170  
FXUS61 KBOX 250231  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BOSTON/NORTON MA  
1031 PM EDT FRI SEP 24 2021  
   
SYNOPSIS
 
 
MAINLY DRY WEATHER TONIGHT INTO SATURDAY MORNING EXCEPT FOR A  
PERSISTENT BAND OF SHOWERS ACROSS THE CAPE AND ISLANDS AND  
NEARBY WATERS. A SECOND LOW PRESSURE WILL BRING ANOTHER CHANCE  
FOR SHOWERS SATURDAY AFTERNOON AND NIGHT, PRIMARILY ACROSS  
EASTERN MASSACHUSETTS AND RHODE ISLAND. COOLER AND LESS HUMID  
WEATHER IS ON TAP FOR THE SECOND HALF OF THIS WEEKEND AND MUCH  
OF NEXT WEEK; ESPECIALLY BY THE LATTER HALF OF THE WEEK. MUCH  
OF NEXT WEEK WILL BE DRY, EXCEPT FOR A FEW SHOWERS POSSIBLE  
LATER MONDAY INTO EARLY TUESDAY. BY LATE NEXT WEEK WILL HAVE TO  
WATCH AN OFFSHORE LOW PRESSURE, BUT IT REMAINS UNCERTAIN IF IT  
WILL TRACK CLOSE ENOUGH TO BRING A PERIOD A SOAKING RAIN.  
 

 
   
NEAR TERM /UNTIL 6 AM SATURDAY MORNING/
 
 
A NEARLY STATIONARY FRONT WAS PARKED ACROSS THE CAPE AND  
ISLANDS THIS EVENING, AS WELL AS THE ADJACENT COASTAL WATERS.  
THIS BOUNDARY PROVIDED ENOUGH CONVERGENCE TO MAINTAIN A  
PERSISTENT BAND OF SHOWERS. WILL NEED TO MONITOR RAINFALL TOTALS  
CLOSELY OVERNIGHT, AS THIS COULD LEAD TO SOME FLOODING. THUS  
FAR, RAINFALL RATES HAVE BEEN LIGHT ENOUGH WHERE NOT CONCERNED  
ABOUT MUCH MORE THAN NUISANCE FLOODING OF POOR-DRAINAGE AND LOW-  
LYING AREAS.  
 
MADE SIGNIFICANT CHANGES TO RAINFALL CHANCES OVERNIGHT. TRIED  
TO TAKE ADVANTAGE OF THE LATEST RUNS OF THE HRRR, WHICH HAD THE  
RIGHT IDEA, ALBEIT SLIGHTLY WEST OF WHERE RAINFALL WAS OBSERVED  
ON RADAR. MINOR TWEAKS TO TEMPERATURES.  
 
PREVIOUS DISCUSSION...  
 
THE SLOW MOVING COLD FRONT WAS BEGINNING TO WASHOUT ACROSS  
EASTERN MA/RI, SO THE DRIER AIR WILL STRUGGLE TO MAKE IT MUCH  
FURTHER EAST TONIGHT. MOIST SOUTHERLY FLOW JUST OFF THE DECK  
WILL ALLOW FOR A FEW SPOT SHOWERS AT TIMES ACROSS PARTS OF  
EASTERN MA OVERNIGHT, BUT DRY WEATHER WILL DOMINATE. HOWEVER,  
SHOWERS WILL BE A BIT MORE NUMEROUS ACROSS THE CAPE/ISLANDS  
WHERE SOME SURFACE INSTABILITY REMAINED ALONG WITH A BIT BETTER  
LOW LEVEL CONVERGENCE.  
 
