162
FXUS63 KLOT 211720
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1120 AM CST SAT DEC 21 2024
KEY MESSAGES
- CHANCE (30%) FOR LAKE EFFECT SNOW SHOWERS TODAY WITH MINOR
SNOW ACCUMULATIONS ACROSS LAKE AND PORTER COUNTIES IN
NORTHWEST IN.
- 20% CHANCE OF LIGHT FREEZING DRIZZLE/DRIZZLE LATE SUNDAY NIGHT
THROUGH EARLY MONDAY MORNING.
- TURNING MILD, WITH ON-AND-OFF CHANCES FOR PERIODS OF WET
WEATHER DURING THE HOLIDAY WEEK.
DISCUSSION
ISSUED AT 303 AM CST SAT DEC 21 2024
THROUGH SUNDAY:
LAKE EFFECT SNOW SHOWERS WILL CONTINUE TO BE POSSIBLE TODAY
ACROSS PORTER AND NORTHEAST LAKE COUNTIES THOUGH THERE IS QUITE
A BIT OF UNCERTAINTY REGARDING HOW ORGANIZED OR PERSISTENT THE
LAKE EFFECT MAY BECOME. AS HIGH PRESSURE BUILDS ACROSS THE
REGION THIS EVENING, LAKE EFFECT SNOW SHOWERS MAY BE CONFINED TO
THE OPEN WATERS. HAVE CONTINUED WITH CHANCE POPS FOR NOW ENDING
EARLY THIS EVENING. NOT EXPECTING ANY LAKE EFFECT SNOW SHOWERS
TO MAKE IT BACK TO THE IL SHORE TONIGHT.
NORTHWEST WINDS GENERALLY UNDER 10 MPH WILL CONTINUE THROUGH
LATE THIS AFTERNOON. AS THE HIGH MOVES ACROSS THE AREA THIS
EVENING, WINDS WILL BECOME CALM FOR MOST AREAS THEN SHIFT TO
LIGHT SOUTHEAST OVERNIGHT. SOUTHERLY WINDS MAY GUST INTO THE
20-25 MPH RANGE SUNDAY AFTERNOON.
TEMPS WILL ONLY WARM BACK INTO THE MID/UPPER 20S TODAY, POSSIBLY
ONLY LOWER 20S ACROSS THE NORTHWEST CWA. TEMPS ARE EXPECTED TO
QUICKLY DROP THIS EVENING, POSSIBLY INTO THE LOWER TEENS AND
THEN LIKELY BECOME STEADY OVERNIGHT. HIGHS ON SUNDAY WILL BE
BACK INTO THE LOWER 30S. CMS
SUNDAY NIGHT THROUGH FRIDAY:
ANOMALOUSLY DEEP TROUGHING ACROSS THE GULF OF ALASKA IS
EXPECTED TO FOSTER A STRONG AND PERSISTENT ZONALLY ORIENTED MID-
LATITUDE UPPER JET ACROSS THE PACIFIC THROUGH MUCH OF THE
PERIOD. THIS WEATHER PATTERN WILL ESSENTIALLY FLOOD MUCH OF THE
CONUS WITH MILD PACIFIC ORIENTED WEATHER SYSTEMS THROUGH THE
PERIOD. WITH ANY REAL COLD AIRMASSES EXPECTED TO BE SHUNTED WELL
NORTH OF THE REGION, THE PROSPECTS FOR A WHITE CHRISTMAS
CONTINUE TO LOOK BLEAK.
THE FIRST IN A SERIES OF QUICK MOVING PACIFIC IMPULSES TRACKING
EASTWARD TOWARDS THE WESTERN GREAT LAKES SUNDAY NIGHT INTO
MONDAY WILL BRING AN ASSOCIATED COLD FRONT ACROSS OUR AREA
DURING THE DAY ON MONDAY. PRIOR TO ITS PASSAGE, A BROAD REGION
OF ISENTROPIC UPGLIDE (WARM AIR ADVECTION) IS EXPECTED TO
QUICKLY MOISTEN THE LOW-LEVEL AIRMASS. THIS CERTAINLY LOOKS TO
SUPPORT THE DEVELOPMENT OF A LOW STRATUS DECK SUNDAY NIGHT INTO
MONDAY MORNING, AND MAY ALSO SUPPORT A PERIOD OF DRIZZLE AND/OR
FREEZING DRIZZLE. CONFIDENCE ON THE EXTENT OF FREEZING DRIZZLE
REMAINS OF LOW CONFIDENCE AT THIS TIME. HOWEVER, WITH SURFACE
TEMPERATURES EXPECTED TO BE HOVERING AROUND, OR JUST BELOW,
FREEZING FOR A PERIOD LATE SUNDAY NIGHT INTO EARLY MONDAY
MORNING, WE CANNOT RULE OUT THE POSSIBILITY FOR SOME FREEZING
PRECIPITATION. THE MAIN CHANGE TO THE FORECAST AT THIS TIME WAS
TO ADD IN THE MENTION OF DRIZZLE AND FREEZING DRIZZLE BEGINNING
SUNDAY NIGHT AND PERSISTING IT INTO EARLY MONDAY MORNING.
