807
FXUS63 KLOT 152139
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
339 PM CST SUN DEC 15 2024
KEY MESSAGES
- AREAS OF DENSE FOG AGAIN THIS EVENING THROUGH TOMORROW MORNING,
ESPECIALLY FOR LOCATIONS NEAR AND NORTHWEST OF I-55.
- 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.
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 /18Z TAFS THROUGH 00Z TUESDAY/
ISSUED AT 1203 PM CST SUN DEC 15 2024
LIFR CEILINGS AND IFR VISIBILITY AT TAF ISSUANCE WILL CONTINUE
TO SLOWLY IMPROVE, WITH SOME PERIODS OF MVFR CEILINGS AND VFR
VISIBILITY EXPECTED BY MID TO LATE EVENING. A LOW-LEVEL TROUGH
WILL THEN BRING A BAND OF SHOWERS ACROSS THE TERMINALS LATE
TONIGHT, FOLLOWED BY A PERIOD OF DZ WITH LIFR CEILINGS THROUGH
MID MORNING MONDAY. A COLD FRONT WILL THEN END PRECIP AND
QUICKLY RAISE CEILINGS INTO MVFR LEVELS LATE IN THE MORNING.
WINDS UNDER 10 KNOTS WILL FAVOR SSW THROUGH THIS EVENING, SSE
OVERNIGHT AND SSW MONDAY MORNING. WINDS WILL THEN SHIFT WSW AND
GUST OVER 25 KNOTS BEHIND THE FRONT LATE MORNING THROUGH THE
AFTERNOON.
KLUBER
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY UNTIL 3 PM CST THIS AFTERNOON FOR THE IL
AND IN NEARSHORE WATERS.
VISIT US AT WEATHER.GOV/CHICAGO
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