WE DO EXPECT PLENTY OF CLOUDS TO PERSIST ACROSS CENTRAL/EASTERN  
MA AND RI GIVEN THE WEAKENING PUSH OF DRIER LOW LEVEL AIR ALONG  
WITH SOUTHERLY FLOW OFF THE DECK. MEANWHILE, AREAS NEAR AND  
WEST OF THE CT RIVER VALLEY SHOULD SEE JUST SOME SCATTERED  
CLOUDS AT TIMES TONIGHT. THIS COUPLED WITH THE LARGE MOISTURE  
GRADIENT WILL ALLOW FOR A BIG SPREAD IN OVERNIGHT LOW TEMPS.  
READINGS SHOULD BOTTOM OUT IN THE UPPER 40S TO LOWER 50S NEAR  
AND WEST OF THE CT RIVER; WHERE SOME PATCHY DENSE GROUND FOG MAY  
DEVELOP LATE. MEANWHILE, LOW TEMPS ACROSS EASTERN MA/RI WILL  
ONLY BOTTOM OUT IN THE UPPER 50S TO THE MIDDLE 60S WITH THE  
MILDEST OF THOSE READINGS FOUND ACROSS THE CAPE AND ISLANDS.  
 

 
   
SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/
 
 
WESTERN MA AND CT WILL WAKE UP TO MOSTLY SUNNY CONDITIONS ON  
SATURDAY WHILE EASTERN MA AND RI WILL CONTINUE TO BE SOCKED IN  
WITH CLOUDS FOR MOST OF THE DAY. WHILE THE DAY STARTS OUT MOSTLY  
DRY, AN APPROACHING LOW PRESSURE ALONG THE AXIS OF THE COLD  
FRONT WHICH PASSED ACROSS OUR AREA FRIDAY/FRIDAY NIGHT WILL  
CAUSE SHOWERS AND EMBEDDED DOWNPOURS TO ROTATE BACK IN ACROSS  
EASTERN AREAS. IT IS EXPECTED THAT THERE WILL BE A SHARP  
GRADIENT IN SHOWERS, SUCH THAT AREAS WEST OF WORCESTER WILL SEE  
LITTLE TO NO PRECIPITATION, AND AREAS EAST WILL SEE UPWARDS OF  
AN INCH OF RAIN THROUGH SATURDAY NIGHT. THE TRICKY PART OF THE  
FORECAST LIES IN WHERE THIS PRECIPITATION GRADIENT SETS UP, WITH  
SOME HIGH RESOLUTION GUIDANCE AND THE GFS KEEPING THE  
PRECIPITATION SHIELD MUCH FARTHER EAST THAN OTHER GUIDANCE,  
NAMELY THE ECMWF, WHICH BRINGS PRECIPITATION INTO WORCESTER  
COUNTY AND EASTERN CONNECTICUT. DRY UPPER LEVEL AIR CONTINUES TO  
REMAIN IN PLACE BUT WILL NOT WORK DOWN TO THE SURFACE UNTIL  
SOMETIME ON SUNDAY. TEMPERATURES WILL BE SEASONABLE ON  
SATURDAY, IN THE UPPER 60S AND LOW 70S WITH PRIMARILY N/NE FLOW.  
THE WARMEST AREAS WILL BE ACROSS THE CT RIVER VALLEY WHERE  
SUNSHINE DOMINATES THE MORNING HOURS AND CAPE COD WHERE HIGH  
DEWPOINTS SET THE AREA UP FOR A UNSEASONABLY MILD START.  
 

 
   
LONG TERM /SUNDAY THROUGH FRIDAY/
 
 
HIGHLIGHTS...  
 
* COOLER/LESS HUMID NEXT WEEK WITH EARLY FALL-LIKE TEMPERATURES  
PARTICULARLY BY THE SECOND HALF OF NEXT WEEK  
 
* A FEW SHOWERS POSSIBLE LATE MON INTO EARLY TUE & WE WILL NEED TO  
WATCH AN OFFSHORE LOW PRESSURE SYSTEM BY LATE IN THE WEEK  
 
DETAILS...  
 
A PATTERN CHANGE TO MORE TYPICAL/SEASONABLE EARLY FALL TEMPERATURES  
IS IN THE CARDS FOR NEXT WEEK. UPPER LEVEL RIDGING THAT HAS  
DOMINATED MOST OF THE MONTH SO FAR WILL BE REPLACED BY A NORTHEAST  
TROUGH. WE WILL BREAK IT DOWN A BIT MORE BELOW.  
 
