283
FXUS61 KBOX 211842
AFDBOX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOSTON/NORTON MA
242 PM EDT MON JUL 21 2025
SYNOPSIS
COOLER PATTERN PERSISTS THROUGH TUESDAY NIGHT UNDER HIGH
PRESSURE.WARMING TREND STARTS MIDWEEK AND HUMIDITY INCREASES GOING INTO
FRIDAY. DANGEROUS HEAT IS POSSIBLE FOR FRIDAY AS HIGHS APPROACH THE
UPPER 90S AND HEAT INDICES CLIMB INTO THE LOWER 100S. HEAT AND
HUMIDITY CONTINUE THROUGH THE WEEKEND, BUT AT A LESSER DEGREE
FOLLOWING A COLD FRONT FRIDAY. THE CHANCE FOR SHOWERS AND STORMS
RETURNS FRIDAY THROUGH THE WEEKEND AFTER DRY CONDITIONS FOR MUCH OF
THE WEEK.
NEAR TERM /THROUGH TONIGHT/
2:30 PM UPDATE:
KEY MESSAGE:
* PLEASANT WEATHER CONTINUES THROUGH THE REST OF THE AFTERNOON WITH
JUST A FEW FAIR WEATHER DIURNAL CUMULUS AND HAZE ALOFT.
* EFFICIENT RADIATIONAL COOLING OVERNIGHT WITH WIDESPREAD LOWS
IN THE 40S AND 50S
* SIMILAR CONDITIONS ON TUESDAY WITH SEABREEZES
DETAILS:
REST OF THE AFTERNOON:
HIGH PRESSURE OVER ONTARIO CONTINUES TO BUILD OVER NEW ENGLAND
THROUGH THIS AFTERNOON. AT THE SURFACE THIS AS RESULTED IN PLEASANT,
ALBEIT BREEZY CONDITIONS. NORTHWEST WINDS SHOULD CONTINUE TO
DECREASE THROUGH THE REMAINDER OF THE AFTERNOON AS THE PRESSURE
GRADIENT WANES. OTHERWISE, HIGH TEMPERATURES ARE RUNNING A FEW
DEGREES HIGHER THAN THE NBM, ESPECIALLY IN THE INTERIOR. STILL
THINKING THAT MOST LOCATIONS TOP OFF IN THE UPPER 70S TO PERHAPS THE
LOWER 80S WITH FALL-LIKE DEWPOINTS.
OVERNIGHT:
CLEAR SKIES CONTINUE OVERNIGHT AS THE CENTER OF HIGH PRESSURE CRESTS
OVER THE REGION. THESE CLEAR SKIES AND A DECOUPLING BOUNDARY LAYER
WILL RESULT IN STRONG RADIATIONAL COOLING REGIONWIDE. CERTAINLY A
COMFORTABLE, IF NOT SLIGHTLY CHILLY NIGHT AHEAD WITH MOST AREAS
DROPPING INTO THE LOWER 50S AND PERHAPS AS LOW AS THE UPPER 40S IN
PLACES WHERE COOLING IS MAXIMIZED. THERE IS ALSO A CHANCE FOR SOME
LOCALIZED PATCHY FOG ALONG PORTIONS OF THE CT RIVER VALLEY AND IN
LOW-LYING SWAMPY AREAS.
SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/
230 AM UPDATE:
KEY MESSAGES:
* COOLER WEATHER CONTINUES
* WEAKER SYNOPTIC-SCALE WINDS ALLOW FOR STRONGER SEABREEZES
DETAILS:
COOL TEMPERATURES TUESDAY MORNING QUICKLY RECOVER AS THE COLUMN
QUICKLY BECOMES WELL-MIXED. EXPECTING SLIGHTLY WARMER TEMPS
TOMORROW WITH LOWER WINDS. HIGHS SHOULD TOP OUT IN THE UPPER 70S
FOR MOST, BUT A FEW MORE INTERIOR LOCATIONS WILL ECLIPSE THE
80-DEGREE MARK. WEAKER SYNOPTIC PRESSURE GRADIENT ALLOWS FOR
STRONGER SEABREEZES TOMORROW AFTERNOON. FURTHEST INLAND EXTENT
OF THE SEABREEZES WILL BE ACROSS EASTERN MASSACHUSETTS WHERE THE
LOW LEVEL WIND FIELD SHIFTS TO THE EAST AS HIGH PRESSURE SHIFTS
OFFSHORE. AS A RESULT, THE NBM HAS HIGH TEMPERATURES STAYING IN
THE LOW TO MID 70S ACROSS COASTAL MASSACHUSETTS.
