731
FXUS63 KLOT 160343
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
943 PM CST SUN DEC 15 2024
KEY MESSAGES
- AREAS OF DENSE FOG SOUTH OF KANKAKEE RIVER AND EAST OF I-55
THIS EVENING, WITH POTENTIAL FOR ADDITIONAL DENSE FOG
DEVELOPMENT ACROSS NORTHERN IL INTO MONDAY MORNING.
- TREND TOWARD COLDER, MORE SEASONABLE WEATHER CONDITIONS MID-
WEEK AND BEYOND. LIGHT SNOW ACCUMULATIONS ARE POSSIBLE TUESDAY
NIGHT INTO EARLY WEDNESDAY, MAINLY ACROSS FAR NORTHERN IL.
UPDATE
ISSUED AT 943 PM CST SUN DEC 15 2024
HAVE ISSUED A NEW DENSE FOG ADVISORY FOR SOUTHEASTERN PARTS OF
THE FORECAST AREA THIS EVENING, MAINLY EAST OF I-55 AND
ALONG/SOUTH OF THE KANKAKEE RIVER. ALSO HAVE TRIMMED THE CHICAGO
METRO PORTIONS OF THE PREVIOUS DENSE FOG ADVISORY, WITH
VISIBILITIES HAVING IMPROVED SIGNIFICANTLY SINCE EARLY EVENING.
CONFIDENCE IS FAIRLY LOW WITH FOG TRENDS OVERNIGHT, THOUGH SOME
REDEVELOPMENT OF DENSE FOG DOES APPEAR POSSIBLE BY EARLY MONDAY
MORNING, AHEAD OF A COLD FRONT.
WEAK OCCLUDED SURFACE WAVE FROM YESTERDAY'S SYSTEM FILLED
ACROSS NORTHERN IL EARLIER TODAY. WITH ANOTHER MID-LEVEL SHORT
WAVE CURRENTLY TRACKING EASTWARD ACROSS THE PLAINS, LOW LEVEL
FLOW HAS TURNED SOUTHERLY AND HAS BEEN GRADUALLY INCREASING IN
ADVANCE OF A COLD FRONT WHICH WILL PUSH ACROSS THE AREA TOWARD
MIDDAY MONDAY AND MONDAY AFTERNOON. WHILE EXTENSIVE LOW STRATUS
REMAINS IN PLACE ACROSS MUCH OF THE FORECAST AREA THIS EVENING,
FOG HAS LIFTED WITH CONSIDERABLE IMPROVEMENT IN VISIBILITIES
THIS EVENING AS SOUTH WINDS INCREASE. THE EXCEPTION, HOWEVER,
HAS BEEN ACROSS CENTRAL ILLINOIS AND CENTRAL INDIANA, WHERE
CLEAR SKIES SOUTH OF THE STRATUS DECK HAD HAS ALLOWED DENSE FOG
TO RAPIDLY DEVELOP. THIS AREA OF FOG WAS DEVELOPING AND
ADVECTING NORTHWARD INTO WFO LOT'S SOUTHEASTERN COUNTIES AS THE
TRAILING EDGE OF OUR STRATUS LIFTS NORTH. FAIRLY HIGH CONFIDENCE
THAT THESE COUNTIES WILL SEE A PERIOD OF DENSE FOG THIS
EVENING, AND THUS ISSUED A DENSE FOG ADVISORY FOR THESE AREAS.
CONFIDENCE IS MUCH LOWER IN FOG TRENDS ACROSS THE REMAINDER OF
THE AREA, AND EVEN IN THE SOUTHEAST LATER INTO TONIGHT WHERE
INCREASING SOUTH WINDS AND INCREASING MID/HIGH CLOUD COVER MAY
HAVE AN IMPACT ON STRATUS BUILD-DOWN AND FOG DEVELOPMENT.
