863
FXUS61 KBOX 130830
AFDBOX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOSTON/NORTON MA
330 AM EST SAT DEC 13 2025
SYNOPSIS
HIGH PRESSURE MOVES OFFSHORE THIS AFTERNOON THEN A FAST MOVING LOW
PRESSURE SYSTEM WILL BRING ACCUMULATING SNOW OVERNIGHT INTO SUNDAY
MORNING, ESPECIALLY SOUTH OF THE MASS PIKE. OCEAN EFFECT SNOW
SHOWERS WILL LINGER INTO SUNDAY AFTERNOON TOWARDS THE CAPE AND
ISLANDS. A BRIEF SHOT OF ARCTIC AIR FOLLOWS SUNDAY NIGHT INTO
MONDAY WITH WIND CHILL DROPPING TO BETWEEN 5 BELOW AND 5 ABOVE.
IT REMAINS COLD TUESDAY, BUT A PATTERN CHANGE WITH A
SIGNIFICANT WARMING TREND IS LIKELY WEDNESDAY INTO THURSDAY. THE
MILDER WILL LIKELY BE ACCOMPANIED BY A PERIOD OF GUSTY WINDS AND
SHOWERS SOMETIME IN THE LATE THURSDAY INTO FRIDAY TIME FRAME.
NEAR TERM /UNTIL 6 PM THIS EVENING/
TODAY
MAINLY DRY WEATHER TODAY WITH HIGH PRESSURE IN CONTROL. WILL
SEE INCREASING MID AND HIGH CLOUDS AS A DISTURBANCE APPROACHES
FROM THE GREAT LAKES. 850MB TEMPERATURES WILL WARM TO AROUND -5C
BY THE AFTERNOON WITH A LIGHT RETURN FLOW BEHIND DEPARTING HIGH
PRESSURE. HIGH TEMPERATURES WILL BE WARMER THAN WHAT WE'VE
RECENTLY SEEN WITH HIGHS WELL INTO THE 30S WITH EVEN SOME LOWER
40. MAINLY DRY TODAY...BUT A FEW SPOT SNOW SHOWERS ARE POSSIBLE
ACROSS INTERIOR OR RAIN SHOWERS NEAR THE COAST AFTER 21Z WITH
WEAK LIFT AHEAD OF AN INCOMING SHORTWAVE.
SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY NIGHT/
KEY MESSAGES...
* ACCUMULATING SNOW VERY LATE TONIGHT-SUN MORNING ESPECIALLY
SOUTH OF I-90...HIGHEST ACCUMULATIONS NEAR SOUTH COAST
* ADVISORY LEVEL SNOWFALL EXPECTED TOWARDS THE SOUTH COAST, CAPE
AND ISLANDS.
* OCEAN EFFECT SNOW SHOWERS LINGER ON THE OUTER CAPE INTO SUN
NIGHT WITH ADDITIONAL MINOR ACCUM POSSIBLE
* BRIEF SHOT OF ARCTIC AIR RESULTS IN WIND CHILLS DROPPING TO
BETWEEN -5 AND 5 ABOVE LATE SUN NIGHT INTO EARLY MON MORNING
DETAILS...
TONIGHT...
STARTING TO SEE SOME BETTER AGREEMENT AMONG GUIDANCE WITH
RESPECT TO THE SEASON'S FIRST WIDESPREAD SNOW EVENT ALONG THE I95
CORRIDOR SLATED FOR TONIGHT INTO SUNDAY MORNING. NOTABLY, THE GFS
HAS TRENDED FURTHER NORTH WITH THE HIGHER QPF TO BE MORE IN LINE
WITH THE CMC AND ECMWF. AS A RESULT, GLOBAL MODELS ARE NEARLY
IDENTICAL IN TERMS OF QPF PLACEMENT AND AMOUNTS. HIGH RES GUIDANCE
IS GENERALLY SIMILAR WITH THE EXCEPTION OF THE HRRR WHICH HAS THE
BULK OF THE PRECIP SHIELD FURTHER OFFSHORE AND THUS A DRIER
SOLUTION.
