608
FXUS63 KLOT 201815
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1215 PM CST FRI DEC 20 2024
KEY MESSAGES
- PERIODS OF SNOW EARLY THIS MORNING, WITH ACCUMULATIONS UP TO 1
INCH POSSIBLE. UNTREATED SURFACES EXPECTED TO BECOME SNOW
COVERED AND SLICK.
- LAKE EFFECT SNOW SHOWERS LATE MORNING/EARLY AFTERNOON FOR
NORTHEAST IL, THEN MOVING INTO NORTHWEST IN BY MID/LATE
AFTERNOON. SNOWFALL TOTALS 1-3 INCHES POSSIBLE.
- NORTHERLY WIND GUSTS TO 35 MPH THROUGH THIS AFTERNOON.
- WARMER TEMPS WITH PERIODIC LOW CHANCES FOR RAIN NEXT WEEK.
DISCUSSION
ISSUED AT 317 AM CST FRI DEC 20 2024
THROUGH SATURDAY:
LOW PRESSURE WILL BE MOVING SOUTHEAST OF THE AREA EARLY THIS
MORNING AND AS IT DOES, COOLER AIR WILL SETTLE ACROSS THE AREA
ENDING ANY MIXED PRECIP TYPE CONCERNS. AS A WAVE ROTATES AROUND
THE DEPARTING LOW, SNOW IS EXPECTED TO INCREASE IN COVERAGE
ACROSS NORTHERN IL IN THE PREDAWN HOURS AND CONTINUE ACROSS MOST
OF THE AREA DURING THE MORNING COMMUTE, ENDING FROM NORTHWEST
TO SOUTHEAST THROUGH THE MID/LATE MORNING. SOME PERIODS OF
MODERATE SNOW WILL BE POSSIBLE DURING THIS TIME PERIOD. WHILE
NEW SNOWFALL AMOUNTS WILL LIKELY BE AN INCH OR LESS, AS TEMPS
SLOWLY DROP BELOW FREEZING, UNTREATED SURFACES ARE EXPECTED TO
BECOME SNOW COVERED AND SLICK.
A BAND OF LAKE EFFECT SNOW IS EXPECTED TO DEVELOP LATE THIS
MORNING AND STEADILY MOVE EAST/SOUTHEAST ACROSS NORTHEAST IL
FROM LATE MORNING THROUGH EARLY AFTERNOON AND THEN SHIFT INTO
NORTHWEST IN. THERE IS STILL SOME UNCERTAINTY REGARDING HOW FAR
INLAND THIS BAND MAY REACH ACROSS NORTHEAST IL. WHEREVER THE
BAND DOES SET-UP, A SHORT PERIOD OF MODERATE TO PERHAPS HEAVY
SNOW WILL BE POSSIBLE WITH A QUICK INCH OR TWO OF ACCUMULATION.
ONCE IT SHIFTS INTO NORTHWEST IN, A BIT LONGER RESIDENCE TIME
MAY LEAD TO HIGHER SNOW TOTALS THOUGH IT WILL STILL BE SLOWLY
MOVING EAST. SNOWFALL TOTALS IN THE 1-3 INCH RANGE SEEM
REASONABLE BUT THERE COULD BE LOCALLY HIGHER AMOUNTS. THE LAKE
EFFECT SNOW SHOWERS MAY CONTINUE INTO SATURDAY ACROSS NORTHEAST
PORTER COUNTY BUT CONFIDENCE IS LOW.
AS THE SURFACE LOW DEPARTS AND THE GRADIENT TIGHTENS, WINDS WILL
INCREASE AROUND/JUST AFTER DAYBREAK WITH A PERIOD OF GUSTS INTO
THE 35 MPH RANGE EXPECTED. THESE NORTHERLY WINDS WILL REMAIN
GUSTY INTO THE AFTERNOON THOUGH SOME DECREASE IS EXPECTED BY
MID/LATE AFTERNOON AND THEN WIND SPEEDS AND GUSTS SHOULD
DIMINISH QUICKLY THIS EVENING.
