412  
FXUS61 KBOX 230815  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BOSTON/NORTON MA  
415 AM EDT FRI APR 23 2021  
   
SYNOPSIS
 
 
DRY, BUT BREEZY CONDITIONS TODAY WITH A WARMING TREND THROUGH  
SATURDAY. A COASTAL STORM WILL BRING PERIODS OF RAIN SUNDAY FOLLOWED  
BY BLUSTERY AND DRIER CONDITIONS MONDAY. DRY WITH A WARMING TREND  
TUESDAY, THEN A BACKDOOR FRONT COULD BRING COOLER TEMPERATURES  
WEDNESDAY AND THURSDAY, BUT THE LOCATION OF THE FRONT IS UNCERTAIN.  
 

 
   
NEAR TERM /UNTIL 6 PM THIS EVENING/
 
 
HIGHLIGHTS  
 
* ELEVATED FIRE WEATHER CONCERNS FOR MUCH OF SOUTHERN NEW ENGLAND  
TODAY. WILL BE GUSTY WITH MODERATING TEMPERATURES.  
 
CUTOFF LOW WILL CONTINUE ROTATE NEAR/JUST NORTH OF NEW BRUNSWICK  
TODAY. A RIDGE AXIS WILL BUILD FROM THE CENTRAL GREAT LAKES INTO THE  
EASTERN GREAT LAKES. AT THE SURFACE SOUTHERN NEW ENGLAND WILL REMAIN  
WEDGED BETWEEN HIGH PRESSURE BUILDING OFFSHORE FROM THE CAROLINAS  
AND A DEEP LOW TO THE NORTH.  
 
EXPECT DRY AND QUIET WEATHER, BUT WILL BE GUSTY DUE TO THE TIGHT  
PRESSURE GRADIENT IN PLACE. ALOFT WILL HAVE W TO WNW WINDS ADVECTING  
IN +5 TO + 7 DEGREE CELSIUS AIR. GIVEN THE WIND DIRECTION AM ALSO  
ANTICIPATING DOWNSLOPING WHICH WILL WARM AND DRY THINGS FURTHER.  
GIVEN THIS HAVE GONE WITH THE 75TH PERCENTILE OF GUIDANCE FOR HIGH  
TEMPERATURES TODAY. HELD OFF FROM GOING HIGHER AS THERE MAY BE SOME  
CLOUDINESS GIVEN A WEAK SHORTWAVE SLIDING OFFSHORE ALOFT. THIS IS AN  
AREA WHERE IF THERE IS LESS CLOUD COVER TEMPS WILL NEED TO BE  
INCREASED FURTHER. HIGHS GENERALLY IN THE MID TO UPPER 50S, BUT  
THERE WILL BE SOME 60 DEGREE READINGS ACROSS THE EASTERN MA AND THE  
CT RIVER VALLEY.  
 
SHOULD SEE STRONG MIXING WITHIN THE BOUNDARY LAYER THROUGH THE DAY  
GIVEN THE TIGHT PRESSURE GRADIENT AND HEATING. HAVE LEANED GUSTS  
TOWARD THE HRRRE/NAMNEST GUIDANCE AND NUDGED THINGS UP A BIT MORE  
BASED ON BUFKIT PROFILES. MOSTLY SHOULD SEE 30-35 MPH GUSTS THIS  
AFTERNOON. GIVEN THE SETUP HAVE LOWERED DEW POINTS TO THE 10TH  
PERCENTILE OF GUIDANCE, WHICH BRINGS MINIMUM RELATIVE HUMIDITIES  
INTO THE 20S AND 30S FOR MUCH OF SOUTHERN NEW ENGLAND. PER  
COORDINATION WITH STATE FIRE WEATHER PARTNERS WE HAVE ISSUED ANOTHER  
SPS HIGHLIGHTING THE ELEVATED FIRE WEATHER CONCERN.  
 

 
   
SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/
 
 
HIGHLIGHTS  
 
* DRY AND QUIET WEATHER PERSISTS WITH TEMPERATURES CONTINUING TO  
MODERATE.  
 
RIDGE AXIS BUILDS INTO NEW ENGLAND TONIGHT, BUT FLATTENS OUT A BIT.  
THERE WILL BE SOME RIDGING ACROSS THE MID ATLANTIC TONIGHT THAT  
BUILDS INTO SOUTHERN NEW ENGLAND ON SATURDAY. WILL SEE A TROUGH  
BEGIN LIFTING FROM THE LOW/MID MISSISSIPPI RIVER VALLEY INTO THE  
OHIO VALLEY BY LATE SATURDAY. AT THE SURFACE HIGH PRESSURE WILL  
CONTINUE TO NUDGE IN FROM OFFSHORE OF THE CAROLINAS TONIGHT THROUGH  
SATURDAY. WILL SEE INCREASING MID TO HIGH CLOUDS LATER ON SATURDAY.  
 
