865
FXUS61 KBOX 210544
AFDBOX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOSTON/NORTON MA
1244 AM EST SAT DEC 21 2024
SYNOPSIS
A COASTAL STORM WILL MOVE OUT TO SEA TONIGHT WITH SNOWFALL
ENDING. MAINLY DRY BUT BLUSTERY AND VERY COLD THIS WEEKEND INTO
EARLY NEXT WEEK. A WEAK CLIPPER SYSTEM MAY BRING LIGHT SNOW
ACCUMULATIONS CHRISTMAS EVE, THEN MAINLY DRY FOR THE REST OF THE
CHRISTMAS WEEK WITH TEMPERATURES MODERATING INTO THE 30S AND
LOW 40S.
NEAR TERM /UNTIL 6 AM THIS MORNING/
1230 AM UPDATE...
BACK EDGE OF THE LIGHT SNOW IS SHIFTING SOUTH ACROSS FAR SE MA
AND THE CAPE/ISLANDS AND WILL TAPER OFF DURING THE NEXT FEW
HOURS. ANY ADDITIONAL ACCUM WILL BE LESS THAN AN INCH AND THE
WINTER WEATHER ADVISORIES HAVE BEEN CANCELLED. GUSTY N-NE
WINDS ALONG THE COAST WILL SLOWLY DIMINISH LATE TONIGHT.
SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SUNDAY/
KEY MESSAGES...
* DRIER AND COLDER ON SATURDAY AND VERY COLD ON SATURDAY NIGHT
SATURDAY THE MID LEVEL TROUGH REMAINS OVERHEAD BUT THE LOW QUICKLY
EXITS EAST. WE'LL SEE BREEZY NW WINDS 10 TO 15 MPH WITH GUSTS AS
HIGH AS 25 MPH. GIVEN THE CYCLONIC FLOW ALOFT WE MAY SEE SOME WIDELY
SCATTERED LIGHT SNOW BUT MOSTLY JUST CONTINUED CLOUDCOVER. IN THE
AFTERNOON HEIGHTS WILL BE STARTING TO RISE AND DRIER AIR ADVECTED IN
ON THAT NW FLOW SO CLOUDS WILL DISSIPATE THROUGH THE AFTERNOON AND
EVENING. THIS WILL BE THE TRANSITION TOWARD OUR COLDEST DAY OF THE
SEASON ON SUNDAY, WITH HIGHS ONLY MAKING IT INTO THE UPPER 20S AND
LOW 30S. THE REAL COLD ARRIVES OVERNIGHT, THOUGH, AS FRIGID AIR
ARRIVES. 850 MB REACH AROUND -15C, WHILE AT THE SURFACE LOWS WILL
DROP INTO THE SINGLE DIGITS (INTERIOR) AND MID TEENS (COAST). BREEZY
WINDS WILL MAKE IT FEEL MORE LIKE SINGLE DIGIT NEGATIVES TO NEAR 0
IN THE INTERIOR.
LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/
KEY MESSAGES:
* ARCTIC AIRMASS CONTINUES TO BRING HIGHS IN THE 20S AND LOWS IN
THE SINGLE DIGITS SUNDAY INTO MONDAY
* GRADUAL WARM-UP THE REST OF THE WEEK WITH HIGHS IN THE 30S AND
LOWS IN THE 20S
* WEAK CLIPPER SYSTEM MOVES THROUGH CHRISTMAS EVE, BUT CONFIDENCE
IS STILL LOW
1040MB HIGH PRESSURE AND ARCTIC AIRMASS REMAIN OVER THE REGION
THROUGH MONDAY. DESPITE SUNNY SKIES, HIGHS WILL STRUGGLE TO TOP 30F,
WITH MOST OF THE REGION IN THE LOW 20S. WITH BLUSTERY NW WINDS AT 10-
15MPH, THE WIND CHILL FACTOR WILL MAKE IT FEEL LIKE THE SINGLE
DIGITS. OVERNIGHT LOWS WILL LIKELY DROP TO SOME OF THE COLDEST WE
HAVE SEEN THUS FAR FOR THE SEASON, WITH LOWS IN THE SINGLE DIGITS,
POSSIBLY BELOW ZERO IN HIGH TERRAIN IN NW MA. WINDS WILL DECREASE
OVERNIGHT, WHICH WILL HELP PREVENT THE WIND CHILL FACTOR FROM GOING
FAR BELOW ZERO. SURFACE FLOW TURNS SOUTHERLY ON MONDAY, ALLOWING
HIGH TEMPS TO MODERATE SLIGHTLY INTO THE UPPER 20S TO LOW 30S.
