634  
FXUS61 KBOX 231143  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BOSTON/NORTON MA  
743 AM EDT MON JUN 23 2025  
   
SYNOPSIS  
 
DANGEROUS HEAT AND HUMIDITY THROUGH EARLY NEXT WEEK PEAKS ON  
TUESDAY. THE HEAT BEGINS TO EASE ON WEDNESDAY THEN TURNING  
COOLER FOR THE END OF THE WEEK INTO NEXT WEEKEND WITH DAILY  
CHANCES OF SHOWERS AND POSSIBLY A FEW THUNDERSTORMS.  
 
 
   
NEAR TERM /THROUGH TONIGHT/  
 
400 AM UPDATE:  
 
KEY MESSAGES:  
 
* HOT AND OPPRESSIVELY HUMID CONDITIONS FOR MOST OF SOUTHERN NEW  
ENGLAND TODAY, WITH LIGHT TO CALM WINDS. HIGHS IN THE MID 90S TO  
AROUND 100F AWAY FROM THE COAST, WITH DANGEROUS HEAT INDICES 100-  
110F. EXTREME HEAT WARNINGS/HEAT ADVISORIES REMAIN VALID.  
 
* SEABREEZE THIS MORNING WILL KEEP THE NORTH SHORE AND IMMEDIATE  
BOSTON/SOUTH SHORE COASTS "LESS-HOT".  
 
* MUGGY AND VERY WARM NIGHT TONIGHT, OFFERING NO RELIEF.  
 
DETAILS:  
 
ITS BEEN A PRETTY WARM AND MUGGY OVERNIGHT, WITH DEWPOINT TEMPS  
UPPER 60S TO LOW 70S. WITH LIGHT WINDS, AIR TEMPS ARE A LITTLE MORE  
VARIED BUT ARE GENERALLY IN THE UPPER 60S TO THE MID TO EVEN UPPER  
70S (CURRENT 06Z OB AT BOSTON LOGAN WAS 78 DEGREES). PATCHY  
RADIATION FOG HAS DEVELOPED IN SOME LOCATIONS, BUT UNDER EXPECTED  
STRONG INSOLATION, ANY MIST OR FOG SHOULD DISPERSE SHORTLY AFTER  
SUNRISE. THE MAIN FEATURE OF INTEREST IS AN ANOMALOUSLY STRONG UPPER  
LEVEL RIDGE LOCATED NEAR THE ALLEGHENY MTNS, A FEATURE WHICH IS  
EXPECTED TO BUILD NORTHEAST TODAY AND TONIGHT. MEANWHILE A SFC RIDGE  
WAS NOSING SOUTHWARD FROM ME INTO THE CANADIAN MARITIMES, WHICH WILL  
HELP BRING A PERIOD OF ONSHORE FLOW TO THE IMMEDIATE EASTERN COAST  
TODAY.  
 
WHILE THE IMMEDIATE EAST COAST OF MA ENDS UP BEING "LESS-HOT" TODAY  
WITH AN ONSHORE FLOW/SEABREEZE DEVELOPING EARLY TODAY, WE STILL  
EXPECT TODAY AND TOMORROW TO HAVE A COMBO OF HOT TEMPERATURES AND  
OPPRESSIVE LEVELS OF HUMIDITY LEADING TO DANGEROUSLY HIGH HEAT  
INDICES FOR THE MAJORITY OF SOUTHERN NEW ENGLAND. THERE HAVE BEEN NO  
CHANGES TO THE EXISTING HEAT HEADLINES AND REMAIN VALID. WE AGAIN  
ENCOURAGE EVERYONE TO TAKE PROTECTIVE MEASURES TO MITIGATE AGAINST  
DEVELOPING HEAT-RELATED ILLNESSES, INCLUDING TAKING FREQUENT BREAKS  
IN SHADED OR COOLED/AIR CONDITIONED AREAS AND STAYING HYDRATED.  
 