LATER TODAY SHORTWAVE ENERGY ROTATES AROUND A POSITIVELY TILTED
TROUGH NORTH OF THE GREAT LAKES. TROUGH STARTS TO DIG OVERNIGHT
BRINGING A DEEP MOISTURE PLUME NORTHWARD INTO SNE. PWATS INCREASE
FROM 0.3" TO 0.5-0.6" OVERNIGHT SO THERE WILL BE PLENTY OF MOISTURE
TO WORK WITH. FURTHER ALOFT, THE REGION WILL FIND ITSELF UNDER THE
RIGHT ENTRANCE REGION OF A 140-150 KT UPPER JET OVERNIGHT INTO
SUNDAY MORNING. HIGH CONFIDENCE THAT THIS COMBINATION WILL BRING THE
FIRST WIDESPREAD ACCUMULATING SNOWS FOR MUCH OF RI, AND AREAS S OF
THE MASS PIKE. PRECIPITATION WILL LIKELY START AT LIGHT SNOW LATE
TONIGHT FOR MUCH OF THE REGION EXCEPT FOR THE CAPE AND ISLANDS WHERE
TEMPERATURES WILL TAKE SOME TIME TO COOL. STILL EXPECTING MUCH OF
THE ACCUMULATING SNOW TO FALL OVER A 8-12 HOUR PERIOD LATER TONIGHT
INTO SUNDAY MORNING. HIGH RES GUIDANCE HAS ALSO HONED IN ON THE
CHANCE FOR LINGERING OCEAN EFFECT SNOW FOR THE CAPE AND ISLANDS INTO
SUNDAY AFTERNOON. WHILE THIS CERTAINLY DOES NOT LOOK LIKE A HEAVY
SNOW EVENT, BUFKIT SOUNDINGS HAVE BECOME SOMEWHAT MORE IMPRESSIVE
FOR THIS EVENT. SPECIFICALLY THE 00Z NAM HAS MODEST AMOUNTS OF OMEGA
ON THE ORDER OF -10 UBAR/SEC COLLOCATED WITH A 6-8KFT DGZ ACROSS
MUCH OF SE MASSACHUSETTS. THUS, UNSURPRISINGLY, THE HREF SHOWS A
BRIEF WINDOW OF HOURLY SNOWFALL RATES BETWEEN 0.25 AND 0.5 INCHES
MAINLY ACROSS S RI AND SE MA BETWEEN 08 AND 12Z SUNDAY MORNING.
IN TERMS OF TOTALS, WHILE THIS WON'T BE A MAJOR EVENT IT WILL BE THE
FIRST ACCUMULATING SNOW OF THE 2025-26 SEASON FOR MANY OF US.
DESPITE A SOMEWHAT DEEP DGZ AND TEMPS IN THE MID AND LOWER 20S SNOW
RATIOS WILL BE LIMITED BY A LACK OF STRONG MID-LEVEL FRONTOGENESIS
AND OMEGA. ALL TOLD, THIS WILL BE A GENERAL 1-3 INCH EVENT S OF THE
MASS PIKE WITH HIGHEST AMOUNTS ALONG THE SOUTH COAST. EXPECTING
AROUND 4-4.5 INCHES ON CAPE COD AND THE SOUTH COAST. MEANWHILE, JUST
A COATING TO AN INCH FOR AREAS NORTH OF THE MA PIKE. THINK THE RRFS
SHOWS A REASONABLE WORST CASE SCENARIO IF THERE IS A NORTHERN SHIFT
THERE COULD BE UP TO 6 INCHES ACROSS RI AND SE MA AND CAPE COD BUT
THIS IS STILL A LOW PROBABILITY (LESS THAN 25%) OUTCOME. IF THE
SYSTEM TRENDS SOUTH IT WOULD BE CLOSER TO 1-2 INCHES NEAR THE SOUTH
COAST WITH DECREASING AMOUNTS NORTHWARD.
SUNDAY AND SUNDAY NIGHT...
STEADIEST SNOW WILL QUICKLY END FROM WEST TO EAST THROUGH MID
MORNING SUNDAY. EXPECTING OCEAN EFFECT SNOW SHOWERS TO LINGER THE
OUTER CAPE SUN AFTERNOON AND NIGHT AS ARCTIC AIR POURS INTO THE
REGION ON NNW-NW FLOW. OCEAN INDUCED CAPES EXPECTED INCREASE TO 500-
600 J/KG WITH SST DIFFERENTIAL AROUND 25C. AN ADDITIONAL INCH OR 2
IS POSSIBLE ON THE OUTER CAPE BUT BOUNDARY LAYER TEMPERATURE
PROFILES MAY BE A BIT WARM FOR ADDITIONAL ACCUMULATIONS DURING THE
AFTERNOON.
