901
FXUS63 KLOT 190447
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1047 PM CST WED DEC 18 2024
KEY MESSAGES
- SNOW WILL MOVE ACROSS THE AREA THURSDAY EVENING INTO FRIDAY.
BEST CHANCES FOR SNOW ACCUMULATIONS EXIST NORTH OF I-80 AND
ESPECIALLY UP TOWARD THE WISCONSIN STATE LINE WITH UPWARDS OF
A COUPLE OF INCHES POSSIBLE.
- ACCUMULATING LAKE EFFECT SNOW WITH GUSTY NORTH WINDS IS
EXPECTED ACROSS NORTHWEST INDIANA FRIDAY NIGHT INTO SATURDAY
MORNING.
DISCUSSION
ISSUED AT 216 PM CST WED DEC 18 2024
THROUGH FRIDAY:
CONDITIONS ARE QUIET AND COOL OUT THERE THIS AFTERNOON FOLLOWING
LAST NIGHT'S BAND OF SNOW. TEMPERATURES ARE UP IN THE MIDDLE 30S
FOR MOST WHILE OUR NORTHWEST CWA HAS BEEN KEPT A FEW TO SEVERAL
DEGREES COOLER THANKS TO THE FRESH SNOWPACK. DESPITE
TEMPERATURES REMAINING BELOW FREEZING OUT THAT WAY, AREA WEBCAMS
SHOW THAT THE FILTERED SUNSHINE HAS BEGUN TO SLOWLY CHIP AWAY
AT SOME OF THE ACCUMULATION. SURFACE HIGH PRESSURE TO THE WEST
WILL PROPAGATE OVER CENTRAL IL TONIGHT BEHIND THE DEPARTING
UPPER TROUGH AXIS LEAVING US WITH LIGHT WINDS AND COOL
CONDITIONS WITH LOW TEMPERATURES IN THE LOWER AND MIDDLE 20S.
AN UPPER WAVE IS IN THE PROCESS OF CRASHING ONSHORE THE PNW
COAST THIS AFTERNOON. IT WILL RIDE THE US/CANADIAN BORDER INTO
THE HIGH PLAINS TONIGHT BEFORE DIVING SOUTHEASTWARD INTO THE
MIDWEST BY EARLY TOMORROW. THIS CLIPPER WILL PROVIDE US WITH OUR
NEXT CHANCE FOR ACCUMULATING SNOW TOMORROW AFTERNOON INTO
FRIDAY. THIS SYSTEM CAN SEEMINGLY GO ONE OF TWO WAYS; ALL GLOBAL
GUIDANCE HAS CONSISTENTLY BEEN TRACKING THE LOW PRESSURE CENTER
RIGHT ACROSS FAR NORTHERN IL AND ALONG THE IL/WI STATE LINE.
ALL ENSEMBLE SYSTEMS HEAVILY FAVOR SUCH A TRACK, AS DO A FEW OF
THE HIGH RES CAMPS THAT ARE STARTING TO STRETCH INTO THE PERIOD.
HOWEVER, THE RAP, HRRR, AND NAM ARE WANTING TO TAKE IT ACROSS
SOUTH-CENTRAL WI. THE DISCREPANT FACTOR IS A JET MAX EMBEDDED
ALONG THE BASE OF THE LOW LEVEL TROUGH. THESE MODELS WRAP THAT
LLJ UP FARTHER ALONG THE LEEWARD SIDE OF THE TROUGH STEERING THE
SURFACE LOW FARTHER TO THE NORTH THAN OTHER GUIDANCE.
DESPITE THIS UNCERTAINTY IN THE TRACK, DISTRIBUTION OF SNOW
ACCUMULATIONS RELATIVE TO THE LOW TRACK IS IN SURPRISINGLY GOOD
AGREEMENT. THE FARTHER SOUTH SOLUTIONS (WHICH WERE FAVORED IN
THIS FORECAST) CALL FOR MORE SNOW AREA-WIDE AND OVERALL LOWER
PROBABILITIES OF SEEING ANY RAIN MIX IN. TOTALS WITH SUCH A
TRACK ARE LOOKING LIKE AROUND AN INCH OR TWO ACROSS THE CHICAGO
AND ROCKFORD METRO AREAS WITH UPWARDS OF THREE INCHES PERHAPS IN
THE NORTH AND NORTHWEST SUBURBS. GENERALLY LESS THAN AN INCH
WOULD BE EXPECTED SOUTH AND SOUTHWEST OF THE CHICAGO METRO. WE
MAY FIND A PERIOD OF LIGHT RAIN/WINTRY MIX OR POSSIBLY EVEN A
LITTLE BIT OF FREEZING RAIN, PRIMARILY DURING THE EVENING, AS
THE STORM'S DRY SLOT WORKS IN AND CLOUD ICE COULD BECOME SCARCE.