TONIGHT...  
 
DRY AND QUIET WEATHER WITH THE MIXED LAYER DECOUPLING DURING THE  
EVENING AND WINDS BECOMING LIGHTER AND GENERALLY W TO WSW. SHOULD  
HAVE WNW FLOW ALOFT BRINGING +6 TO +9 DEGREE CELSIUS AIR OVERHEAD AT  
925 HPA. SHOULD HAVE SOME RADIATIONAL COOLING, BUT GIVEN THE WARM  
AIR ADVECTION TEMPERATURES WON'T DROP TOO MUCH AND WILL FEEL MILD  
COMPARED TO THIS MORNING. LOWS BOTTOMING OUT IN THE UPPER 30S ACROSS  
THE HIGHER TERRAIN AND 40S ELSEWHERE.  
 
SATURDAY...  
 
ANOTHER DAY OF DRY AND QUIET WEATHER. WILL SEE INCREASING MID TO  
HIGH CLOUD COVER AS A SYSTEM DEVELOPS WELL TO THE SOUTHWEST. AS WITH  
THE PREVIOUS PERIODS WILL HAVE CONTINUED WARM AIR ADVECTION ALOFT.  
THOUGH WILL SEE WINDS SHIFT FROM A WESTERLY DIRECTION TO THE WSW/SW.  
AT 925 HPA WILL HAVE +9 TO +12 DEGREE CELSIUS AIR OVERHEAD. BROUGHT  
HIGH TEMPERATURES TOWARD THE 75TH PERCENTILE OF GUIDANCE GIVEN I  
HAVE SOME CONCERNS ON HOW QUICKLY THE MID/HIGH CLOUDS MOVE IN. HIGH  
TEMPERATURES MOSTLY IN THE UPPER 60S TO LOW 70S. THE ONLY EXCEPTION  
IS ALONG THE SOUTH COAST WHERE SOUTHWESTERLY FLOW WILL KEEP THINGS  
IN THE UPPER 50S TO LOW 60S.  
 

 
   
LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/
 
 
HIGHLIGHTS  
 
* COOL WITH PERIODS OF RAIN LATE SATURDAY NIGHT INTO SUNDAY  
* DRY AND BLUSTERY MONDAY WITH SEASONABLE TEMPS  
* DRY WITH A WARMING TUE  
* POSSIBLE BACKDOOR FRONT WED/THU? LOW CONFIDENCE TEMP FORECAST  
 
SATURDAY NIGHT INTO SUNDAY...  
 
TREND IN THE DETERMINISTIC AND ENSEMBLE GUIDANCE IS FOR A MORE  
OFFSHORE TRACK OF COASTAL LOW, BUT THERE IS STILL A FAIR AMOUNT OF  
SPREAD WITHIN THE ENSEMBLE DISTRIBUTION WHICH WILL IMPACT POTENTIAL  
RAINFALL AMOUNTS. MOST OF THE GEFS AND ECMWF MEMBERS HAVE LOW TRACK  
ALONG OR SOUTH OF 40N BUT THERE ARE SOME MEMBERS CLOSE TO SNE COAST.  
BEST CHANCE FOR A SOAKING RAINFALL OF 0.50"+ WILL BE NEAR THE SOUTH  
COAST, BUT WITH THE QPF GRADIENT POSSIBLY ACROSS SNE THERE IS MORE  
UNCERTAINTY FURTHER TO THE N WHERE ONLY LIGHT AMOUNTS OF RAIN ARE  
POSSIBLE IF STORM TRACK TRENDS FURTHER SOUTH. LATEST TRENDS WILL  
CONTINUE TO BE MONITORED. TIMING OF RAINFALL IS LATE SAT NIGHT INTO  
SUN WITH BULK OF RAINFALL EXITING DURING THE AFTERNOON AS THIS IS A  
PROGRESSIVE SYSTEM.  
 
