731
FXUS61 KBOX 211133
AFDBOX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOSTON/NORTON MA
733 AM EDT TUE JUL 21 2026
WHAT HAS CHANGED
GALE WATCH CONVERTED TO SMALL CRAFT ADVISORIES DUE TO LOW
CONFIDENCE IN WIDESPREAD/CONSISTENT GALE-FORCE WINDS TONIGHT AND
WEDNESDAY.
KEY MESSAGES
- SCATTERED SHOWERS AND THUNDERSTORMS RETURN THIS EVENING
THROUGH WEDNESDAY MORNING. RISK FOR A FEW STRONG TO SEVERE
STORMS AND HEAVY DOWNPOURS. LOCALIZED FLASH FLOODING POSSIBLE
IN POOR DRAINAGE AREAS.
- SCATTERED THUNDERSTORMS POSSIBLE LATER WEDNESDAY, BUT WILL BE
DEPENDENT ON DEGREE OF CLEARING DURING THE DAY.
- DRYING OUT THURSDAY INTO THE LATTER PART OF THE WEEK
WITH SEASONABLE TEMPERATURES AND LOWER HUMIDITY INTO THE
WEEKEND.
DISCUSSION
KEY MESSAGE 1...SCATTERED SHOWERS AND THUNDERSTORMS RETURN THIS EVENING
THROUGH WEDNESDAY MORNING. RISK FOR A FEW STRONG TO SEVERE
STORMS AND HEAVY DOWNPOURS. LOCALIZED FLASH FLOODING POSSIBLE IN
POOR DRAINAGE AREAS.
AN UPPER LEVEL TROUGH SLOWLY PUSHES ACROSS EASTERN U.S./CANADA TODAY
THROUGH THURSDAY WITH A SEVERAL PIECES OF SHORTWAVE ENERGY MOVING
THROUGH THE FLOW. AT THE SURFACE, THIS WILL SWEEP A FEW FRONTAL
BOUNDARIES ACROSS THE NORTHEAST AS A SURFACE LOW TRACKS ACROSS
QUEBEC. THIS WILL SUPPORT THE RETURN OF UNSETTLED WEATHER WITH
POTENTIAL FOR STRONG STORMS AND MINOR LOCALIZED FLASH FLOODING
TONIGHT INTO WEDNESDAY. A 40-50 KT LLJ WITH BE THE MAIN PLAYER WITH
THE SET-UP, HELPING ADVECT IN RICHER MOISTURE (DEWPOINTS AROUND 70F)
WITH PRECIPITABLE WATER VALUES RISING TO 1.5-2.0"+ ACROSS SOUTHERN
NEW ENGLAND THIS EVENING. INSTABILITY VARIES FROM MARGINAL TO
MODERATE ACROSS HIGH-RESOLUTION GUIDANCE WITH MU/SBCAPE VALUES 800-
1500 J/KG. THIS IS SUFFICIENT TO SUPPORT THUNDERSTORM DEVELOPMENT IF
INSTABILITY IS AVAILABLE WHILE ALIGNING WITH AN INCOMING SHORTWAVE.
MODEL SOUNDINGS DO SHOW HODOGRAPHS SUPPORTIVE OF STRONGER SHEAR AND
HELICITY VALUES IN THE 0-3 KM LAYER. THIS ENVIRONMENT WILL NOT ONLY
BE SUPPORT OF HEAVY DOWNPOURS, BUT ALSO A STRONG TO SEVERE STORM OR
TWO WITH DAMAGING WINDS. CAN'T RULE OUT THE LOW RISK OF A BRIEF
"SPIN-UP" GIVEN THE SUPPORTIVE WIND/SHEAR PROFILES.
