322
FXUS63 KLOT 202330
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
630 PM CDT SUN APR 20 2025
KEY MESSAGES
- WIDESPREAD SHOWERS WITH EMBEDDED THUNDERSTORMS TONIGHT. A FEW
STRONGER STORMS WITH LOCALLY GUSTY WINDS POSSIBLE, ESPECIALLY
SOUTH OF I-80.
- WINDY CONDITIONS ON MONDAY WITH WEST-SOUTHWEST GUSTS IN THE
35-45 MPH RANGE.
- WELL ABOVE NORMAL TEMPERATURES EXPECTED INLAND OF THE LAKE
FOR THE REST OF THE UPCOMING WEEK AFTER A COOL MONDAY.
DISCUSSION
ISSUED AT 258 PM CDT SUN APR 20 2025
THROUGH MONDAY NIGHT:
A SWATH OF SHOWERS IS MOVING ACROSS NORTHERN IL EARLY THIS
AFTERNOON. THESE SHOWERS ARE BLOOMING NORTH OF A WARM FRONT AS
IT PROGRESSES NORTHWARD INTO OUR CWA. AS OF AROUND 2 PM, THE
BOUNDARY RESIDES NEAR THE KANKAKEE RIVER AND CONDITIONS ARE DRY
IMMEDIATELY ALONG AND BEHIND IT. A FEW EMBEDDED THUNDERSTORMS
AND HEAVIER SHOWERS HAVE BEEN CLINGING ONTO A MUCAPE GRADIENT
IMMEDIATELY NORTH OF THE FRONT. THE SHOWERS AND EMBEDDED THUNDER
WILL CONTINUE TO BE PUSHED ALONG BY THE FRONT UNTIL THEY GET
SHUNTED NORTH OF THE CWA LATE THIS AFTERNOON AND THE AREA SHOULD
BE LARGELY DRY THEN UNTIL LATER IN THE EVENING.
THE WARM FRONT IS EXPECTED TO GET HUNG UP OVER OUR CWA, ROUGHLY
NEAR THE I-88/90 CORRIDORS LATER THIS AFTERNOON BEFORE SURGING
NORTHWARD AGAIN THIS EVENING WITH THE APPROACH OF THE LOW
CENTER AND COLD FRONT. A PRETTY SHARP TEMPERATURE GRADIENT IS
SETTING UP ACROSS OUR AREA ON EITHER SIDE OF THE FRONT,
ESPECIALLY NOW THAT OUR SOUTH HAS DRIED OUT AND IS BEGINNING TO
SEE SOME SUN. TEMPERATURES SHOULD BE RATHER STEADY THIS EVENING
WHILE THIS FRONT REMAINS STATIONARY. AFTER THE FRONT BEGINS ITS
TREK NORTHWARD AGAIN, MUCH OF THE AREA NORTH OF I-80 WILL LIKELY
EVEN WARM A COUPLE OF DEGREES TONIGHT.
THE STORM'S COLD FRONT WILL PROPAGATE ACROSS THE CWA LATE THIS
EVENING INTO TONIGHT, BRINGING WITH IT AN ADDITIONAL PUSH OF
RAIN AND PROBABLY SOME EMBEDDED THUNDERSTORMS. CONTINUED LOW
LEVEL WARM ADVECTION THIS EVENING WILL GENERATE A POOL OF
ELEVATED INSTABILITY SUFFICIENT FOR THUNDERSTORM DEVELOPMENT
JUST AHEAD OF THE COLD FRONT. WHILE SEVERE WEATHER IS NOT REALLY
ANTICIPATED, WE COULD SEE SOME STRONGER WINDS ASSOCIATED WITH
THESE STORMS. SEVERAL PIECES OF GUIDANCE ARE RESOLVING A
CORRIDOR OF GUSTY WINDS COINCIDENT WITH A NARROW OPPORTUNITY FOR
THE LOW LEVELS TO BECOME ONLY WEAKLY STABLE NEAR THE FRONT. AN
IMPRESSIVE LOW LEVEL JET WILL TRACK JUST OFF THE DECK AND IT'S
VERY POSSIBLE THAT SOME OF THESE STRONGER WINDS COULD PUNCH
THROUGH TO THE SURFACE, ESPECIALLY WITH THE HEAVY RAIN AND
STORMS TO HELP OUT. THIS IS ESPECIALLY TRUE CLOSER TO CENTRAL
AND WESTERN IL WHERE THEY COULD MAINTAIN A LITTLE BIT OF MIXED-
LAYER INSTABILITY INTO THE EVENING. AN SPC MARGINAL RISK ABUTS
OUR SOUTHWEST CWA FOR THIS WIND POTENTIAL.