SUNDAY...  
 
LOW RISK FOR A LEFT OVER SHOWER OR TWO EARLY=MID MORNING SUNDAY NEAR  
THE COAST IN ASSOCIATION WITH THE DEPARTING WAVE OF LOW PRESSURE.  
OTHERWISE, PLENTY OF SUNSHINE ON SUNDAY TO CLOSE OUT THE WEEKEND  
WITH HIGH TEMPS MAINLY IN THE LOWER TO MIDDLE 70S. IT WILL ALSO BE  
TURNING LESS HUMID AS DRIER LOW LEVEL AIR WORKS IN FROM THE WEST.  
 
MONDAY AND TUESDAY...  
 
A FEW SHOWERS ARE POSSIBLE SOMETIME LATER MON INTO EARLY TUE IN  
ASSOCIATION WITH A SECONDARY COLD FRONT. LOW LEVEL MOISTURE THOUGH  
WILL BE LIMITED; SO ANY RAINFALL THAT OCCURS WILL BE ON THE LIGHT  
SIDE. HIGH TEMPERATURES PROBABLY REACH THE 70S IN MOST LOCATIONS  
MON, BUT PROBABLY THE UPPER 60S TO LOWER 70S ON TUE BEHIND THE COLD  
FRONT. LOW TEMPS WILL MAINLY BE IN THE 40S AND 50S.  
 
WEDNESDAY THROUGH FRIDAY...  
 
A 1035 MB HIGH PRESSURE SYSTEM ACROSS EASTERN CANADA WILL COMBINED  
WITH SOME SORT OF OFFSHORE LOW PRESSURE SYSTEM TO GENERATE NORTHEAST  
LOW LEVEL FLOW FOR THE SECOND HALF OF NEXT WEEK. HIGH TEMPERATURES  
WILL PROBABLY BE HELD IN THE 60S TO NEAR 70 MUCH OF THIS PERIOD. THE  
BIGGER UNCERTAINTY REVOLVES AROUND WHETHER THIS OFFSHORE LOW TRACKS  
FAR ENOUGH NORTH TO BRING A SOAKING RAIN WITH PERHAPS GUSTY NE WINDS  
BY VERY LATE NEXT WEEK. THIS REMAINS QUITE UNCERTAIN GIVEN A LARGE  
SPREAD IN THE ENSEMBLES, BUT IT WILL NEED TO BE WATCHED.  
 

 
   
AVIATION /02Z SATURDAY THROUGH WEDNESDAY/
 
 
FORECASTER CONFIDENCE LEVELS.  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
TONIGHT...MODERATE CONFIDENCE. MAINLY VFR CONDITIONS WILL  
CONTINUE, BUT SOME PATCHY DENSE GROUND FOG IS POSSIBLE LATE  
ACROSS THE TYPICALLY PRONE LOCATIONS OF WESTERN MA. OTHERWISE,  
LOWER CEILINGS WILL MAINLY BE CONFINED TO THE SOUTHEAST NEW  
ENGLAND COAST TOWARDS THE CAPE/ISLANDS. THIS IS WHERE MVFR  
CONDITIONS ALONG WITH SCATTERED SHOWERS ARE EXPECTED AT TIMES.  
LIGHT TO CALM WINDS.  
 
SATURDAY...MAINLY VFR ACROSS THE INTERIOR, WITH MVFR MORE LIKELY  
TOWARDS SOUTHEAST MA, INCLUDING THE CAPE AND ISLANDS.  
SCATTERED SHOWERS DEVELOPING BY AFTERNOON AS ANOTHER LOW PRESSURE  
TRAVERSES A STALLED FRONT. LIGHT W/NW FLOW ACROSS THE INTERIOR, SE/E  
FLOW ACROSS CAPE AND ISLANDS.  
 
