009
FXUS61 KBOX 210708
AFDBOX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOSTON/NORTON MA
308 AM EDT TUE APR 21 2026
WHAT HAS CHANGED
THE RISK FOR FIRE WEATHER CONCERNS THURSDAY NOW LOOKS LIMITED,
AS CLOUD COVER AND POTENTIAL FOR SHOWERS COULD DEVELOP DURING
THE DAYTIME HOURS.
KEY MESSAGES
- MOSTLY SUNNY AND DRY TODAY GIVES WAY TO OVERCAST LATER
TONIGHT, WITH SCATTERED RAIN SHOWERS WED AS LOW PRESSURE
PASSES TO OUR SOUTH AND WEST.
- SLOW-MOVING UPPER-LEVEL LOW OVER ATLANTIC CANADA MAINTAINS
COOLER UNSETTLED CONDITIONS THURSDAY THROUGH THE WEEKEND.
BETTER CHANCES FOR SHOWERS ON THURSDAY BEFORE TRENDING DRIER
FOR FRIDAY INTO THE WEEKEND.
DISCUSSION
KEY MESSAGE 1...MOSTLY SUNNY AND DRY TODAY GIVES WAY TO OVERCAST
LATER TONIGHT, WITH SCATTERED RAIN SHOWERS WED AS LOW PRESSURE
PASSES TO OUR SOUTH AND WEST.
MIDLEVEL FLOW PATTERN BEGINS TO (BRIEFLY) DEAMPLIFY THRU WED.
SOME PESKY CLOUD COVER ACROSS THE CAPE AND ISLANDS MOVES
OFFSHORE EARLY THIS MORNING; EXPECTING A MOSTLY SUNNY REST OF
THE DAY TODAY WITH GOOD MIXING ALLOWING FOR DEWPOINTS TO PLUMMET
INTO THE SINGLE DIGITS TO LOWER TEENS IN THE INTERIOR AND RHS
FALLING TO AROUND 20 PERCENT. SEABREEZES DEVELOP NEAR THE COASTS
WHICH WILL KEEP TEMPS COOLER IN THE 40S, BUT SHOULD REACH INTO
THE LOW TO MID 50S AWAY FROM THE COAST, COMING OUT OF A CHILLY
OVERNIGHT.
CLOUD COVER THEN INCREASES TONIGHT FROM WEST TO EAST AS A LOW-
AMPLITUDE SHORTWAVE IN A FAST WNW FLOW BRINGS AN ASSOCIATED WEAK
LOW PRESSURE AND WARM FRONTAL BOUNDARY INTO SOUTHERN NEW
ENGLAND. LOOKS TO BE A DECENT PERIOD OF ISENTROPIC ASCENT WHICH
COULD ALLOW FOR WARM FRONTAL PRECIP TO BREAK OUT AS SOON AS THE
WEDNESDAY PRE-DAWN HOURS IN INTERIOR WESTERN NEW ENGLAND; AN
EARLIER ARRIVAL OF PRECIP WOULD OPEN UP THE DOOR FOR LIGHT RAIN
SHOWERS TO MIX WITH WET SNOWFLAKES THROUGH DYNAMIC/WET-BULBING
EFFECTS WITH PERHAPS SOME COATINGS ON NON-PAVED SURFACES. IT
LEADS TO A RATHER GRAY, DREARY WED WITH PERIODS OF RAIN SHOWERS
AND MODEST S WINDS. DESPITE MODEST WARM ADVECTION, TEMPS ON WED
COULD STRUGGLE TO GET OUT OF THE 40S WITH REDUCED INSOLATION AND
SOME OF THE PRECIP LOST TO WET-BULBING, LEADING TO COOLER
TEMPS. QPF AMTS ARE ON THE LIGHT SIDE - MORE OF A NUISANCE THAN
ANYTHING SIGNIFICANT OR IMPACTFUL. CLOUD COVER SHOULD BEGIN TO
DECREASE SOMEWHAT BY WED NIGHT BUT CONSIDERABLE CLOUDINESS COULD
LINGER FOR EASTERN MA/RI.