THE HIGHEST PROBS FOR SEEING ANY MIXED BAG STUFF ARE NEAR AND
SOUTH OF I-88 WHILE AREAS NORTH ARE MORE LIKELY TO REMAIN SNOW.
THE FARTHER NORTH SOLUTIONS FAVOR LESS THAN AND UP TO AN INCH OF
ACCUMULATION AND A BETTER POTENTIAL FOR LIQUID PRECIP. TRENDS
IN GUIDANCE WILL HAVE TO BE MONITORED CLOSELY WHILE THERE ARE NO
REAL APPARENT TRENDS TO CLING ONTO AS OF YET.
MOST OF THE AREA WILL BE DRY BY THE END OF FRIDAY MORNING. AS
THE COLD BACKSIDE OF THE LOW WORKS OVER THE LAKE, WE'RE LIKELY
TO SEE SOME LAKE EFFECT SNOW SHOWERS GO UP DURING THE DAY.
LAKE-EFFECT MAY FALL ON AREAS ROUGHLY EAST OF I-57 AND I-355
DURING THE AFTERNOON, BUT THE POTENTIAL SHOULD REALLY FAVOR
NORTHWEST INDIANA, ESPECIALLY DURING THE EVENING. ADDITIONALLY,
FORECAST SOUNDINGS ARE GENERATING A SHALLOW CONDITIONALLY
UNSTABLE LAYER AROUND THE CWA IN THE AFTERNOON THAT LOOKS
SUPPORTIVE OF FLURRIES. SATURATION REMAINS A QUESTION THOUGH SO
A FORMAL MENTION OF FLURRIES WAS LEFT OUT OF THE FORECAST FOR
NOW. FINALLY, CONDITIONS LOOK TO GET PRETTY BREEZY IN THE WAKE
OF THE CLIPPER. GUSTS DURING THE DAY ON FRIDAY WILL GET INTO THE
25 TO 30 MPH RANGE, ALTHOUGH THERE IS NOTABLE SUPPORT FOR 35 TO
EVEN NEAR 40 MPH GUSTS AT TIMES, ESPECIALLY DURING THE MORNING.
DOOM
FRIDAY NIGHT THROUGH WEDNESDAY:
BEHIND FRIDAY'S SYSTEM, GUSTY NORTHERLY LOW-LEVEL FLOW FRIDAY
NIGHT COMBINED WITH INVERSION HEIGHTS GROWING TO AROUND 7KFT AND
MARGINAL SST-850HPA DELTA TEMPS WILL SUPPORT A PERIOD OF LIGHT
TO BRIEFLY MODERATE LES INTO NORTHWEST INDIANA AND INCLUDING
AROUND THE IL/IN LINE. WOULDN'T BY SURPRISED TO SEE A FEW INCHES
OF SNOW DURING THIS PERIOD, ESPECIALLY IF A DOMINANT BAND OR
TWO REMAINS STATIONARY FOR SEVERAL HOURS.
DRIER AIR ADVECTING IN FROM THE NORTHWEST AND LOWERING
INVERSION HEIGHTS SHOULD DIMINISH LES POTENTIAL THROUGH THE DAY
ON SATURDAY, WITH SOME SPARSE LIGHT LES SHOWERS POSSIBLY
SWINGING CLOCKWISE ACROSS NORTHEAST ILLINOIS SATURDAY NIGHT AS A
SURFACE RIDGE PASSES TO THE NORTH.