SATURDAY NIGHT...MAINLY VFR ACROSS WESTERN TERMINALS, POSSIBLE  
MVFR ACROSS EASTERN TERMINALS AS SHOWERS DEVELOP. LIGHT  
WESTERLY FLOW DEVELOPS EXCEPT ACROSS CAPE COD AND THE ISLANDS  
WHERE SOUTHEAST FLOW PREVAILS.  
 
KBOS TERMINAL...MODERATE CONFIDENCE. VFR CONDITIONS PUSH EAST ACROSS  
OUR AREA THIS EVENING. TERMINAL EXPECTED TO LINGER BETWEEN VFR/MVFR  
THROUGH THE DAY SATURDAY. WINDS SHIFT TO THE WEST BY 00Z THIS  
EVENING.  
 
KBDL TERMINAL...HIGH CONFIDENCE. VFR CONDITIONS PERSIST THROUGH THE  
END OF THE TAF PERIOD. WINDS SHIFT WESTERLY BY 00Z.  
 
OUTLOOK /SUNDAY THROUGH WEDNESDAY/...  
 
SUNDAY THROUGH MONDAY: VFR. BREEZY.  
 
MONDAY NIGHT THROUGH TUESDAY: MAINLY VFR, WITH AREAS MVFR POSSIBLE.  
BREEZY. SLIGHT CHANCE SHRA.  
 
TUESDAY NIGHT: VFR.  
 
WEDNESDAY: VFR. BREEZY.  
 

 
   
MARINE
 
 
FORECASTER CONFIDENCE LEVELS.  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
PERSISTENT SOUTHERLY FLOW WILL MAINTAIN ROUGH SEAS ON THE OUTER  
COASTAL WATERS. STILL LOOKING LIKE A PERIOD OF GUSTS UP TO 25 KT  
LATER TODAY AHEAD OF A COLD FRONT AS IT CRAWLS EAST ACROSS  
SOUTHERN NEW ENGLAND AND THE WATERS. THIS FRONT IS NOT LIKELY  
TO PASS COMPLETELY EAST OF THE WATERS THROUGH SATURDAY. WINDS  
DIMINISH SOME TONIGHT, WHICH WILL PERMIT SEAS TO SUBSIDE  
OVERNIGHT. TWEAKED THE TIMING OF SMALL CRAFT ADVISORIES.  
 
OUTLOOK /SUNDAY THROUGH WEDNESDAY/...  
 
SUNDAY: WINDS LESS THAN 25 KT. SEAS UP TO 5 FT.  
 
SUNDAY NIGHT: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH  
GUSTS UP TO 25 KT. SEAS UP TO 5 FT.  
 
MONDAY: WINDS LESS THAN 25 KT. AREAS OF ROUGH SEAS.  
 
MONDAY NIGHT: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH  
GUSTS UP TO 25 KT. SEAS UP TO 5 FT. CHANCE OF RAIN SHOWERS.  
 
TUESDAY: WINDS LESS THAN 25 KT. SEAS UP TO 5 FT. CHANCE OF RAIN  
SHOWERS.  
 
TUESDAY NIGHT THROUGH WEDNESDAY: WINDS LESS THAN 25 KT. AREAS  
OF SEAS APPROACHING 5 FT.  
 

 
   
BOX WATCHES/WARNINGS/ADVISORIES
 
 
CT...NONE.  
MA...NONE.  
RI...NONE.  
MARINE...SMALL CRAFT ADVISORY UNTIL 2 AM EDT SATURDAY FOR ANZ250-255-  
256.  
SMALL CRAFT ADVISORY UNTIL 3 AM EDT SATURDAY FOR ANZ254.  
 

 
 

 
SYNOPSIS...FRANK/KS  
NEAR TERM...BELK/FRANK  
SHORT TERM...KS  
LONG TERM...FRANK  
AVIATION...BELK/FRANK/KS  
MARINE...BELK/FRANK/KS  
 
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