344
FXUS63 KLOT 300858
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
358 AM CDT WED JUL 30 2025
KEY MESSAGES
- FLOOD WATCH IN EFFECT FROM 1 PM CDT TODAY THROUGH 1 PM CDT
THURSDAY.
- PERIODS OF THUNDERSTORMS TODAY THROUGH THURSDAY MORNING, SOME
POSSIBLY STRONG TO SEVERE WITH TORRENTIAL RAIN WHICH COULD
LEAD TO LOCALIZED FLASH FLOODING.
- POSSIBLE PERIOD OF PROLONGED HEAVY RAIN TONIGHT INTO EARLY
THURSDAY MORNING.
- DANGEROUS SWIMMING CONDITIONS AT LAKE MICHIGAN BEACHES THIS
AFTERNOON THROUGH FRIDAY.
DISCUSSION
ISSUED AT 358 AM CDT WED JUL 30 2025
THROUGH THURSDAY:
MAIN FORECAST CONCERNS FOCUS ON PERIODS OF THUNDERSTORMS TODAY
THROUGH TONIGHT, SOME OF WHICH MAY PRODUCE SEVERE WEATHER AND
TORRENTIAL RAINFALL AND POTENTIAL FLOODING. INCREASING NORTHEAST
WINDS WILL ALSO PRODUCE HAZARDOUS SWIMMING CONDITIONS ON LAKE
MICHIGAN LATER TODAY INTO FRIDAY.
EARLY MORNING WATER VAPOR IMAGERY DEPICTS A CONVECTIVELY-
ENHANCED MID-LEVEL SHORT WAVE TROUGH ACROSS THE CENTRAL PLAINS.
THIS WAVE IS PROGGED TO MOVE SLOWLY EAST ACROSS THE REGION LATER
TODAY INTO THURSDAY, AND WILL AID IN PRODUCING MULTIPLE ROUNDS
OF SHOWERS AND THUNDERSTORMS AS IT TRACKS ALONG A WEST TO EAST
ORIENTED LOW-LEVEL BAROCLINIC ZONE AND INSTABILITY GRADIENT.
REGIONAL RADAR IMAGERY DEPICTS AN AREA OF THUNDERSTORM FROM
NORTHEAST KS INTO SOUTHWEST WI EARLY THIS MORNING, WITH AT LEAST
A COUPLE OF EMBEDDED MCVS WORKING THEIR WAY EAST ACROSS IA.
HIGH-RES GUIDANCE HAS BEEN SOMEWHAT POOR IN DEPICTING THE
EASTERN EXTENT AND TIMING WITH STORMS OVER EASTERN IA, THOUGH
THE GENERAL EXPECTATION IS THAT THE MCS OVER NORTHEAST IA WILL
MOVE INTO OUR NORTHWESTERN CWA AROUND SUNRISE, AND TRACK MAINLY
ALONG/NORTH OF I-88 THROUGH MID-MORNING WITH SOME WEAKENING
LIKELY GIVEN MORE STABLE LOW-LEVELS WITH EASTWARD EXTENT.
SPC/RAP MESOANALYSIS DEPICTS 30-35 KTS OF EFFECTIVE SHEAR, WHICH
ALONG WITH THE MCV MAY ALLOW FOR SOME CONTINUED ORGANIZATION
AND GUSTY SURFACE WIND THREAT.
