222
FXUS61 KBOX 211843
AFDBOX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOSTON/NORTON MA
243 PM EDT THU MAY 21 2026
WHAT HAS CHANGED
NO SIGNIFICANT CHANGES.
KEY MESSAGES
- COOLER TEMPERATURES BUT GENERALLY DRY WEATHER AND ONSHORE
BREEZES THROUGH SATURDAY. LESS CLOUD COVER FRIDAY, BUT TURNING
OVERCAST WITH EVEN COOLER TEMPS (60S) FOR SATURDAY, WITH RAIN
DEVELOPING LATER SATURDAY EVENING.
- COOL WITH WIDESPREAD RAIN SUNDAY.
- WARMING TREND NEXT WEEK. SCATTERED SHOWERS LINGERING MONDAY
WITH ANOTHER CHANCE OF SHOWERS WED.
DISCUSSION
KEY MESSAGE 1...COOLER TEMPERATURES BUT GENERALLY DRY WEATHER AND
ONSHORE BREEZES THROUGH SATURDAY. LESS CLOUD COVER FRIDAY, BUT
TURNING OVERCAST WITH EVEN COOLER TEMPS (60S) FOR SATURDAY, WITH
RAIN DEVELOPING LATER SATURDAY EVENING.
A SLOWLY-SAGGING FRONTAL BOUNDARY ALONG THE SOUTHERN COAST WILL
CONTINUE TO SAG SOUTHWARD INTO THE COASTAL PORTION OF THE NORTHERN
MID-ATLANTIC REGION. MEANWHILE A 1028+ MB HIGH PRESSURE CELL OVER
NORTHEAST ONTARIO, ASSOCIATED WITH LOW-LEVEL TEMPERATURES RUNNING
SEVERAL DEGREES COOLER THAN LATE-MAY NORMALS, WILL BE BUILDING INTO
SOUTHERN NEW ENGLAND TONIGHT AND REMAIN ACROSS EASTERN MA/ADJACENT
EASTERN WATERS FRI AND SAT. AFTER THE FIRST TASTE OF SUMMER-LIKE
WARMTH THE LAST COUPLE DAYS, WE'LL FLIP THE CALENDAR BACK TO
TEMPERATURES MORE REMINISCENT OF LATE APRIL. WE SHOULD ALSO SEE
RELATIVELY DRY WEATHER, ALTHOUGH THE RISK FOR APPROACHING RAIN
DEVELOPS LATER SAT AND PARTICULARLY SAT NIGHT.
PLENTY OF MID-LEVEL CLOUD COVER ONGOING ON THE COLD SIDE OF THE
FRONTAL BOUNDARY, ALTHOUGH EXPECTATION IS FOR THAT TO DECREASE FROM
NORTH TO SOUTH AS WE MOVE INTO TONIGHT. AS THIS CLOUD COVER HAS
TEMPERED DAYTIME WARMING AND WITH OTHERWISE GOOD RADIATIONAL
COOLING, IT SETS STAGE FOR A COOL AND DRY NIGHT. LOWS TONIGHT SHOULD
BOTTOM TO THE UPPER 30S TO LOW 40S, WITH THE COOLEST READINGS IN
NORTHWEST MA. THERE COULD BE PATCHES OF FROST IN THE MORE SHELTERED
AREAS IN NORTHWEST MA, BUT THE ANTICIPATED COVERAGE OF FROST SEEMS
LOW ENOUGH TO NOT RISE TO THE LEVEL OF WARRANTING FROST HEADLINES.
PRETTY STARK CHANGE IN AIRMASS AND SENSIBLE WEATHER COMPARED TO THE
PAST FEW DAYS!
FRI AND SAT FEATURE MORE-OR-LESS SIMILAR CONDITIONS WITH ONSHORE
BREEZES, WITH THE ONLY DIFFERENCES BEING THE EXTENT OF CLOUD COVER
BEING QUITE A BIT MORE ON SAT. WITH LESS CLOUD COVER FRI, EXPECT THE
MILDEST TEMPERATURES TO REACH INTO THE 60S WITH A FEW SPOT 70S OUT
IN THE CT VALLEY AWAY FROM THE ONSHORE FLOW, AND LOWS IN THE 40S.
