227
FXUS63 KLOT 151119
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
519 AM CST FRI NOV 15 2024
KEY MESSAGES
- LOW CHANCE (20%) OF SHOWERS SATURDAY NIGHT INTO SUNDAY.
- PERIODS OF RAIN EXPECTED MONDAY NIGHT.
- A COOLER WEATHER PATTERN, POTENTIALLY ACCOMPANIED BY PERIODIC
SHOWERS, LOOKS TO MATERIALIZE MID-LATE NEXT WEEK.
DISCUSSION
ISSUED AT 220 AM CST FRI NOV 15 2024
THROUGH SATURDAY:
BROAD UPPER RIDGING ACROSS THE CENTRAL CONUS WILL EDGE EASTWARD
ACROSS THE AREA THROUGH SATURDAY. THE MAIN FORECAST CONCERN
DURING THIS PERIOD WILL REVOLVE AROUND CLOUD COVER TRENDS AS AN
EXPANSIVE AREA OF STRATUS OVER THE WESTERN GREAT LAKES REMAINS
TRAPPED UNDER A STOUT SUBSIDENCE INVERSION AHEAD OF THE RIDGE.
THOUGH CLOUD DEPTHS HAVE NOT BEEN ALL THAT IMPRESSIVE, WEAK LOW-
LEVEL ISENTROPIC ASCENT LAST EVENING RESULTED IN PATCHES OF
LIGHT DRIZZLE/MIST. RECENT RADAR TRENDS AND DIMINISHING FORCING
(PER GUIDANCE) EARLY THIS MORNING SUGGEST REMAINING DRIZZLE
SHOULD END PRIOR TO SUNRISE. MEANWHILE, THE WESTERN EDGE OF THE
STRATUS HAS BEEN STEADILY DRIFTING EASTWARD THROUGH THE NIGHT,
REACHING JUST WEST OF THE MISSISSIPPI RIVER AS OF 2AM.
EXPECTATIONS ARE THAT SOME CLEARING SHOULD REACH AREAS WEST OF
I-39 AFTER SUNRISE, BUT INCREASING DIURNAL SUPPORT FROM WEAK
MIXING UNDER THE STRONG INVERSION WILL LIKELY MAINTAIN A DECENT
STRATUS DECK FARTHER EAST ACROSS THE CWA THROUGH MUCH OF THE
DAY.
AS THE SURFACE RIDGE CROSS THE FORECAST AREA LATE THIS
AFTERNOON AND EVENING, SHALLOW LOW-LEVEL ISENTROPIC ASCENT AMID
VEERING WINDS WILL LIKELY MAINTAIN THE STRATUS DECK WHILE
ULTIMATELY EXPANDING BACK TO THE NORTHWEST THROUGH SATURDAY.
OPTED TO LEAN TOWARD COLDER GUIDANCE WITH DAYTIME HIGHS TODAY
AND SATURDAY, BUT GIVEN HOW GUIDANCE USUALLY STRUGGLES WITH THE
EVOLUTION OF SHALLOW STRATUS IN THE COOL SEASON, HIGH
TEMPERATURES COULD EASILY OVERPERFORM IF CLOUDS ERODE QUICKER
THAN EXPECTED. ADDITIONALLY, ANY SUBSTANTIAL CLEARING THAT
PERSISTS TONIGHT MAY FOSTER FOG DEVELOPMENT WITHIN THE PASSING
RIDGE.
KLUBER
SATURDAY NIGHT THROUGH THURSDAY:
SURFACE LOW PRESSURE IS FORECAST TO LIFT NORTHEAST FROM THE
DAKOTAS INTO ONTARIO SATURDAY NIGHT, IN RESPONSE TO A FAIRLY
STRONG SHORT WAVE TRACKING NORTH OF THE REGION. WHILE THE BEST
LARGE-SCALE FORCING REMAINS NORTH OF THE FORECAST AREA,
SOUTHWESTERLY LOWER AND MID-LEVEL FLOW DOES LOOK TO PROVIDE
MODEST ISENTROPIC ASCENT AND SHALLOW MOISTURE ADVECTION ACROSS
THE FORECAST AREA LATER SATURDAY NIGHT INTO SUNDAY AHEAD OF THE
SYSTEM'S TRAILING COLD FRONT. GUIDANCE CONTINUES TO DEPICT SOME
SPOTTY QPF PARTICULARLY LATER SUNDAY NIGHT, AND HAVE MAINTAINED
SLIGHT CHANCE (15-20%) POPS ESPECIALLY ALONG/NORTHWEST OF THE
I-55 CORRIDOR FOR SOME LIGHT RAIN. THE FRONT COMPLETES ITS
TRANSIT OF THE CWA SUNDAY, THOUGH WITH THE BULK OF THE BETTER
MOISTURE ADVECTION SHIFTING EAST OF THE AREA, FROPA LOOKS TO BE
LARGELY DRY. WEAK SURFACE HIGH PRESSURE DEVELOPS ACROSS THE AREA
BEHIND THE FRONT SUNDAY NIGHT.
