067
FXUS61 KBOX 051827
AFDBOX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOSTON/NORTON MA
227 PM EDT WED AUG 5 2026
WHAT HAS CHANGED
ISSUED A HEAT ADVISORY FOR THE MAJORITY OF THE REGION EXCEPT FOR THE
CAPE AND ISLANDS STARTING THURSDAY MORNING AND CONTINUING THROUGH
FRIDAY EVENING. DURING THIS TIME, HEAT INDEX VALUES CLIMB TO 95-99
DEGREES IN THE AFTERNOON WITH ELEVATED HEAT AND HUMIDITY LINGERING
THROUGH THE OVERNIGHT.
KEY MESSAGES
- ADVISORY-LEVEL HEAT BUILDS INTO THE REGION STARTING TOMORROW
AND LINGERING THROUGH FRIDAY. THE HEAT AND HUMIDITY HELP TO
FUEL THE CHANCE FOR WIDELY SCATTERED THUNDERSTORMS THURSDAY
AND FRIDAY AFTERNOONS.
- MIDSUMMER WARMTH AND HUMIDITY CONTINUE ACROSS MUCH OF SOUTHERN
NEW ENGLAND THROUGH THE WEEKEND. AFTERNOON POP-UP
THUNDERSTORMS ARE MOST LIKELY SATURDAY, WITH A LOWER CHANCE ON
SUNDAY. UNSETTLED WEATHER MAY RETURN EARLY NEXT WEEK,
ALTHOUGH CONFIDENCE REMAINS LOW IN THE EXACT DETAILS.
DISCUSSION
KEY MESSAGE 1...ADVISORY-LEVEL HEAT BUILDS INTO THE REGION STARTING
TOMORROW AND LINGERING THROUGH FRIDAY. THE HEAT AND HUMIDITY HELP TO
FUEL THE CHANCE FOR WIDELY SCATTERED THUNDERSTORMS THURSDAY AND
FRIDAY AFTERNOON.
HEAT AND HUMIDITY RAMP UP THURSDAY AS RETURN FLOW AROUND SPRAWLING
SUBTROPICAL HIGH PRESSURE ADVECTS A WARM AND HUMID AIR MASS INTO THE
REGION. BY THURSDAY MORNING, THE MOST NOTICEABLE CHANGE WILL BE IN
HUMIDITY VALUES AS DEW POINT TEMPERATURES SURGE INTO THE LOW 70S
ACROSS THE AREA. STILL SEEING GUIDANCE PAINT A BROAD AREA OF VERY
WARM 925 MB TEMPERATURES ON THE ORDER OF +22-26C THURSDAY AND
FRIDAY. THESE VERY WARM LOW LEVEL TEMPERATURES TRANSLATE TO HIGHS IN
THE UPPER 80S TO MID 90S. COMBINED WITH NEAR OPPRESSIVE DEW POINTS
OF 72-76, APPARENT TEMPERATURES WILL CLIMB TO THE UPPER 90S,
POSSIBLY NEAR 100 AT TIMES. GREATEST RISK OF HEAT INDICIES >100 WILL
BE FOUND IN THE CT AND MERRIMACK RIVER VALLEYS WHERE LOCALIZED
DOWNSLOPE WINDS LIKELY HELP BOOST TEMPERATURES. SOME UNCERTAINTY AS
TO THE MAGNITUDE OF HEAT ELSEWHERE RESULTING FROM CLOUD COVER FROM
ANY THUNDERSTORMS THAT DEVELOP THURSDAY AND FRIDAY AFTERNOONS.
STILL, AT A MINIMUM HEAT INDEX VALUES WILL LIKELY REACH OR EXCEED 95
FOR MOST LOCATIONS BOTH THURSDAY AND FRIDAY AFTERNOONS. FINALLY,
ELEVATED OVERNIGHT TEMPS IN THE LOW TO MID 70S PAIRED WITH ELEVATED
DEW POINTS KEEPING HEAT INDICIES NEAR 80 OVERNIGHT. THE WARM
OVERNIGHT TEMPERATURES WILL BE DANGEROUS FOR THOSE WITHOUT ADEQUATE
ACCESS TO COOLING, ESPECIALLY IN URBAN AREAS.
