221
FXUS61 KBOX 291720
AFDBOX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOSTON/NORTON MA
120 PM EDT MON JUN 29 2026
WHAT HAS CHANGED
NO SIGNIFICANT CHANGES.
KEY MESSAGES
- WARMING TREND TAKES HOLD. CONFIDENCE CONTINUES TO INCREASE IN
DANGEROUS HEAT WEDNESDAY THROUGH FRIDAY.
- SHOWERS AND THUNDERSTORMS POSSIBLE MID TO LATE WEEK.
DISCUSSION
KEY MESSAGE 1...WARMING TREND TAKES HOLD. CONFIDENCE CONTINUES
TO INCREASE IN DANGEROUS HEAT WEDNESDAY THROUGH FRIDAY.
MORNING FOG THAT DEVELOPED ALONG THE SOUTH COAST AND PARTS OF
THE CAPE (PLUS MARTHA'S VINEYARD) SHOULD ERODE AWAY AFTER
SUNRISE THIS MORNING. HIGH PRESSURE CONTINUES TO EXERT ITS
INFLUENCE OVER THE REGION AHEAD OF A STRENGTHENING UPPER LEVEL
RIDGE TO OUR WEST. HIGHS TODAY CLIMB INTO THE MID TO UPPER 80S
FOR MOST, STAYING A BIT COOLER TOWARDS THE COASTS AND OVER THE
CAPE AND ISLANDS.
NOT MUCH HAS CHANGED IN THE OVERALL TRENDS OF THE FORECAST
OVERNIGHT. A STRONG UPPER LEVEL RIDGE CONTINUES BUILDING IN FROM
THE WEST, SHIFTING OVER THE NORTHEAST CONUS LATE THIS WEEK.
ENSEMBLES REMAIN IN STRONG AGREEMENT THAT WE WILL SEE
TEMPERATURES OVER 90-95 STARTING WEDNESDAY AND CONTINUING
THROUGH THE REST OF THE WEEK. THE HIGHEST PROBABILITIES OF
TEMPERATURES REACHING AND/OR EXCEEDING 100F OVER URBAN AREAS AND
THE RIVER VALLEYS, ESPECIALLY ON THURSDAY, ALSO CONTINUE TO
INCREASE. GEFS PROBABILITIES OF 100F+ FOR THURSDAY AFTERNOON
RANGE NOW REACH UP TO 60-70 PERCENT WITH CANADIAN ENSEMBLE
PROBABILITIES PEAKING SLIGHTLY HIGHER AT UP TO 80 PERCENT. ALL
ENSEMBLES ARE IN PRETTY GOOD AGREEMENT HAVING THE HIGHEST
PROBABILITIES IN THE CT VALLEY AND TOWARDS THE BOSTON METRO UP
INTO THE MERRIMACK VALLEY. THE CONTINUED OVERALL CONSENSUS
ACROSS THE DIFFERENT GUIDANCE SUITE AIDS IN INCREASING
CONFIDENCE IN THE RISK FOR THIS DANGEROUS HEAT OVERALL. MEAN 850
MB TEMPERATURES ACROSS THE ENSEMBLES CONTINUE TO REACH 20-24C
DURING THIS STRETCH, AND 925 MB TEMPERATURES IN THE
DETERMINISTIC GUIDANCE CONTINUE TO KEY IN ON 25C TEMPERATURES
AND HIGHER, EVEN TO 30C. NOTABLY, THE GFS HAS THE HIGHEST 925 MB
TEMPERATURES CENTERED OVER CT AND EASTERN MA. THIS IS ALL
BEFORE DEW POINTS AND OVERALL MOISTURE ARE BEING TAKEN INTO
ACCOUNT. CONSIDERING DEW POINTS ARE EXPECTED TO BE IN THE UPPER
60S AND EVEN INTO THE LOW 70S, HEAT INDICES TO 110F ARE NOT OUT
OF THE QUESTION FOR SOME AREAS. AN EXTREME HEAT WATCH WILL BE IN
EFFECT FROM WEDNESDAY MORNING THROUGH FRIDAY EVENING FOR THIS
REASON, ALONG WITH LIMITED OVERNIGHT TEMPERATURE RECOVERY. MAJOR
(3/4) TO EXTREME (4/4) HEAT RISK IMPACTS ARE VERY POSSIBLE,
WITH THE EXTREME IMPACTS MORE LIKELY OVER URBAN AREAS AND IN
RIVER VALLEYS.
