844
FXUS63 KLOT 220820
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
320 AM CDT TUE APR 22 2025
KEY MESSAGES
- PERIODIC BOUTS OF SCATTERED SHOWERS/STORMS EXPECTED THROUGH
THURSDAY WITH MANY DRY HOURS AND SOME AREAS MISSING OUT ON
RAIN ALTOGETHER.
- WELL ABOVE NORMAL TEMPERATURES EXPECTED INLAND THROUGH WEEK'S
END, THEN TURNING MORE SEASONABLE FOR THE WEEKEND.
- THE STORMY AND WARMER PATTERN WILL RESUME EARLY NEXT WEEK.
DISCUSSION
ISSUED AT 320 AM CDT TUE APR 22 2025
THROUGH WEDNESDAY:
WATER VAPOR IMAGERY EARLY THIS MORNING SHOWS A VIGOROUS
SHORTWAVE TROUGH MOVING EAST FROM THE NORTHERN HIGH PLAINS
TOWARD LAKE SUPERIOR. SCATTERED SHOWERS AND STORMS ACROSS
SOUTHERN MINNESOTA INTO IOWA ARE ASSOCIATED WITH THE SOUTHERN
EXTENT OF THIS TROUGH. AIR MASS OVER OUR CWA AND DOWNSTREAM OF
THIS CONVECTION IS DRIER AND MORE STABLE, SO ANTICIPATE A
WEAKENING TREND AS THESE SHOWERS/STORMS MOVE EAST INTO NORTHERN
ILLINOIS. HOW FAST THIS ACTIVITY WEAKENS AND DISSIPATES ISN'T
CLEAR, SO CARRY SLIGHT CHANCE POPS INTO OUR EASTERN CWA, BUT
HIGHER CHANCES FOR RAIN SHOULD REMAIN FARTHER WEST CLOSER TO
THE MISSISSIPPI RIVER.
THIS AFTERNOON THROUGH WEDNESDAY AFTERNOON, FORECAST CONFIDENCE
WITH RESPECT TO RAIN CHANCES IS ON THE LOWER END OF THE
SPECTRUM. OUR CWA LOOKS TO REMAIN ON THE SOUTHERN EDGE OF A BELT
OF BRISK, ZONAL WESTERLY MID-UPPER LEVEL FLOW. THIS WESTERLY
FLOW WILL ADVECT STEEP MID LEVEL LAPSE RATES ASSOCIATED WITH AN
EML EAST INTO THE AREA, AIDING IN DESTABILIZATION NEEDED FOR
CONVECTION. AT THE SFC, AN EAST-WEST BOUNDARY IS EXPECTED TO BE
IN THE AREA, THE EXACT POSITION POTENTIALLY AUGMENTED BY
CONVECTION. ALOFT, THERE'S PRETTY GOOD AGREEMENT IN THE GUIDANCE
THAT LOW AMPLITUDE, SUBTLE WAVES WILL TRAVERSE THE ZONAL FLOW
ACROSS THE REGION, LIKELY LEADING TO OCCASIONAL BOUTS OF
INCREASED COVERAGE OF SCATTERED SHOWERS AND T-STORMS ANYTIME
FROM THIS AFTERNOON THROUGH WEDNESDAY AFTERNOON.
UNFORTUNATELY, THE SUBTLE NATURE OF THESE WAVES, LEADS TO A
GREAT DEAL OF UNCERTAINTY WITH REGARDS TO TIMING AND THEIR
ABILITY TO KICK OFF CONVECTION GIVEN ONLY MODEST FRONTAL
CONVERGENCE. THERE'S A PRETTY SOLID SIGNAL IN CAMS THAT
CONVECTION WILL DEVELOP IN THE AREA THIS AFTERNOON, THOUGH IT IS
POSSIBLE THAT THE BOUNDARY LAYER COULD END UP DRIER THAN PROGGED
AND LEAD TO SOME CAPPING ISSUES THAT PREVENT CONVECTION FROM
DEVELOPING OR LIMITS COVERAGE. TONIGHT, THERE'S ANOTHER PRETTY
NOTEWORTHY QPF SIGNAL IN GUIDANCE OVER NORTHERN IL. NO
APPRECIABLE LOW LEVEL JET TO DRIVE STORMS TONIGHT, SO AGAIN,
UNCERTAINTY IS A BIT HIGHER THAN NORMAL, SO KEPT POPS IN CHECK
TONIGHT TOO.
