691
FXUS63 KLOT 220618
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
118 AM CDT TUE APR 22 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 /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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