129  
FXUS61 KBOX 060016  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BOSTON/NORTON MA  
716 PM EST SAT DEC 5 2020  
   
SYNOPSIS
 
 
A RAPIDLY INTENSIFYING STORM SYSTEM OFF CAPE COD WILL PRODUCE  
GUSTY WINDS, HEAVY RAIN, AND A PERIOD OF ACCUMULATING HEAVY,  
WET SNOW. THE WIND AND PRECIPITATION WILL TAPER OFF TONIGHT.  
THE STORM EXITS THROUGH THE MARITIMES OVERNIGHT. DRY AND COLDER  
WEATHER MOVES IN FOR SUNDAY THROUGH TUESDAY WITH A MODERATING  
TREND FOR THE MIDDLE OF NEXT WEEK.  
 

 
   
NEAR TERM /UNTIL 6 AM SUNDAY MORNING/
 
 
7 PM UPDATE...  
 
WE'RE IN THE THICK OF IT THIS EVENING WITH HEAVY WET SNOW  
CONTINUING AS WINDS CONTINUE TO RAMP UP. THE LOW IS CENTERED  
DIRECTLY EAST OF MA OFFSHORE THIS EVENING WITH WINDS NOW HAVING  
COME OUT OF THE NORTHWEST. HEARING MANY REPORTS OF EXTREMELY  
WET FLAKES COMING DOWN ACROSS EASTERN MA WHICH MAKES SENSE GIVEN  
THE EXTREMELY MILD AIRMASS. SFC TEMPERATURES ACROSS THE REGION  
GENERALLY 32-35 WHERE WE'RE SEEING SNOW. INTENSITY HAS BACKED  
OFF SINCE THIS AFTERNOON GIVEN THE BEST FRONTOGENESIS NOW LIFTED  
INTO NORTHERN NEW ENGLAND. WHILE THE BACK EDGE OF THE PRECIP IS  
NOW APPROACHING CENTRAL MA, WHAT EARLIER SEEMED LIKE A DRASTIC  
DROP IN RADAR RETURNS TOWARD NORTHERN MA CAN LIKELY BE  
ATTRIBUTED TO ERRONEOUS RADAR ATTENUATION DUE TO THE HEAVY WET  
SNOW. ADDITIONAL ACCUMULATIONS WILL BE SLOW AND LIKELY LESS THAN  
PREVIOUSLY EXPECTED IN THE I-95 CORRIDOR OWING TO THE WARM  
TEMPERATURES AND RELATIVELY HIGH DEWPOINTS (AT OR ABOVE  
FREEZING) LIMITING ADDITIONAL COOLING.  
 
PREVIOUS DISCUSSION...  
 
COASTAL LOW PRESSURE NEAR OUTER CAPE COD WILL MOVE OFF THROUGH  
THE MARITIMES OVERNIGHT. RAIN AND SNOW THIS EVENING WILL TAPER  
OFF FROM WEST TO EAST TONIGHT, ENDING LATEST ALONG THE  
MASSACHUSETTS NORTH SHORE DURING THE OVERNIGHT.  
 
THE RAIN/SNOW LINE MID AFTERNOON EXTENDED FROM BOSTON AND THE  
NORTH SHORE THROUGH THE WESTERN SUBURBS OF BOSTON, THE NW CORNER  
OF RHODE ISLAND, AND NORTHEAST CT. AS THE COASTAL LOW LIFTS PAST  
NANTUCKET AND OUTER CAPE COD, EXPECT THE COLDER AIR INLAND TO  
MOVE FARTHER EAST AND CHANGE THE RAIN IN RI AND SE MASS TO SNOW.  
THAT SHOULD BE ROUGHLY 4 PM TO 7 PM. HEAVIEST AMOUNTS WILL  
REMAIN FROM THE CENTRAL HILLS THROUGH THE MERRIMACK VALLEY.  
NO SIGNIFICANT CHANGES IN FORECAST AMOUNTS FROM PREVIOUS  
FORECASTS.  
 
AS THE COASTAL LOW PULLS AWAY FROM THE COAST OVERNIGHT, THE  
PRECIPITATION WILL TAPER OFF FROM WEST TO EAST, AND CLEARING  
SKIES WILL MOVE IN FROM THE WEST. TEMPS WILL COOL TO THE 20S  
INLAND AND 30-35 ALONG THE COAST.  
 