DEEP LAYER SHEAR WOULD LIKELY SUPPORT STORM SCALE UPDRAFT
SEPARATION AND POTENTIAL FOR SOME STRONG TO SEVERE STORMS GIVEN
SUFFICIENT INSTABILITY. GIVEN ALL OF THE UNCERTAINTIES
(SHORTWAVE TIMING, BOUNDARY LAYER MOISTURE AND SUBSEQUENT
DESTABILIZATION, POSSIBLE CAPPING, ETC) THE LEVEL 1 OF 5 SEVERE
WEATHER RISK FROM SPC IS QUITE REASONABLE.
SYNOPTICALLY, GUIDANCE SUGGESTS THERE COULD BE ENOUGH OF A
SOUTHWESTERLY GRADIENT TO KEEP LAKE BREEZE AT BAY OVER ALL BUT
PERHAPS THE IL NORTH SHORE. ASSUMING THE UPSTREAM CONVECTION
OVER IA DISSIPATES AS EXPECTED AND DOESN'T ALTER SFC PRESSURE
PATTERN SIGNIFICANTLY REMNANT COLD POOL/MESO HIGH, THEN HIGHS
TODAY SHOULD BE ABLE TO CLIMB UPPER 60S TO MID 70S, THOUGH
COOLER NORTH SHORE. IF IA CONVECTION PERSISTS LONGER THAN
EXPECTED, IT RAISES THE POSSIBILITY OF A MORE PROMINENT LAKE
BREEZE THAN IS CURRENTLY FORECAST. WEDNESDAY SHOULD BE WARMER
WITH HIGHS IN THE 70S ACROSS MOST OF THE CWA, EXCEPT NEAR LAKE
MICHIGAN WHERE LAKE BREEZE IS EXPECTED TO KEEP TEMPS NOTICEABLY
COOLER.
- IZZI
WEDNESDAY NIGHT THROUGH MONDAY:
THE FRONTAL BOUNDARY THAT WILL SERVE AS THE FOCUS FOR SHOWERS
AND THUNDERSTORMS IN THE NEAR TERM IS EXPECTED TO BE SHIFTING
NORTHWARD OUT OF NORTHERN IL WEDNESDAY NIGHT. HOWEVER, SOME
LINGERING SHOWERS AND PERHAPS EVEN AN ISOLATED STORM OR TWO WILL
LIKELY BE ONGOING AS THE BOUNDARY EXITS. THAT SAID, THURSDAY IS
LOOKING TO BE A MOSTLY DRY DAY AS PLUME OF MID-LEVEL DRY AIR
SHOULD PIVOT OVERHEAD AND KEEP PRECIPITATION TO OUR NORTH IN WI.
CONTINUED WARM ADVECTION ACROSS THE AREA WILL ALLOW TEMPERATURES
TO WARM WELL INTO THE 70S WITH LOCATIONS SOUTH OF I-80 LIKELY
TO SEE READINGS NEAR 80 DEGREES THURSDAY AFTERNOON. THE EXCEPTION,
HOWEVER, WILL BE THOSE ALONG THE LAKESHORE WHERE TEMPERATURES
ARE FORECAST TO BE IN THE MID TO UPPER 50S DUE TO A LAKE BREEZE.
WHILE WE ENJOY A REPRIEVE FROM THE ACTIVE WEATHER, OUR NEXT
SYSTEM WILL BE GETTING ORGANIZED IN THE SOUTHERN PLAINS. THE
SYSTEM WILL BE DRIVEN BY A SHORTWAVE TROUGH THAT WILL BE
EJECTING INTO THE SOUTH CENTRAL PLAINS ON THURSDAY BEFORE
LIFTING INTO THE MISSISSIPPI AND OHIO RIVER VALLEYS ON FRIDAY.