REGARDING THE THUNDERSTORM POTENTIAL LATER IN THE WEEK... A FEW
WEAK, UPPER LEVEL DISTURBANCES PASSING THROUGH NEW ENGLAND COMBINING
WITH THE HIGH HEAT/HUMIDITY AND JUST ENOUGH INSTABILITY WILL LIKELY
BE ENOUGH TO POP A FEW DIURNAL SHOWERS/THUNDERSTORMS EACH DAY
THURSDAY THROUGH THE WEEKEND, WITH GREATEST CHANCES ACROSS THE
INTERIOR ON THURSDAY. ANY THUNDERSTORMS THAT DO POP HAVE THE
POTENTIAL TO PRODUCE FREQUENT LIGHTNING, GUSTY WINDS, AND TORRENTIAL
DOWNPOURS AS PWATS WILL LIKELY BE AROUND 2.0". GIVEN THE AMOUNT OF
RAIN SOUTHERN NEW ENGLAND HAS SEEN OVER THE LAST WEEK OR SO, ANY
HEAVY DOWNPOURS COULD LEAD TO LOCALIZED FLOODING.
KEY MESSAGE 2...MIDSUMMER WARMTH AND HUMIDITY CONTINUE ACROSS MUCH
OF SOUTHERN NEW ENGLAND THROUGH THE WEEKEND. AFTERNOON POP-UP
THUNDERSTORMS ARE MOST LIKELY SATURDAY, WITH A LOWER CHANCE ON
SUNDAY. UNSETTLED WEATHER MAY RETURN EARLY NEXT WEEK, ALTHOUGH
CONFIDENCE REMAINS LOW IN THE EXACT DETAILS.
CONFIDENCE REMAINS HIGH THAT MIDSUMMER WARMTH AND HUMIDITY WILL
CONTINUE THROUGH THIS WEEKEND, ALONG WITH DAILY CHANCES FOR
AFTERNOON POP-UP THUNDERSTORMS. OF THE TWO WEEKEND DAYS, SATURDAY
APPEARS TO HAVE THE GREATER PROBABILITY OF SHOWERS AND
THUNDERSTORMS. HOWEVER, A WIDESPREAD WASHOUT IS NOT ANTICIPATED.
GIVEN THE ABUNDANT RAINFALL EARLIER THIS WEEK, ANY STORMS CAPABLE OF
PRODUCING HEAVY DOWNPOURS COULD LEAD TO LOCALIZED INSTANCES OF FLASH
FLOODING. THIS IS REFLECTED IN THE WPC MARGINAL RISK (LEVEL 1 OF 4)
FOR EXCESSIVE RAINFALL ACROSS WESTERN NEW ENGLAND ON SATURDAY.
THERE IS LITTLE CHANGE IN THE SYNOPTIC PATTERN, WITH BERMUDA HIGH
PRESSURE REMAINING ANCHORED OVER THE WESTERN ATLANTIC. PERSISTENT
SOUTHWESTERLY FLOW WILL CONTINUE TO ADVECT ABOVE-NORMAL TEMPERATURES
AND INCREASING HUMIDITY INTO SOUTHERN NEW ENGLAND THROUGH THE
WEEKEND. WHILE TEMPERATURES WILL REMAIN ABOVE CLIMATOLOGICAL
NORMALS, THEY ARE NOT PARTICULARLY UNUSUAL FOR EARLY AUGUST. HIGH
TEMPERATURES SATURDAY AND SUNDAY SHOULD CLIMB INTO THE UPPER 80S TO
AROUND 90 DEGREES, WHILE DEWPOINTS REMAIN IN THE LOWER 70S.