 
   
SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/
 
 
STILL CYCLONIC FLOW ON SUNDAY AROUND THE MARITIME CLOSED LOW.  
HOWEVER THERE WILL ALSO BE DRIER AIR MOVING IN. CROSS SECTIONS  
OF MOISTURE SHOW A LITTLE LINGERING MOISTURE AT OR BELOW 850 MB,  
BUT LOTS OF DRY AIR ABOVE THAT. WHILE THERE MAY BE SOME DIURNAL  
CLOUDS, EXPECT A PARTLY TO MOSTLY SUNNY DAY. MIXING IS FORECAST  
TO REACH 925-MB, WITH WINDS OF 25-30 KT AVAILABLE FOR GUSTS.  
TEMPS AT 925-MB WILL BE -4 TO -5C, SO MAX SFC TEMPS MOSTLY MID  
30S TO AROUND 40.  
 
DRY AIR LINGERS SUNDAY NIGHT WITH LIGHTER WEST-NORTHWEST WINDS.  
WITH DEW POINTS 15 TO 25, EXPECT MIN TEMPS CLOSE TO THAT.  
 

 
   
LONG TERM /MONDAY THROUGH SATURDAY/
 
 
FAIRLY QUIET WEATHER EXPECTED THROUGH THE PERIOD. WE ARE  
WATCHING ANOTHER POTENTIAL CUTOFF LOW FROM THE OHIO VALLEY TO  
THE MID ATLANTIC STATES EARLY NEXT WEEK, BUT WITH LACK OF  
DOWNSTREAM BLOCKING THIS TIME (I.E., NO RIDGING OVER GREENLAND)  
SYSTEM IS LIKELY TO PASS WELL SOUTH OF NEW ENGLAND. DID INCLUDE  
SOME CHANCE POPS NEAR SOUTH COAST, CAPE, AND ISLANDS BUT FOR  
MOST PART EXPECT THIS SYSTEM TO HAVE LITTLE IMPACT ON SNE (AS OF  
RIGHT NOW, ANYWAY). UPPER FLOW TURNS MORE ZONAL FOR MID TO LATE  
WEEK WHICH SHOULD ALLOW FOR TEMPERATURES TO MODERATE INTO 40S  
TO AROUND 50.  
 

 
   
AVIATION /00Z SUNDAY THROUGH THURSDAY/
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
TONIGHT...MODERATE CONFIDENCE.  
 
IFR/LIFR THROUGH THE EVENING. RAIN CHANGING TO SNOW IN EASTERN  
MA AND RI, WITH MAINLY SNOW IN WESTERN/CENTRAL MA AND NRN CT.  
ALL RAIN FOR CAPE/ISLANDS. EXPECT THESE CONDITIONS TO CHANGE TO  
SNOW MOST PLACES DURING THE EVENING, THEN TAPER OFF FROM WEST TO  
EAST DURING THE FIRST HALF OF THE NIGHT, ROUGHLY 01-05Z/8PM TO  
MIDNIGHT. SKIES IMPROVE TO VFR WITH CLEARING SKIES. CLEARING AT  
BOSTON TOWARD MORNING.  
 
STRONGEST WINDS EXPECTED THIS EVENING WITH NORTH WINDS TURNING  
FROM THE NORTHWEST WHILE GUSTING TO 25-35 KT INLAND AND 40-50  
KT ALONG THE COAST WITH 50 KT GUSTS MOST LIKELY ON CAPE  
COD/ISLANDS.  
 
SUNDAY...VFR. NORTHWEST WINDS GUSTING 25 TO 30 KT INLAND AND 30  
TO 35 KT ALONG THE COAST INCLUDING CAPE AND ISLANDS.  
 
SUNDAY NIGHT...VFR. WEST-NORTHWEST WINDS LESS THAN 20 KT AND  
DIMINISHING.  
 
KBOS TAF...MODERATE CONFIDENCE IN THE TAF.  
 
KBDL TAF...MODERATE CONFIDENCE IN THE TAF.  
 
OUTLOOK /MONDAY THROUGH THURSDAY/...  
 
MONDAY: VFR.  
 
MONDAY NIGHT: MAINLY VFR, WITH LOCAL MVFR POSSIBLE. BREEZY.  
 
TUESDAY THROUGH TUESDAY NIGHT: VFR. BREEZY.  
 
WEDNESDAY: VFR.  
 