AS THIS OCCURS, A BROAD AREA OF SHOWERS AND THUNDERSTORMS IS
EXPECTED TO DEVELOP IN THE HUMID AIRMASS BENEATH THE WAVE AND
GRADUALLY WORK ITS WAY NORTHEAST INTO MO THURSDAY NIGHT AND THEN
ACROSS OUR AREA ON FRIDAY. GUIDANCE HAS GENERALLY REMAINED IN
GOOD AGREEMENT WITH THIS EVOLUTION OVER THE PAST COUPLE DAYS,
BUT THERE REMAINS SOME UNCERTAINTY AS TO WHETHER OR NOT A WEAK
SURFACE LOW WILL DEVELOP ALONG THE AFOREMENTIONED FRONTAL
BOUNDARY THAT IS FORECAST TO STILL BE STRETCHING FROM SOUTHERN
WI TO EASTERN NE. IF THIS LOW DOES DEVELOP AS THE ECMWF AND
CANADIAN GUIDANCE SUGGEST, THEN THE SHOWERS AND STORMS IN OUR
AREA ON FRIDAY WOULD BE MORE WIDESPREAD AS OPPOSED TO THE MORE
SCATTERED COVERAGE NOTED IN THE GFS SOLUTION. IN THE GRAND
SCHEME OF THINGS THE FORECAST IS MORE OR LESS THE SAME FOR A
50-80% CHANCE OF RAIN, BUT WHETHER OR NOT FRIDAY IS A WASHOUT OR
THERE ARE SOME DRY HOURS STILL NEEDS TO BE IRONED OUT.
REGARDLESS OF WHICH SOLUTION COMES TO FRUITION FOR FRIDAY, THE
SHORTWAVE AND ASSOCIATED PRECIPITATION WILL GRADUALLY MOVE EAST
FRIDAY NIGHT AS THE FRONT FINALLY GETS FORCED THROUGH THE AREA
BY A NORTHERN STREAM SHORTWAVE PIVOTING OVER THE NORTHERN GREAT
LAKES. THEREFORE, DRY CONDITIONS ARE EXPECTED BEHIND THE SYSTEM
FOR SATURDAY AND SUNDAY. HOWEVER, MODEST COLD ADVECTION WILL
KEEP TEMPERATURES IN LINE WITH MORE TYPICAL LATE APRIL VALUES
WITH HIGHS IN THE 60S TO AROUND 70 (INLAND OF THE LAKE) AND LOWS
IN THE 40S TO AROUND 50.
HEADING INTO NEXT WEEK, THE UPPER PATTERN IS FORECAST TO BECOME
MORE AMPLIFIED ONCE AGAIN WHICH WILL RETURN THE CHANCES FOR
SHOWERS AND THUNDERSTORMS THROUGH AT LEAST THE MIDDLE OF NEXT
WEEK. ON THE BRIGHT SIDE, TEMPERATURES DURING THIS TIME ARE
FORECAST TO RETURN TO THEIR ABOVE NORMAL READINGS WITH HIGHS
BACK NEAR 80 FOR MONDAY AND TUESDAY.
YACK
AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/
ISSUED AT 118 AM CDT TUE APR 22 2025
FORECAST CONCERNS FOR THE TERMINALS...
- SCATTERED SHOWERS TO MOVE ACROSS NORTHWEST IL (NEAR RFD) EARLY
TUESDAY MORNING.
- PERIODS OF SHOWERS AND THUNDERSTORMS TUESDAY AFTERNOON AND
AGAIN LATE TUESDAY NIGHT INTO WEDNESDAY MORNING.
- BREEZY SOUTHWEST WINDS TUESDAY AFTERNOON WITH GUST OF 20-25
KT.
THE AREA OF HIGH PRESSURE OVERHEAD WILL GRADUALLY MOVE EAST
OVERNIGHT, BUT STILL REMAIN IN CONTROL ENOUGH TO MAINTAIN LIGHT
AND VARIABLE WINDS AND MOSTLY CLEAR SKIES TONIGHT. THAT SAID,
THERE HAS BEEN SOME SHALLOW GROUND FOG DEVELOPING NEAR THE
KANKAKEE RIVER VALLEY THIS EVENING WHERE TEMPERATURE-DEW POINT
SPREADS ARE LESS THAN TWO DEGREES. WHILE THE DRY LOW-LEVEL
ATMOSPHERE OVERHEAD SHOULD LIMIT FOG COVERAGE, THERE IS A SMALL
CHANCE (<10%) THAT SOME SHALLOW BR COULD BE SEEN AT THE
OUTLYING TERMINALS (DPA, GYY, AND RFD) DURING THE PREDAWN HOURS
TUESDAY MORNING IF TEMPERATURES COOL ENOUGH. GIVEN THE LOWER
CONFIDENCE HAVE DECIDED TO LEAVE OUT OF THE TAFS FOR NOW, BUT
WILL MONITOR OBSERVATIONS CLOSELY.
