGE HAIL, WHILE ANY
CONVECTION THAT MANAGES TO STAY ALONG OR AHEAD OF THE COLD FRONT
WILL ALSO FEATURE A THREAT FOR DAMAGING WINDS. SOME POTENTIAL
FOR FLASH FLOODING ALSO APPEARS EVIDENT IN OUR SOUTHEASTERN CWA
GIVEN THE AFOREMENTIONED STORM MOTIONS AND POTENTIAL FOR
TRAINING CONVECTION.
OGOREK
SATURDAY THROUGH WEDNESDAY:
THE COLD FRONT WILL STALL ACROSS SOUTHERN IL/IN SATURDAY AND
SATURDAY NIGHT. A CONTINUOUS SOUTHERLY FEED OF LOW-LEVEL
MOISTURE UNDER A SERIES OF WEAK MID-LEVEL DISTURBANCES WITHIN
BROADER ENE FLOW ALOFT WILL RESULT IN AN EXTENDED PERIOD OF RAIN
WITH SOME EMBEDDED STORMS AROUND AND NORTH OF THE STALLED
FRONT. GUIDANCE CONTINUES TO DRIFT NORTHWARD WITH THE PLACEMENT
OF THE FRONT WITH SUCCESSIVE MODEL CYCLES, WHICH SUPPORTS A
CORRESPONDING INCREASE IN POPS SOUTH OF I-80 AND ESPECIALLY IN
THE SOUTHERN PORTIONS OF THE FORECAST AREA.
THE MAIN TROUGH RESPONSIBLE FOR THE APPROACHING SURFACE LOW ON
FRIDAY WILL FINALLY EJECT NORTHEASTWARD WHILE BECOMING
NEGATIVELY TILTED OVER THE UPPER MISSISSIPPI RIVER VALLEY LATE
SUNDAY. THE VARIOUS ENSEMBLE MODEL SUITES HAVE COME INTO MUCH
BETTER AGREEMENT WITH THE EVOLUTION OF THE SURFACE LOW, WITH THE
FAVORED MEAN TRACK ACROSS EASTERN IOWA OR FAR NORTHWEST
ILLINOIS SUNDAY NIGHT. MASS RESPONSE AHEAD OF THIS TROUGH/LOW
WILL QUICKLY ADVECT THE MOISTURE-RICH AIRMASS SOUTH OF THE
FRONT NORTHWARD ACROSS THE AREA ON SUNDAY, RESULTING IN AN AXIS
OF RAIN WITH EMBEDDED THUNDERSTORMS LIFTING OVER THE CWA THROUGH
THE DAY. AN EFFECTIVE WARM IS PROGGED TO APPROACH THE SOUTHERN
CWA LATE IN THE DAY AS IMPRESSIVE DEEP LAYER FORCING NEARS FROM
THE SOUTHWEST. WILL NEED TO KEEP A CLOSE EYE ON TRENDS IN
GUIDANCE AS THE LATEST FAVORED SCENARIO IS FOR A CONDITIONAL
SEVERE STORM THREAT WITHIN A HIGHLY SHEARED ENVIRONMENT IN THE
VICINITY OF THE FRONT OVER AT LEAST THE FAR SOUTHERN CWA LATE
SUNDAY AFTERNOON AND EVENING. EVEN IF A SEVERE STORM RISK DOES
NOT MATERIALIZE, THE DYNAMIC SYSTEM WILL STILL BRING WIDESPREAD
RAIN AND SOME STORMS OVER THE AREA SUNDAY NIGHT INTO EARLY
MONDAY MORNING.
AFTER SUNDAY'S SYSTEM DEPARTS ACROSS THE GREAT LAKES REGION
EARLY MONDAY, A MOSTLY ZONAL REGIME WILL PREVAIL ACROSS MUCH OF
NORTH AMERICA FOR SEVERAL DAYS. THIS WILL BRING A PERIOD OF
SEASONABLE TO SEASONABLY WARM WEATHER TO THE REGION, WITH
LOCALLY COOLER CONDITIONS FROM DAILY LAKE BREEZES AROUND THE
LAKE MICHIGAN SHORE. THE ONE NOTABLE PERTURBATION IN THE ZONAL
PATTERN WILL BE A LOW-AMPLITUDE WAVE TRACKING ALONG THE
U.S./CANADIAN BORDER TUESDAY INTO WEDNESDAY. AN ASSOCIATED WEAK
COLD FRONT MAY SLOW OR STALL ACROSS THE AREA TUESDAY NIGHT INTO
WEDNESDAY, WITH MARGINAL MOISTURE PROFILES RESULTING IN PERHAPS
ISOLATED TO SCATTERED SHOWERS NEAR THE FRONT.
KLUBER
AVIATION /06Z TAFS THROUGH 12Z FRIDAY/
ISSUED AT 1245 AM CDT THU APR 17 2025
EXPECT VFR CONDITIONS THROUGH THE MORNING. E WINDS AROUND 10
KNOTS AT TAF ISSUANCE WILL GRADUALLY VEER SE THROUGH DAYBREAK,
THEN CONTINUE TO VEER SSE/S WHILE GUSTING UP TO AROUND 25 KNOTS
THROUGH LATE MORNING.
A MID-LEVEL WAVE OVER KANSAS WILL SHIFT ENE OVER ILLINOIS THIS
AFTERNOON AND POSSIBLY BRING AN AXIS OF HIGH-BASED -SHRA OVER
THE TERMINALS. MAINTAINED A PROB30 MENTION FOR NOW AS OVERALL
MID-LEVEL SATURATION LOOKS TO BE QUITE MARGINAL. OTHERWISE,
S/SSE (160-180 DEGREES) WINDS WILL CONTINUE TO INCREASE THIS
AFTERNOON WITH GUSTS OVER 30 KNOTS.
ONGOING CONVECTION OVER SOUTH-CENTRAL KANSAS MAY RESULT IN A
CONVECTIVELY-INDUCED WAVE THAT TRACKS NE OVER THE TERMINALS VERY
LATE THIS AFTERNOON OR EARLY EVENING. THIS WILL OCCUR AS MID-
LEVEL LAPSE RATES QUICKLY STEEPEN, THOUGH SUFFICIENT SATURATION
REMAINS QUESTIONABLE. WITH TS POTENTIAL REMAINING UNDER 20% AT
THIS TIME, DID NOT INCLUDE A MENTION IN THE TAF. HOWEVER, FUTURE
TAF UPDATES MAY REQUIRE THE INTRODUCTION OF PROB30 FOR ELEVATED
TS ROUGHLY 23-01Z AT THE CHICAGO TERMINALS.
POTENTIAL CONVECTION OVER THE MISSOURI RIVER BASIN EARLY THIS
EVENING MAY GROW UPSCALE AND PERSIST ACROSS SOUTHERN WISCONSIN
LATE TONIGHT INTO EARLY FRIDAY MORNING. TSRA SHOULD REMAIN NORTH
OF THE TERMINALS, THOUGH OUTFLOW WINDS COULD PUSH INTO NORTHERN
ILLINOIS LATE TONIGHT. MEANWHILE, SSE WINDS WILL CONTINUE TO
GUST UP TO 30 KNOTS THIS EVENING AS A 60-70 KNOT LLJ PASSES
OVERHEAD. OPTED TO INCLUDE LLWS DURING THIS TIME AS INCREASING
LOW-LEVEL STABILITY MAY RESULT IN LOWER GUSTS THAN CURRENTLY
FORECAST.
KLUBER
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY FROM 7 AM THIS MORNING TO 10 PM CDT
FRIDAY FOR THE IL AND IN NEARSHORE WATERS.
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