ANOMALOUS PWATS COMBINED WITH WARM CLOUD DEPTHS OF 11,000-13,000+ FT
ALLOW FOR EFFICIENT RAIN PROCESSES AND MORE IMPORTANTLY SUPPORT
HEAVY RAINFALL. AS FAR AS THE QPF PROBS GO, 18Z GUIDANCE BACKED OFF
A LITTLE WITH THE PROBS OF 1"+ AND 2"+ OVERALL, BUT IT'S JUST ONE
RUN. WE ARE STILL OVERALL SEEING A GOOD SIGNAL FOR 24HR AMOUNTS 1"+
SHOWN BY THE MODERATE TO HIGH PROBABILITIES (50-80%) ESPECIALLY
ALONG THE SOUTH COAST AND CAPE AND ISLANDS AND LOW TO MODERATE
PROBABILITIES FOR 2"+ FOCUSED ALONG THE IMMEDIATE SOUTH COAST AND
CAPE/ISLANDS.
THE TIMEFRAME AT WHICH THIS FALLS WILL BE THE BIG FACTOR FOR FLASH
FLOODING POTENTIAL. GIVEN THAT EMBEDDED STORMS ARE POSSIBLE,
LOCALIZED FLASH FLOODING IS CERTAINLY A CONCERN. THE HREF PMM
REFLECTS THIS WELL WITH LOCALIZED AREAS OF 2"+ ACROSS WESTERN CT, RI
AND SOUTHEAST MA, BUT ALSO MANY STREAKS OF 1-1.25" ACROSS THE
REGION. SLOW STORM MOTION WILL NOT BE A CONCERN WITH MID-LEVEL
FLOW >30KTS; HOWEVER, THERE IS A PROMINENT LLJ SUPPLING
PLENTIFUL MOISTURE UPSTREAM WHILE STEERING STORMS CONSISTENTLY
SW TO NE. TRAINING OF HEAVIER RAIN AND THUNDERSTORM MAY BE
POSSIBLE AS A RESULT. THE HREF PROBABILITY OF 1 HR PRECIP
EXCEEDING 1 HR FFG REFLECTS THIS WELL WITH HIGHER PROBABILITIES
IN NJ AND SOUTHERN NY WITH LOW PROBS EXTENDING INTO WESTERN CT.
THERE ARE A FEW SPOTS OF LOW PROBS ACROSS MA AND RI
TONIGHT/EARLY WEDNESDAY. ALL THIS IS POINTING TO IS A LOWER
PROBABILITY OF SEEING WIDESPREAD FLASH FLOOD IMPACTS. THE HREF
SHOWING SCATTERED LOW PROBABILITIES(< 20%) OF >1.0"/HR RAIN
RATES MAINLY ACROSS PORTIONS OF CT AND MORESO RI AND SOUTHEAST
MA/CAPE & ISLANDS. SO WE'LL HAVE TO KEEP AN EYE ON LOCALIZED
MINOR FLASH FLOODING ISSUES, ESPECIALLY IN THE MORE FLASHY AREAS
OR URBAN/POOR DRAINAGE AREAS (PROVIDENCE, HARTFORD). THIS IS
FAIRLY CONSISTENT WITH THE PREVIOUS FORECAST WITH US SEEING THE
RISK FOR LOCALIZED FLASH FLOODING; HOWEVER, IT IS NOT WIDESPREAD
ENOUGH OF A THREAT TO WARRANT A FLOOD WATCH FOR PORTIONS OF
SOUTHERN NEW ENGLAND.
FOR TIMING, THIS WILL PRIMARILY BE AND EVENING AND OVERNIGHT EVENT
INTO THE EARLY MORNING HOURS OF WEDNESDAY. DEPENDING ON THE TIMING
OF THESE SHORTWAVES SHOWERS/STORMS COULD DEVELOP MAY DEVELOP AS
EARLY AS LATE AFTERNOON; HOWEVER, CHANCES INCREASE FOR THE EVENING
AND OVERNIGHT TIMEFRAME.
KEY MESSAGE 2...SCATTERED THUNDERSTORMS POSSIBLE LATER WEDNESDAY,
BUT WILL BE DEPENDENT ON DEGREE OF CLEARING DURING THE DAY.