TRAILING MCS(S) ACROSS IA/NORTHERN MO ARE THEN EXPECTED TO MOVE
INTO THE AREA LATER THIS MORNING/MIDDAY. GENERAL INCREASE IN
SYNOPTIC FORCING AHEAD OF THE APPROACHING SHORT WAVE, PRESENCE
OF UPPER LEVEL DIVERGENCE BENEATH THE RIGHT ENTRANCE TO A 100+
KT 250 MB JET STREAK ACROSS THE UPPER MIDWEST/NORTHERN LAKES AND
INCREASING DIURNAL INSTABILITY SHOULD SUPPORT ADDITIONAL
CLUSTERS OF STORMS DURING THE AFTERNOON AND INTO TONIGHT. WHILE
SOME POTENTIAL FOR DAMAGING WINDS WILL EXIST (WET
DOWNBURSTS/MICROBURSTS), THESE REPEATED ROUNDS OF STORMS IN A
VERY MOIST ENVIRONMENT RAISE THE CONCERN FOR INCREASED FLOODING
POTENTIAL. FORECAST PRECIPITABLE WATER VALUES INCREASE INTO THE
2-2.50" RANGE (ABOUT AS HIGH AS THEY GET PER SPC DVN/ILX
SOUNDING CLIMATOLOGY) INTO TONIGHT, WHICH SHOULD SUPPORT VERY
EFFICIENT RAIN PRODUCING STORMS. WHILE EXACT TRACK PLACEMENT IS
UNCERTAIN, STORM CLUSTERS MAY EASILY PRODUCE 1-2 INCHES OF RAIN,
AND THIS COULD LEAD TO PERHAPS LOCALLY 3-5 INCHES WHERE STORMS
REPEATEDLY TRACK OVER THE SAME AREA. WITH THIS IN MIND HAVE
HOISTED A FLOOD WATCH FOR THE ENTIRE FORECAST AREA FROM 18Z
TODAY THROUGH 18Z THURSDAY. SURFACE LOW PRESSURE WAVE (AND THE
SHEARING MID-LEVEL TROUGH AXIS) EVENTUALLY WORKS EAST OF THE
AREA THURSDAY AFTERNOON, ALLOWING THE TRAILING COLD FRONT TO SAG
SOUTH OF THE AREA LATE. THIS SHOULD DECREASE HEAVY RAINFALL
THREAT FROM NORTH TO SOUTH WITH PRECIPITATION EVENTUALLY ENDING.
AS THE SURFACE LOW TRACKS EAST TODAY, AND SURFACE HIGH PRESSURE
BUILDS ACROSS THE UPPER MIDWEST AND NORTHERN LAKES, SURFACE
WINDS WILL TURN NORTHEASTERLY AND BECOME BREEZY FROM THIS
AFTERNOON INTO TONIGHT AND THURSDAY. WINDS MAY GUST AS HIGH AS
30-35 MPH TONIGHT, ESPECIALLY NEAR LAKE MICHIGAN. THESE WINDS
WILL BUILD WAVES ON THE LAKE THAT WILL MAKE FOR DANGEROUS
CURRENTS AND SWIMMING CONDITIONS. BEACH HAZARD STATEMENTS ARE
ALREADY IN EFFECT FOR THIS.|
RATZER
THURSDAY NIGHT THROUGH TUESDAY:
A BROAD SURFACE HIGH IS EXPECTED TO BE PARKED OVER THE GREAT
LAKES THURSDAY NIGHT AND REMAIN IN PLACE THROUGH THE WEEKEND. AS
A RESULT, DRY CONDITIONS WITH PLENTIFUL SUNSHINE ARE IN STORE
FOR US. AS AN ADDED BONUS, PERSISTENT NORTHWEST FLOW ALOFT ON
THE BACK SIDE OF AN UPPER TROUGH OVER THE NORTHEAST CONUS AND
NORTHEAST WINDS AT THE SURFACE WILL KEEP TEMPERATURES AND
HUMIDITY IN A MORE COMFORTABLE RANGE WITH DAILY HIGHS IN THE
MID-70S TO AROUND 80 AND OVERNIGHT LOWS IN THE 50S TO AROUND 60.