AS BRIEFLY HIGHLIGHTED ABOVE, ANOTHER ISSUE WITH THESE HIGH
DAYTIME TEMPERATURES IS THAT NOT MUCH RELIEF IS EXPECTED
OVERNIGHT. NBM HAS LOW PROBABILITIES FOR TEMPERATURES GETTING
BELOW 70F OVERNIGHT BETWEEN WEDNESDAY AND FRIDAY, GENERALLY
BELOW 10 PERCENT ACROSS MUCH OF SOUTHERN NEW ENGLAND. IT ALSO
HAS PROBABILITIES BETWEEN 75-90 PERCENT FOR EARLY THURSDAY
MORNING AND EARLY FRIDAY MORNING TEMPERATURES IN EASTERN MA
(ESPECIALLY BOSTON) REMAINING ABOVE 75F FROM OVERNIGHT. THE
OTHER ENSEMBLES ARE EQUALLY PESSIMISTIC WITH RECOVERY; GEFS,
ECMWF ENS, AND THE CANADIAN ENSEMBLE ARE ALL ESSENTIALLY SHOWING
MAXIMUM PROBABILITIES THAT THE REGION STAYS AT OR ABOVE 70F
OVERNIGHT BETWEEN WEDNESDAY AND FRIDAY NIGHT.
KEY MESSAGE 2...SHOWERS AND THUNDERSTORMS POSSIBLE MID TO LATE
WEEK.
SHORTWAVES ORIGINATING FROM A DISTURBANCE IN CENTRAL CANADA WILL
TRACK EASTWARD AND MAY IMPACT SOUTHERN NEW ENGLAND BEFORE THE
UPPER LEVEL RIDGE FULLY BUILDS UP OVER THE REGION. THESE WAVES
WILL TRACK ALONG THE EASTERN PERIPHERY, WITH ONE LIKELY ARRIVING
TUESDAY NIGHT AND ANOTHER ARRIVING ONCE THE RIDGE STARTS
BREAKING DOWN TOWARDS THE END OF THE WEEK. SHOWERS AND STORMS
ARE A POSSIBILITY TUESDAY NIGHT, AND SOME GUIDANCE IS HINTING AT
INCREASED INSTABILITY OVERNIGHT THAT COULD FUEL ANY STORMS THAT
DO DEVELOP. CSU ML PROBS AND OTHER GUIDANCE AREN'T SHOWING MUCH
IN THE WAY OF A SEVERE SIGNAL AT THIS TIME, BUT WE WILL
CONTINUE TO MONITOR FOR ANY RISK THAT COULD DEVELOP. WITH THE
RIDGE FULLY BUILD UP OVER THE REGION WEDNESDAY AND THURSDAY,
CHANCES FOR ANY SHOWERS OR STORMS DROP SIGNIFICANTLY. CHANCES
RETURN AS THE RIDGE BREAKS DOWN TOWARDS THE END OF THE WEEK, AND
THE RISK FOR SEVERE WEATHER COULD BE HIGHER TOWARDS FRIDAY AND
SATURDAY. CIPS ANALOGS ARE HINTING AT IT PARTICULARLY FOR
WESTERN AND CENTRAL MA. MORE REFINED DETAILS WILL COME INTO THE
PICTURE AS WE GET CLOSER TO BOTH EVENTS.
AVIATION /18Z MONDAY THROUGH SATURDAY/
FORECASTER CONFIDENCE LEVELS...
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
THROUGH 00Z TODAY...HIGH CONFIDENCE.
VFR WITH LIGHT WINDS. SEABREEZES CONTINUE THROUGH SUNSET.
TONIGHT...HIGH CONFIDENCE.