RAIN CONTINUES THROUGH THE EARLY MORNING HOURS OF WEDNESDAY. THERE
IS SOME QUESTION ON WHEN THE BULK OF THE RAIN EXITS AND THE COVERAGE
OF SHOWERS. MOST MODEL GUIDANCE HAS THE BULK OF RAIN OUT BY LATE
MORNING; HOWEVER, THERE IS MORE SPREAD ON THE DEGREE OF "CLEARING"
IN THE AFTERNOON. IF THERE ARE LINGERING SHOWERS, AS SOME GUIDANCE
SUGGESTS, THE SUPPRESSED HEATING WILL LIKELY END UP LOWERING THE
RISK OF STORMS LATER IN THE DAY. IF WE GET ENOUGH OF A WINDOW WITH
CLEARING OR BREAKS IN THE CLOUDS, INSTABILITY WILL BE SUFFICIENT TO
SUPPORT THUNDERSTORMS DEVELOPING AHEAD OF A COLD FRONT WITH VALUES
1000-1800 J/KG OF SBCAPE. MOISTURE WON'T BE AS ANOMALOUS AS THE
PREVIOUS EVENING THROUGH THE WHOLE COLUMN; HOWEVER, THE HREF HAS
BEEN KEEN ON ANOTHER SURGE OF HIGHER DEWPOINT AIR AHEAD OF THE
FRONT. ACROSS THE INDIVIDUAL CAMS, THERE IS PLENTY OF SPREAD WITH
REGARDS TO THE TIMING, COVERAGE, AND INTENSITY OF CONVECTION (IF
ANY). A COUPLE HINT AT THE POTENTIAL FOR SCATTERED SHOWERS AND
THUNDERSTORMS DEVELOPING AFTER MID-AFTERNOON MOVING EASTWARD INTO
THE EVENING. THE WESTERN AND CENTRAL PORTIONS OF SOUTHERN NEW
ENGLAND LIKELY HAVE A HIGHER RISK GIVEN THEY WOULD LIKELY CLEAR
EARLIER AND HAVE LONGER TO RECOVER AND HEAT THROUGH THE DAY.
INSTABILITY AND SHEAR VALUES ARE SUFFICIENT TO SUPPORT A STRONG TO
SEVERE STORM OR TWO AS WELL. THIS WILL BECOME HIGHER CONFIDENCE AS
MODELS DEVELOP A BETTER CONSENSUS ON THE EXTENT OF CLEARING
WEDNESDAY.
KEY MESSAGE 3...DRYING OUT THURSDAY INTO THE LATTER PART OF THE
WEEK WITH SEASONABLE TEMPERATURES AND LOWER HUMIDITY INTO THE
WEEKEND.
THE COLD FRONT EXITS THE REGION BY THURSDAY MORNING, LEAVING
DRIER AND SEASONABLE CONDITIONS IN ITS WAKE. WITH THE FRONT, THE
UPPER LEVEL TROUGH CENTERED OVER QUEBEC ALSO MOVES OFF TO THE
NORTHEAST. HIGH PRESSURE STARTS TO BUILD IN OVER SOUTHERN NEW
ENGLAND FROM THE GREAT LAKES, CONTINUING THE DRIER CONDITIONS
INTO THE WEEKEND. TEMPERATURES ALOFT FALL SLIGHTLY, WITH 925 MB
TEMPERATURES FALLING TO AROUND 16C FOR MUCH OF THE SECOND HALF
OF THE WEEK. NOTABLY, WEDNESDAY NIGHT WILL LIKELY BE COOLER AS
925 MB TEMPERATURES MAY FALL TO AS LOW AS 10C OVER THE INTERIOR.
LOWS THERE COULD GET INTO THE LOW 50S. 850 MB TEMPERATURES ARE
EXPECTED TO MOSTLY BE AROUND 10C AS WELL THROUGH THE BACK HALF
OF THE WEEK. EVEN WITH THESE REDUCED TEMPERATURES, THE CONTINUED
HIGH SUN ANGLE WILL KEEP TEMPERATURES FROM FALLING TOO LOW,
KEEPING THEM SEASONABLE. CONDITIONS REMAIN DRY AND SEASONABLE
UNTIL AROUND SUNDAY WHEN THE FLOW SHIFTS MORE S AGAIN,
INCREASING HUMIDITY. A SURFACE LOW MAY ALSO PASS JUST OFFSHORE,
BUT ANY IMPACTS FROM IT -- IF ANY AT ALL -- ARE NOT CERTAIN AT
THIS TIME.