THEN TEMPS MAY STRUGGLE TO REACH THE MID 60S SAT WITH INCREASING
CLOUDINESS; THE BETTER CHANCE FOR LIGHT RAINS INTO WESTERN NEW
ENGLAND THEN BEGINS TO ARRIVE LATE SAT EVENING, SPREADING EASTWARD
THROUGH THE NIGHTTIME HOURS. THE EXACT TIMING OF RAINS LATE SAT/SAT
NIGHT IS STILL SUBJECT TO ADJUSTMENT GIVEN RAIN FALLING INTO A COOL
AND DRY AIRMASS. BUT THE BULK OF THE RAIN ARRIVES INTO SUNDAY.
KEY MESSAGE 2...COOL WITH WIDESPREAD RAIN SUNDAY.
SURFACE WAVE WILL BE LIFTING NORTH FROM THE MID ATLC COAST ON
SUNDAY. AHEAD OF THE LOW PRES A 40-50 KT SE LOW LEVEL JET WILL
TRANSPORT DEEP MOISTURE PLUME INTO SNE WITH PWATS EXCEEDING 1.5".
FAVORABLE FORCING FOR ASCENT ACTING ON THIS MOISTURE WILL RESULT IN
WIDESPREAD SOAKING RAIN ACROSS SNE WHICH WILL ESSENTIALLY BE A
WASHOUT. EPS ENSEMBLES SHOW HIGH PROBS (70-100%) FOR QPF OVER 0.50"
AND MODERATE PROBS OVER AN INCH. CURRENT THINKING IS RAINFALL
AVERAGING 0.50" TO 1.0" WITH LOCALLY HIGHER AMOUNTS. THERE IS ALSO
SOME ELEVATED INSTABILITY ON THE NORTHERN GRADIENT OF HIGHER THETA-E
AIR MOVING UP FROM THE SOUTH SO CAN'T RULE OUT AN ISOLATED T-STORM,
MAINLY NEAR THE SOUTH COAST. IT WILL BE A COOL DAY WITH TEMPS MAINLY
IN THE 50S, AND IT'S POSSIBLE TEMPS STRUGGLE TO GET TO 50F OVER THE
HIGHER ELEVATIONS IN INTERIOR MA. GUSTY E WINDS WILL IMPACT COASTAL
LOCATIONS SUN AFTERNOON AND EVENING ASSOCIATED WITH THE LOW LEVEL
JET. STEADIER RAIN WILL BEGIN TO MOVE OUT SUN NIGHT AS THE MOISTURE
PLUME MOVES TO THE EAST, BUT RISK OF SHOWERS WILL CONTINUE AS THE
LOW PRES LIFTS NE ACROSS SNE.
KEY MESSAGE 3...WARMING TREND NEXT WEEK. SCATTERED SHOWERS LINGERING
MONDAY WITH ANOTHER CHANCE OF SHOWERS WED.
CONDITIONS SHOULD IMPROVE SOMEWHAT MON AS THE LOW PRES MOVES TO THE
NE, BUT SCATTERED SHOWERS MAY LINGER AS A SHORTWAVE APPROACHES FROM
THE WEST. GFS AND ITS ENSEMBLES ARE MOST AGGRESSIVE WITH ANOTHER
PERIOD OF RAIN MOVING IN, ESPECIALLY SOUTH OF THE MA PIKE SO WILL
HAVE TO WATCH THIS. OTHERWISE, WARMING TREND NEXT WEEK WITH WARMEST
DAYS TUE AND WED WHEN TEMPS SHOULD GET BACK ABOVE 80F AWAY FROM THE
COAST. GEFS AND EPS ENSEMBLES BOTH SHOW MODERATE PROBS OF 80+. LOOKS
DRY TUE THEN CHANCE OF SHOWERS RETURN WED AS A NORTHERN STREAM
SHORTWAVE ROTATES SOUTHWARD INTO THE REGION. SOMEWHAT COOLER AIRMASS
FOLLOWS FOR NEXT THU.
AVIATION /18Z THURSDAY THROUGH TUESDAY/
FORECASTER CONFIDENCE LEVELS...
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
18Z TAF UPDATE...