WEDNESDAY NIGHT: VFR. BREEZY. SLIGHT CHANCE SHSN.  
 
THURSDAY: VFR. BREEZY.  
 

 
   
MARINE
 
 
TONIGHT...  
 
COASTAL LOW PRESSURE PASSES NEAR NANTUCKET THIS EVENING AND EAST  
OF OUTER CAPE COD EARLY TONIGHT, THEN HEADS THROUGH THE GULF OF  
MAINE OVERNIGHT. STRONG SHIFTING WINDS NEAR THE PATH OF THE LOW,  
WITH DIRECTIONS SHIFTING OUT OF THE NORTHWEST DURING THE NIGHT.  
 
WINDS GUSTING 50-55 KT THIS EVENING, DIMINISHING TO 35-40 KT  
AFTER MIDNIGHT. STORM WARNING CONTINUES ON MOST WATERS, WITH  
GALES ON THE REMAINING WATERS. STORMS MAY BE LOWERED TO GALES  
LATE AT NIGHT. SEAS 10 TO 15 FEET ON THE EXPOSED WATERS  
TONIGHT.  
 
SUNDAY...DIMINISHING NORTHWEST WINDS WITH GUSTS AROUND 35 KT IN  
THE MORNING, THEN AROUND 30 KT IN THE AFTERNOON. SEAS SUBSIDE  
TO 5-7 FEET IN THE AFTERNOON. GALES EXPECTED THROUGH THE FIRST  
HALF OF THE DAY.  
 
SUNDAY NIGHT...DIMINISHING WEST-NORTHWEST WINDS AT SMALL CRAFT  
ADVISORY LEVELS THE FIRST HALF OF THE NIGHT. SEAS 5 TO 7 FEET ON  
THE EXPOSED WATERS.  
 
OUTLOOK /MONDAY THROUGH THURSDAY/...  
 
MONDAY: WINDS LESS THAN 25 KT. AREAS OF SEAS APPROACHING 5 FT.  
 
MONDAY NIGHT: WINDS LESS THAN 25 KT. AREAS OF SEAS APPROACHING  
5 FT. SLIGHT CHANCE OF RAIN SHOWERS.  
 
TUESDAY: WINDS LESS THAN 25 KT. SEAS UP TO 5 FT. SLIGHT CHANCE  
OF RAIN SHOWERS.  
 
TUESDAY NIGHT THROUGH WEDNESDAY: WINDS LESS THAN 25 KT. SEAS UP  
TO 5 FT.  
 
WEDNESDAY NIGHT: WINDS LESS THAN 25 KT. SEAS UP TO 5 FT. SLIGHT  
CHANCE OF RAIN SHOWERS.  
 
THURSDAY: WINDS LESS THAN 25 KT. SEAS UP TO 5 FT.  
 

 
   
BOX WATCHES/WARNINGS/ADVISORIES
 
 
CT...WINTER STORM WARNING UNTIL 7 AM EST SUNDAY FOR CTZ003-004.  
WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR CTZ002.  
MA...HIGH WIND WARNING UNTIL MIDNIGHT EST TONIGHT FOR MAZ007-019-  
022>024.  
WINTER WEATHER ADVISORY UNTIL 1 AM EST SUNDAY FOR MAZ016>019.  
WIND ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR MAZ013>018-020-  
021.  
WINTER STORM WARNING UNTIL 7 AM EST SUNDAY FOR MAZ003>007-  
010>015-026.  
WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR MAZ002-  
008-009.  
RI...HIGH WIND WARNING UNTIL MIDNIGHT EST TONIGHT FOR RIZ008.  
WINTER WEATHER ADVISORY UNTIL 1 AM EST SUNDAY FOR RIZ002>004.  
WIND ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR RIZ002>007.  
WINTER STORM WARNING UNTIL 7 AM EST SUNDAY FOR RIZ001.  
MARINE...STORM WARNING UNTIL 3 AM EST SUNDAY FOR ANZ231>234-250-251-  
254>256.  
GALE WARNING UNTIL 11 AM EST SUNDAY FOR ANZ230-236.  
STORM WARNING UNTIL 1 AM EST SUNDAY FOR ANZ235-237.  
 

 
 

 
SYNOPSIS...WTB/KJC  
NEAR TERM...WTB/BW  
SHORT TERM...WTB  
LONG TERM...KJC  
AVIATION...WTB/BW  
MARINE...WTB/BW  
 
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