106  
FXUS61 KBOX 240229  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BOSTON/NORTON MA  
1029 PM EDT THU SEP 23 2021  
   
SYNOPSIS
 
 
A SLOW-MOVING FRONT WILL BRING ISOLATED STRONG TO SEVERE  
THUNDERSTORMS WITH LOCALIZED FLOODING POSSIBLE OVERNIGHT INTO  
FRIDAY. A SECONDARY WAVE OF LOW PRESSURE WILL LIKELY BRING  
ANOTHER ROUND OF RAIN SOMETIME SATURDAY INTO SATURDAY NIGHT  
ACROSS EASTERN MASSACHUSETTS AND RHODE ISLAND. OTHERWISE,  
CANADIAN HIGH PRESSURE WILL BRING EARLY FALL-LIKE WEATHER WITH  
COOL NIGHTS AND VERY PLEASANT DAYS FOR THE FIRST HALF OF NEXT  
WEEK. MAINLY DRY WEATHER EXPECTED TOO WITH THE BEST CHANCE FOR A  
ROUND OF SHOWERS SOMETIME LATE MONDAY INTO MONDAY NIGHT WITH A  
COLD FRONT.  
 

 
   
NEAR TERM /UNTIL 6 AM FRIDAY MORNING/
 
 
* ISOLATED STRONG TO SEVERE THUNDERSTORMS WITH LOCALIZED  
FLOODING POSSIBLE BETWEEN 4 AM AND NOON FRIDAY  
* FLASH FLOOD WATCH IN EFFECT FOR OUR WESTERN ZONES.  
* ELEVATED RIP CURRENT RISK THROUGH TOMORROW AFTERNOON.  
 
1029 PM UPDATE...  
 
NO MAJOR CHANGES TO THE OVERALL FORECAST OVERNIGHT. DID TRY TO  
TWEAK RAINFALL AND THUNDERSTORM CHANCES AND TIMING BASED ON THE  
LATEST NEAR TERM GUIDANCE AND OBSERVED TRENDS. THE MAIN CONCERNS  
OVERNIGHT CONTINUE TO BE THE RISK FOR ISOLATED STRONG TO SEVERE  
THUNDERSTORMS, ALONG WITH DOWNPOURS.  
 
LATEST SPC MESOANALYSIS STILL SHOWED AN AXIS OF HIGHER  
INSTABILITY, ALBEIT ON THE WEAKER SIDE, EXTENDING NORTH THROUGH  
THE CT RIVER VALLEY. BOTH EFFECTIVE AND 0-500 M AGL HELICITY  
VALUES WERE ON THE HIGHER SIDE OF CLIMATOLOGY FOR OUR REGION,  
APPROACHING 200 M2/S2. WILL NEED TO MONITOR ANY THUNDERSTORMS  
CLOSELY OVERNIGHT FOR POSSIBLE ROTATION. THUS FAR, THE MAJORITY  
OF ANY THUNDERSTORMS REMAINED TO OUR WEST.  
 
750 PM UPDATE...  
 
WIDELY SCATTERED BRIEF HEAVY RAIN SHOWERS CONTINUED TO IMPACT  
THE REGION THIS EVENING. WHILE SHOWERS WERE SHORT-LIVED IN ANY  
GIVEN LOCATION...A MODEST SOUTHEAST LLJ COUPLED WITH TROPICAL  
MOISTURE IN PLACE WERE ALLOWING FOR THEM TO CONTAIN BRIEF HEAVY  
RAINFALL. OVERALL; AREAL COVERAGE AND DURATION OF THIS ACTIVITY  
WILL REMAIN SOMEWHAT LIMIT UNTIL AFTER MIDNIGHT. HOWEVER, VERY  
STRONG FORCING WILL APPROACH WESTERN MA AND WESTERN CT AFTER 3  
OR 4 AM AND COMBINED WITH THE TROPICAL AIRMASS IN PLACE. THE  
PREVIOUS FORECAST DISCUSSES THIS BELOW.  
 