THERE IS FAIRLY GOOD AGREEMENT IN GUIDANCE THAT A MID-LEVEL
WAVE WILL BEGIN TO CARVE OUT A DEAMPLIFYING WESTERN RIDGE LATE
THIS WEEKEND INTO EARLY NEXT WEEK. THIS WAVE IS PROGGED TO SHIFT
OVER THE WESTERN GREAT LAKES AS A STREAM OF MODEST LOW-LEVEL
MOISTURE ADVECTS NORTHEASTWARD AHEAD OF AN ASSOCIATED COLD
FRONT. BROAD LOW-LEVEL ISENTROPIC ASCENT WILL LIKELY PRODUCE AT
LEAST LIGHT PRECIP ACROSS THE AREA THROUGH THE DAY. WHILE PRECIP
TYPE SHOULD FALL AS LIQUID AMID STRONG WAA ALOFT, A LAG IN
SURFACE WARMING RAISES SOME FREEZING RAIN CONCERNS ACROSS
NORTHERN ILLINOIS AND NORTHWEST INDIANA MONDAY MORNING. A LOT OF
MOVING PARTS AT THIS POINT, BUT SOMETHING TO KEEP AN EYE ON
OVER THE COMING DAYS. HEADING INTO CHRISTMAS, A SOUTHERN GREAT
PLAINS TROUGH WILL LIKELY BRING AN EXPANSIVE AREA OF WET-
WEATHER ACROSS THE OHIO VALLEY AND POSSIBLY AS FAR NORTH AS THE
SOUTHERN GREAT LAKES. TEMPS SHOULD BE SEASONABLY MILD BY THIS
TIME, WITH ANY PRECIP LIKELY TO FALL AS RAIN.
KLUBER
AVIATION /06Z TAFS THROUGH 12Z FRIDAY/
ISSUED AT 1047 PM CST WED DEC 18 2024
AVIATION FORECAST CONCERNS FOR 06Z TAFS:
- MVFR CIGS AROUND 3000 FT MAY SCATTER OUT FOR A TIME THURSDAY
MORNING.
- WINDS BECOME SOUTH-SOUTHEAST AND GRADUALLY INCREASE MID-LATE
MORNING WITH OCCASIONAL GUSTS 20-25 KT IN THE AFTERNOON.
- LIGHT SNOW DEVELOPS BY EARLY-MID AFTERNOON AT KRFD, AND TOWARD
SUNSET FOR CHICAGO TERMINALS. MVFR/BRIEF IFR CONDITIONS
POSSIBLE INTO THE EVENING, WITH SOME ACCUMULATIONS.
- SNOW SHOWERS LINGER OVERNIGHT WITH MVFR/IFR CONDITIONS. WINDS
EVENTUALLY SHIFT WEST-NORTHWEST AFTER MIDNIGHT.
SURFACE HIGH PRESSURE RIDGE WILL DRIFT EAST ACROSS THE TERMINALS
OVERNIGHT, ALLOWING WINDS TO BECOME LIGHT/VARIABLE BEFORE
SETTLING TO A SSE DIRECTION THURSDAY MORNING. AN AREA OF LOW
PRESSURE WILL THEN TRACK INTO THE REGION FROM THE NORTHWEST
THROUGH THURSDAY NIGHT, WITH THE SOUTH-SOUTHEAST WINDS GRADUALLY
INCREASING AND BECOMING AT LEAST OCCASIONALLY GUSTY AROUND 20
KTS BY THURSDAY AFTERNOON AS THE PRESSURE GRADIENT TIGHTENS
MVFR STRATUS IN PLACE ACROSS THE AREA LATE THIS EVENING MAY
SCATTER OUT FOR A TIME EARLY THURSDAY, BEFORE REDEVELOPING LATE
MORNING/AFTERNOON AHEAD OF THE APPROACHING LOW PRESSURE SYSTEM.
LIGHT SNOW WILL ALSO LIKELY DEVELOP BY EARLY AFTERNOON INTO
KRFD AND BY LATE AFTERNOON/SUNSET INTO THE CHICAGO AREA. A
PERIOD OF LIGHT SNOW WITH SOME ACCUMULATION (AROUND AN INCH OR
SO) IS LIKELY THURSDAY EVENING, BEFORE TAPERING TO SNOW SHOWERS
LATE IN THE EVENING. BRIEF IFR CONDITIONS ARE POSSIBLE DURING
THE EVENING WITH THE LIGHT SNOW.
THE SURFACE LOW PRESSURE CENTER IS FORECAST TO MOVE ACROSS THE
FORECAST AREA LATE THURSDAY NIGHT. THIS MAY MAKE FOR A PERIOD OF
SOMEWHAT VARIABLE WIND DIRECTIONS, BUT WINDS SHOULD EVENTUALLY
TURN NORTHWEST (MORE NORTHERLY TOWARD MORNING) IN ITS WAKE.
THERE MAY ALSO BE A PERIOD OF LOWER (IFR) CIGS AND SOME FOG IN
THE VICINITY OF THE LOW CENTER, WITH SOME PERSISTENT LIGHT
SNOW/FLURRIES.
RATZER
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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