DEVELOPMENT OF SHOWERS AFTER MIDNIGHT WITH THE APPROACHING WAVE
WILL HELP TO MOISTEN LOW LEVELS FURTHER AND GUIDANCE IS FAIRLY
BULLISH WITH LOW VISIBILITIES DEVELOPING AGAIN ACROSS A GOOD
PORTION OF NORTHERN IL, THOUGH IMPROVING TRENDS OVER THE PAST
SEVERAL HOURS LENDS TOWARD LOWER CONFIDENCE. BASED ON THIS HAD
TRIMMED EASTERN PARTS OF THE FORMER ADVISORY ACROSS THE CHICAGO
METRO AREA, WHERE REDEVELOPMENT IN THE NEAR TERM APPEARS LEAST
FAVORABLE. CERTAINLY CAN'T RULE OUT SOME REDEVELOPMENT LATE
TONIGHT OR PERHAPS TOWARD/DURING MONDAY MORNING AHEAD OF THE
FRONT WHICH MIGHT REQUIRE EXPANSION OR RENEWED HEADLINE
ISSUANCE, THOUGH FOR NOW CONFIDENCE IS LOW.
OTHER THAN THESE FOG/HEADLINE ISSUES (DID ADD PATCHY DRIZZLE TO
THE FORECAST EARLIER), NO SIGNIFICANT CHANGES APPEAR NEEDED
THIS EVENING.
RATZER
DISCUSSION
ISSUED AT 339 PM CST SUN DEC 15 2024
THROUGH MONDAY:
FOG AND DRIZZLE CONTINUES TO BE A NUISANCE ACROSS THE AREA THIS
AFTERNOON, WITH VISIBILITIES QUICKLY TANKING AGAIN IN SPITE OF
INCREASING BOUNDARY LAYER FLOW. SEVERAL SITES ARE ALREADY
QUICKLY DROPPING WELL BELOW A HALF MILE. WITH THESE TRENDS, AND
NO REAL IMPROVEMENT LIKELY, WE WILL BE DEALING WITH DENSE FOG
AGAIN TONIGHT, ESPECIALLY ACROSS NORTHERN IL NORTHWEST OF I-55.
WE HAVE THUS ISSUED A NEW DENSE FOG ADVISORY THROUGH EARLY
MONDAY MORNING FOR AREAS GENERALLY ALONG AND NORTHWEST OF I-55
WHERE VISIBILITIES HAVE ALREADY FALLEN TO AROUND 1/2 MILE OR
LESS AND WHERE CONFIDENCE IS HIGHEST THAT ADDITIONAL DENSE FOG
WILL DEVELOP THROUGH TONIGHT. AN EASTWARD OR SOUTHWARD EXPANSION
TO THE ADVISORY MAY ULTIMATELY BE NEEDED AT SOME POINT TONIGHT,
BUT CONFIDENCE IN DENSE FOG OCCURRING IN AREAS OUTSIDE OF THE
CURRENT ADVISORY AREA WAS TOO LOW TO JUSTIFY INCLUDING THESE
AREAS IN THE ADVISORY AT THE TIME.
RAIN SHOWERS ARE EXPECTED TO DEVELOP NORTHEASTWARD INTO THE
AREA OVERNIGHT TONIGHT AS WARM AIR ADVECTION RAMPS UP. THE
GREATEST COVERAGE OF SHOWERS AND HIGHEST QPF AMOUNTS IS/ARE
EXPECTED TO REMAIN GENERALLY ALONG AND EAST OF I-55, WITH
LESSER COVERAGE/LIGHTER AMOUNTS TO THE NORTHWEST. WE MAY VERY
WELL SEE SOME IMPROVEMENTS IN THE VISIBILITY WITH THE RAIN LATER
TONIGHT, BUT WITH LESS RAIN EXPECTED TO OCCUR IN OUR
NORTHWESTERN COUNTIES, CONFIDENCE ON VISIBILITIES IMPROVING IS
LOW AT THIS TIME.
OTHERWISE, A COLD FRONTAL PASSAGE WILL OCCUR ON MONDAY, SO ANY
LINGERING EARLY MORNING FOG WILL QUICKLY ERODE BY LATE MORNING.