THE STORMS WILL BE OFF TO OUR EAST PRIOR TO DAYBREAK TOMORROW. A
TRAILING SECONDARY COLD FRONT WILL MOVE ACROSS THE AREA DURING
THE MORNING HOURS. IN FACT, MORNING LOW TEMPERATURES TOMORROW
WILL LIKELY OCCUR WELL AFTER DAYBREAK BEHIND THIS BOUNDARY. WITH
APPRECIABLE LOW LEVEL MOISTURE HANGING ON BEHIND THE INITIAL
FRONT, SOME DRIZZLE MAY MATERIALIZE DURING THE MORNING BEFORE
THE SECONDARY FRONT PASSES. CONDITIONS SHOULD ALSO BE WINDY
TOMORROW, ESPECIALLY DURING THE MORNING, BUT CONFIDENCE IS SHAKY
IN WHAT SORT OF WINDS WE'LL BE LOOKING AT. THE LACK OF
CONFIDENCE BOILS DOWN TO TWO PRIMARY DISCREPANCIES AMONG MODELS:
THE MAGNITUDE OF THE LOW LEVEL FLOW AND THE QUALITY OF LOW LEVEL
MOISTURE. THE EURO AND UKMET BRING IN MUCH DRIER NEAR- SURFACE
AIR BEHIND THE INITIAL COLD FRONT THAN OTHER CAMPS LEADING TO
SLIGHTLY DEEPER AND OVERALL MORE EFFICIENT MIXING IN THE
MORNING. THESE ARE TWO OF THE MORE AGGRESSIVE SOLUTIONS FOR
WINDS TOMORROW. 925MB WINDS DURING THE MORNING ARE ALSO BEING
MODELED AT ANYWHERE BETWEEN 35 AND 45 KT. THE HRRR FOR INSTANCE
IS STRONGER WITH THE LOW LEVEL FLOW SO, DESPITE BEING MONDAY
NIGHT SATURATED IN THE LOW LEVELS WITH LESSER MIXING, IT'S
STILL WANTING TO RESOLVE GUSTS TO AROUND 40 MPH. SO IT'S TOUGH
TO SAY EXACTLY WHAT SORT OF FLOW WE WILL HAVE UPSTAIRS AND HOW
EFFICIENTLY WE CAN MIX THAT DOWN TO THE SURFACE. BUT A PERIOD OF
AT LEAST 30 TO 35 MPH GUSTS LOOKS LIKELY TOMORROW MORNING,
ALTHOUGH 40 TO 45 MPH CERTAINLY LOOKS ATTAINABLE.
WINDS COULD REMAIN STRONG INTO THE EARLY AFTERNOON BUT SHOULD
START STEPPING DOWN DURING THE AFTERNOON AS THE LOW LEVEL FLOW
RELAXES. AFTER THE MORNING DRIZZLE POTENTIAL MOVES AWAY, NO
RAIN IS EXPECTED FOR THE REST OF THE DAY. A FEED OF DRY AIR WILL
CHIP AWAY AT THE CLOUDY SKIES AND SOME GOOD SUNSHINE SHOULD
FALL ON THE AREA LATER IN THE DAY WHILE AFTERNOON TEMPERATURES
LOOK TO BE IN THE 50S.
