227
FXUS61 KBOX 291408
AFDBOX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOSTON/NORTON MA
1008 AM EDT FRI SEP 29 2023
SYNOPSIS
SLOW-MOVING LOW PRESSURE MOVING OFF THE MID ATLANTIC COAST WITH
A BOUNDARY EXTENDING TO THE NORTH WILL BRING RAIN TO PORTIONS
OF SOUTHERN NEW ENGLAND INTO SATURDAY. THIS RAIN WILL BE FOCUSED
ACROSS WESTERN CT/MA THIS MORNING SHIFTING TO SE NEW ENGLAND
TONIGHT INTO SATURDAY. HEAVY RAINFALL IS POSSIBLE, ESPECIALLY
ACROSS WESTERN CT. HIGH PRESSURE BUILDS INTO THE REGION SUNDAY
THROUGH MUCH OF THE UPCOMING WEEK. THIS WILL BRING DRY AND QUIET
WEATHER WITH SEASONABLE TEMPERATURES ON SUNDAY AND MONDAY.
TEMPERATURES TREND ABOVE NORMAL FOR THE REST OF THE WEEK.
NEAR TERM /UNTIL 6 PM THIS EVENING/
10 AM UPDATE...
HEAVY RAIN MOVING N ACROSS WESTERN CT/MA WITH RAINFALL RATES
0.25-0.50"/HR. HOWEVER, CONVECTIVE ELEMENTS WHICH HAVE
PRODUCED 1-2"/HR RATES ARE CONFINED TO THE SW CLOSER TO NYC.
THIS IS WHERE LOW LEVEL CONVERGENCE IS MAXIMIZED ALONG A SURFACE
BOUNDARY. NOSE OF THE LOW LEVEL JET WILL REMAIN FOCUSED NEAR
NYC AREA WHICH WILL CONTINUE TO GENERATE HEAVY RAIN HERE WHICH
THEN LIFTS NORTHWARD, KEEPING HEAVIEST RAINFALL IN BOX CWA
ACROSS WESTERN CT INTO WESTERN MA THROUGH THE AFTERNOON. GIVEN
INSTABILITY ALOFT IS CONFINED TO THE SW, WE ARE NOT EXPECTING
EXCESSIVE RATES TO SPREAD INTO BOX CWA WHICH SHOULD LIMIT FLOOD
THREAT TO AREAS OF MINOR STREET FLOODING ACROSS PORTIONS OF
WESTERN CT AND ADJACENT WESTERN MA. TOTAL RAINFALL HERE MAY
EXCEED 3 INCHES BUT WILL OCCUR OVER 12-24 HOURS.
RAIN HAS EXTENDED FURTHER E INTO EASTERN MA WHERE POPS WERE
INCREASED, BUT ONLY EXPECTING LIGHT RAIN HERE AS THERE IS LOW
LEVEL DRY AIR TO OVERCOME, ESPECIALLY IN NE MA WHERE HIGH CLOUD
BASES ARE PRESENT.
TEMPS WILL REMAIN IN THE 50S IN WESTERN MA/CT WITH HIGHS 60-65
IN EASTERN MA.
SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/
STILL THINKING TONIGHT IS A RATHER WET PERIOD FOR MOST OF
SOUTHERN NEW ENGLAND, BEFORE THE SLOW-MOVING LOW PRESSURE
FINALLY MOVES FAR ENOUGH EAST TO DRAG ITS PRECIPITATION SHIELD
OFFSHORE WITH IT. THAT PROCESS SHOULD TAKE MOST, IF NOT ALL, OF
SATURDAY TO DO. RAINFALL WILL LAST LEAVE THE CAPE AND ISLANDS.
IT IS POSSIBLE THAT THIS FORECAST TIMING WILL NEED TO BE CHANGED
WITH LATER FORECASTS. MAY HAVE HELD ONTO RAINFALL CHANCES TOO
LONG BASED ON A VERY QUICK LOOK AT THE 06Z GUIDANCE JUST COMING
IN AT THE TIME OF THIS WRITING.