HOWEVER, BREEZIER WINDS ARE LIKELY TO PERSIST THROUGH FRIDAY
EVENING ESPECIALLY OVER THE OPEN WATERS OF LAKE MICHIGAN WHICH
WILL RESULT IN CONTINUED HIGH WAVES AND LIFE THREATENING RIP
CURRENTS AT AREA BEACHES. WHILE OUR CURRENT BEACH HAZARD
STATEMENT RUNS THROUGH FRIDAY AFTERNOON, THERE IS A CHANCE WE
MAY NEED TO EXTEND IT IF THE FORECAST CONTINUES TO TREND AS
EXPECTED. THAT SAID, ANYONE WITH PLANS TO HEAD TO THE BEACH
FRIDAY SHOULD PLAN ON STAYING OUT OF THE WATER UNTIL WINDS AND
WAVES SUBSIDE.
HEADING INTO NEXT WEEK, THE DRY WEATHER DOES LOOK TO LINGER
THROUGH AT LEAST MONDAY BEFORE THE UPPER PATTERN SHIFTS BACK TO
AN ACTIVE SOUTHWEST FLOW REGIME TOWARDS THE MIDDLE OF THE WEEK.
THIS PATTERN SHIFT WILL RESULT IN TEMPERATURES AND HUMIDITY
LEVELS RETURNING TO MORE TYPICAL AUGUST READINGS (HIGHS IN THE
80S AND DEW POINTS IN THE 60S TO NEAR 70) AND OF COURSE CHANCES
FOR SHOWERS AND THUNDERSTORMS. WHILE THERE IS SOME UNCERTAINTY
AS TO WHEN EXACTLY THE RAIN RETURNS, IT LOOKS LIKE CHANCES WILL
BE INCREASING MONDAY NIGHT ONWARD.
YACK
AVIATION /06Z TAFS THROUGH 12Z THURSDAY/
ISSUED AT 113 AM CDT WED JUL 30 2025
FORECAST CONCERNS FOR THE TERMINALS...
- SEVERAL PERIODS OF SHOWERS AND THUNDERSTORMS WEDNESDAY. SOME
OF WHICH COULD BE STRONG WITH GUSTY WINDS AND TORRENTIAL
RAINFALL.
- BREEZY EASTERLY WINDS BEHIND COLD FRONT WEDNESDAY AFTERNOON
WITH GUSTS OF 20-25 KTS.
- LOWERING CEILINGS THROUGH THE PERIOD WITH MVFR CONDITIONS
EXPECTED THROUGH WEDNESDAY NIGHT. IFR CEILINGS POSSIBLE.
THE TAF PERIOD WILL START ON A QUIET NOTE WITH LIGHT EASTERLY
WINDS EXPECTED TONIGHT AND OTHERWISE JUST INCREASING CLOUD
COVER. THAT SAID, THE FORECAST WILL BECOME MUCH MESSIER HEADING
INTO WEDNESDAY MORNING AS THE COMPLEX OF STORMS ONGOING IN IA
BEGINS TO APPROACH. CURRENT THINKING REMAINS GENERALLY THE SAME
AS BEFORE WITH SHOWERS AND THUNDERSTORMS ARRIVING AT RFD AROUND
13-14Z AND THEN THE CHICAGO AREA TERMINALS AROUND 15-16Z.
HOWEVER, IS THE CHANCE (<20%) THAT SOME ISOLATED TO SCATTERED
SHOWERS AND/OR STORMS COULD DEVELOP AHEAD OF THE MAIN COMPLEX AS
THE PLUME OF DEEPER MOISTURE ADVECTS INTO NORTHERN IL AND
NORTHWEST IN AFTER 09Z TONIGHT. GIVEN THAT THE BETTER
INSTABILITY NOT EXPECTED TO ARRIVE UNTIL JUST BEFORE THE
AFOREMENTIONED COMPLEX THE THINKING IS THAT ANY LEADING ACTIVITY
SHOULD STRUGGLE AND FALL APART RATHER QUICKLY. IT WAS THIS
UNCERTAINTY THAT HAS LEAD TO THE MAINTAINING OF THE PROB30S FOR
THE MORNING ROUND OF SHOWERS/STORMS, BUT SUSPECT IF TRENDS
CONTINUE THEN AN UPGRADE TO A TEMPO MAY BE WARRANTED.