WITH A MORE OFFSHORE TRACK, WIND AND COASTAL FLOOD RISKS ARE  
BECOMING LESS OF A CONCERN AS MAIN CORE OF LOW LEVEL JET IS LIKELY  
TO REMAIN OFFSHORE WITH LESS SURGE AND WAVE ACTION. THE SUNDAY  
EVENING HIGH TIDE IS THE ONLY TIDE CYCLE THAT NEEDS TO BE MONITORED  
BUT WINDS WILL ALREADY HAVE SHIFTED TO NW BY THAT TIME AND PEAK  
SURGE, ONLY AROUND 1 FT, IS PRECEDING THE HIGH TIDE. UNLESS THE  
STORM TRACK SHIFTS BACK TO THE NORTH AND WE GET INTO THE CORE OF THE  
LOW LEVEL JET, COASTAL FLOODING APPEARS UNLIKELY.  
 
MONDAY...  
 
BLUSTERY CONDITIONS BUT DRY AS STORM DEPARTS INTO THE MARITIMES. NW  
WIND GUSTS 25 TO 35 MPH EXPECTED WITH MOSTLY SUNNY SKIES. NEAR  
SEASONABLE TEMPS, UPPER 50S TO LOWER 60S.  
 
TUESDAY THROUGH THURSDAY...  
 
MAINLY DRY WEATHER THROUGH THE PERIOD. WARMING TREND BEGINS TUE AS  
UPPER RIDGE BEGINS TO BUILD IN FROM THE WEST. TEMPS SHOULD REACH  
WELL INTO THE 60S WITH SOME LOWER 70S IN THE CT VALLEY. THEN  
FORECAST CONFIDENCE DECREASES WED/THU DUE TO POTENTIAL BACKDOOR  
FRONT. LARGE SPREAD IN DETERMINISTIC AND ENSEMBLE GUIDANCE FOR MAX  
TEMPS WED AND THU DEPENDING ON LOCATION OF THE FRONT. TEMPS COULD  
REACH WELL INTO 70S AND EVEN 80S, BUT IF THE BACKDOOR FRONT MOVES  
THROUGH THIS WOULD HOLD TEMPS IN THE 50S/60S, ESPECIALLY NEAR THE  
COAST. OBVIOUSLY A LOW CONFIDENCE FORECAST. FORECAST WILL HAVE HIGHS  
IN THE 70S AWAY FROM THE COAST, BUT COULD BE MUCH COOLER OR EVEN  
WARMER DEPENDING ON FRONT LOCATION WHICH IS UNCERTAIN AT THIS TIME  
RANGE.  
 

 
   
AVIATION /08Z FRIDAY THROUGH TUESDAY/
 
 
FORECASTER CONFIDENCE LEVELS.  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
THROUGH 12Z...HIGH CONFIDENCE.  
 
VFR CONDITIONS WITH A FEW CLOUDS AT BASES OF 6-8 KFT. STILL MAY  
BE BREEZY AT TIMES OF OUT THE W WITH SUSTAINED WINDS BETWEEN  
10-15 KTS. SOME LOCATIONS HAVE SEEN THE MIXED LAYER DECOUPLE,  
BUT HAVE KEPT THE 20-25 KT GUSTS IN FOR A FEW AREAS GIVEN BUFKIT  
PROFILES SHOW THESE WINDS NOT TOO FAR AGL.  
 
TODAY...HIGH CONFIDENCE.  
 
VFR WITH A FEW TO SCATTERED CLOUDS BETWEEN 5-8 KFT. SHOULD BE  
MOST PRONOUNCED ACROSS THE INTERIOR. STILL GUSTY OUT OF THE W  
WITH SUSTAINED WINDS BETWEEN 15-25 KTS AND GUSTS OF 25-30 KTS.  
THERE COULD BE A FEW GUSTS UP TO 35 KTS AT TIMES.  
 
TONIGHT...HIGH CONFIDENCE.  
 
VFR WITH SKIES CLEARING. EXPECT THE GUSTY WINDS TO COME TO AN  
END AS THE MIXED LAYER DECOUPLES. SPEEDS DIMINISH TO 5-10 KTS  
WITH THE HIGHER SPEEDS ALONG THE HIGHER TERRAIN AND COASTLINE.  
 
SATURDAY...HIGH CONFIDENCE.  
 
VFR WITH W WINDS SHIFTING TO THE SW AT SPEEDS OF 5-15 KTS. COULD  
HAVE SOME 20 KT GUSTS ALONG THE SOUTH COAST DURING THE  
AFTERNOON.  
 
KBOS TAF...HIGH CONFIDENCE IN TAF.  
 
KBDL TAF...HIGH CONFIDENCE IN TAF.  
 
OUTLOOK /SATURDAY NIGHT THROUGH TUESDAY/...  
 
SATURDAY NIGHT: MAINLY VFR, WITH AREAS MVFR POSSIBLE. BREEZY.  
CHANCE RA.  
 