ATTENTION THEN TURNS TO ANOTHER MID-LEVEL DISTURBANCE EMERGING
FROM NORTHERN MEXICO SUNDAY NIGHT. GUIDANCE IS IN GOOD AGREEMENT
IN LIFTING THIS NEGATIVE-TILT SHORT WAVE NORTHEAST INTO EASTERN
KANSAS BY LATE MONDAY, THEN BECOMING STACKED ABOVE ITS
OCCLUDING SURFACE LOW AS IT CONTINUES TO LIFT ACROSS IOWA AND
INTO THE UPPER MISSISSIPPI VALLEY INTO TUESDAY. FOR OUR FORECAST
AREA, SHOWER CHANCES DEVELOP AGAIN ON MONDAY AHEAD OF THE
SYSTEM'S APPROACHING WARM FRONT, ESPECIALLY ACROSS OUR IL
COUNTIES. MORE WIDESPREAD RAIN BECOMES LIKELY MONDAY NIGHT
HOWEVER, AS THE MAIN MID-LEVEL VORT AND LOW-LEVEL OCCLUDED FRONT
MOVE INTO THE AREA. RAIN SHOULD TAPER OFF TO SHOWERS OR DRIZZLE
TUESDAY AS THE MID-LEVEL DRY SLOT SPREADS IN ALOFT. DAYTIME
TEMPERATURES ARE EXPECTED TO BE IN THE 50S TO AROUND 60 THROUGH
TUESDAY.
PATTERN EVOLUTION BECOMES MORE COMPLEX BY THE MIDDLE OF NEXT
WEEK, AS LONGER-RANGE ENSEMBLES INDICATE ANOTHER DIGGING SHORT
WAVE MOVES INTO THE PLAINS, EVENTUALLY PHASING WITH THE OCCLUDED
SYSTEM OVER THE UPPER MIDWEST. THE GENERAL GEFS/EPS AND CMC
ENSEMBLE CONSENSUS DEPICTS A RESULTING CLOSED UPPER LOW AND DEEP
(SUB-1000 MB) SURFACE LOW MOVING THROUGH THE REGION
WEDNESDAY/THURSDAY. THERE IS CONSIDERABLE SPREAD AMONGST
INDIVIDUAL ENSEMBLE MEMBERS AND DETERMINISTIC RUNS HOWEVER, AND
GIVEN THIS IS STILL OUT IN THE DAYS 6-7 TIME FRAME IT'S STILL
TOO EARLY TO GET TOO SPECIFIC WITH THE DETAILS. NBM BLENDED
GUIDANCE REMAINS WARM ENOUGH WITH LOW-LEVEL PROFILES TO REMAIN
ALL LIQUID PRECIPITATION, THOUGH A TREND TOWARD COOLER
TEMPERATURES IS EXPECTED IN THE WAKE OF THE SYSTEM BY THE END OF
NEXT WEEK.
RATZER
AVIATION /12Z TAFS THROUGH 18Z SATURDAY/
ISSUED AT 519 AM CST FRI NOV 15 2024
AVIATION FORECAST CONCERNS FOR THE 12Z TAFS:
- MVFR CEILINGS LINGER THROUGH MUCH OF THE PERIOD. BEST
POTENTIAL FOR A PERIOD OF SCT CONDITIONS IS AT KRFD LATER
TODAY/THIS EVENING.
EXTENSIVE MVFR STRATUS DECK LINGERS ACROSS THE WESTERN GREAT
LAKES REGION EARLY THIS MORNING, IN THE WAKE OF THE LOW PRESSURE
SLOWLY DEPARTING TO OUR EAST. CEILINGS WERE GENERALLY IN THE
2000-2500 FOOT RANGE ACROSS NORTHERN IL/SOUTHERN WI, THOUGH
THERE HAVE BEEN SOME RELATIVELY PERSISTENT PATCHES BETWEEN
1500-1900 FT OVER THE CHICAGO METRO. IR SATELLITE IMAGERY SHOWS
THE TRAILING EDGE OF THE STRATUS WAS FROM WESTERN IL NORTHWARD
ALONG THE MISSISSIPPI RIVER, MAKING ONLY VERY SLOW EASTWARD
PROGRESS (WITH LIFR/VLIFR FOG WHERE IT HAD CLEARED OUT ACROSS
EASTERN IA). VARIOUS MODEL GUIDANCE SUGGESTS CEILINGS MAY
SCATTER OUR FOR A TIME LATER TODAY AND THIS EVENING FOR KRFD,
THOUGH WITH SCATTERING LESS LIKELY ACROSS THE CHICAGO TERMINALS
GIVEN SHALLOW INVERSION HEIGHTS AND WEAK MIXING.
LIGHT WEST-NORTHWEST TO NORTHWEST SURFACE WINDS WILL EVENTUALLY
FLOP OVER TO AN EASTERLY DIRECTION BY EARLY THIS EVENING, AS
SURFACE HIGH PRESSURE DRIFTS EAST ACROSS THE AREA. WINDS THEN
WILL BECOME SOUTH-SOUTHEAST SATURDAY MORNING AND INCREASE
SLIGHTLY, PERHAPS 8-10 KTS BY THE 18Z END OF THE KORD/KMDW
FORECASTS.
RATZER
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
VISIT US AT WEATHER.GOV/CHICAGO
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page