IFR LIKELY TO RETURN WITH FOG OVERNIGHT ACROSS PORTIONS OF SE
MA, RI, CT, AND THE CAPE AND ISLANDS. WINDS MOSTLY S, REMAINING
LIGHT AND GOING CALM FROM TIME TO TIME.
TUESDAY...HIGH CONFIDENCE.
VFR. WINDS PICK UP IN THE AFTERNOON FROM THE SSW, GUSTING TO
20 KT ACROSS MUCH OF SE MA, RI, AND CT. SHOWERS POSSIBLE
TOWARDS THE LATE EVENING HOURS.
TUESDAY NIGHT...HIGH CONFIDENCE.
VFR. LIGHT SOUTHWEST WINDS.
KBOS TERMINAL...HIGH CONFIDENCE IN TAF.
KBDL TERMINAL...HIGH CONFIDENCE IN TAF.
OUTLOOK /WEDNESDAY THROUGH SATURDAY/...
WEDNESDAY THROUGH WEDNESDAY NIGHT: VFR. BREEZY. SLIGHT CHANCE
SHRA.
THURSDAY THROUGH THURSDAY NIGHT: VFR. BREEZY.
FRIDAY: VFR. BREEZY. SLIGHT CHANCE SHRA, SLIGHT CHANCE TSRA.
FRIDAY NIGHT: VFR. SLIGHT CHANCE SHRA, SLIGHT CHANCE TSRA.
INDEPENDENCE DAY: VFR. CHANCE TSRA, SLIGHT CHANCE SHRA.
MARINE
FORECASTER CONFIDENCE LEVELS...
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
THROUGH TUESDAY NIGHT: HIGH CONFIDENCE.
RELATIVELY LIGHT WINDS AND SEAS EXPECTED THROUGH AT LEAST
TUESDAY MORNING. INCREASING SOUTHWEST WINDS AHEAD OF A COLD
FRONT COULD RESULT IN SOME GUSTS NEAR 25 KT TUESDAY AFTERNOON
INTO TUESDAY NIGHT. AREAS OF FOG RETURN TONIGHT, RESULTING IN
POOR VISIBILITY LESS THAN 1 MILE AT TIMES.
OUTLOOK /WEDNESDAY THROUGH SATURDAY/...
WEDNESDAY: MODERATE RISK FOR SMALL CRAFT ADVISORY WINDS WITH
GUSTS UP TO 30 KT. SEAS UP TO 5 FT. SLIGHT CHANCE OF RAIN
SHOWERS.
WEDNESDAY NIGHT: MODERATE RISK FOR SMALL CRAFT ADVISORY WINDS
WITH GUSTS UP TO 25 KT. SEAS UP TO 5 FT. CHANCE OF RAIN
SHOWERS.
THURSDAY: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS UP
TO 20 KT. AREAS OF SEAS APPROACHING 5 FT.
THURSDAY NIGHT: WINDS LESS THAN 25 KT. AREAS OF SEAS
APPROACHING 5 FT.
FRIDAY: WINDS LESS THAN 25 KT. SLIGHT CHANCE OF RAIN SHOWERS.
FRIDAY NIGHT: WINDS LESS THAN 25 KT. SLIGHT CHANCE OF RAIN
SHOWERS, SLIGHT CHANCE OF THUNDERSTORMS.
INDEPENDENCE DAY: WINDS LESS THAN 25 KT. SLIGHT CHANCE OF RAIN
SHOWERS.
BOX WATCHES/WARNINGS/ADVISORIES
CT...EXTREME HEAT WATCH FROM WEDNESDAY MORNING THROUGH SATURDAY
EVENING FOR CTZ002>004.
MA...EXTREME HEAT WATCH FROM WEDNESDAY MORNING THROUGH SATURDAY
EVENING FOR MAZ002>021-026.
RI...EXTREME HEAT WATCH FROM WEDNESDAY MORNING THROUGH SATURDAY
EVENING FOR RIZ001>007.
MARINE...NONE.
DISCUSSION...BELK/LOCONTO
AVIATION...BELK/LOCONTO
MARINE...BELK/LOCONTO
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