FULL SUN AND 925 MB TEMPS WARMING TO AS MUCH AS +27C WILL HELP PUSH  
HIGH TEMPERATURES AWAY FROM THE RI/MA COASTS INTO THE MID 90S TO LOW  
100S, WITH HEAT INDICES IN THE 105-110 DEGREE RANGE. COMPARED TO  
TUESDAY, TODAY MIGHT ARGUABLY FEEL THE MOST OPPRESSIVE WHEN YOU  
FACTOR IN THAT WINDS WILL ALSO BE VERY LIGHT. ALONG THE IMMEDIATE  
COAST, WE EXPECT HIGH TEMPS IN THE MID TO UPPER 80S, THOUGH BOSTON  
LOGAN PROBABLY SEES A LATE-DAY HIGH ONCE WINDS FROM THE SEABREEZE  
FLIP TO AN OFFSHORE/SSW DIRECTION.  
 
FOR TONIGHT, THE UPPER RIDGE AXIS CRESTS OVER SNE. AT THE SAME TIME,  
WE START TO GET INTO MORE OF A WESTERLY SFC GRADIENT AND MODEST  
WESTERLY WINDS. WE EXPECT ANOTHER VERY WARM AND MUGGY NIGHT,  
OFFERING NO APPRECIABLE RELIEF FROM THE DAYTIME HEAT AND HUMIDITY.  
LOWS IN THE LOW TO MID 70S (MID/UPPER 60S CAPE AND ISLANDS), AND  
SHOULD BE A FEW DEGREES WARMER THAN TONIGHT. COULD SEE SOUTH-COASTAL  
FOG RE-DEVELOP AGAIN GIVEN THE VERY MUGGY CONDITIONS AND WEAKER WEST  
WINDS.  
 
 
   
SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/  
 
400 AM UPDATE:  
 
KEY MESSAGES:  
 
* TUESDAY IS THE HOTTEST DAY OF THE STRETCH OF HEAT AND  
HUMIDITY.  
 
* AWAY FROM THE CAPE AND ISLANDS, WIDESPREAD UPPER 90S TO LOW 100S  
HIGH TEMPERATURES ARE EXPECTED WHICH COULD THREATEN RECORDS.  
HEAT INDICES 105-110F.  
 
* WESTERLY WINDS AROUND 10 MPH WITH SOME MODEST GUSTS TOO.  
 
* WARM AND MUGGY NIGHT, AND GENERALLY DRY.  
 
DETAILS:  
 
TUESDAY ENDS UP BEING THE HOTTEST DAY OF THE STRETCH ACROSS ALL OF  
SNE, AS THE VERY WARM TEMPS FROM OVERNIGHT ARE EXPECTED TO SOAR  
UNDER FULL SUN. THERE WILL ALSO BE A BOOST FROM WESTERLY DOWNSLOPED  
WINDS, WHICH ACTUALLY ARE A LITTLE ON THE BREEZY SIDE (AROUND 10 MPH  
WITH GUSTS UP TO 20 MPH). WITH SIMILAR 925 MB TEMPS TO TODAY,  
FORECAST HIGH TEMPS SHOULD REACH WELL INTO THE UPPER 90S TO LOW  
100S! THE WEST WINDS MITIGATING ANY SEABREEZES WILL MEAN THAT EVEN  
THE IMMEDIATE COAST WILL SEE HIGH TEMPERATURES TO THESE VALUES,  
WHICH INCLUDES SITES SUCH AS LOGAN AIRPORT AND THE BOSTON  
WATERFRONT. DAILY RECORD HIGHS SEEM LIKELY AT SOME OF OUR CLIMATE  
SITES ON TUESDAY, AND IN SOME INSTANCES COULD POSSIBLY THREATEN ALL-  
TIME JUNE HIGH TEMPS. IT WOULDN'T SURPRISE EVEN IF SOME LOCATIONS ON  
THE CAPE SEE HIGHS REACH 90 DEGREES, ALTHOUGH THE FORECAST CALLS FOR  
MID TO UPPER 80S. DEWPOINTS PROBABLY MIX A FEW DEGREES LOWER DURING  
THE AFTERNOON THRU WESTERLY DOWNSLOPING FLOW AND GOOD MIXING, WHICH  
MEANS THAT HEAT INDICES SHOULD BE GENERALLY SIMILAR TO TODAY  
(THOUGH QUITE A BIT HOTTER NEAR THE IMMEDIATE COAST), IN THE  
105-110F RANGE FOR MOST, AND AROUND 95-104 DEGREE RANGE FOR THE  
BERKSHIRES.  
 