A CLIPPER SYSTEM DROPS OUT OF THE NORTHERN GREAT LAKES ON CHRISTMAS
EVE, WHICH COULD BRING ANOTHER ROUND OF LIGHT WINTRY PRECIPITATION.
UNCERTAINTY REMAINS HIGH WITH THIS SYSTEM AS MODELS ARE USUALLY TOO
QUICK TO KICK OUT STRONG HIGH-PRESSURE SYSTEMS. CURRENT ENSEMBLE
GUIDANCE SHOWS HIGH PROBS FOR 1 INCH ACROSS THE REGION, WITH LOW
PROBS FOR 3 INCHES IN THE HIGH TERRAIN OF THE BERKSHIRES.
TEMPERATURES TUESDAY CONTINUE TO MODERATE INTO THE LOW TO MID-30S.
HIGH PRESSURE BUILDS BACK IN FROM THE NORTH FOR CHRISTMAS DAY
THROUGH THE END OF THE WEEK. HIGH TEMPERATURES CONTINUE TO MODERATE
INTO THE MID TO UPPER 30S TO EVEN LOW 40S BY THE END OF THE WEEK.
AVIATION /06Z SATURDAY THROUGH WEDNESDAY/
FORECAST CONFIDENCE LEVELS:
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
THROUGH 12Z...
MVFR-IFR CONDITIONS IN LIGHT SNOW ACROSS CAPE/ISLANDS WILL
IMPROVE BY 08Z AS THE SNOW ENDS AND VSBYS IMPROVE. OTHERWISE,
MVFR CIGS IMPROVE TO VFR 09-12Z, BUT LOWER CIGS MAY LINGER
BEYOND 12Z OVER OUTER CAPE AND ACK. ALSO, SCATTERED SNOW
SHOWERS ARE POSSIBLE 09-12Z WESTERN MA/CT WHICH MAY BRING
LOCALLY REDUCED VSBYS.
TODAY...MODERATE CONFIDENCE.
MAINLY VFR CIGS, BUT LOWER MVFR CIGS POSSIBLE EARLY
CAPE/ISLANDS. NW WIND 10-20 KT WITH SOME HIGHER GUSTS.
TONIGHT AND SUNDAY...HIGH CONFIDENCE.
VFR, BUT OCEAN EFFECT CLOUDS MAY LOWER CIGS TO MVFR AT TIMES
OVER THE OUTER CAPE, MAINLY ALONG AND EAST OF HYA. NW WIND 10-20
KT WITH HIGHER GUSTS NEAR THE COAST, DIMINISHING SUNDAY
AFTERNOON.
KBOS TAF...HIGH CONFIDENCE IN IMPROVING TREND TO VFR BY 12Z.
KBDL TAF...MODERATE CONFIDENCE. MVFR CIGS THROUGH 12Z, AND MAY
SEE BRIEF SNOW SHOWERS DEVELOP AFTER 10Z WHICH COULD REDUCE
VSBYS. IMPROVING TO VFR AFTER 12Z.
OUTLOOK /SUNDAY NIGHT THROUGH WEDNESDAY/...
SUNDAY NIGHT THROUGH MONDAY: VFR.
MONDAY NIGHT: MAINLY VFR, WITH LOCAL MVFR POSSIBLE. CHANCE SN.