TEMPERATURES WILL RISE PRIOR TO THE COLD FRONTAL PASSAGE AROUND
MIDDAY MONDAY, WITH WELL ABOVE NORMAL HIGHS IN THE 50-55F RANGE
EXPECTED NEAR AND SOUTHEAST OF I-55, AND GENERALLY MID TO UPPER
40S EXPECTED FARTHER NORTHWEST. BREEZY WESTERLY WINDS WILL GUST
UP TO 30-35 MPH MONDAY AFTERNOON BEHIND THE COLD FRONT AS COOLER
AIR FILTERS IN.
KJB/OGOREK
MONDAY NIGHT THROUGH SUNDAY:
A PROGRESSIVE UPPER-LEVEL WEATHER PATTERN IS EXPECTED TO
PERSIST THROUGH MUCH OF THE WEEK BEFORE THE PATTERN AMPLIFIES
NEXT WEEKEND. OVERALL, THIS IS EXPECTED TO RESULT IN SEASONAL
TEMPERATURES, ALONG WITH A FEW CHANCES FOR LIGHT PRECIPITATION
THROUGH THE PERIOD.
AT THE START OF THE PERIOD ON TUESDAY, CONDITIONS LOOK QUIET
WEATHER-WISE FOLLOWING A PERIOD OF BREEZY WEATHER MONDAY NIGHT.
SEASONABLY MILD TEMPERATURES IN THE UPPER 30S TO LOW 40S ARE
EXPECTED DURING THE DAY. WHILE QUIET LOCALLY, EYES WILL BE ON
THE EVOLUTION OF A POSITIVELY TILTED TROUGH TRANSVERSING THE
COLORADO ROCKIES LATE IN DAY. THIS FEATURE IS EXPECTED TO TRACK
EASTWARD THROUGH THE MIDWEST WHILE DRIVING A DEVELOPING AREA OF
SURFACE LOW PRESSURE FROM THE OZARKS INTO THE LOWER OHIO VALLEY
TUESDAY NIGHT INTO EARLY WEDNESDAY. IN RESPONSE, PRECIPITATION
CHANCES WILL RAMP-UP TO OUR WEST AND SOUTHWEST LATE TUESDAY INTO
TUESDAY EVENING, BEFORE SPREADING EASTWARD INTO MISSISSIPPI
VALLEY LATER TUESDAY NIGHT. THE OVERALL TRACK OF THE LOW SHOULD
FAVOR MOST OF THE PRECIPITATION FALLING SOUTH OF OUR AREA.
HOWEVER, THE COMBINATION OF A STRENGTHENING LOW TO MID-LEVEL
BAROCLINIC ZONE WITHIN THE DEFORMATION ZONE NORTH OF THE LOW AND
THE INCREASED UPPER-LEVEL DIVERGENCE WITHIN THE ENTRANCE REGION
OF A JET-STREAK SHOULD PROVIDE SUPPORT FOR LIGHT PRECIPITATION
INTO OUR AREA LATE TUESDAY NIGHT INTO EARLY WEDNESDAY.
PRECIPITATION TYPE COULD END UP FAVORING SNOW WITH SOME MINOR
ACCUMULATIONS (UNDER AN INCH), ESPECIALLY AREAS NORTH OF I-80.
SOME PHASING OF THIS SHORT WAVE, AND ANOTHER ROTATING ACROSS
THE NORTHERN GREAT LAKES ON WEDNESDAY/WEDNESDAY NIGHT, IS
PROGGED TO LEAD TO AMPLIFICATION OF A LONG-WAVE UPPER TROUGH
OVER THE EASTERN NOAM/CONUS. COMBINED WITH A BUILDING UPPER
RIDGE OVER THE WEST COAST IS EXPECTED TO LEAD TO A COLDER TREND
FOR THE MIDWEST FOR THE REMAINDER OF THE WEEK AND THE WEEKEND.