A SHORT DURATION SHOT OF ARCTIC AIR WILL POUR INTO THE REGION SUN
NIGHT AND MON. LOWS WILL DROP INTO THE SINGLE NUMBERS AND TEENS WITH
WIND CHILLS BOTTOMING OUT BETWEEN -5F AND +5F LATE SUN NIGHT AND MON
MORNING, WITH -10F POSSIBLE IN THE BERKSHIRES.
LONG TERM /MONDAY THROUGH FRIDAY/
KEY MESSAGES...
* BLUSTERY AND BITTERLY COLD MON AM WITH WIND CHILLS BETWEEN 5 BELOW
& 5 ABOVE AND AFTERNOON HIGHS ONLY RECOVERING INTO THE 20S
* A FEW BRIEF SNOW SHOWERS POSSIBLE MONDAY NIGHT, OTHERWISE DRY AND
STILL CHILLY TUE WITH HIGHS MAINLY IN THE LOWER-MIDDLE 30S
* PATTERN CHANGE WITH SIGNIFICANTLY MILDER TEMPERATURES WED-FRI WITH
UNSETTLED/MAINLY WET WEATHER POSSIBLE SOMETIME LATE THU INTO FRI
DETAILS...
MONDAY...
A BRIEF SHOT OF ARCTIC AIR AND GUSTY NW WINDS WILL RESULT IN
BITTERLY COLD WIND CHILLS EARLY MON MORNING IN THE 5 BELOW AND 5
ABOVE RANGE. UNDER A MIXTURE OF CLOUDS AND SUNSHINE WILL RESULT IN
MON AFTERNOON HIGH TEMPERATURES ONLY RECOVERING INTO THE 20S.
MONDAY NIGHT AND TUESDAY...
A FAST MOVING MOISTURE STARVED NORTHERN STREAM SHORTWAVE MAY BRING A
FEW BRIEF SNOW SHOWERS TO THE REGION MONDAY NIGHT. OTHERWISE...THE
MAIN STORY WILL BE THE CONTINUED CHILLY WEATHER. LOWS MON NIGHT WILL
GENERALLY BE IN THE TEENS. HIGHS ON TUE WILL RANGE FROM THE UPPER
20S IN THE HIGHEST TERRAIN...TO MAINLY THE LOWER TO MIDDLE 30S
ELSEWHERE.
WEDNESDAY THROUGH FRIDAY...
THE LONG RANGE MODEL GUIDANCE CONTINUES TO BE IN VERY GOOD AGREEMENT
IN A SIGNIFICANT PATTERN CHANGE. A -PNA DEVELOPING WILL ALLOW FOR
MILDER PACIFIC AIR TO OVERSPREAD MUCH OF THE LOWER 48. THIS IS QUITE
THE CHANGE FROM THE VERY COLD WEATHER WE HAVE SEEN FOR THE FIRST OF
OF DECEMBER. HIGH TEMPERATURES SHOULD REACH WELL INTO THE 40S ON WED
AND PERHAPS 50+ THU AND/OR FRI. IN FACT...THU NIGHT MAY END UP QUITE
MILD WITH GUSTY SOUTHERLY WINDS AND STEADY/RISING TEMPS IF CURRENT
MODEL TIMING PANS OUT. THIS A RESULT OF SHORTWAVE ENERGY MOVING INTO
THE GREAT LAKES RESULTING IN STRONG SURFACE LOW PRESSURE TRACKING
WELL TO OUR NORTH ACROSS QUEBEC. THIS WOULD ALLOW A STRONG SOUTHERLY
LLJ TO DEVELOP...2+ STANDARD DEVIATIONS ABOVE NORMAL ALSO BRINGING
SHOWERS AND THE POTENTIAL FOR GUSTY WINDS SOMETIME IN THE LATE
THURSDAY TO FRIDAY TIME FRAME.
AVIATION /08Z SATURDAY THROUGH WEDNESDAY/
FORECASTER CONFIDENCE LEVELS...