TUESDAY: MAINLY VFR, WITH AREAS MVFR POSSIBLE. CHANCE SN,
CHANCE RA.
TUESDAY NIGHT: MAINLY VFR, WITH LOCAL MVFR POSSIBLE. CHANCE SN.
CHRISTMAS DAY: VFR. SLIGHT CHANCE RA, SLIGHT CHANCE SN.
MARINE
FORECASTER CONFIDENCE LEVELS:
LOW - LESS THAN 30 PERCENT.
MEDIUM - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
KEY MESSAGES:
* SMALL CRAFT ADVISORY IN EFFECT THROUGH SUNDAY.
TONIGHT...MODERATE CONFIDENCE.
SURFACE LOW PRESSURE SYSTEM MOVES UP THE COAST AND REMAINS OUT TO
SEA. INCREASING EAST/NORTHEAST WINDS 15 TO 20 KNOTS WITH GUSTS
UP TO 30 KNOTS ON THE OUTERMOST WATERS, NEARSHORE WATERS GUSTS
ARE CLOSER TO 25 KNOTS. SEAS BUILDING 4 TO 9 FEET FOR THE
WATERS. PERIODS OF RAIN AND SNOW TONIGHT, DIMINISHING EARLY
SATURDAY MORNING.
SATURDAY...HIGH CONFIDENCE.
LOW PRESSURE SYSTEM LIFTS NORTHEAST FROM SOUTHERN NEW ENGLAND, BUT
WITH HIGH PRESSURE BUILDING TO THE WEST, IT WILL LEAD TO NORTHWEST
FLOW WITH GUSTS CONTINUING THROUGHOUT THE DAY. HAVE EXTENDED THE
SMALL CRAFT ADVISORY AS A RESULT THROUGH THE DAY. SEAS REMAIN ROUGH
3 TO 6 FEET ON THE SOUTHERN WATERS AND 5 TO 8 FEET ON THE EASTERN
WATERS.
SATURDAY NIGHT...HIGH CONFIDENCE.
HIGH PRESSURE MOVING OVERHEAD. NW WINDS 15-20 KTS GUSTING TO 25
KTS. SEAS 5-7 FT.
OUTLOOK /SUNDAY NIGHT THROUGH WEDNESDAY/...
SUNDAY: WINDS LESS THAN 25 KT. SEAS UP TO 5 FT. CHANCE OF SNOW.
LOCAL VISIBILITY 1 TO 3 NM.
SUNDAY NIGHT: WINDS LESS THAN 25 KT. AREAS OF SEAS APPROACHING
5 FT. CHANCE OF SNOW.
MONDAY: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING 5 FT.
SLIGHT CHANCE OF SNOW.
MONDAY NIGHT: WINDS LESS THAN 25 KT. CHANCE OF RAIN, CHANCE OF
SNOW.
TUESDAY: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING 5 FT.
RAIN LIKELY. LOCAL VISIBILITY 1 TO 3 NM.
TUESDAY NIGHT: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING
5 FT. CHANCE OF RAIN, CHANCE OF SNOW.
CHRISTMAS DAY: WINDS LESS THAN 25 KT. AREAS OF SEAS APPROACHING
5 FT. CHANCE OF RAIN.
BOX WATCHES/WARNINGS/ADVISORIES
CT...NONE.
MA...NONE.
RI...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 4 AM EST EARLY THIS MORNING FOR
ANZ230.
SMALL CRAFT ADVISORY UNTIL 7 AM EST SUNDAY FOR ANZ231-232-251.
SMALL CRAFT ADVISORY UNTIL 7 AM EST THIS MORNING FOR
ANZ233>235-237.
SMALL CRAFT ADVISORY UNTIL 7 PM EST SUNDAY FOR ANZ250-256.
GALE WARNING UNTIL 4 AM EST EARLY THIS MORNING FOR ANZ254-255.
SYNOPSIS...BW/KP
NEAR TERM...KJC
SHORT TERM...BW
LONG TERM...KP
AVIATION...KJC/KP
MARINE...BW/KP
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