LATER TONIGHT, THE CLOSED LOW LIFTS INTO SOUTHERN QUEBEC AND  
THE 500MB TROUGH BECOMES NEGATIVELY TILTED. A 40 KT 850MB LOW  
LEVEL JET WILL ALSO OVERSPREAD OUR REGION, HELPING TO ORGANIZE  
STORMS. TOGETHER WITH 35-45 KT BULK SHEAR AND 150-200 M2/S2 OF  
LOW-LEVEL HELICITY, A FEW ISOLATED STORMS COULD BECOME STRONG OR  
SEVERE AND CAPABLE OF DAMAGING WIND GUSTS AND EVEN A TORNADO OR  
TWO. AND DUE TO THE SLOW-MOVING NATURE OF THE FRONT ALONG WITH  
PWATS 2 TO 3 STANDARD DEVIATIONS ABOVE NORMAL, THERE IS A RISK  
OF LOCALIZED FLASH FLOODING WHERE HEAVY RAIN DEVELOPS. THAT  
COULD IMPACT EARLY MORNING COMMUTE IN CITIES LIKE SPRINGFIELD,  
MA AND HARTFORD, CT. A FLASH FLOOD WATCH HAS BEEN ISSUED FOR THE  
EAST SLOPES OF THE BERKSHIRES INTO HARTFORD COUNTY.  
 
IN ADDITION, PERSISTENT SOUTHEAST FLOW WILL ALSO GENERATE  
SWELLS FOR MUCH OF OUR COASTLINE INTO TOMORROW. A RIP CURRENT  
STATEMENT HAS BEEN ISSUED FOR THE ELEVATED RIP CURRENT RISK.  
 

 
   
SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/
 
 
FRIDAY...  
 
* RISK CONTINUES FOR A FEW ISOLATED ROTATING STORMS AND LOCALIZED  
FLASH FLOODING.  
 
DYNAMIC CLOSED LOW STARTS LIFTING TO THE NORTHEAST, ALONG WITH THE  
THREAT FOR A FEW ISOLATED ROTATING STORMS AND HEAVY RAIN THREAT. WE  
CONTINUE TO BE IN A TROPICAL ENVIRONMENT WITH PWATS APPROACHING 2  
INCHES OUT AHEAD OF THE SLOW-MOVING COLD FRONT, WHICH IS 2 TO 3  
STANDARD DEVIATIONS ABOVE NORMAL. WHILE LOW- LEVEL FLOW AND  
DYNAMICS ARE IMPRESSIVE, WIDESPREAD CLOUDINESS AND LOW- LEVEL  
INVERSION GIVEN THE PREDOMINANT SOUTHEAST FLOW SHOULD KEEP  
OVERALL SEVERE WEATHER THREAT SCATTERED TO ISOLATED IN NATURE.  
HAVING SAID THAT, IT IS POSSIBLE WE GET A STORM OR TWO TO TAP  
INTO THE STRONG VERTICAL WIND SHEAR AND LOW-LEVEL HELICITY,  
RESULTING IN A FEW EMBEDDED BOWING SEGMENTS OR EVEN SUPERCELL  
STRUCTURES. IF THAT WERE TO OCCUR, WE COULD GET DAMAGING WIND  
GUSTS ALONG WITH A BRIEF TORNADO OR TWO, ESPECIALLY ALONG THE  
MESOLOW AND CERTAINLY IN THE VICINITY OF THE TRIPLE POINT.  
 
TEMPERATURE FORECAST WISE, IT LOOKS LIKE EASTERN MA AND RI COULD  
SEE BREAKS IN SUNSHINE THAT SHOULD SEND HIGHS INTO THE UPPER 70S  
AND EVEN LOW 80S, WHICH IS 5-10 DEGREES ABOVE CLIMATOLOGICAL  
NORMAL. WITH DEW POINTS IN THE UPPER 60S TO LOWER 70S, IT WOULD  
FEEL UNCOMFORTABLY MILD AND MUGGY.  
 
ANY LEFTOVER SHOWERS SHOULD COME TO AN END ACROSS WESTERN MA  
AND CT BY MID TO LATE AFTERNOON, WITH PARTIAL CLEARING POSSIBLE  
ALONG WITH DEW POINTS FALLING INTO THE MID 50S TO LOW 60S.  
 
FRIDAY NIGHT...  
 
LINGERING SHOWERS ACROSS EASTERN MA AND RI GRADUALLY COME TO AN  
END IN THE EVENING. IT APPEARS THAT THERE WOULD BE QUITE A DEW  
POINT SPREAD OVERNIGHT AS THE COLD FRONT WOULD BE SLOW TO CLEAR  
THE REGION. WHILE WESTERN MA AND CT SHOULD SEE DEW POINTS  
FALLING INTO THE UPPER 40S TO LOW 50S, EASTERN MA COULD STILL BE  
RATHER HUMID WITH DEW POINTS REMAINING IN THE LOW TO MID 60S  
OVERNIGHT.  
 