KEY MESSAGE 2...SLOW-MOVING UPPER-LEVEL LOW OVER ATLANTIC CANADA
MAINTAINS COOLER UNSETTLED CONDITIONS THURSDAY THROUGH THE WEEKEND.
BETTER CHANCES FOR SHOWERS ON THURSDAY BEFORE TRENDING DRIER FOR
FRIDAY INTO THE WEEKEND.
AN INCREASINGLY BLOCKY MID-LEVEL PATTERN DOWNSTREAM OF US IN THE
NORTH ATLANTIC THEN ALLOWS FOR THE TROUGH CURRENTLY MOVING OFFSHORE
TO DEVELOP INTO A BROAD CLOSED CIRCULATION NEAR THE CANADIAN
MARITIMES. THE WESTERN EXTENT OF THIS ANTICIPATED CLOSED LOW SEEMS
POISED TO DRIVE OUR WEATHER PATTERN FOR LATE IN THE WEEK AND INTO
THE WEEKEND, WITH A COOLER MARITIME-POLAR FLOW GOVERNING OUR
WEATHER. THIS WILL ALSO MEAN A PERIOD OF TEMPS RUNNING NEAR TO
SLIGHTLY COOLER THAN LATE-APRIL NORMALS.
WHAT WAS PREVIOUSLY LOOKING LIKE A POTENTIAL DRY AND GUSTY DAY
THURSDAY NOW COULD FEATURE VARIABLE AMTS OF CLOUDINESS WITH MORE
EAST AND LESS WEST AND AT LEAST ISOLATED TO SCATTERED DIURNAL-
INSTABILITY SHOWERS. PROGGED WET- BULB-ZERO HEIGHTS ARE
EXTREMELY LOW AT AROUND 3500 FT, WHICH SUGGESTS SHOWERS WOULD BE
ACCOMPANIED BY GRAUPEL. GUIDANCE SOURCES MORE BULLISH ON
SHALLOW INSTABILITY (E.G. NAM) EVEN SUGGEST POTENTIAL FOR LOW-
TOPPED STORMS WITH LIGHTNING AND SMALL HAIL IN STRONGEST OF
CORES, BEST CHANCE OVER THE EASTERN HALF OF SOUTHERN NEW
ENGLAND, WITH A PRETTY POTENT SHORTWAVE DIGGING SOUTHWARD.
SOMETHING TO CONSIDER IN LATER FORECASTS AS WE GET INTO THE
MESOSCALE NWP FORECAST HORIZON. AREAS IN WESTERN NEW ENGLAND
PROBABLY HAVE THE BEST CHANCE TO MIX DOWN LOWER DEWPOINTS BUT
WAS HESISTANT TO BRING DEWPOINTS TOO LOW IN CASE THE UPPER
TROUGH CONTINUES TO COURSE- CORRECT WESTWARD.
OTHERWISE, FRI INTO THE WEEKEND ARE UNSETTLED WITH A COOL
POCKET OF AIR ALOFT, BUT GENERALLY DRIER. EXPECT A SIMILAR SKY-
COVER PICTURE IN THIS PERIOD, WITH DIURNALLY DRIVEN CUMULUS/FAIR
WEATHER CLOUDS WITH LESS OF THEM DURING THE EVENING. AS SFC
RIDGING LOOKS TO BUILD IN FROM THE WEST ON THE WEEKEND, THIS
COULD BRING A MODEST ONSHORE FLOW TO EASTERN COASTAL AREAS. THE
UPSHOT IS THAT THE RETROGRADING MARITIMES LOW SHOULD SUPPRESS
STORMINESS COMING OUT OF THE NORTHERN PLAINS/GT LAKES TO OUR
SOUTH AND WEST.
AVIATION /06Z TUESDAY THROUGH SATURDAY/
FORECASTER CONFIDENCE LEVELS...
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
06Z TAF UPDATE:
THROUGH 12Z TUESDAY: HIGH CONFIDENCE.
MAINLY VFR, THOUGH BKN LOW-END VFR/PERIODS MVFR FOR THE CAPE
AIRPORTS AND PERIODS OF UNRESTRICTED-VISBY -SHRA CONTINUE THRU
ABOUT 10Z. N WINDS 5-10 KT, LIGHT TO CALM INTERIOR AIRPORTS.