OVERNIGHT LOWS IN THE 70S WILL PROVIDE LITTLE RELIEF. THIS
COMBINATION WILL RESULT IN DAYTIME HEAT INDEX VALUES OF 90 TO 95
DEGREES, WHICH IS BELOW HEAT ADVISORY CRITERIA AND IS WHY THE
CURRENT ADVISORY DOES NOT EXTEND INTO SATURDAY. ANOTHER UNCERTAINTY
IS THE DEGREE OF AFTERNOON CLOUD COVER AND THUNDERSTORM DEVELOPMENT,
WHICH COULD TEMPER TEMPERATURES SOMEWHAT. FORECAST TRENDS WILL
CONTINUE TO BE MONITORED TO DETERMINE WHETHER THE HEAT ADVISORY WILL
NEED TO BE EXTENDED INTO SATURDAY. TEMPERATURES TREND SOMEWHAT LOWER
MONDAY INTO TUESDAY AS CLOUD COVER INCREASES AND THE POTENTIAL FOR
MORE WIDESPREAD SHOWER ACTIVITY DEVELOPS.
REGARDING THUNDERSTORM CHANCES, THE MID-LEVEL RIDGE OFFSHORE
GRADUALLY FLATTENS, RESULTING IN A MORE ZONAL FLOW ALOFT. EMBEDDED
SHORTWAVE DISTURBANCES MOVING THROUGH THE FLOW SHOULD PROVIDE
SUFFICIENT LIFT TO INITIATE SCATTERED AFTERNOON AND EVENING
THUNDERSTORMS ON SATURDAY AND POTENTIALLY AGAIN ON SUNDAY, ALTHOUGH
SUNDAY CURRENTLY APPEARS TO BE THE DRIER OF THE TWO WEEKEND DAYS.
WHILE DEEP-LAYER SHEAR REMAINS WEAK, WITH 0-6 KM BULK SHEAR
GENERALLY BELOW 30 KT, INSTABILITY WILL BE PLENTIFUL, WITH FORECAST
CAPE VALUES AROUND 1,500 J/KG. AS A RESULT, STORMS SHOULD REMAIN
LARGELY PULSE-TYPE AND DISORGANIZED RATHER THAN ORGANIZED SEVERE
CONVECTION. BUFKIT SOUNDINGS DEPICT TALL, SKINNY CAPE PROFILES,
SUGGESTING EFFICIENT WARM-RAIN PROCESSES AND THE POTENTIAL FOR
LOCALLY HEAVY RAINFALL. PWAT VALUES BETWEEN 1.7 AND 2.0 INCHES
FURTHER SUPPORT THE THREAT OF TORRENTIAL DOWNPOURS. IN ADDITION TO
LOCALIZED FLOODING, GUSTY WINDS AND FREQUENT LIGHTNING WILL BE THE
PRIMARY HAZARDS. THAT SAID, NOT EVERY COMMUNITY WILL EXPERIENCE
THUNDERSTORMS, AND MANY LOCATIONS WILL REMAIN DRY, SO THERE IS NO
REASON TO CANCEL OUTDOOR PLANS AT THIS POINT. THE DETAILS REGARDING
STORM COVERAGE AND PLACEMENT WILL BECOME CLEARER ONCE CONVECTION-
ALLOWING GUIDANCE COMES INTO RANGE OVER THE NEXT COUPLE OF DAYS.
EARLY NEXT WEEK, THE SUBTROPICAL RIDGE EXTENDS ACROSS THE SOUTHERN
CONUS WHILE NEARLY ZONAL FLOW PERSISTS ACROSS THE NORTHERN CONUS.
THIS PATTERN WILL ALLOW ADDITIONAL SHORTWAVE DISTURBANCES TO MOVE
THROUGH THE FLOW, BRINGING THE POTENTIAL FOR MORE WIDESPREAD SHOWERS
AND THUNDERSTORMS MONDAY NIGHT INTO TUESDAY ALONG AN APPROACHING
COLD FRONT. CONFIDENCE IN THE EXACT DETAILS REMAINS LOW GIVEN THE
FORECAST LEAD TIME, SO FORECAST REFINEMENTS ARE LIKELY OVER THE
COMING DAYS.
