358
FXUS63 KAPX 201523
AFDAPX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GAYLORD MI
1023 AM EST FRI DEC 20 2024
KEY MESSAGES
- ACCUMULATING SNOW IS EXPECTED TO CONTINUE INTO THE EARLY
AFTERNOON.
- ANOTHER BRIEF VERY COLD SPELL SATURDAY INTO SATURDAY NIGHT,
WITH HIGHS IN THE TEENS SATURDAY, AND POTENTIAL FOR SUB-ZERO
LOWS SATURDAY NIGHT.
- POTENTIAL FOR A WIDESPREAD SNOWFALL MONDAY INTO MONDAY NIGHT
AS ANOTHER SYSTEM PASSES THROUGH THE REGION.
- TRENDING WARMER AND DRIZZLY FOR THE REMAINDER OF THE FORECAST
PERIOD, INCLUDING THE CHRISTMAS HOLIDAY. SNOWPACK WILL SUFFER
CONSIDERABLY AS TEMPERATURES AND DEWPOINTS BECOME STAGNANT
ABOVE FREEZING.
UPDATE
ISSUED AT 1022 AM EST FRI DEC 20 2024
SNOWFALL CONTINUES TO TAPER OFF ACROSS PARTS OF NORTHERN MICHIGAN
THIS MORNING. STEADIEST SNOWFALL RESULTING IN SOME TRAVEL IMPACTS
WILL PERSIST THROUGH THE MORNING HOURS FOR AREAS NEAR SAGINAW BAY
AND GRAND TRAVERSE BAY. THE WINTER WEATHER ADVISORY HAS BEEN
CANCELLED FOR PRESQUE ISLE, ALPENA, AND ALCONA COUNTIES AS SNOW HAS
LARGELY MOVED SOUTH OF THESE AREAS, AND HAVE SHORTENED THE ENDING
TIME FOR THE REMAINING COUNTIES IN THE ADVISORY TO NOON.
SHORT TERM /THROUGH TONIGHT/
ISSUED AT 258 AM EST FRI DEC 20 2024
PATTERN SYNOPSIS AND FORECAST:
A DIGGING LONGWAVE TROUGH CENTERED ACROSS THE GREAT LAKES
REGION AT THE START OF THE PERIOD WILL CONTINUE TO SWING
EASTWARD AS EMBEDDED WAVES ROTATE THROUGH THE FLOW. LIGHT
SNOWFALL HAS BEEN OBSERVED ACROSS MUCH OF NORTHERN MICHIGAN INTO
THIS MORNING WITH A FOCUS OF HEAVIER SNOWFALL CONCENTRATED
ACROSS NORTHEAST LOWER, ESPECIALLY ALPENA COUNTY EARLY THIS
MORNING. AS THE AFOREMENTIONED TROUGH AND ASSOCIATED SURFACE LOW
TRACK FURTHER EAST, WINDS WILL BACK/TURN MORE NORTHEAST THROUGH
THE MORNING, SHIFTING LAKE ENHANCED BANDING FROM THE ALPENA/
ALCONA AREAS SOUTHWARD TOWARDS SAGINAW BAY AS WE PROGRESS
THROUGH THE DAY--FOR ADDITIONAL DETAILS, PLEASE SEE ONGOING
WINTER WEATHER ADVISORIES. BY THIS EVENING WINDS WILL TURN MORE
NORTH-NORTHWEST AND INITIATE LIGHT LAKE EFFECT SNOW SHOWERS
ACROSS THE TYPICAL SNOWBELTS OF NORTHERN LOWER THROUGH TONIGHT.
LIGHT ACCUMULATIONS OF 1-2" ARE EXPECTED AS DRIER AIR WORKS INTO
THE REGION LATE FRIDAY NIGHT INTO SATURDAY WHILE SURFACE HIGH
PRESSURE BUILDS. TEMPERATURES WILL LARGELY BE IN THE MID 20S
ACROSS THE EASTERN U.P. AND UPPER 20S TO LOW 30S ACROSS NORTHERN
LOWER TODAY WITH OVERNIGHT LOWS DIPPING INTO THE SINGLE DIGITS
FOR MOST OF NORTHERN MICHIGAN. WIND CHILL VALUES FOR TONIGHT
WILL BE QUITE CHILLY ACROSS THE FORECAST AREA WITH AREAS IN THE
EASTERN U.P. DROPPING TO THE NEGATIVE TEENS (FAR EASTERN
CHIPPEWA COUNTY) AND SEVERAL AREAS ACROSS NORTHERN LOWER IN THE
SINGLE DIGIT NEGATIVES AS CLOUDS BEGIN TO CLEAR.