TEMPERATURES SHOULD WARM ABOVE FREEZING THROUGH THE MORNING ON
MONDAY, SO THE THREAT FOR FREEZING PRECIPITATION SHOULD COME TO
A QUICK END.
THE COLD FRONT MOVING ACROSS THE AREA MONDAY AFTERNOON IS
EXPECTED TO SETTLE SOUTH OF OUR AREA ON TUESDAY. WITH NO REAL PUSH
OF COLD AIR IN ITS WAKE, TEMPERATURES WILL REMAIN SEASONABLY MILD
(IN THE 30S TO AROUND 40) ON TUESDAY. WHILE TUESDAY IS LOOKING TO
BE DRY, THERE WILL BE PERIODIC CHANCES FOR RAIN FROM CHRISTMAS
DAY THROUGH THE REMAINDER OF THE HOLIDAY WEEKEND. WHILE IT WILL
NOT BE RAINING CONSTANTLY DURING THIS PERIOD, A SERIES OF AT LEAST
3 TO 4 ADDITIONAL PACIFIC IMPULSES ARE LIKELY TO TRAVERSE THE
CENTRAL PART OF THE COUNTRY AND RESULT IN SOME PERIODS OF
INCLEMENT WEATHER THROUGH THE SECOND HALF OF THE WEEK.
TEMPERATURES WILL REMAIN MILD TO UNSEASONABLY MILD (40S TO NEAR
50 DURING THE DAY AND 30S TO AROUND 40 AT NIGHT), SO WINTRY
PRECIPITATION IS NOT EXPECTED TO BECOME A PROBLEM.
KJB
AVIATION /18Z TAFS THROUGH 00Z MONDAY/
ISSUED AT 1120 AM CST SAT DEC 21 2024
FORECAST CONCERNS FOR THE TERMINALS...
- LAKE EFFECT MVFR CLOUDS TO BRUSH GYY THIS AFTERNOON
- BREEZY SOUTH-SOUTHEAST WINDS SUNDAY AFTERNOON WITH 20-25 KT
GUSTS
MUCH QUIETER WEATHER CONDITIONS ARE EXPECTED TODAY AS A SURFACE
HIGH BUILDS INTO THE GREAT LAKES. AS A RESULT, FEW TO SCT VFR
SKIES ARE EXPECTED THIS AFTERNOON WHICH WILL GIVE WAY TO BKN
8000-10000 FT CLOUDS THIS EVENING THROUGH SUNDAY. HOWEVER,
THERE ARE SOME LINGERING MVFR LAKE EFFECT CLOUDS BRUSHING
PORTIONS OF NORTHWEST IN WHICH LOOK TO IMPACT GYY AT TIMES THIS
AFTERNOON BEFORE SCATTERING OUT THIS EVENING.
ASIDE FROM THE CLOUDS, WINDS WILL REMAIN 5-10 KTS OUT OF THE
NORTHWEST TODAY BEFORE BECOMING LIGHT AND VARIABLE OVERNIGHT AS
THE SURFACE HIGH MOVES OVERHEAD. WINDS WILL SETTLE INTO A
SOUTH-SOUTHEASTERLY DIRECTION SUNDAY MORNING AND GRADUALLY
INCREASE IN SPEED THROUGH THE DAY. WHILE GUSTS SHOULD GENERALLY
RESIDE IN THE 20-25 KT RANGE SUNDAY AFTERNOON, OCCASIONAL GUSTS
OVER 25 KTS ARE POSSIBLE ESPECIALLY TOWARDS THE TAIL END OF THE
FORECAST PERIOD.
YACK
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 3 PM CST THIS AFTERNOON FOR THE IN
NEARSHORE WATERS.
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