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
06Z UPDATE
TODAY...HIGH CONFIDENCE
MOSTLY VFR, POSSIBLY BORDERLINE MVFR FOR THE CAPE AND ISLANDS AFTER
21Z. SOUTHWEST WINDS BETWEEN 5 AND 10 KNOTS WITH GUSTS UP TO 15
KNOTS. SLIGHT CHANCE FOR AREAS OF -SHRA/-SHSN ACROSS THE CAPE AND
ISLANDS NEAR 00Z.
TONIGHT... MODERATE CONFIDENCE
MAINLY MVFR WITH AREAS OF IFR DEVELOPING ALONG THE SOUTH COAST AND
CAPE/ISLANDS. AREAS OF -SN MOVING IN FROM W TO E BETWEEN 05 AND 07Z.
LIGHT SW WINDS THROUGH THE NIGHT.
SUNDAY... MODERATE CONFIDENCE
MOSTLY VFR EXCEPT FOR THE CAPE AND ISLANDS WITH LINGERING AREAS OF
MVFR AND IFR ACROSS THE CAPE AND ISLANDS THROUGH 21Z. -SN COMES TO
AN END FROM W-E AFTER 16Z EXCEPT OVER THE CAPE WHERE OCEAN EFFECT
SNOW SHOWERS CONTINUE PAST 00Z.
KBOS TERMINAL...HIGH CONFIDENCE IN TAF.
KBDL TERMINAL...HIGH CONFIDENCE IN TAF.
OUTLOOK /MONDAY THROUGH WEDNESDAY/...
MONDAY: VFR. WINDY WITH GUSTS UP TO 35 KT.
MONDAY NIGHT: VFR. BREEZY. SLIGHT CHANCE SHSN.
TUESDAY THROUGH TUESDAY NIGHT: VFR. BREEZY.
WEDNESDAY: VFR. WINDY WITH LOCAL GUSTS UP TO 30 KT.
MARINE
FORECASTER CONFIDENCE LEVELS...
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
TODAY THROUGH SUNDAY NIGHT ...HIGH CONFIDENCE.
SMALL CRAFT ADVISORY CONDITIONS REDEVELOP LATER TODAY INTO THIS
EVENING WITH GUSTY SW WINDS/CHOPPY SEAS DEVELOPING AHEAD OF AN
APPROACHING COLD FRONT. GALE WATCH SUNDAY NIGHT INTO MONDAY AS
STRONG CAA WILL RESULT IN EXCELLENT MIXING OVER THE WATERS.
AREAS OF VERY LIGHT FREEZING SPRAY POSSIBLE SUNDAY NIGHT.
OUTLOOK /MONDAY THROUGH WEDNESDAY/...
MONDAY: MODERATE RISK FOR GALE FORCE WINDS WITH GUSTS UP TO
40 KT. AREAS OF ROUGH SEAS.
MONDAY NIGHT: MODERATE RISK FOR SMALL CRAFT ADVISORY WINDS WITH
GUSTS UP TO 30 KT. SEAS UP TO 5 FT. SLIGHT CHANCE OF SNOW
SHOWERS.
TUESDAY: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS UP
TO 25 KT. AREAS OF SEAS APPROACHING 5 FT.
TUESDAY NIGHT: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH
GUSTS UP TO 30 KT. SEAS LOCALLY APPROACHING 5 FT.
WEDNESDAY: STRONG WINDS WITH GUSTS UP TO 30 KT. SEAS UP TO
5 FT.
BOX WATCHES/WARNINGS/ADVISORIES
CT...NONE.
MA...WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 7 PM EST
SUNDAY FOR MAZ020>024.
RI...WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 7 PM EST
SUNDAY FOR RIZ003>008.
MARINE...SMALL CRAFT ADVISORY FROM 10 AM THIS MORNING TO 1 AM EST
SUNDAY FOR ANZ231>235-237-250-251-254>256.
GALE WATCH FROM SUNDAY EVENING THROUGH MONDAY AFTERNOON FOR
ANZ231>235-237-250-251-254>256.
SYNOPSIS...FT/FRANK
NEAR TERM...FT
SHORT TERM...FT
LONG TERM...FRANK
AVIATION...FT/FRANK
MARINE...FT/FRANK
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