THE MORE NOTABLE FORECAST CONCERN FOR TONIGHT WILL BE THE AREA
OF SHOWERS AND EMBEDDED THUNDERSTORMS MOVING ACROSS IA WHICH IS
FORECAST TO REACH NORTHERN IL AROUND 12Z TUESDAY MORNING. RECENT
RADAR TRENDS HAS SHOWN THE CLUSTER OF SHOWERS/STORMS TO BE
WEAKENING AND THAT TREND SHOULD CONTINUE AS THE SHOWERS INTERACT
WITH THE MORE STABLE AND DRIER ENVIRONMENT IN EASTERN IA AND
WESTERN IL. HOWEVER, IT DOES SEEM THAT JUST ENOUGH MOISTURE WILL
HANG ON TO SUPPORT AT LEAST SOME SCATTERED SHOWERS REACHING
NORTHWEST IL AND RFD AROUND DAYBREAK TUESDAY MORNING BEFORE
SHOWERS FULLY DISSIPATE PRIOR TO REACHING THE CHICAGO
TERMINALS. THEREFORE, HAVE LEFT THE SHOWER MENTION IN AT RFD FOR
THIS ALONG WITH THE PROB30 FOR AN ISOLATED RUMBLE OF THUNDER.
THOUGH, IF LIGHTNING TRENDS CONTINUE TO DIMINISH AS EXPECTED WE
SHOULD BE ABLE TO REMOVE THE PROB30 WITH THE 09Z AMENDMENT.
WHILE TUESDAY MORNING WILL BE DRY FOR MOST AREAS ASIDE FROM THE
AFOREMENTIONED SHOWERS, WINDS WILL BECOME SOUTHWESTERLY AND
INCREASE IN SPEED WHICH SHOULD REPLENISH THE CURRENTLY LACKING
MOISTURE. COUPLE THIS WITH THE PASSING OF A WEAK DISTURBANCE AND
APPROACHING FRONT, CONDITIONS SHOULD BE IN PLACE FOR SCATTERED
SHOWERS AND THUNDERSTORMS TO REDEVELOP OVERHEAD TUESDAY
AFTERNOON AND PERSIST THROUGH THE EARLY EVENING HOURS.
CONFIDENCE ON THESE SHOWERS AND STORMS DEVELOPING IS MODERATELY
HIGH BUT THE SCATTERED COVERAGE MAKES IMPACTS AT THE TERMINALS
LESS CERTAIN AND THUS THE REASON FOR MAINTAINING THE PROB30S IN
THE TAFS AT THIS TIME.
AS THE DISTURBANCE EXITS TUESDAY EVENING SHOWERS AND STORMS ARE
EXPECTED TO DISSIPATE. HOWEVER, THE FRONTAL BOUNDARY IS EXPECTED
TO STALL NEAR THE I-80 CORRIDOR AND SERVE AS THE BREEDING GROUND
FOR YET ANOTHER ROUND OF SHOWERS AND EMBEDDED THUNDERSTORMS LATE
TUESDAY NIGHT INTO WEDNESDAY MORNING. CONFIDENCE IS YET AGAIN
HIGH THAT SHOWERS WILL DEVELOP ALONG THE BOUNDARY AND IMPACT THE
TERMINALS TUESDAY NIGHT, BUT SINCE THESE SHOWERS ARE NOT
EXPECTED UNTIL AFTER 06Z IT WAS ONLY INCLUDED IN THE 30-HOUR TAF
SITES FOR NOW. FURTHERMORE, THE LESS FAVORABLE DIURNAL TIME DOES
MAKE THE CONFIDENCE IN THUNDER COVERAGE LOWER AND HENCE THE
REASON FOR HANDLING WITH ANOTHER PROB30.
FINALLY, OUTSIDE OF THE PERIODS OF SHOWERS AND STORMS VFR
CONDITIONS ARE EXPECTED THROUGH THE FORECAST PERIOD. THOUGH, A
BRIEF PERIOD OF MVFR CEILINGS MAY BE SEEN WITH THE SHOWERS
TUESDAY NIGHT. OTHERWISE, BREEZY WINDS GUSTING IN THE 20-25 KT
RANGE CAN BE EXPECTED TUESDAY AFTERNOON BEFORE WINDS SUBSIDE
AGAIN TUESDAY EVENING WITH DIRECTIONS REMAINING OUT OF THE
SOUTHWEST.
YACK
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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