 
   
LONG TERM /SATURDAY THROUGH THURSDAY/
 
 
HIGHLIGHTS...  
 
* ANOTHER ROUND OF RAIN LIKELY SOMETIME SAT INTO SAT NIGHT AT  
LEAST ACROSS PORTIONS OF EASTERN MA AND RI  
 
* EARLY FALL-LIKE WEATHER FOR THE FIRST HALF OF NEXT WEEK WITH  
DRY WEATHER DOMINATING WITH COOL NIGHTS AND VERY PLEASANT  
DAYS  
 
DETAILS...  
 
SATURDAY AND SATURDAY NIGHT...  
 
THE MAIN CONCERN WITH THIS FORECAST WILL REVOLVE AROUND THE  
POTENTIAL FOR ANOTHER ROUND OF RAIN SOMETIME SAT INTO SAT NIGHT.  
UPPER LEVEL RIDGING OFF THE EAST COAST COUPLED WITH MERIDIONAL  
FLOW WILL CONTINUE TO RESULT IN VERY SLOW WEST TO EAST MOVEMENT  
OF A COLD FRONT. IT APPEARS THAT THIS FRONT WILL TEMPORARILY  
STALL NEAR OR JUST OFF THE COAST AS A WAVE OF LOW PRESSURE WORKS  
NORTHWARD ALONG IT SAT INTO SAT NIGHT.  
 
THERE IS UNCERTAINTY IN REGARDS TO WHERE EXACTLY THIS FRONT  
STALLS AND THE WESTWARD EXTENT OF THIS NEXT RAIN SHIELD.  
INDIVIDUAL GEFS/EPS ENSEMBLES ARE SHOWING SOME DECENT SPREAD; SO  
THIS FORECAST CERTAINLY MAIN CHANGE. CURRENTLY IT LOOKS LIKE  
EASTERN MA AND RI ARE AT THE GREATEST RISK FOR ANOTHER ROUND OF  
RAIN FOCUSED SAT AFTERNOON AND NIGHT. HOWEVER, THIS CERTAINLY  
COULD SHIFT FURTHER WEST INTO THE CT RIVER VALLEY OR EASTWARD  
SPARING A LOT OF THE REGION. AGAIN, ADJUSTMENTS MAY NEED TO BE  
MADE BUT RIGHT NOW OUR FOCUS FOR ANOTHER ROUND OF RAIN IS ACROSS  
EASTERN MA/RI.  
 
SUNDAY THROUGH NEXT THURSDAY...  
 
THE EPS/GEFS ARE IN VERY GOOD AGREEMENT IN A PATTERN CHANGE TO  
COOLER EARLY FALL-LIKE WEATHER DURING THE FIRST HALF OF NEXT  
WEEK. NORTHEAST TROUGH WILL FINALLY RESULT IN SEASONABLE EARLY  
FALL-LIKE WEATHER WITH MUCH LESS HUMIDITY. LOW TEMPERATURES MUCH  
OF NEXT WEEK WILL BE IN THE 40S/50S WITH HIGHS GENERALLY IN THE  
UPPER 60S TO THE LOWER 70S.  
 
CANADIAN HIGH PRESSURE WILL RESULT IN MAINLY DRY WEATHER FOR  
MOST OF THE FIRST HALF OF NEXT WEEK. THE BEST CHANCE FOR A ROUND  
OF SHOWERS WILL BE LATE MON INTO MON NIGHT WITH ANOTHER COLD  
FRONT. BUT OVERALL, EXPECT DRY EARLY FALL-LIKE WEATHER FOR THE  
FIRST HALF OF NEXT WEEK.  
 

 
   
AVIATION /02Z FRIDAY THROUGH TUESDAY/
 
 
FORECASTER CONFIDENCE LEVELS.  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
TONIGHT...MODERATE CONFIDENCE. CIGS/VSBYS LOWER TO MVFR/IFR IN  
LOW CLOUDS AND AREAS OF FOG FROM WEST TO EAST AS THE NIGHT  
PROGRESSES. LOWEST OF THE CIGS/VSBYS WILL BE NORTHWEST OF I-95  
AND ITS POSSIBLE AREAS TOWARDS THE CAPE/ISLANDS REMAIN  
BORDERLINE VFR THROUGH DAYBREAK. SCATTERED SHRA TO START,  
BECOMING MORE NUMEROUS OVERNIGHT WITH SCT TSRA POSSIBLE AFTER 08Z  
ACROSS WESTERN MA AND WESTERN CT. SOUTHEAST WINDS 10-20 KT WITH  
20-25 KT GUSTS.  
 