AVIATION /18Z WEDNESDAY THROUGH MONDAY/
FORECASTER CONFIDENCE LEVELS...
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
18Z TAF UPDATE:
TONIGHT...HIGH CONFIDENCE.
GENERALLY VFR. INCREASING MOISTURE TONIGHT SHOULD RESULT IN
MVFR/IFR CIGS, ESPECIALLY ACROSS THE SOUTHERN COASTAL AREAS AND
THE CAPE. MAY ALSO SEE A FEW -SHRA DEVELOP PRIOR TO 12Z
THURSDAY ACROSS CT. MOST MVFR/IFR CIGS MIX OUT AFTER 12-14Z
THURS.
THURSDAY...HIGH CONFIDENCE.
MIX OF VFR WITH MVFR CIGS FOR WESTERN TERMINALS EARLY, BECOMING
VFR. CHANCE FOR -SHRA AND -TSRA ACROSS WESTERN TERMINALS WELL
AFTER 18Z. SW WINDS 5-10 KTS.
KBOS TERMINAL...HIGH CONFIDENCE IN TAF.
KBDL TERMINAL...HIGH CONFIDENCE IN TAF.
OUTLOOK /THURSDAY NIGHT THROUGH MONDAY/...
FRIDAY: VFR. BREEZY. CHANCE SHRA, CHANCE TSRA.
FRIDAY NIGHT: VFR. SLIGHT CHANCE SHRA, SLIGHT CHANCE TSRA.
SATURDAY: VFR. BREEZY. CHANCE SHRA, SLIGHT CHANCE TSRA.
SATURDAY NIGHT: VFR. BREEZY. SLIGHT CHANCE SHRA.
SUNDAY: VFR. BREEZY.
SUNDAY NIGHT: VFR.
MONDAY: VFR. BREEZY.
MARINE
FORECASTER CONFIDENCE LEVELS...
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
THROUGH FRIDAY... HIGH CONFIDENCE.
A FEW PERIODS OF GUSTY SW WINDS NEAR 20 KTS ARE POSSIBLE
TONIGHT ACROSS THE NORTHEASTERN WATERS AND THURSDAY ACROSS THE
SOUTHERN WATERS. WINDS CALM FRIDAY AS HIGH PRESSURE BUILDS OVER
THE REGION. WATERS AND WINDS WILL BE BELOW SCA FOR THE
FORESEEABLE FUTURE.
OUTLOOK /THURSDAY NIGHT THROUGH MONDAY/...
FRIDAY: WINDS LESS THAN 25 KT.
FRIDAY NIGHT: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING
5 FT. SLIGHT CHANCE OF RAIN SHOWERS.
SATURDAY: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING 5 FT.
SATURDAY NIGHT: WINDS LESS THAN 25 KT. AREAS OF SEAS
APPROACHING 5 FT. SLIGHT CHANCE OF RAIN SHOWERS.
SUNDAY: WINDS LESS THAN 25 KT. AREAS OF SEAS APPROACHING 5 FT.
SUNDAY NIGHT: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING
5 FT.
MONDAY: WINDS LESS THAN 25 KT.
BOX WATCHES/WARNINGS/ADVISORIES
CT...HEAT ADVISORY FROM 11 AM THURSDAY TO 8 PM EDT FRIDAY FOR
CTZ002>004.
MA...HEAT ADVISORY FROM 11 AM THURSDAY TO 8 PM EDT FRIDAY FOR
MAZ003>007-010>021-026.
RI...HEAT ADVISORY FROM 11 AM THURSDAY TO 8 PM EDT FRIDAY FOR
RIZ001>007.
MARINE...NONE.
DISCUSSION...DOOLEY/FT
AVIATION...MCMINN/FT
MARINE...FT
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page