THE UPPER LEVEL HEAT RIDGE BUILDS FURTHER SOUTHWARD ON TUESDAY  
EVENING, AS A COLD FRONT DRAPES ITSELF OVER NORTHERN NEW ENGLAND. WE  
COULD HAVE SOME SHOWERS OR THUNDERSTORMS TO MONITOR TO OUR NORTH,  
BUT THESE APPEAR MORE LIKELY REMAIN NORTH OF SNE AND THUS OFFERED  
DRY WEATHER. COMING OUT OF THE VERY HOT TUESDAY AND WITH WESTERLY  
WINDS CONTINUING, LOWS TUESDAY NIGHT STAY IN THE 70S ACROSS MOST OF  
SOUTHERN NEW ENGLAND.  
 
 
   
LONG TERM /WEDNESDAY THROUGH SUNDAY/  
 
KEY MESSAGES:  
 
* VERY WARM AGAIN ON WEDNESDAY, ALTHOUGH COOLER NEAR THE COAST  
WITH ONSHORE FLOW. POSSIBLE NEED FOR HEAT ADVISORIES FOR  
INTERIOR SOUTHERN NEW ENGLAND.  
 
* COOLING TREND TOWARD NEAR TO COOLER THAN NORMAL TEMPS FOR THU  
THRU THE WEEKEND AS ONSHORE FLOW DEVELOPS.  
 
* DAILY CHANCES OF SHOWERS AND PERHAPS A FEW T-STORMS THU  
THROUGH SUN AS WELL.  
 
WE THEN GET INTO A STRONGER WESTERLY MID-LEVEL FLOW ON WEDNESDAY,  
AS UPPER LEVEL RIDGE CONTINUES TO SHIFT SOUTHWARD. SLIGHTLY  
COOLER TEMPS ALOFT AND A NE TO E WIND SHIFT, LEADING TO AN  
ONSHORE FLOW FOR THE EASTERN COAST. BUT STILL A HOT DAY WITH  
HIGHS LOW- MID 90S INLAND AND MID- UPPER 80S ALONG THE COAST,  
COOLER CAPE/ISLANDS. WE COULD STILL SEE HEAT INDICES AROUND HEAT  
ADVISORY CRITERIA AGAIN ON WEDNESDAY IN WESTERN AND CENTRAL MA  
AND CT. SO WE COULD NEED HEAT ADVISORIES FOR THESE AREAS AFTER  
THE EXTREME HEAT WARNINGS EXPIRE, THOUGH THERE WILL BE MORE IN  
THE WAY OF CLOUD COVER AND EVEN POSSIBLY SOME SHOWERS AND  
T-STORMS GIVEN PWAT VALUES NEAR 2" AND MUCAPES ON THE 1000-1500  
J/KG RANGE.  
 
WE FINALLY COOL OFF IN ALL AREAS ON THURSDAY RIGHT THROUGH THE  
WEEKEND WITH A PROLONGED PERIOD OF ONSHORE FLOW. ANTICIPATE  
HIGHS CLOSER TO THE LOW TO MID 70S, WHICH ARE COOLER THAN  
NORMAL FOR LATE JUNE. HOWEVER DAILY SHOWER/THUNDERSTORM CHANCES  
APPEAR EACH DAY AS A SERIES OF WEAK/HARD TO TIME WAVES MOVE  
THROUGH THE WEST FLOW. IT STILL LOOKS LIKE THUNDERSTORM  
PARAMETERS ON THE GLOBAL MODELS/ENSEMBLES ARE LOW ENOUGH SUCH  
THAT SEVERE WEATHER DOESN'T LOOK LIKELY WITH THESE DAILY  
STORM CHANCES.  
 
 
   
AVIATION /12Z MONDAY THROUGH FRIDAY/  
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
12Z TAF UPDATE:  
 
TODAY: HIGH CONFIDENCE OVERALL, THOUGH MODERATE ON START TIME  
OF COASTAL SEABREEZES.  
 
VFR. LIGHT AND VARIABLE WINDS. SEABREEZES AT BOS, PVD AND THE  
CAPE AIRPORTS AROUND 10 KTS. THINKING SEABREEZE DEVELOPS EARLY  
IN THE DAY, AS SOON AS 14Z AT BOS AND 16Z AT PVD.  
 