DOOM
TUESDAY THROUGH SUNDAY:
THE UPPER LEVEL PATTERN ACROSS THE CONUS WILL TRANSITION TO MORE
OF A QUASI-ZONAL FLOW (WEST-TO-EAST ORIENTED) PATTERN FOR THE
MIDDLE PART OF THE WEEK, BEFORE BECOMING MORE AMPLIFIED AGAIN
LATER THIS WEEK INTO NEXT WEEKEND. THIS IS EXPECTED TO CURTAIL THE
THREAT OF ANY STRONGER (AND PERSISTENT PRECIPITATION GENERATING)
STORM SYSTEMS FROM IMPACTING THE EASTERN HALF OF THE COUNTRY
TUESDAY THROUGH AT LEAST THURSDAY. IN SPITE OF THIS, ENSEMBLE AND
DETERMINISTIC GUIDANCE ARE IN AGREEMENT IN TRACKING SOME SMALLER
SCALE PERTURBATIONS EASTWARD ACROSS OUR REGION DURING THIS
PERIOD. ACCORDINGLY, WHILE THERE IS LIKELY TO BE MAINLY
PRECIPITATION FREE HOURS, THERE WILL BE SOME ON-AND-OFF SHOTS OF
SHOWERS AND THUNDERSTORMS THROUGH MUCH OF THE WEEK.
GUIDANCE REMAINS IN GOOD AGREEMENT WITH TRACKING AN INITIAL LOW
AMPLITUDE DISTURBANCE EASTWARD ACROSS THE MIDWEST INTO THE WESTERN
GREAT LAKES THROUGH TUESDAY NIGHT. WEAK HEIGHT FALLS ASSOCIATED
WITH THIS WAVES SHOULD ENCOURAGE THE DEVELOPMENT OF A MODEST
SOUTHERLY LOW-LEVEL JET AND STRENGTHEN THETA-A ADVECTION TUESDAY
NIGHT. THIS WILL IN TURN SUPPORT OUR FIRST DECENT POTENTIAL
(50-60% CHANCE) FOR SHOWERS AND STORMS LATE TUESDAY INTO
TUESDAY NIGHT. AT THIS TIME THE BEST CHANCES FOR THIS RESIDE
ALONG AND NORTH OF I-80. ANOTHER, SIMILAR QUICK MOVING IMPULSE
MAY SHIFT INTO THE AREA AND RESULT IN ANOTHER PERIOD OF (~30%
CHANCE) OF RAIN LATE WEDNESDAY INTO WEDNESDAY NIGHT. OTHERWISE,
OUR NEXT GOOD SHOT (50-60% CHANCE) OF SHOWERS AND STORMS COMES
LATE IN THE WEEK (THURSDAY NIGHT INTO FRIDAY) AS A STRONGER COLD
FRONT MOVES ACROSS THE AREA.
TEMPERATURES ARE EXPECTED TO BE ON A WARMING TREND TO SOLIDLY
ABOVE AVERAGE TEMPERATURES THROUGH THE MIDDLE OF THE WEEK,
PARTICULARLY FOR INLAND SECTIONS OF NORTHERN IL AND IN. AS IS
OFTEN THE CASE THIS TIME OF YEAR, LAKE BREEZES EACH AFTERNOON WILL
KEEP TEMPERATURES NOTABLY COOLER ALONG AND NEAR THE LAKE MICHIGAN
SHORE. TEMPERATURES ARE THEN LIKELY TO COOL BACK CLOSER TO
SEASONABLE LEVELS NEXT WEEKEND FOLLOWING A COLD FRONT PASSAGE LATE
THIS WEEK.
KJB
AVIATION /00Z TAFS THROUGH 06Z MONDAY/
ISSUED AT 630 PM CDT SUN APR 20 2025
AVIATION FORECAST CONCERNS FOR THE 00Z TAFS:
- SCATTERED TSRA POSSIBLE LATE THIS EVENING.
- MVFR CEILINGS DEVELOP OVERNIGHT AND PERSIST THROUGH MOST OF
MONDAY WHILE SLOWLY RISING.
- BREEZY ESE WINDS BECOME WSW BY MORNING. GUSTS 30-35 KT
POSSIBLE MONDAY, EASING LATER IN THE DAY.