IN THE WAKE OF THE MORNING SHOWERS/STORMS, A BRIEF LULL IN
ACTIVITY MAY DEVELOP AS THE ATMOSPHERE TRIES TO DESTABILIZE FOR
THE AFTERNOON. THOUGH, THE HUMID AIR MASS AND PRESENCE OF AN
UPPER DISTURBANCE OVERHEAD WILL LIKELY KEEP SCATTERED SHOWERS
AROUND THROUGH VIRTUALLY THE ENTIRE AFTERNOON. IT IS FOR THIS
REASON THAT SHRA WAS KEPT IN THE TAFS. THAT SAID, THE NEXT ROUND
OF SHOWERS AND THUNDERSTORMS LOOKS TO GET UNDERWAY AFTER 19Z
WHEN ANOTHER DISTURBANCE PIVOTS IN AND INTERACTS WITH THE
DESTABILIZING ATMOSPHERE. GIVEN THAT THE THUNDER COVERAGE WITH
THE SECOND ROUND IS A BIT MORE UNCERTAIN IN ADDITION TO EXACT
TIMING, HAVE OPTED TO EXTEND THE PROB30 BY AN HOUR AT ALL SITES.
REGARDLESS, ANY SHOWERS AND STORMS THAT DEVELOP TODAY WILL HAVE
THE POTENTIAL TO HAVE LOCALIZED GUSTY WINDS AND TORRENTIAL
RAINFALL WHICH COULD LEAD TO INSTANCES OF FLOODING ESPECIALLY
IF STORMS REDEVELOP OVER THE SAME AREA REPEATEDLY. WHILE THE
THUNDER THREAT IS EXPECTED TO MOVE SOUTH OF THE TAF SITES AFTER
00Z, SHOWERS ARE EXPECTED TO PERSIST THROUGH WEDNESDAY NIGHT
BEFORE RAIN TAPERS THURSDAY MORNING.
OUTSIDE OF THE RAIN, WINDS WILL INCREASE BEHIND A COLD FRONT
WEDNESDAY AFTERNOON RESULTING IN 20-25 KT GUSTS THROUGH THE
REMAINDER OF THE PERIOD. THOUGH DIRECTIONS WILL REMAIN
NORTHEASTERLY THROUGHOUT. CEILINGS ON THE OTHER HAND WILL
GRADUALLY LOWER THROUGH THE PERIOD WITH MVFR CONDITIONS EXPECTED
TO DEVELOP BY WEDNESDAY EVENING. ONCE MVFR CEILINGS ARRIVE THEY
ARE EXPECTED TO PERSIST INTO THURSDAY MORNING WITH THE POTENTIAL
FOR IFR CEILINGS TO DEVELOP WEDNESDAY NIGHT.
YACK
LOT WATCHES/WARNINGS/ADVISORIES
IL...FLOOD WATCH FROM 1 PM CDT THIS AFTERNOON THROUGH THURSDAY
AFTERNOON FOR ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
ILZ011-ILZ012-ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-
ILZ033-ILZ039-ILZ103-ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.
BEACH HAZARDS STATEMENT FROM 1 PM CDT THIS AFTERNOON THROUGH
FRIDAY AFTERNOON FOR ILZ006-ILZ103-ILZ104.
IN...FLOOD WATCH FROM 1 PM CDT /2 PM EDT/ THIS AFTERNOON THROUGH
THURSDAY AFTERNOON FOR INZ001-INZ002-INZ010-INZ011-INZ019.
BEACH HAZARDS STATEMENT FROM 1 PM CDT THIS AFTERNOON THROUGH
FRIDAY AFTERNOON FOR INZ001-INZ002.
LM...SMALL CRAFT ADVISORY FROM 1 PM THIS AFTERNOON TO 9 AM CDT
FRIDAY FOR THE IL AND IN NEARSHORE WATERS.
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