269
FXUS61 KBOX 300815
AFDBOX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOSTON/NORTON MA
415 AM EDT TUE JUN 30 2026
WHAT HAS CHANGED
THE EXTREME HEAT WATCH HAS BEEN UPGRADED TO AN EXCESSIVE HEAT
WARNING FOR ALL OF SOUTHERN NEW ENGLAND EXCEPT THE SOUTH COAST AND
BERKSHIRES.
KEY MESSAGES
- DANGEROUS PROLONGED HEAT AND HUMIDITY WED THROUGH SAT WITH
AFTERNOON HEAT INDICES IN THE 98 TO 112 DEGREE RANGE WITH
LITTLE RELIEF AT NIGHT. PEAK OF THE HEAT THU INTO FRI.
- A CLUSTER OF SCATTERED SHOWERS AND A FEW T-STORMS MAY WORK
INTO PARTS OF OUR REGION VERY LATE TODAY AND TONIGHT. ACTIVITY
LIKELY WEAKENING WITH MAIN SEVERE WEATHER RISK TO OUR NORTHWEST,
BUT CAN NOT RULE OUT A LOW RISK IN WESTERN MA/CT.
- W/NW FLOW ALOFT MAY BRING A LOW CONVECTIVE/SEVERE WEATHER RISK
GIVEN HIGH CAPE/REMNANT EML WED-FRI...BUT LIMITED FORCING AND CAP
MAY KEEP US MAINLY DRY. GREATEST RISK FOR THUNDERSTORMS/SEVERE
WEATHER POTENTIAL MIGHT WAIT UNTIL SAT JULY 4TH WITH THE ACTUAL
COLD FRONT.
DISCUSSION
KEY MESSAGE 1...DANGEROUS PROLONGED HEAT AND HUMIDITY WED THROUGH
SAT WITH AFTERNOON HEAT INDICES IN THE 98 TO 112 DEGREE RANGE WITH
LITTLE RELIEF AT NIGHT. PEAK OF THE HEAT THU INTO FRI.
HIGH CONFIDENCE FORECAST IN DANGEROUS PROLONGED HEAT AND HUMIDITY
WED THROUGH SAT. THIS CONTINUES TO BE SUPPORTED BY THE NAEFS
SITUATIONAL AWARENESS TABLE WHICH INDICATES MANY PARAMETERS OUTSIDE
THE MODELS CLIMATOLOGY. THE EFI/SHIFT OF TAILS ALSO INDICATES BOTH
MIN/MAX TEMPERATURES ON THE EDGE OR OUTSIDE OF THE MODELS
CLIMATOLOGY. 925T PEAK ON THU AND FRI IN THE +28C TO +30C DEGREE
RANGE AND THAT IS WHEN WE EXPECT THE WORST OF THE EXTREME HEAT AND
HUMIDITY.
TODAY WILL BE VERY WARM AND WITH 850T CLIMBING TO +16C/+17C WE
SHOULD SEE HIGHS TOP OUT IN THE UPPER 80S TO THE LOWER 90S AWAY FROM
THE SOUTH COAST. THE DANGEROUS HEAT AND HUMIDITY STARTS ON WED WHEN
850T CLIMB TO +20C/+21C AND EXPECT HIGHS TO REACH THE MIDDLE 90S
AWAY FROM THE SOUTH COAST AND POSSIBLY UPPER 90S IN A FEW SPOTS.
THIS COUPLED WITH DEWPOINTS RISING TO 70+ WILL RESULT IN DANGEROUS
HEAT AND HUMIDITY. HEAT INDICES WILL RISE TO BETWEEN 98 AND 108
DEGREES AWAY FROM THE SOUTH COAST. THE WORST OF THE HEAT AND
HUMIDITY WILL LIKELY BE IN THE CT RIVER VALLEY AND MERRIMACK
VALLEYS. THE EXTREME HEAT AND HUMIDITY PEAK ON THU AND FRI WHEN 850T
REACH BETWEEN +22C AND +24C. HIGH TEMPERATURES WILL LIKELY REACH
BETWEEN 97 AND 103 AWAY FROM THE SOUTH COAST AND ANY VERY LOCALIZED
SEA BREEZES. HEAT INDICES WILL REACH DANGEROUS LEVELS IN THE 102 TO
113 DEGREE RANGE. IT WILL REMAIN HOT AND HUMID ON SAT JULY 4TH AS
WELL. WHILE IT MAY BE A FEW DEGREES LOWER THAN THU/FRI...DANGEROUS
HEAT AND HUMIDITY MAY CONTINUE AND WILL BE DETERMINED BY THE TIMING
OF A COLD FRONT.
