595
FXUS63 KLOT 211915
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
215 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 /18Z TAFS THROUGH 00Z WEDNESDAY/
ISSUED AT 1232 PM CDT MON APR 21 2025
THE KEY AVIATION MESSAGES ARE:
- BLUSTERY WESTERLY WINDS WILL CONTINUE THIS AFTERNOON BEFORE
EASING SHARPLY THIS EVENING. OCCASIONAL GUSTS TO AROUND 35
KNOTS.
- SMALL POTENTIAL FOR MIFG/BR TONIGHT, MAINLY INVOF GYY, DPA,
AND RFD. TOO LOW FOR A MENTION IN THE TAFS.
- SEVERAL THREATS FOR SHOWERS/STORMS ON TUESDAY, 1ST IN THE MID-
LATE MORNING AND THEN IN THE AFTERNOON.
WESTERLY WINDS WILL CONTINUE TO GUST ROUTINELY AROUND 30 KNOTS,
WITH OCCASIONAL GUSTS JUST ABOVE 35 KTS THROUGH THE REST OF THE
AFTERNOON. WINDS WILL THEN EASE SHARPLY THIS EVENING (AFTER
00-01Z). THEREAFTER, WINDS WILL BECOME LIGHT AND VARIABLE,
BEFORE EVENTUALLY ACQUIRING A SOUTHEASTERLY DIRECTION LATE
TONIGHT/EARLY TUESDAY MORNING. EVENTUALLY, WINDS WILL BECOME
SOUTHWESTERLY TOWARDS MIDDAY/EARLY AFTERNOON, AND MAY ALSO
BECOME GUSTY.
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, HOWEVER.
THERE WILL BE A FEW PERIODS ON TUESDAY WHICH COULD FEATURE A
THREAT FOR SHOWERS AND THUNDERSTORMS. THE FIRST IS MID-LATE
MORNING INVOF RFD WHERE A PROB30 FOR TSRA HAS BEEN INTRODUCED.
WHILE THIS ACTIVITY MAY GET CLOSE TO THE CHICAGO-AREA TERMINALS,
CHANCES WITH THIS FIRST ROUND APPEAR TO BE UNDER 30 PERCENT AT
THIS TIME. THE SECOND WINDOW IS LATER IN THE AFTERNOON, FOR
WHICH A SEPARATE PROB30 HAS BEEN INTRODUCED AT ORD/MDW DURING
THE EXTENDED TAF WINDOW.
CARLAW
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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