SUNDAY: MAINLY MVFR, WITH AREAS IFR POSSIBLE. BREEZY. RA  
LIKELY.  
 
SUNDAY NIGHT: MAINLY VFR, WITH LOCAL MVFR POSSIBLE. BREEZY.  
 
MONDAY: VFR. WINDY WITH LOCAL GUSTS UP TO 30 KT.  
 
MONDAY NIGHT: VFR. BREEZY.  
 
TUESDAY: VFR.  
 

 
   
MARINE
 
 
TODAY...  
 
GALE FORCE GUSTS CONTINUE FOR A GOOD PORTION OF THE WATERS INTO AT  
LEAST LATE MORNING. DID OPT TO EXTEND THE GALE WARNING FOR THE FAR  
SOUTHERN WATERS. THOUGH GUSTS FOR THE FAR SOUTHERN WATERS ARE SUB-  
GALE FORCE NOW WE SHOULD SEE AN ACCELERATION LATE THIS MORNING INTO  
THE AFTERNOON AS WESTERLY LOW LEVEL JET STRENGTHENS. THIS WILL BRING  
BACK THE GALE FORCE GUSTS. MOST OTHER LOCATIONS WILL SEE GUSTS  
DIMINISHING TO THE 20-25 KT RANGE, SO ANY OTHER AREAS WILL NEED  
SMALL CRAFT ADVISORIES IN PLACE OF THE GALE WARNINGS. WAVE HEIGHTS  
OF 6-10 FT.  
 
TONIGHT AND SATURDAY...  
 
WESTERLY AND WSW WINDS DIMINISHING TONIGHT. WINDS CONTINUE TO  
DIMINISH ON SATURDAY, BUT WILL SHIFT MORE TO THE SW. GUSTS FALLING  
TO THE 15 TO 20 KT RANGE TONIGHT AND THIS CONTINUES THROUGH  
SATURDAY. SEAS 5-7 FT TONIGHT AND 3-5 FT ON SATURDAY.  
 
OUTLOOK /SATURDAY NIGHT THROUGH TUESDAY/...  
 
SATURDAY NIGHT: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING  
5 FT. CHANCE OF RAIN.  
 
SUNDAY: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS UP  
TO 30 KT. LOCAL ROUGH SEAS. RAIN.  
 
SUNDAY NIGHT: MODERATE RISK FOR SMALL CRAFT ADVISORY WINDS WITH  
GUSTS UP TO 30 KT. ROUGH SEAS UP TO 10 FT. SLIGHT CHANCE OF  
RAIN SHOWERS.  
 
MONDAY: MODERATE RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS  
UP TO 25 KT. AREAS OF ROUGH SEAS.  
 
MONDAY NIGHT: WINDS LESS THAN 25 KT. SEAS UP TO 5 FT.  
 
TUESDAY: WINDS LESS THAN 25 KT. AREAS OF SEAS APPROACHING 5 FT.  
 

 
   
FIRE WEATHER
 
 
* ELEVATED FIRE WEATHER POTENTIAL ACROSS MUCH OF SOUTHERN NEW  
ENGLAND TODAY.  
 
AS HIGHLIGHTED ABOVE IN THE SHORT TERM SECTION, TODAY WILL  
FEATURE GUSTY WESTERLY WINDS AND DEEP BOUNDARY LAYER MIXING.  
GIVEN THE STRONG WINDS AND LOW RELATIVELY HUMIDITIES, HAVE GONE  
WITH A SPECIAL WEATHER STATEMENT TO HIGHLIGHT THE ELEVATED FIRE  
WEATHER POTENTIAL PER COORDINATION WITH FIRE WEATHER PARTNERS.  
SHOULD SEE MINIMUM RELATIVE HUMIDITIES FALL TO 20 TO 35 PERCENT  
WITH GUSTS OF 25 TO 35 MPH.  
 

 
   
BOX WATCHES/WARNINGS/ADVISORIES
 
 
CT...NONE.  
MA...NONE.  
RI...NONE.  
MARINE...GALE WARNING UNTIL 8 PM EDT THIS EVENING FOR ANZ232-255-256.  
SMALL CRAFT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR ANZ230-  
231-233-234-236.  
SMALL CRAFT ADVISORY UNTIL 2 AM EDT SATURDAY FOR ANZ235-237.  
GALE WARNING UNTIL NOON EDT TODAY FOR ANZ250-251-254.  
 

 
 

 
SYNOPSIS...KJC  
NEAR TERM...BL  
SHORT TERM...BL  
LONG TERM...KJC  
AVIATION...KJC/BL  
MARINE...KJC/BL  
FIRE WEATHER...  
 
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