NOT ONLY WILL THIS BE A DANGEROUS PROLONGED HEATWAVE...THERE WILL BE
LITTLE RELIEF AT NIGHT. LOW TEMPERATURES WILL ONLY DROP INTO THE
MIDDLE 70S IN MOST LOCATIONS AND 75 TO 80 DEGREES IN THE URBAN
CENTERS. IN FACT...BOSTON MAY NOT DROP BELOW 80 DEGREES DURING THE
PEAK OF THE HEAT AND HUMIDITY!
GIVEN THE ABOVE...WE OPTED TO UPGRADE MOST OF OUR REGION TO AN
EXTREME HEAT WARNING WED THROUGH SAT. WHILE SOME AREAS MAY
TECHNICALLY NOT HIT WARNING CRITERIA UNTIL THU AND MAY NOT ON SAT
DEPENDING ON THE TIMING OF THE COLD FRONT...THE OVERALL MESSAGE
REMAINS THE SAME. WE DID HOLD THE EXCESSIVE HEAT WATCH ALONG THE
BERKS AND SOUTH COAST OF MA/RI. HOWEVER...THIS AREA WILL STILL
EXPERIENCE DANGEROUS HEAT AND HUMIDITY BUT WANTED TO GO WITH THE
WARNING WHERE OUR CONFIDENCE WAS HIGHEST AT THIS POINT.
KEY MESSAGE 2...A CLUSTER OF SCATTERED SHOWERS AND A FEW T-STORMS
MAY WORK INTO PARTS OF OUR REGION VERY LATE TODAY AND TONIGHT.
ACTIVITY LIKELY WEAKENING WITH MAIN SEVERE WEATHER RISK TO OUR
NORTHWEST, BUT CAN NOT RULE OUT A LOW RISK IN WESTERN MA/CT.
THE OTHER CONCERN FOR LATE TODAY AND ESPECIALLY TONIGHT IS A
SHORTWAVE THAT WILL BE DROPPING SOUTHEAST IN NORTHWEST FLOW ALOFT
AROUND THE DEVELOPING RING OF FIRE. EFFECTIVE SHEAR OF 30-40 KNOTS
IS FAVORABLE FOR THIS ACTIVITY TO WORK INTO OUR REGION...BUT
INSTABILITY WILL BE RATHER MARGINAL. SO EXPECT A CLUSTER OF
WEAKENING SCATTERED SHOWERS AND PERHAPS A FEW THUNDERSTORMS TO
IMPACT PORTIONS OF OUR REGION. THE GREATEST RISK IS ACROSS WESTERN
MA/CT. THE OVERALL SEVERE WEATHER THREAT IS LOW GIVEN THE LIMITED
INSTABILITY IN OUR REGION...BUT GIVEN NORTHWEST FLOW ALOFT AND
LINGERING MOMENTUM CAN NOT RULE OUT A LOW PROBABILITY FOR SOME
SEVERE WEATHER IN WESTERN MA/CT. HOWEVER...CURRENTLY THINKING
GREATEST RISK IS NORTHWEST OF OUR REGION.
KEY MESSAGE 3...W/NW FLOW ALOFT MAY BRING A LOW CONVECTIVE/SEVERE
WEATHER RISK GIVEN HIGH CAPE/REMNANT EML WED-FRI...BUT LIMITED
FORCING AND CAP MAY KEEP US MAINLY DRY. GREATEST RISK FOR
THUNDERSTORMS/SEVERE WEATHER POTENTIAL MIGHT WAIT UNTIL SAT JULY 4TH
WITH THE ACTUAL COLD FRONT.
ANOMALOUS HEAT AND HUMIDITY WILL RESULT IN RATHER HIGH INSTABILITY
ACROSS OUR REGION WED THROUGH FRI. IN ADDITION...A REMNANT EML IN
NORTHWEST FLOW ALOFT IS PRESENT. IF SOMEHOW WE CAN GET A FEW
THUNDERSTORMS GOING THEY COULD QUICKLY BECOME SEVERE EVEN DURING THE
OVERNIGHT/MORNING HOURS. HOWEVER...LACK OF OVERALL SYNOPTIC FORCING
AND A MID LEVEL CAP MAY KEEP THIS RISK LOW BUT IT WILL STILL NEED TO
WATCHED. GREATEST RISK FOR CONVECTION AND POTENTIALLY SOME SEVERE
WEATHER MAY WAIT UNTIL SAT JULY 4TH WHEN THE COLD FRONT/STRONG
FORCING ARRIVES.
AVIATION /08Z TUESDAY THROUGH SATURDAY/
FORECASTER CONFIDENCE LEVELS...
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
06Z TAF UPDATE...
TODAY AND TONIGHT...HIGH CONFIDENCE.