THROUGH TONIGHT...HIGH CONFIDENCE.
VFR. FEW LINGERING RAIN SHOWERS ALONG THE IMMEDIATE COAST COME TO AN
END THIS EVENING, BUT NOT EXPECTING ANY OPERATIONAL IMPACTS. N WIND
5-10 KT WITH SEA-BREEZES. WINDS BECOMING LIGHT/VARIABLE OR CALM
OVERNIGHT.
FRIDAY...HIGH CONFIDENCE.
VFR. NE WINDS 5-10 KT.
FRIDAY NIGHT...HIGH CONFIDENCE.
VFR. INCREASING MID AND HIGH-LEVEL CLOUDS NE WINDS LESS THAN 5 KT.
KBOS...HIGH CONFIDENCE IN TAF.
KBDL...HIGH CONFIDENCE IN TAF.
OUTLOOK /FRIDAY NIGHT THROUGH TUESDAY/...
SATURDAY: VFR. CHANCE SHRA.
SATURDAY NIGHT: VFR. BREEZY. SHRA LIKELY.
SUNDAY: MAINLY VFR, WITH LOCAL IFR POSSIBLE. BREEZY. SHRA.
SUNDAY NIGHT: MVFR/IFR CONDITIONS POSSIBLE. BREEZY. CHANCE
SHRA.
MEMORIAL DAY: MAINLY VFR, WITH LOCAL IFR POSSIBLE. CHANCE SHRA.
MONDAY NIGHT: MAINLY VFR, WITH LOCAL MVFR POSSIBLE. SLIGHT
CHANCE SHRA.
TUESDAY: VFR.
MARINE
FORECASTER CONFIDENCE LEVELS...
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
WINDS AND SEAS TO REMAIN BELOW SMALL CRAFT ADVISORY CRITERIA THROUGH
AT LEAST MIDDAY SAT. NE TO E WINDS TONIGHT THROUGH FRI NIGHT
AROUND 10-15 KT, WITH E/ESE WINDS AT SIMILAR SPEEDS FOR THE
SOUTHERN WATERS, AND SEAS 4 FT OR LESS ALL WATERS.
INTO SAT OF THE HOLIDAY WEEKEND, ESE WINDS AROUND 15-20 KT WITH
FRINGE SMALL CRAFT ADVISORY WINDS/SEAS OVER THE SOUTHERN WATERS
ESPECIALLY LATER IN THE DAY. RAIN WILL ALSO DEVELOP AROUND LATE
SAT/SAT NIGHT OVER THE SOUTHERN WATERS. INCREASING, MORE SOLID-SCA
E/SE WINDS 25-30 KT AND SEAS 5-9 FT (HIGHER SOUTHERN WATERS OVER THE
OPEN-OCEAN) THEN DEVELOP FOR SUNDAY FOR YOUR HOLIDAY BOATING PLANS,
TO GO ALONG WITH STEADY RAIN WHICH COULD REDUCE VISIBILITY.
OUTLOOK /FRIDAY NIGHT THROUGH TUESDAY/...
SATURDAY: WINDS LESS THAN 25 KT.
SATURDAY NIGHT: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH
GUSTS UP TO 30 KT. SEAS LOCALLY APPROACHING 5 FT. CHANCE OF
RAIN SHOWERS.
SUNDAY: MODERATE RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS
UP TO 30 KT. AREAS OF ROUGH SEAS. RAIN SHOWERS.
SUNDAY NIGHT: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH
GUSTS UP TO 25 KT. AREAS OF ROUGH SEAS. RAIN SHOWERS LIKELY.
MEMORIAL DAY: WINDS LESS THAN 25 KT. AREAS OF ROUGH SEAS.
CHANCE OF RAIN SHOWERS.
MONDAY NIGHT: WINDS LESS THAN 25 KT. SEAS UP TO 5 FT. SLIGHT
CHANCE OF RAIN SHOWERS.
TUESDAY: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING 5 FT.
BOX WATCHES/WARNINGS/ADVISORIES
CT...NONE.
MA...NONE.
RI...NONE.
MARINE...NONE.
DISCUSSION...KJC/LOCONTO
AVIATION...KJC/DOOLEY
MARINE...KJC/LOCONTO
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