LONG TERM /SATURDAY THROUGH THURSDAY/
ISSUED AT 258 AM EST FRI DEC 20 2024
PATTERN SYNOPSIS / FORECAST:
DEEP LONGWAVE TROUGHING WILL BE GRADUALLY FORCED EASTWARD BY AN
AMPLIFYING RIDGE BUILDING OVER THE ROCKIES, DRIVEN BY A ROBUST
180- 200KT PACIFIC JET THAT WILL BE DOMINANT THROUGHOUT THE
FORECAST PERIOD. ANOMALOUSLY STRONG SURFACE HIGH PRESSURE WITH
ARCTIC ORIGINS (~1040MB; +2 SIGMA) WILL PASS OVER LAKE SUPERIOR
SATURDAY NIGHT, SCOURING OUT LOW LEVEL MOISTURE AND CLEARING OUT
SKIES WITH CALM WINDS SATURDAY NIGHT. EVENTUALLY, THAT AREA OF
RIDGING WILL SLOWLY FOLD OVER THE REGION, BRINGING CONSIDERABLE
500MB HEIGHT RISES AND AMPLE WARM / MOIST ADVECTION TO THE
REGION AS AN ANOMALOUSLY MILD PACIFIC AIRMASS INTRUDES FOR
CHRISTMAS WEEK... THOUGH A WARM ADVECTION DRIVEN SHORTWAVE MAY
BRING A FINAL ROUND OF ACCUMULATING SNOWFALL MONDAY INTO MONDAY
NIGHT BEFORE WE COMMENCE ON A MORE PROLONGED WARMUP.
PRIMARY FORECAST CONCERNS:
COLD START TO THE FORECAST PERIOD: ANY LINGERING LAKE EFFECT
SNOW WILL CERTAINLY BE ON A DOWNWARD TREND AS SURFACE HIGH
PRESSURE MOVING CLOSE BY SLACKENS THE PRESSURE GRADIENT AND
REALLY PUTS THE BRAKES ON SURFACE FLOW, LEAVING THE REGION IN A
LIGHT NORTH TO NORTH- NORTHEASTERLY DRAINAGE FLOW. IN ADDITION,
SUBSIDENCE WILL LEAD TO CLEARING SKIES THROUGHOUT THE DAY. SO
DESPITE THE INCREASING SUNSHINE, THE RESULT WILL NONETHELESS BE
JUST A DOWNRIGHT COLD DAY SATURDAY WITH HIGHS LARGELY IN THE MID
TEENS TO LOWER 20S. WITH THIS TREND CARRYING INTO THE OVERNIGHT
HOURS, COUPLED WITH A LAYER OF FRESH SNOW AND THE PERFECT WIND
DIRECTION (BEST COLD AIR ADVECTION ACROSS THE REGION COMES FROM
N TO NNE FLOW WITH OPEN LAKES AS LATENT HEAT FROM THE LAKES
DOESN'T MODERATE THE AIRMASS MUCH... OR TO PUT IT VERY SIMPLY,
THE COLD AIR CROSSES THE MACKINAC BRIDGE AND SPILLS INTO
NORTHERN LOWER)... CERTAINLY LOOKS LIKE WE WILL MAKE A RUN FOR
THE COLDEST NIGHT OF THE SEASON THUS FAR AS TEMPS DROP LIKE A
TON OF BRICKS SHORTLY AFTER SUNSET ON SATURDAY. WOULDN'T BE
SURPRISING TO SEE LOCALES PUSHING OR EVEN GETTING BELOW -10
SATURDAY NIGHT (ICEBOX INTERIOR AREAS OF NORTHERN LOWER
SPECIFICALLY... GRAYLING, PELLSTON, ATLANTA, ETC...). SOUTHERLY
RETURN FLOW BEGINS TO LOAD INTO THE REGION SUNDAY AS THE SURFACE
HIGH PASSES EASTWARD INTO ONTARIO, WITH HIGHS REACHING INTO THE
20S AND OVERNIGHT LOWS IN THE TEENS AND 20S (ABOVE ZERO) SUNDAY
NIGHT.