MAINLY VFR AFTER AREAS OF LOW CLOUDS/GROUND FOG MAINLY ACROSS RI/SE
MA BY MID MORNING. OTHERWISE...WE ALSO WILL NEED TO WATCH FOR A
CLUSTER OF WEAKENING SCATTERED SHOWERS AND PERHAPS A FEW T-STORMS
TOWARD EVENING AND INTO TONIGHT. GREATEST RISK FOR THIS ACTIVITY
WILL BE ACROSS WESTERN MA/CT. S-SW WINDS 6-13 KNOTS THIS AFTERNOON
INTO TONIGHT...BUT 10-20 KNOTS LATER TONIGHT ACROSS THE CAPE/ISLANDS.
WEDNESDAY...HIGH CONFIDENCE.
MAINLY VFR BUT CAN NOT RULE OUT WIDELY SCATTERED SHOWERS/T-STORMS
LATER WED INTO WED NIGHT. SW WINDS 10 TO 15 KNOTS WITH 20 TO 25 KNOT
GUSTS IN THE AFTERNOON. STRONGEST OF THOSE GUSTS TOWARD THE
CAPE/ISLANDS.
KBOS TERMINAL...HIGH CONFIDENCE IN TAF. SEA BREEZE DEVELOPS BY MID
TO LATE MORNING BUT SHOULD BE KNOCKED OUT AND TURN S-SW BY MID TO
LATE AFTERNOON.
OUTLOOK /WEDNESDAY NIGHT THROUGH SATURDAY/...
WEDNESDAY NIGHT: VFR. BREEZY. SLIGHT CHANCE SHRA, ISOLATED
TSRA.
THURSDAY THROUGH FRIDAY NIGHT: VFR. BREEZY.
INDEPENDENCE DAY: VFR. CHANCE SHRA, CHANCE TSRA.
MARINE
FORECASTER CONFIDENCE LEVELS...
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
TODAY THROUGH WEDNESDAY...HIGH CONFIDENCE.
BERMUDA HIGH PRESSURE WILL RESULT IN A PERSISTENT SW FLOW ACROSS OUR
WATERS. DESPITE THE INVERSION ENOUGH MIXING ESPECIALLY BY
WEDNESDAY...PARTICULARLY NEAR SHORE SHOULD YIELD SW WIND GUSTS UP TO
25 KNOTS. IN ADDITION....LONG SOUTHWEST FETCH SHOULD BUILD SEAS TO 3-
6 FEET ACROSS OUR SOUTHERN WATERS. SMALL CRAFT HEADLINES HAVE BEEN
POSTED FOR OUR SOUTHERN WATERS AND SOUNDS TOWARDS DAYBREAK AND
THROUGH WEDNESDAY.
OUTLOOK /WEDNESDAY NIGHT THROUGH SATURDAY/...
WEDNESDAY NIGHT: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH
GUSTS UP TO 25 KT. AREAS OF ROUGH SEAS. SLIGHT CHANCE OF RAIN
SHOWERS, ISOLATED THUNDERSTORMS.
THURSDAY THROUGH THURSDAY NIGHT: LOW RISK FOR SMALL CRAFT
ADVISORY WINDS WITH GUSTS UP TO 25 KT. SEAS UP TO 5 FT.
FRIDAY: WINDS LESS THAN 25 KT.
FRIDAY NIGHT: WINDS LESS THAN 25 KT. SLIGHT CHANCE OF RAIN
SHOWERS.
INDEPENDENCE DAY: WINDS LESS THAN 25 KT. SLIGHT CHANCE OF RAIN
SHOWERS, SLIGHT CHANCE OF THUNDERSTORMS.
BOX WATCHES/WARNINGS/ADVISORIES
CT...AIR QUALITY ALERT FROM 11 AM THIS MORNING TO 11 PM EDT THIS
EVENING FOR CTZ002.
EXTREME HEAT WARNING FROM 10 AM WEDNESDAY TO 8 PM EDT SATURDAY
FOR CTZ002>004.
MA...EXTREME HEAT WARNING FROM 10 AM WEDNESDAY TO 8 PM EDT SATURDAY
FOR MAZ003>007-010>019-026.
EXTREME HEAT WATCH FROM WEDNESDAY MORNING THROUGH SATURDAY
EVENING FOR MAZ002-008-009-020-021.
RI...EXTREME HEAT WARNING FROM 10 AM WEDNESDAY TO 8 PM EDT SATURDAY
FOR RIZ001>004.
EXTREME HEAT WATCH FROM WEDNESDAY MORNING THROUGH SATURDAY
EVENING FOR RIZ005>007.
MARINE...SMALL CRAFT ADVISORY FROM 8 AM TO 11 PM EDT WEDNESDAY FOR
ANZ231>237.
SMALL CRAFT ADVISORY FROM 5 AM WEDNESDAY TO 4 PM EDT THURSDAY
FOR ANZ254>256.
DISCUSSION...FRANK
AVIATION...FRANK
MARINE...FRANK
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