AVIATION /12Z TUESDAY THROUGH SATURDAY/
FORECASTER CONFIDENCE LEVELS...
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
12Z TAF UPDATE:
TODAY...MODERATE CONFIDENCE.
POCKETS OF MVFR CIGS THIS MORNING BRIEFLY INCREASE TO VFR FOR A
FEW HOURS BEFORE GENERALLY DETERIORATING TO MVFR-IFR CEILINGS
BY LATE AFTERNOON. RISK OF SHOWERS INCREASED AFTER 18Z FROM W TO
E. A FEW EMBEDDED THUNDERSTORMS ARE POSSIBLE AND CONSENSUS HAS
INCREASED ENOUGH TO INCLUDE IN PROB30S, GENERALLY 23-03Z
(EARLIER FOR WESTERN TERMINALS, LATER FOR EASTERN TERMINALS).
WINDS BECOME SE TO S AND INCREASE TO 10-15 KT WITH GUSTS 20-25
KT, NEAR 30KTS FOR THE CAPE/ISLAND TERMINALS.
TONIGHT...MODERATE CONFIDENCE.
MVFR/IFR POSSIBLE IN ANY SHRA/TSRA, POSSIBLY EVEN LIFR AT TIMES
FOR SOUTH COAST AND CAPE TERMINALS. RAIN OVERSPREADS THE REGION
THIS EVENING AND TONIGHT WITH CHANCES FOR TSRA ACROSS THE
REGION. WINDS 10-20 KT SUSTAINED PARTICULARLY OVER SE MA, CAPE &
ISLANDS. GUSTS 20-25 KT, 30 KT ACROSS THE CAPE/ISLANDS, REMAIN
POSSIBLE THROUGH THE NIGHTTIME PERIOD IN THESE AREAS AS WELL.
KBOS TERMINAL...MODERATE CONFIDENCE IN TAF. TIMING SHOWER
ARRIVAL AND DETERIORATION OF CEILINGS LOWER CONFIDENCE. SHOULD
SEE SHOWERS AROUND AFTER 20Z WITH CEILINGS FALLING TO MVFR WITH
THEIR ARRIVAL BY 23/00Z. LOCALIZED HEAVY DOWNPOURS POSSIBLE IN
HEAVIER SHOWERS AND EMBEDDED THUNDERSTORMS AFTER 00Z. LOWER
CONFIDENCE ON POTENTIAL FOR THUNDERSTORMS DUE TO UNCERTAINTY IN
HOW FAR EAST THE INSTABILITY EXTENDS TONIGHT.
KBDL TERMINAL...MODERATE CONFIDENCE IN TAF. SHOWERS DEVELOPING
MAINLY AFTER 18Z WITH LOCALIZED DOWNPOURS AND EMBEDDED
THUNDERSTORMS POSSIBLE AFTER 20Z.
OUTLOOK /WEDNESDAY THROUGH SATURDAY/...
TUESDAY NIGHT: MAINLY IFR, WITH AREAS MVFR POSSIBLE. WINDY WITH
GUSTS UP TO 30 KT. CHANCE SHRA, CHANCE TSRA.
WEDNESDAY: MAINLY VFR, WITH LOCAL IFR POSSIBLE. WINDY WITH
GUSTS UP TO 35 KT. CHANCE SHRA, ISOLATED TSRA.
WEDNESDAY NIGHT: VFR. WINDY WITH LOCAL GUSTS UP TO 30 KT.
SLIGHT CHANCE SHRA.
THURSDAY THROUGH SATURDAY: VFR.
MARINE
FORECASTER CONFIDENCE LEVELS...