SURFACE LOW PRESSURE WAS ANALYZED OVER MO EARLY THIS EVENING,
WITH A NORTHWARD LIFTING WARM FRONT EXTENDING SOUTHEAST ACROSS
WEST-CENTRAL IL INTO SOUTHWEST IN. BREEZY EAST-SOUTHEAST WINDS
WITH GUSTS 20-25 KTS WILL PERSIST ACROSS THE TERMINALS THIS
EVENING AHEAD OF THE APPROACHING WARM FRONT, EVENTUALLY VEERING
SOUTHWEST AFTER MIDNIGHT TONIGHT AS THE LOW MOVES ACROSS WI AND
THE OCCLUDING FRONTAL BOUNDARY SHIFTS EAST OF THE AREA. WEST-
SOUTHWEST WINDS ARE EXPECTED TO STRENGTHEN IN THE WAKE OF THE
LOW, WITH GUSTS 30-35 KTS LIKELY DURING THE MORNING AND EARLY
AFTERNOON HOURS BEFORE DIMINISHING QUICKLY EARLY MONDAY
EVENING.
HIGH-RES CAMS ARE IN GENERALLY GOOD AGREEMENT IN BRINGING A LINE
OF CONVECTIVE SHRA/TSRA (CURRENTLY APPROACHING THE MS RIVER FROM
EASTERN IA/MO) NORTHEAST INTO THE AREA LATE THIS EVENING, WITH
SOME POTENTIAL FOR ISOLATED ELEVATED SHRA/TSRA DEVELOPMENT
AHEAD OF THE MAIN ARE OF PRECIPITATION IN STRONG WARM-ADVECTION.
THUS HAVE INTRODUCED A VCTS BY 03Z/10PM AND A TEMPO FOR TSRA IN
THE 04Z-06Z WINDOW (AN HOUR EARLIER FOR KRFD). SHRA COVERAGE
SHOULD DIMINISH TO SCATTERED/WIDELY SCATTERED COVERAGE DURING
THE REMAINDER OF THE OVERNIGHT HOURS. CURRENT VFR CONDITIONS ARE
EXPECTED TO DETERIORATE WITHIN THE HEAVIER PRECIP LATE THIS
EVENING, WITH MVFR CEILINGS LIKELY THEN PERSISTING INTO MUCH OF
MONDAY BEFORE EVENTUALLY SCATTERING TO VFR FROM THE WEST LATER
IN THE DAY/EVENING.
RATZER
MARINE
ISSUED AT 258 PM CDT SUN APR 20 2025
A SMALL CRAFT ADVISORY IS IN EFFECT TODAY. A GALE WARNING GOES
INTO EFFECT TONIGHT AND LASTS INTO TOMORROW EVENING.
LOW PRESSURE AT OR JUST UNDER 1000 MB WILL TRACK FROM
IOWA TONIGHT TO NORTHERN LOWER MICHIGAN MONDAY AFTERNOON AND
ACROSS LAKE HURON MONDAY EVENING. BREEZY EAST-SOUTHEAST WINDS
TONIGHT WILL RESULT IN HAZARDOUS WAVES FOR SMALL CRAFT ALONG
THE ILLINOIS AND INDIANA NEARSHORES. A PERIOD OF GALES IS ALSO
POSSIBLE LATE TONIGHT COINCIDENT WITH A PUSH OF SHOWERS AND
THUNDERSTORMS. THEN IN THE WAKE OF THE SYSTEM ON MONDAY, WINDS
WILL QUICKLY SHIFT TO SOUTHWEST AND THEN WEST WHILE RAPIDLY
INCREASING. WHILE SOME UNCERTAINTY REMAINS, FELT CONFIDENCE WAS
HIGH ENOUGH TO UPGRADE THE WATCH TO A GALE WARNING FOR TOMORROW.
ALSO MADE THE DECISION TO HAVE THE WARNING GO INTO EFFECT AT 06Z
FOR THE BRIEF GALE POTENTIAL TONIGHT.
DOOM/YACK
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 1 AM CDT MONDAY FOR THE IL AND IN
NEARSHORE WATERS.
GALE WARNING FROM 1 AM TO 7 PM CDT MONDAY FOR THE IL AND IN
NEARSHORE WATERS.
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