NBM TEMPS LOCALLY DIP BELOW AVERAGE BY THE WEEKEND, WITH HIGHS
IN THE UPPER 20S FORECAST BY SATURDAY. ECMWF/GFS/CMC ENSEMBLES
ALL DEPICT ANOTHER MID-LEVEL SHORT WAVE TRANSITING THE NORTHERN
PLAINS AND UPPER MIDWEST IN THE THURSDAY THROUGH THURSDAY NIGHT
TIME FRAME WHICH MAY POSE AN ADDITIONAL CHANCE FOR SOME LIGHT
SNOW ESPECIALLY JUST NORTH OF THE CWA ACROSS THE UPPER MIDWEST.
ADDITIONAL VORT LOBES ARE DEPICTED ROTATING ACROSS THE UPPER
MIDWEST/GREAT LAKES REGION INTO THE WEEKEND, AND AGAIN WHILE
BEST LIGHT SNOW CHANCES REMAIN JUST OFF TO THE NORTH/NORTHEAST
OF THE FORECAST AREA, WE'LL CONTINUE TO MONITOR THAT POTENTIAL
OVER THE DOMING DAYS.
KJB/RATZER
AVIATION /00Z TAFS THROUGH 06Z TUESDAY/
ISSUED AT 539 PM CST SUN DEC 15 2024
FORECAST CONCERNS INCLUDE...
LIFR/VLIFR CIGS/VIS THROUGH LATE MONDAY MORNING.
STRONG/GUSTY WESTERLY WINDS MONDAY AFTERNOON/EVENING.
DENSE FOG IS EXPECTED TO CONTINUE ACROSS MUCH OF NORTHWEST IL,
WEST OF THE CHICAGO TERMINALS, THROUGH MID MORNING MONDAY. ORD
WILL AGAIN TO BE ON THE EDGE OF THE DENSE FOG POTENTIAL AND
TRENDS WILL NEED TO BE MONITORED THIS EVENING. THE BEST CHANCE
OF VISIBILITIES 1/2SM OR LESS, FOR BOTH ORD/MDW, APPEAR TO BE
FROM SUNRISE THROUGH MID MORNING, AS A COLD FRONT MOVES ACROSS
THE AREA. VISIBILITIES SHOULD QUICKLY IMPROVE BEHIND THIS FRONT
WITH CIGS LIFTING INTO MVFR. THESE MVFR CIGS MAY SCATTER OUT BY
MONDAY EVENING, BUT LOW CONFIDENCE AT THIS TIME.
AREAS OF DRIZZLE WILL BE POSSIBLE INTO THE EARLY MORNING HOURS
WHERE DENSE FOG IS OCCURRING. LIGHT RAIN OR SCATTERED SHOWERS
ARE EXPECTED IN THE PREDAWN HOURS MONDAY MORNING WITH DRIZZLE
LIKELY UNTIL THE COLD FRONT MOVES THROUGH.
LIGHT SOUTH/SOUTHEAST WINDS WILL BECOME MORE SOUTHERLY BY
DAYBREAK THEN TURN TO THE SOUTHWEST AFTER SUNRISE, THEN SHIFT
WESTERLY BEHIND THE COLD FRONT. SPEEDS AND GUSTS WILL INCREASE
WITH GUSTS INTO THE MID TO PERHAPS UPPER 20KT RANGE. THE WINDS
WILL SLOWLY DIMINISH MONDAY EVENING BUT REMAIN GUSTY. CMS
LOT WATCHES/WARNINGS/ADVISORIES
IL...DENSE FOG ADVISORY UNTIL 9 AM CST MONDAY FOR ILZ003-ILZ004-
ILZ008-ILZ010-ILZ011-ILZ019.
DENSE FOG ADVISORY UNTIL 3 AM CST MONDAY FOR ILZ033-ILZ039.
IN...DENSE FOG ADVISORY UNTIL 3 AM CST /4 AM EST/ MONDAY FOR INZ010-
INZ011-INZ019.
LM...NONE.
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