452
FXUS63 KLOT 212335
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
635 PM CDT MON APR 21 2025
KEY MESSAGES
- NEXT WEEK AND BEYOND WILL BE CHARACTERIZED BY WAVES OF
SHOWERS AND STORMS. MANY HOURS WILL BE DRY, AND NOT EVERYONE
WILL SEE RAIN WITH EACH ROUND.
- TUESDAY, WEDNESDAY, AND FRIDAY ARE THE FAVORED DAYS FOR
SHOWERS AND STORMS IN OUR REGION THIS WEEK. THURSDAY AND THIS
WEEKEND SHOULD OFFER RELATIVE BREAKS.
- TEMPERATURES WILL GENERALLY WARM THROUGHOUT THE WEEK OUTSIDE
OF SHOWERS AND THUNDERSTORMS AND AWAY FROM THE LAKESHORE. A
COOLDOWN IS EXPECTED THIS WEEKEND.
- THE STORMY AND WARMER PATTERN WILL RESUME EARLY NEXT WEEK.
DISCUSSION
ISSUED AT 215 PM CDT MON APR 21 2025
THROUGH NEXT MONDAY:
THE LOWER GREAT LAKES ARE ON THE BACKSIDE OF A DEPARTING 1000MB
SURFACE LOW PRESSURE SYSTEM LIFTING INTO CENTRAL ONTARIO,
LEADING TO GUSTY WEST WINDS AND OVERCAST STRATOCUMULUS CLOUDS.
AS A SURFACE RIDGE SLIDES INTO THE REGION TONIGHT, GUSTY WINDS
WILL CEASE AND CLOUDS WILL CLEAR. IDEAL CONDITIONS FOR
RADIATIONAL COOLING SHOULD FACILITATE OVERNIGHT LOW TEMPERATURES
IN THE 40S, WITH A FEW UPPER 30S FAIR GAME IN THE TYPICAL COLD
SPOTS. A FEW SPOTS OF GROUND FOG MAY DEVELOP TOWARD DAYBREAK IN
RIVER VALLEYS AND FARM FIELDS, AND PATCHY FROST CANNOT BE RULED
OUT WHERE OVERNIGHT TEMPERATURES ARE COLDEST.
TOMORROW THROUGH WEDNESDAY, A SERIES OF SUBTLE UPPER-LEVEL
WAVES WITHIN DEVELOPING ZONAL FLOW WILL PROPAGATE ACROSS THE
UPPER MISSISSIPPI RIVER VALLEY ATOP A DEVELOPING BUT BROAD WARM
FRONTAL ZONE. AS A RESULT, WAVES OF SHOWERS AND THUNDERSTORMS
SHOULD DEVELOP AND MEANDER IN THE GENERAL REGION WITHIN A
RELATIVELY PROLONGED TIME PERIOD (FAIRLY QUINTESSENTIAL
SPRINGTIME PATTERN). PIN-POINTING EXACT TIMING AND LOCATION OF
SHOWERS AND STORMS IN THIS TYPE OF PATTERN CAN BE A FUTILE
EFFORT, SO WILL OFFER BROAD-BRUSHED POPS WITH "SCATTERED
THUNDERSTORM" WORDING THROUGH MUCH OF THE PERIOD. IN TERMS OF
THUNDERSTORM INTENSITY, MODEST MID-LEVEL FLOW ALONG THE SOUTHERN
PERIPHERY OF THE ZONAL JET IN TANDEM WITH RELATIVELY LOW
FREEZING LEVELS, STEEP MID-LEVEL LAPSE RATES, AND WELL-MIXED
BOUNDARY (DAYTIME) OR SHALLOW STABLE (NIGHTTIME) LAYERS WILL
SUPPORT A THREAT FOR ISOLATED INSTANCES OF DAMAGING WINDS AND
HAIL (55-60 MPH AND 1" HAIL, RESPECTIVELY). HIGH TEMPERATURES
WILL BE MODULATED BY CONVECTION AND RANGE FROM THE MID 60S TO
LOWER 70S (COOLER NEAR LAKE MICHIGAN). LOWS TOMORROW NIGHT
SHOULD BE RELATIVELY MILD AND IN THE 50S.
WEDNESDAY NIGHT INTO THURSDAY LOOKS LIKE A BRIEF BREAK IN THE
STORMY PATTERN AS MID-LEVEL HEIGHTS BUILD IN RESPONSE TO
DEVELOPING AGGREGATE TROUGHING ACROSS THE WESTERN US. PARTLY
SUNNY SKIES AND INCREASING THICKNESS WILL SUPPORT A WARM SPRING
DAY WITH HIGHS IN THE UPPER 70S TO LOWER 80S. OF COURSE,
LAKESHORE LOCATIONS SHOULD STAY SOME 10 TO 15 DEGREES COLDER.
WITH A SHORTWAVE INDUCING CYCLOGENESIS IN THE PLAINS, WE'LL HAVE
TO KEEP AN EYE ON THE THREAT FOR A BACKDOOR FRONT TO RACE DOWN
THE LAKE DURING THE AFTERNOON, WHICH WOULD SEND TEMPERATURES
NOSEDIVING IN NORTHEASTERN IL BY SUNSET.