TEMPS TODAY ARE A BIT TRICKY, MUCH OF THE GUIDANCE IS TRYING TO
WARM TEMPS THROUGH MIDDAY BEFORE FALLING LATER THIS AFTERNOON
AND HAVE TEMPS WARMING A DEGREE OR TWO FROM THIS MORNING'S LOWS
BUT TEMPS MAY BE STEADY OR EVEN BEGIN TO SLOWLY FALL THIS
AFTERNOON. LOWS TONIGHT EXPECTED TO DIP INTO THE LOW TEENS
ACROSS NORTHWEST IL, PERHAPS A FEW SINGLE DIGITS IN THE USUAL
COOL SPOTS AND THEN HIGHS ONLY REBOUND INTO THE 20S FOR HIGHS ON
SATURDAY. CMS
SATURDAY NIGHT THROUGH THURSDAY:
A LARGE SCALE PATTERN CHANGE TO MILD WEATHER IS EXPECTED ACROSS
THE CONUS FOR THE HOLIDAY WEEK. THIS WILL TAKE PLACE BY EARLY NEXT
WEEK AS A STRONG AND PERSISTENT ZONALLY ORIENTED MID-LATITUDE
PACIFIC JET DEVELOPS ALONG THE SOUTHERN PERIPHERY OF ANOMALOUSLY
DEEP TROUGHING ACROSS THE GULF OF ALASKA. THIS PARTICULAR PACIFIC
PATTERN WILL FAVOR PROGRESSIVE AND MILD WEST-TO-EAST MOVING
WEATHER SYSTEMS ACROSS THE CONUS THROUGH THE HOLIDAY WEEK. WITH
COLD AIRMASS EXPECTED TO BE SHUNTED WELL NORTH OF THE REGION, THE
PROSPECTS FOR A WHITE CHRISTMAS THIS YEAR ARE LOOKING RATHER
BLEAK.
AS THIS WEATHER PATTERN SHIFT TAKES PLACE, THE FIRST IN A SERIES
OF QUICK MOVING PACIFIC IMPULSES IS EXPECTED TO SLIDE EASTWARD
INTO THE WESTERN GREAT LAKES ON MONDAY. MOST OF THE PRECIPITATION
WITH THIS IMPULSE LOOKS TO LARGELY REMAIN NORTH AND EAST OF OUR
AREA. NEVERTHELESS, THE PASSAGE OF A WEAK COLD FRONT ON MONDAY
SUPPORTS THE MENTION FOR SOME LOW (20-40%) CHANCES FOR RAIN MONDAY
INTO MONDAY EVENING. THE FRONT, AND THE MAIN THREAT OF RAIN,
SHOULD SETTLE TO OUR SOUTH ACROSS PARTS OF DOWNSTATE IL AND IN
FOR TUESDAY. LOW CHANCES (20% OR LESS) FOR RAIN WILL CONTINUE
LOCALLY INTO CHRISTMAS DAY. HOWEVER, WITH THE NEXT PACIFIC WAVE
EXPECTED TO SLIDE ACROSS THE OZARKS, OUR AREA MAY LARGELY REMAIN
DRY FOR CHRISTMAS. THIS NEARLY CONTINUOUS PATTERN OF PACIFIC
IMPULSES IS LIKELY TO PERSIST THROUGH THE END OF PERIOD.
THE MILD WEATHER PATTERN NEXT WEEK WILL SUPPORT WELL ABOVE NORMAL
TEMPERATURES IN THE 40S FOR DAYTIME HIGHS. WELL ABOVE NORMAL
OVERNIGHT LOW TEMPERATURES ARE ALSO LIKELY IN THIS PATTERN.
KJB
AVIATION /18Z TAFS THROUGH 00Z SUNDAY/
ISSUED AT 1215 AM CST FRI DEC 20 2024
FORECAST CONCERNS FOR THE TERMINALS...
- LAKE EFFECT SNOW RESULTING IN REDUCED VISIBILITIES AT GYY AND
POSSIBLY ORD AND MDW
- MVFR CEILINGS NEAR THE LAKE THIS AFTERNOON BECOMING VFR
OVERNIGHT INTO SATURDAY MORNING
- BREEZY NORTH-NORTHWEST WINDS GUSTING 25-30 KTS THIS AFTERNOON
AN UPPER DISTURBANCE CONTINUES TO PIVOT OVER THE GREAT LAKES
WHICH HAS ALLOWED FOR THE DEVELOPMENT OF A BAND OF LAKE EFFECT
SNOW ACROSS CENTRAL LAKE MICHIGAN. THIS BAND IS EXPECTED TO
PIVOT SOUTHWARD THIS AFTERNOON AND BEGIN TO IMPACT PORTIONS OF
NORTHEAST IL AND EVENTUALLY NORTHWEST IN THIS EVENING THROUGH
THE EARLY OVERNIGHT HOURS. WHILE CONFIDENCE REMAINS HIGH ON THE
GENERAL TIMING AND LAKE EFFECT SNOW OCCURRING, THE INLAND EXTENT
OF THE BAND, ESPECIALLY NEAR ORD AND MDW, REMAINS UNCERTAIN.