ANOTHER COOL NIGHT ON TAP TUESDAY NIGHT WITH RADIATIONAL COOLING
DRIVING TEMPERATURES DOWN INTO THE MIDDLE 50S. RISING DEWPOINTS
SHOULD KEEP TEMPERATURES FROM FALLING AS MUCH AS MONDAY NIGHT.
MOISTURE WILL CONTINUE TO INCREASE EARLY WEDNESDAY AS RETURN FLOW
BEHIND HIGH PRESSURE INCREASES.
LONG TERM /WEDNESDAY THROUGH MONDAY/
KEY MESSAGES:
* WARMING TREND KICKS OFF MIDWEEK, ALONG WITH INCREASING HUMIDITY
THROUGH FRIDAY
* ELEVATED HEAT INDICES THURSDAY, POSSIBLY REACHING DANGEROUS LEVELS
BY FRIDAY. HEAT HEADLINES POSSIBLE.
* DRY THROUGH THURSDAY BEFORE FRONT ARRIVES FRIDAY, BRINGING A
CHANCE FOR SHOWERS AND STORMS THAT MAY EXTEND INTO THE WEEKEND.
HOWEVER, UNCERTAINTY REMAINS.
DETAILS...
AN UPPER LEVEL RIDGE SETTLED OVER MUCH OF THE EASTERN US AND SURFACE
HIGH PRESSURE OVER THE WATERS JUST EAST OF SOUTHERN NEW ENGLAND
BEGINS TO SHIFT MORE SOUTH AND EAST MIDWEEK HEADING INTO FRIDAY.
THIS WILL HELP KICK OFF A WARMING TREND AND ALLOW HUMIDITY TO
INCREASE WITH IT. THURSDAY HEAT INDICES ARE EXPECTED TO REACH THE
MID 90S, BUT FRIDAY IS EXPECTED TO BE THE HOTTEST DAY OF THIS
STRETCH WITH HEAT INDICES IN THE LOW 100S POSSIBLE. OVERALL GUIDANCE
IS IN GOOD AGREEMENT IN FRIDAY BEING THE HOTTEST; 925 MB
TEMPERATURES ACROSS THE DETERMINISTIC MODELS ARE APPROACHING +30C,
AND THE ENSEMBLES ARE JUST UNDER THAT WITH MEAN 925 MB TEMPERATURES.
WITH GOOD MIXING, SOME BREEZIER CONDITIONS CAN ALSO BE EXPECTED, BUT
IT WON'T BE MUCH RELIEF FROM THE HEAT. HEAT HEADLINES MAY BE NEEDED
FURTHER DOWN THE LINE, ESPECIALLY FOR FRIDAY.
WITH A COLD FRONT APPROACHING FRIDAY, THERE'S A LOW CHANCE FOR SOME
SHOWERS AND STORMS THIS WEEKEND. THERE IS STILL SOME UNCERTAINTY,
THOUGH, ON SEVERITY AND TIMING. CSU ML GUIDANCE HAS THE REGION UNDER
A LOW (5%) PROBABILITY FOR SEVERE WEATHER ON FRIDAY, AND NSSL ML
PROBS ARE ALSO STILL LOW AT THIS TIME FOR FRIDAY. SEVERE RISK WILL
DEPEND ON IF THE FRONT ARRIVES IN TIME TO USE PEAK HEATING TO KICK
OFF SOME STORMS, SO ITS TRACK AND TIMING IS SOMETHING WE WILL
CONTINUE TO MONITOR.