CHANCES FOR SHOWERS AND STORMS WILL RETURN TO THE AREA ON
FRIDAY AS THE AFOREMENTIONED SHORTWAVE AND SURFACE LOW LIFT INTO
THE GREAT LAKES. SINCE THE WAVE WILL BE FAIRLY WEAK (SURFACE
LOW MORE OR LESS VERTICALLY STACKED), THE THREAT FOR SEVERE
WEATHER SHOULD BE CURTAILED TO LOCALIZED INSTANCES OF FLOODING
(SLOW-MOVING CELLS) AND "COLD AIR" FUNNELS (WHICH DO NOT
DEVELOP INTO DAMAGING TORNADOES). SO, IT'LL BE ANOTHER
QUINTESSENTIAL SPRINGTIME REGIME.
THIS WEEKEND, THE BAROCLINIC ZONE WILL GET SHUNTED SOUTHWARD,
LEADING TO COOLER TEMPERATURES AND A BREAK IN THE WAVES OF
SHOWERS AND STORMS. ENSEMBLE MODEL GUIDANCE ADVERTISES AN
UNUSUALLY STRONG SIGNAL FOR MUCH WARMER TEMPERATURES AS WELL AS
SHOWERS AND STORMS RETURNING TO THE REGION EARLY NEXT WEEK,
PRESUMABLY AS DEEP TROUGHING BECOMES ESTABLISHED ACROSS THE
CENTRAL PLAINS. THIS WILL BE A TIMEFRAME TO WATCH FOR SEVERE
WEATHER IN THE BROADER MIDWEST REGION.
BORCHARDT
AVIATION /00Z TAFS THROUGH 06Z TUESDAY/
ISSUED AT 635 PM CDT MON APR 21 2025
KEY AVIATION MESSAGES FOR THE CURRENT TAF PERIOD:
- LOW CHANCE (LESS THEN 15 PERCENT) FOR SHALLOW FOG AT TERMINALS
FARTHER AWAY FROM THE LAKE.
- SEVERAL PERIODS OF SHOWER/STORM CHANCES ON TUESDAY IN THE LATE
MORNING, AFTERNOON, AND THEN CLOSER TO MIDNIGHT.
WESTERLY WIND GUSTS HAVE COME DOWN TO 20 TO 25 KNOTS. AS WINDS
DECOUPLE AFTER SUNSET, GUSTS SHOULD CUT OFF COMPLETELY. WINDS
WILL BECOME LIGHT AND VARIABLE OVERNIGHT BEFORE TURNING TO THE
SOUTHEAST BEFORE DAYBREAK. WINDS WILL THEN TURN TO THE SOUTHWEST
IN THE AFTERNOON WITH GUSTS POTENTIALLY AROUND 20 KNOTS.
LATE TONIGHT/EARLY TUESDAY MORNING, SOME SHALLOW FOG/MIST MAY
DEVELOP AT OUTLYING SITES (DPA, GYY, RFD). THIS POTENTIAL
REMAINS TOO LOW FOR AN INCLUSION IN THE TAFS.
THERE ARE A FEW PERIODS ON TUESDAY WHEN SHOWERS AND
THUNDERSTORMS MAY IMPACT TERMINALS. THE FIRST IS IN THE MORNING
AS THE REMNANTS OF THE TONIGHT'S STORMS OVER THE PLAINS MOVES
EAST. PREVAILING SHOWERS WERE ADDED TO RFDS TAF, BUT AS THESE
SHOWERS MOVE EAST, THEY WILL ENCOUNTER A MORE STABLE AIRMASS,
SO THE PROB30 REMAINS FOR THUNDER. IT IS POSSIBLE THAT SOME OF
THE SHOWERS MAKE IT TO THE CHICAGO TERMINALS, BUT WITH THE
CHANCES LESS THAN 30 PERCENT, IT WAS LEFT OUT OF THE TAF.
AS THAT WAVE EXITS, A WEST TO EAST FRONTAL BOUNDARY WILL LIKELY
DEVELOP ACROSS NORTHERN ILLINOIS. THERE WILL BE A THREAT FOR
SHOWERS AND THUNDERSTORMS TO DEVELOP ALONG IT IN THE AFTERNOON.
HOWEVER, WITH LOWER CONFIDENCE ON COVERAGE, IT REMAINS AS A
PROB30 IN THE TAF.
LASTLY, THERE IS A BETTER SIGNAL FOR SHOWERS AND THUNDER
TUESDAY NIGHT AS A LOW LEVEL JET RAMPS UP ADDING BETTER
CONVERGENCE FOR STORMS TO FIRE ALONG THE BOUNDARY. CURRENT
MODELS HAVE THIS DEVELOPING AT OR JUST BEFORE 06Z. WITH LOWER
CONFIDENCE IN THE START TIME, IT WAS LEFT OUT OF THE TAF FOR
NOW, BUT WILL NEED TO BE REVISITED WITH THE 06Z TAF PACKAGE.
DK
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...GALE WARNING UNTIL 7 PM CDT THIS EVENING FOR THE IL AND IN
NEARSHORE WATERS.
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