TODAY: HIGH CONFIDENCE.
VFR. LIGHT NE WINDS TO SHIFT TO SOUTHERLY 5-10 KT, WITH
SE SEABREEZES ALONG THE EASTERN MA AND RI COASTS STARTING
AROUND 15-17Z.
TONIGHT AND WEDNESDAY: HIGH CONFIDENCE OVERALL, THOUGH MODERATE
ON TIMING.
VFR WITH INITIAL HIGH CLOUDS LOWERING AND THICKENING THRU FIRST
HALF OF THE NIGHT. WARM-FRONTAL PRECIP BREAKS OUT AROUND
~07-10Z WED IN WESTERN NEW ENGLAND, AND WHILE MAINLY RAIN
PREDOMINATES, IT COULD MIX WITH WET SNOWFLAKES FOR HIGHER
TERRAIN LOCATIONS ESPECIALLY IF TIMING IS ON THE EARLIER END OF
THAT WINDOW. PRECIP THEN SPREADS FURTHER EAST THRU 10-15Z AS
RAIN SHOWERS. ARRIVAL OF PRECIP BRINGS CEILINGS DROPPING TO
MAINLY MVFR (WITH INTERVALS IFR). SUB-VFR CEILINGS BEGINNING TO
SLOWLY IMPROVE FOR WESTERN TERMINALS AFTER 22Z BUT PROBABLY
TAKES UNTIL WED NIGHT BEFORE MORE SIGNIFICANT IMPROVEMENT
DEVELOPS.
SE TO S WINDS 5-10 KT, THOUGH SPEEDS COULD TREND LIGHTER ON WED
ONCE PRECIP ARRIVES.
KBOS TERMINAL...HIGH CONFIDENCE IN TAF. SE SEABREEZES COULD
DEVELOP AS SOON AS 14Z BUT IS MORE LIKELY AROUND 15-16Z.
KBDL TERMINAL... HIGH CONFIDENCE IN TAF.
OUTLOOK /WEDNESDAY NIGHT THROUGH SATURDAY/...
WEDNESDAY NIGHT: MAINLY VFR, WITH LOCAL IFR POSSIBLE. SLIGHT
CHANCE RA.
THURSDAY: VFR. BREEZY. SLIGHT CHANCE SHRA.
THURSDAY NIGHT THROUGH FRIDAY NIGHT: VFR.
SATURDAY: VFR. SLIGHT CHANCE SHRA.
MARINE
FORECASTER CONFIDENCE LEVELS...
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
WINDS AND SEAS REMAIN BELOW SCA CRITERION TODAY AND TONIGHT.
LIGHT NORTHERLY WINDS TURN SE AROUND 5-10 KT TODAY, AND BECOME
SOUTHERLY AROUND 10-15 KT TONIGHT. OUTSIDE CHANCE AT SCA
SOUTHERLY GUSTS AROUND 20 KT FOR WED ON SOUTHERN WATERS, BUT
SEEMS MARGINAL FOR HEADLINES GIVEN SCATTERED SHOWERS LIMITING
DEGREE OF MIXING. SEAS 4 FT OR LESS ALL WATERS. SOME BRIEF/LOCAL
REDUCTION IN VISBY POSSIBLE IN SCATTERED SHOWERS WED BUT
PROBABLY NOT PERSISTENT.
OUTLOOK /WEDNESDAY NIGHT THROUGH SATURDAY/...
WEDNESDAY NIGHT: WINDS LESS THAN 25 KT. SEAS LOCALLY
APPROACHING 5 FT. SLIGHT CHANCE OF RAIN.
THURSDAY: WINDS LESS THAN 25 KT. SLIGHT CHANCE OF RAIN SHOWERS.
THURSDAY NIGHT THROUGH FRIDAY NIGHT: WINDS LESS THAN 25 KT.
SATURDAY: WINDS LESS THAN 25 KT. SLIGHT CHANCE OF RAIN SHOWERS.
BOX WATCHES/WARNINGS/ADVISORIES
CT...NONE.
MA...NONE.
RI...NONE.
MARINE...NONE.
DISCUSSION...LOCONTO
AVIATION...LOCONTO
MARINE...LOCONTO
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