GUIDANCE IS STILL INDICATING THAT THIS COLD FRONT MAY STALL OVER THE
WATERS JUST SOUTH OF SOUTHERN NEW ENGLAND, LEADING TO A MORE
UNSETTLED PATTERN FOR THE WEEKEND. ANY SHOWERS AND STORMS THAT POP
UP WILL LIKELY REMAIN AROUND WHEREVER THE FRONT ENDS UP STALLING
OUT. HIGHS THIS WEEKEND WILL DECREASE SLIGHTLY FOLLOWING THE FRONT'S
PASSAGE, BUT IT WILL STILL BE WARM AND HUMID ACROSS THE REGION. NOT
MUCH RECOVERY FROM THE HEAT IS EXPECTED OVERNIGHT STARTING THURSDAY
NIGHT AND LASTING THROUGH MONDAY MORNING, AS LOWS WILL ONLY DIP INTO
THE LOW 70S AND UPPER 60S.
AVIATION /19Z MONDAY THROUGH SATURDAY/
FORECASTER CONFIDENCE LEVELS...
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
18Z TAF UPDATE:
THROUGH 12Z TUESDAY: HIGH CONFIDENCE.
VFR. NW WINDS PICK UP TO AROUND 10-15 KT, WITH GUSTS 20-25 KT
THRU SUNDOWN. WINDS THEN SLACKEN TO 5-10 KT TONIGHT, HIGHER
EASTERN TERMINALS. WINDS BECOME NEARLY CALM OVERNIGHT WITH HIGH
PRESSURE OVERHEAD.
TUESDAY: HIGH CONFIDENCE.
VFR CONTINUES WITH LIGHT NORTH WINDS; SEABREEZES ON BOTH COASTS
WHICH COULD DEVELOP ON THE EARLIER END OF SEABREEZE CLIMO, AROUND
14Z.
TUESDAY NIGHT: HIGH CONFIDENCE.
VFR, WITH LIGHT S WINDS. RADIATION FOG FOR SOUTHERN/SOUTHWEST
AIRPORTS IS POSSIBLE.
KBOS TERMINAL...HIGH CONFIDENCE IN TAF
KBDL TERMINAL...HIGH CONFIDENCE IN TAF
OUTLOOK /WEDNESDAY THROUGH SATURDAY/...
WEDNESDAY THROUGH WEDNESDAY NIGHT: VFR.
THURSDAY THROUGH THURSDAY NIGHT: VFR. BREEZY.
FRIDAY THROUGH FRIDAY NIGHT: VFR. BREEZY. SLIGHT CHANCE SHRA.
SATURDAY: VFR. CHANCE SHRA, ISOLATED TSRA.
MARINE
FORECASTER CONFIDENCE LEVELS...
LOW - LESS THAN 30 PERCENT.
MEDIUM - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
THROUGH TUESDAY NIGHT: HIGH CONFIDENCE.
NW WINDS THEN SUBSIDE TO LIGHT LEVELS TONIGHT, WHICH REMAIN
LIGHT NORTHERLY ON TUE (NEARSHORE SEABREEZES). WINDS THEN BECOME
S/SW AROUND 5-10 KT TUE NIGHT. SEAS MAINLY 3 FT OR LESS THROUGH
THE PERIOD, EXCEPT NEARING 4 FT EARLY THIS MORNING. NO
OBSTRUCTIONS TO VISIBILITY EXPECTED THRU TUE NIGHT.
OUTLOOK /WEDNESDAY THROUGH SATURDAY/...
WEDNESDAY THROUGH WEDNESDAY NIGHT: WINDS LESS THAN 25 KT.
THURSDAY: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS UP
TO 25 KT. SEAS LOCALLY APPROACHING 5 FT.
THURSDAY NIGHT: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH
GUSTS UP TO 25 KT. AREAS OF SEAS APPROACHING 5 FT.
FRIDAY: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS UP
TO 25 KT. AREAS OF SEAS APPROACHING 5 FT. SLIGHT CHANCE OF RAIN
SHOWERS.
FRIDAY NIGHT: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING
5 FT. SLIGHT CHANCE OF RAIN SHOWERS, ISOLATED THUNDERSTORMS.
SATURDAY: WINDS LESS THAN 25 KT. SLIGHT CHANCE OF RAIN SHOWERS.
BOX WATCHES/WARNINGS/ADVISORIES
CT...NONE.
MA...NONE.
RI...NONE.
MARINE...NONE.
SYNOPSIS...HRENCECIN/FT
NEAR TERM...FT
SHORT TERM...FT
LONG TERM...HRENCECIN
AVIATION...FT
MARINE...FT
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