FRIDAY...MIX OF MVFR/VFR AS A COLD FRONT CROSSES THE REGION.  
WIDESPREAD SHOWERS AND ISOLATED THUNDERSTORMS. SOUTH WINDS  
10-15 KT WITH GUSTS UP TO 25 KT ACROSS CAPE TERMINALS.  
 
FRIDAY NIGHT...VFR CONDITIONS FOR WESTERN TERMINALS. MVFR  
IMPROVING TO VFR ACROSS EASTERN TERMINALS AFTER MIDNIGHT EXCEPT  
FOR CAPE TERMINALS, WHERE MVFR CEILINGS COULD LINGER THROUGH  
DAYBREAK. SOUTH WINDS 5-10 KT EXCEPT GUSTS UP TO 20 KT ACROSS  
CAPE TERMINALS EARLY IN THE EVENING.  
 
KBOS TERMINAL...HIGH CONFIDENCE IN TRENDS. MODERATE CONFIDENCE  
IN TIMING.  
 
KBDL TERMINAL...HIGH CONFIDENCE IN TRENDS. MODERATE CONFIDENCE  
IN TIMING.  
 
OUTLOOK /SATURDAY THROUGH TUESDAY/...  
 
SATURDAY: VFR. CHANCE SHRA.  
 
SATURDAY NIGHT: VFR. BREEZY. CHANCE SHRA.  
 
SUNDAY: VFR. BREEZY. SLIGHT CHANCE SHRA.  
 
SUNDAY NIGHT: VFR. BREEZY.  
 
MONDAY: VFR. BREEZY. SLIGHT CHANCE SHRA.  
 
MONDAY NIGHT THROUGH TUESDAY: VFR. BREEZY. CHANCE SHRA.  
 

 
   
MARINE
 
 
FORECASTER CONFIDENCE LEVELS.  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SOUTHEAST WINDS CONTINUE ACROSS THE WATERS. SEAS CONTINUE TO  
BUILD TO 5-7 FT ACROSS MOST OUTER WATERS.  
 
PATCHY SHOWERS/DRIZZLE AND FOG POSSIBLE ACROSS THE WATERS DURING  
THIS PERIOD. THUNDERSTORMS POSSIBLE ACROSS THE COASTAL WATERS  
LATE TONIGHT INTO FRIDAY.  
 
LINGERING SHOWERS ARE POSSIBLE FRIDAY NIGHT AS WINDS SHIFT FROM  
SOUTH TO WEST WITH 25-30 KT GUSTS POSSIBLE AT TIMES BEFORE  
DIMINISHING OVERNIGHT.  
 
OUTLOOK /SATURDAY THROUGH TUESDAY/...  
 
SATURDAY THROUGH SATURDAY NIGHT: WINDS LESS THAN 25 KT. SEAS UP  
TO 5 FT. CHANCE OF RAIN SHOWERS.  
 
SUNDAY: WINDS LESS THAN 25 KT. SEAS UP TO 5 FT. SLIGHT CHANCE  
OF RAIN SHOWERS.  
 
SUNDAY NIGHT THROUGH MONDAY: MODERATE RISK FOR SMALL CRAFT  
ADVISORY WINDS WITH GUSTS UP TO 25 KT. SEAS UP TO 5 FT.  
 
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.  
 

 
   
BOX WATCHES/WARNINGS/ADVISORIES
 
 
CT...FLASH FLOOD WATCH THROUGH FRIDAY MORNING FOR CTZ002.  
MA...HIGH RIP CURRENT RISK THROUGH FRIDAY EVENING FOR MAZ007-015-  
016-019>024.  
FLASH FLOOD WATCH THROUGH FRIDAY MORNING FOR MAZ002-003-  
008>011.  
RI...HIGH RIP CURRENT RISK THROUGH FRIDAY EVENING FOR RIZ006>008.  
MARINE...SMALL CRAFT ADVISORY UNTIL 2 AM EDT SATURDAY FOR ANZ231-232-  
251.  
SMALL CRAFT ADVISORY UNTIL 8 PM EDT FRIDAY FOR ANZ230-233>237-  
255-256.  
SMALL CRAFT ADVISORY UNTIL 8 AM EDT SATURDAY FOR ANZ250-254.  
 

 
 

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