SNOW MONDAY: NEXT ITEM OF BUSINESS WILL BE AN EMBEDDED WARM AIR
ADVECTION SHORTWAVE FORCING ITS WAY INTO THE HEELS OF THE DEEP
ARCTIC AIRMASS THAT WILL BE SLOWLY DEPARTING. RIDGING AND WARM
AIR ADVECTION WILL LIKELY PUT A CAP ON ANY PREDECESSOR SW FLOW
LAKE EFFECT, THOUGH THE SYNOPTIC SCALE OF THIS SYSTEM COULD BE A
TOUCH MORE ROBUST. LATEST LONG TERM GUIDANCE SHOWCASES SOME
PRETTY IMPRESSIVE SYNOPTIC PUZZLE PIECES POTENTIALLY BEING PUT
TOGETHER WITH THIS SYSTEM. DIVERGENCE ALOFT SUPPORTED BY
FAVORABLE JET STREAK DYNAMICS SUPPORTS AMPLE LIFT AND
CYCLOGENESIS AS THE SYSTEM APPROACHES THE GREAT LAKES.
ADDITIONALLY, AMPLE 850MB MOISTURE TRANSPORT (POSSIBLY EVEN
TAPPING INTO THE GULF?) CLASHING WITH THE DEPARTING ARCTIC
AIRMASS MAY PRODUCE AN IMPRESSIVE FRONTOGENETIC LIFT REGION THAT
MAY LEAD TO SOME HEAVIER PRECIPITATION POTENTIAL. CERTAINLY ONE
TO WATCH AS THIS COULD BE A QUICK-HITTING "THUMP" OF SEVERAL
INCHES OF SNOW MONDAY INTO MONDAY NIGHT THAT WILL LIKELY BE THE
PARTING SHOT FROM THE ONGOING WINTRY PATTERN BEFORE THE PACIFIC
AIRMASS KICKS IN. UNCERTAINTY REMAINS REGARDING THE DEVELOPMENT
AND TRACK OF THIS POTENTIAL SYSTEM, SO MORE DETAILS ARE TO COME
IN THE ENSUING FORECAST CYCLES.
REST OF THE PERIOD: ON THE HEELS OF THE MONDAY-MONDAY NIGHT
SHORTWAVE, RIDGING AND WARM AIR ADVECTION WILL BE IN FULL FORCE,
PUMPING IN ABSOLUTELY HEINOUS DRIZZLY / GRUNGY CONDITIONS THAT
UNFORTUNATELY LOOK TO OVERLAP THE CHRISTMAS HOLIDAY AND THE BUSY
ACTIVITY IT BRINGS... AND LIKELY THE REMAINDER OF THE FORECAST
PERIOD. THIS WILL BE DETRIMENTAL TO OUR SNOWPACK CONSIDERING THE
ABOVE FREEZING DEWPOINTS THAT WILL LIKELY ENVELOP THE REGION
FOR POTENTIALLY AS MUCH AS 60 HOURS AS TEMPERATURES PROBABLY
BECOME STAGNANT IN THE UPPER 30S TO MID 40S AT THE MINIMUM.
AVIATION /12Z TAFS THROUGH 12Z SATURDAY/
ISSUED AT 605 AM EST FRI DEC 20 2024
LIGHT SNOW SHOWERS WILL CONTINUE THROUGH EARLY THIS AFTERNOON
AS NORTHEAST WINDS SHIFT NORTH-NORTHWEST (GUSTS TO ~20 KTS) BY
THIS EVENING, SHIFTING LAKE EFFECT SHOWERS TO TVC AND MBL.
CEILINGS AND VISIBILITIES WILL GENERALLY BE MVFR, BUT WILL
LIKELY DROP TO IFR AT TIMES IN THE HEAVIEST LAKE ENHANCED SNOW
BANDS, ESPECIALLY APN AND PLN THIS MORNING AND THEN TVC AND MBL
THIS AFTERNOON/EVENING.
APX WATCHES/WARNINGS/ADVISORIES
MI...WINTER WEATHER ADVISORY UNTIL NOON EST TODAY FOR MIZ036-041-
042.
MARINE...SMALL CRAFT ADVISORY FROM 5 PM THIS AFTERNOON TO 7 AM EST
SATURDAY FOR LHZ347.
SMALL CRAFT ADVISORY UNTIL 7 AM EST SATURDAY FOR LHZ348-349.
SMALL CRAFT ADVISORY FROM 5 PM THIS AFTERNOON TO 7 AM EST
SATURDAY FOR LMZ323-342.
SMALL CRAFT ADVISORY UNTIL 7 AM EST SATURDAY FOR LMZ344>346.
SMALL CRAFT ADVISORY FROM 5 PM THIS AFTERNOON TO 7 AM EST
SATURDAY FOR LSZ321.
UPDATE...DJC
SHORT TERM...NSC
LONG TERM...HAD
AVIATION...NSC
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