THAT SAID, HAVE DECIDED TO MAINTAIN THE PROB30 FOR SNOW SHOWERS
AT ORD AND MDW BETWEEN 18Z AND 21Z WHICH SEEMS REASONABLE AT
THIS TIME. REGARDLESS, AREAS NEAR THE LAKE (INCLUDING GYY) WILL
SEE IFR VISIBILITIES (AROUND 1SM) ASSOCIATED WITH THE LAKE
EFFECT SNOW AND ACCUMULATIONS IN THE 1-2 INCH RANGE THOUGH
LOCALLY HIGHER AMOUNTS UP TO 3 INCHES ARE POSSIBLE IN NORTHWEST
IN. SINCE ORD AND MDW MAY REMAIN JUST OUTSIDE OF THE MAIN BAND,
IMPACTS AT THESE TERMINALS ARE EXPECTED TO BE LESS WITH 2-3
MILE VISIBILITIES AND MAYBE A COUPLE TENTHS TO AROUND HALF AN
INCH OF ACCUMULATION.
AWAY FROM THE LAKE AND LAKE EFFECT SNOW, DRY CONDITIONS ARE
EXPECTED TO PREVAIL THROUGH THE FORECAST PERIOD. WHILE MOST
AREAS WILL SEE SKIES CONTINUING TO SCATTER OUT THIS AFTERNOON,
THOSE NEAR THE LAKE WILL CONTINUE TO SEE MVFR CEILINGS PREVAIL
THROUGH THIS EVENING BEFORE THE LAKE EFFECT CLOUDS SHIFT EAST
INTO NORTHWEST AND NORTHERN IN ALLOWING VFR CONDITIONS TO RETURN
LATE TONIGHT INTO SATURDAY MORNING. THE EXCEPTION HOWEVER, WILL
BE AT GYY WERE MVFR CEILINGS LOOK TO PREVAIL THROUGH THE END OF
THE FORECAST PERIOD.
FINALLY, WINDS TODAY WILL REMAIN BREEZY OUT OF THE NORTH-
NORTHWEST WITH GUSTS IN THE 25-30 KT RANGE THROUGH EARLY
EVENING. HOWEVER, WINDS COULD VERY BETWEEN A 350-010 DIRECTION
AT ORD, MDW, AND GYY WITH THE LAKE EFFECT SNOW THIS AFTERNOON. GUSTS
ARE EXPECTED TO DIMINISH AFTER SUNSET WITH 5-10 KT WINDS
REMAINING THROUGH THE CONCLUSION OF THE PERIOD.
YACK
MARINE
ISSUED AT 245 AM CST FRI DEC 20 2024
A PERIOD OF NORTHERLY GALE FORCE WINDS TO 35 KT MAY OCCUR IN
THE ILLINOIS AND INDIANA NEARSHORE WATERS OF LAKE MICHIGAN
THIS MORNING INTO EARLY THIS AFTERNOON AS A LOW PRESSURE SYSTEM
TRACKS ACROSS THE LOWER GREAT LAKES. OWING TO LOW CONFIDENCE ON
THE FREQUENCY OF GALE FORCE GUSTS, WILL WITHHOLD ISSUING A GALE
WARNING IN THIS FORECAST PACKAGE. HOWEVER, WILL ADVERTISE A FEW
GALE FORCE GUSTS IN THE NEARSHORE AND SMALL CRAFT ADVISORY
PRODUCTS.
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 9 AM CST SATURDAY FOR THE IL
NEARSHORE WATERS.
SMALL CRAFT ADVISORY UNTIL 3 PM CST SATURDAY FOR THE IN
NEARSHORE WATERS.
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