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
THE PROBABILITY FOR MORE WIDESPREAD AND CONSISTENT GUSTS AT OR
ABOVE GALE FORCE HAS DECREASED THUS LEADING TO THE CANCELLATION
OF THE GALE WATCH AND CONVERSION TO SCAS. HOWEVER, SOME MODEL
GUIDANCE HAS STILL INDICATED POTENTIAL FOR BRIEF MORE PATCHY
AREAS OF GUSTS TO GALE FORCE ACROSS THE OUTER WATERS TONIGHT
INTO EARLY WEDNESDAY AS A STRONG LOW LEVEL JET PUSHES IN. ROUGH
SEAS 10-12 FT. NEAR-SHORE WAVES ALONG THE SOUTHERN COAST,
ISLANDS, AND OUTER CAPE ARE LIKELY IN THE 6-10 FT, AND
WARRANTED HIGH SURF ADVISORIES STARTING EARLY WEDNESDAY AND
LINGERING LATE INTO THURSDAY. STRONG RIP CURRENTS AND WAVES NEAR
6 FT ARE POSSIBLE, ESPECIALLY ACROSS THE OUTER CAPE, THURSDAY
AS THE COLD FRONT STALLS OUT NEAR THE COAST, PROMPTING THE LATER
ENDING TO THE HIGH SURF ADVISORY. SCAS CURRENTLY GO OUT THROUGH
WEDNESDAY NIGHT; HOWEVER, WILL LIKELY NEED TO BE EXTENDED FOR
MOST ZONES (SOUTHERN WATERS AND OUTER WATERS) AS 5FT+ WAVES
LINGER.
SHOWERS AND EMBEDDED THUNDERSTORMS TONIGHT INTO EARLY
WEDNESDAY BRINGING HAZARDS OF HEAVY DOWNPOURS, REDUCED
VISIBILITIES TO LESS THAN 2 MILES FOR BRIEF PERIODS IN HEAVIER
SHOWERS/STORMS, AND LIGHTNING.
OUTLOOK /WEDNESDAY THROUGH SATURDAY/...
TUESDAY NIGHT: LOW RISK FOR GALE FORCE WINDS WITH GUSTS UP TO
35 KT. AREAS OF ROUGH SEAS. RAIN SHOWERS, CHANCE OF
THUNDERSTORMS. AREAS OF VISIBILITY 1 TO 3 NM.
WEDNESDAY: LOW RISK FOR GALE FORCE WINDS WITH GUSTS UP TO
35 KT. ROUGH SEAS UP TO 13 FT. CHANCE OF RAIN SHOWERS, SLIGHT
CHANCE OF THUNDERSTORMS.
WEDNESDAY NIGHT: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH
GUSTS UP TO 30 KT. ROUGH SEAS UP TO 12 FT. CHANCE OF RAIN
SHOWERS, SLIGHT CHANCE OF THUNDERSTORMS. LOCAL VISIBILITY 1 TO
3 NM.
THURSDAY: WINDS LESS THAN 25 KT. ROUGH SEAS UP TO 12 FT. CHANCE
OF RAIN SHOWERS, SLIGHT CHANCE OF THUNDERSTORMS.
THURSDAY NIGHT: WINDS LESS THAN 25 KT. SEAS UP TO 5 FT. CHANCE
OF RAIN SHOWERS.
FRIDAY: WINDS LESS THAN 25 KT. SEAS UP TO 5 FT. SLIGHT CHANCE
OF RAIN SHOWERS.
FRIDAY NIGHT THROUGH SATURDAY: WINDS LESS THAN 25 KT. SEAS
LOCALLY APPROACHING 5 FT. SLIGHT CHANCE OF RAIN SHOWERS.
BOX WATCHES/WARNINGS/ADVISORIES
CT...NONE.
MA...HIGH SURF ADVISORY FROM 6 AM WEDNESDAY TO 8 PM EDT THURSDAY
FOR MAZ020>024.
RI...HIGH SURF ADVISORY FROM 6 AM WEDNESDAY TO 8 PM EDT THURSDAY
FOR RIZ006>008.
MARINE...SMALL CRAFT ADVISORY FROM 8 PM THIS EVENING TO 8 PM EDT
WEDNESDAY FOR ANZ231>235-237-250-254>256.
DISCUSSION...HRENCECIN/MENSCH
AVIATION...MCMINN
MARINE...MENSCH
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