TONIGHT: HIGH CONFIDENCE. MODERATE CONFIDENCE (CEILINGS AT ACK)  
 
MAINLY VFR, THOUGH PATCHY BR/FG POSSIBLE AGAIN WITH BETTER  
CHANCE FOR THE CAPE AIRPORTS. ACK COULD SEE A PERIOD OF LOWER  
CEILINGS OVERNIGHT AS A SCT-BKN DECK TRIES TO PUSH IN, BUT  
CONFIDENCE IS CURRENTLY LOW. LIGHT WEST WINDS, INCREASING IN  
SPEED TOWARD MORNING TO AROUND 5-10 KT.  
 
TUESDAY: HIGH CONFIDENCE.  
 
ANY BR/FG FROM OVERNIGHT DISPERSES SHORTLY AFTER SUNRISE WITH  
VFR THEREAFTER. W WINDS INCREASE TO AROUND 8-12 KT WITH GUSTS TO  
20 KT.  
 
KBOS TERMINAL...HIGH CONFIDENCE IN TAF. VFR. SEABREEZE THEN  
DEVELOPS AS SOON AS 14Z.  
 
KBDL TERMINAL...HIGH CONFIDENCE IN TAF. VFR. LIGHT, VALLEY-  
DRIVEN S WINDS TODAY. HAZY CONDITIONS POSSIBLE GIVEN HOT AND  
HUMID WEATHER.  
 
OUTLOOK /WEDNESDAY THROUGH FRIDAY/...  
 
TUESDAY NIGHT: VFR.  
 
WEDNESDAY: VFR. SLIGHT CHANCE SHRA.  
 
WEDNESDAY NIGHT: VFR. CHANCE SHRA, ISOLATED TSRA.  
 
THURSDAY: MAINLY VFR, WITH LOCAL IFR POSSIBLE. CHANCE SHRA,  
ISOLATED TSRA.  
 
THURSDAY NIGHT THROUGH FRIDAY: MAINLY VFR, WITH LOCAL IFR  
POSSIBLE. CHANCE SHRA.  
 
 
   
MARINE  
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MEDIUM - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
THROUGH TUESDAY NIGHT: HIGH CONFIDENCE.  
 
CONDITIONS REMAIN SUB-SCA THROUGH THIS PERIOD. LIGHT WINDS,  
EASTERLY NEAR THE IMMEDIATE COAST, FOR TODAY, WITH AN INCREASING  
WEST WIND TONIGHT THROUGH TUE NIGHT TO AROUND 10-15 KT WITH  
GUSTS 20 KT BY TUE NIGHT. NIGHTLY RISK FOR FOG ON MOST WATERS.  
 
OUTLOOK /WEDNESDAY THROUGH FRIDAY/...  
 
TUESDAY NIGHT THROUGH WEDNESDAY: WINDS LESS THAN 25 KT.  
 
WEDNESDAY NIGHT: WINDS LESS THAN 25 KT. CHANCE OF RAIN SHOWERS.  
 
THURSDAY: WINDS LESS THAN 25 KT. CHANCE OF RAIN SHOWERS,  
ISOLATED THUNDERSTORMS.  
 
THURSDAY NIGHT: WINDS LESS THAN 25 KT. SLIGHT CHANCE OF RAIN  
SHOWERS.  
 
FRIDAY: WINDS LESS THAN 25 KT. CHANCE OF RAIN SHOWERS.  
 
 
   
BOX WATCHES/WARNINGS/ADVISORIES  
 
CT...EXTREME HEAT WARNING UNTIL 8 PM EDT TUESDAY FOR CTZ002>004.  
MA...EXTREME HEAT WARNING UNTIL 8 PM EDT TUESDAY FOR MAZ003>007-  
010>021-026.  
HEAT ADVISORY UNTIL 8 PM EDT TUESDAY FOR MAZ002-008-009.  
RI...EXTREME HEAT WARNING UNTIL 8 PM EDT TUESDAY FOR RIZ001>007.  
MARINE...NONE.  
 
 
 
 
 
SYNOPSIS...LOCONTO  
NEAR TERM...LOCONTO  
SHORT TERM...LOCONTO  
LONG TERM...LOCONTO  
AVIATION...LOCONTO/MENSCH  
MARINE...LOCONTO  
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