NEAR TO SLIGHTLY ABOVE NORMAL TEMPERATURES EXPECTED TONIGHT,
WITH BELOW NORMAL HIGHS SATURDAY.
LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/
HIGHLIGHTS
* ANY LINGERING PRECIP SAT NIGHT TAPERS OFF EARLY SUN.
* DRY WEATHER FOR MUCH OF THE UPCOMING WEEK. SEASONABLE TEMPS ON
SUN/MON WITH ONSHORE FLOW. ABOVE NORMAL TEMPS FOR THE REST OF
THE WEEK.
SATURDAY NIGHT INTO EARLY SUNDAY MORNING...
A CUTOFF LOW WILL BE SITUATED NEARBY SOUTHEAST MA/RI SAT NIGHT,
WHILE A RIDGE AXIS EXTENDS FROM THE LOWER MISSISSIPPI RIVER
VALLEY INTO THE GREAT LAKES REGION. THE CUTOFF WILL SLOWLY
ROTATE FURTHER OFFSHORE BY EARLY SUN, WHILE THE RIDGE REMAINS IN
NEARLY THE SAME PLACE. A BROAD LOW WILL BE OFFSHORE, WHILE AN
INVERTED TROUGH NUDGES INTO PORTIONS OF OUR REGION.
STILL SOME UNCERTAINTY WITH HOW QUICKLY PRECIP WRAPS UP ACROSS
SE MA/RI. AS HAS BEEN THE CASE FOR THIS SYSTEM THE PAST SEVERAL
DAYS THE ECMWF IS ON THE WETTER SIDE OF THINGS AND A BIT SLOWER
TO CEASE THE PRECIP, WHEREAS THE GFS/NAM AND OTHER CAMS ARE MUCH
FASTER. THE GEM STILL A GOOD COMPROMISE AT THIS POINT, SO HAVE
LEANED TOWARD IT IN THE LATEST UPDATE. GIVEN THE ENE/NE LOW
LEVEL JET OF 20-50 KTS IMPINGING ON THE REGION AND BEING ON THE
NW PERIPHERY OF THE 1.25+ INCH PWATS HAVE OPTED TO KEEP UP
PRECIP CHANCES INTO SUN AM. THE NBM MAY BE LEANING A BIT TOO
MUCH ON DRIER SOLUTIONS AT THIS POINT. HOWEVER, FOR THE VAST
MAJORITY OF THE REGION THE PRECIP WILL BE OVER WITH.
HAVE KEPT LOW TEMPS UP A BIT AS HOW QUICKLY THE CLOUDINESS EXITS
IS UNCERTAIN AND WE MAY STAY A BIT WINDIER THAN PREVIOUS
THINKING. LOW TEMPS GENERALLY IN THE 50S.
SUNDAY THROUGH FRIDAY...
RIDGE AXIS IN PLACE OVER THE LOWER MISSISSIPPI RIVER VALLEY TO
THE GREAT LAKES REGION ON SUN. THIS BUILDS INTO THE EASTERN
GREAT LAKES/MID ATLANTIC FOR TUE/WED AND OVER NEW ENGLAND FOR
LATER IN THE WEEK. HIGH PRESSURE NUDGES IN FROM THE EASTERN
GREAT LAKES/MID ATLANTIC ON SUN/MON. THE HIGH BUILDS OVERHEAD
LATE ON MON/TUE BEFORE BEGINNING TO MOVE OFFSHORE AS WE HEAD
LATER INTO THE WEEK.
DRY AND QUIET WEATHER ANTICIPATED THROUGH MUCH OF THIS TIMEFRAME
WITH TEMPERATURES ON THE RISE. THE NBM STILL RUNNING A BIT TOO
WARM IN THE SUN/MON TIMEFRAME WITH ONSHORE FLOW. BUMPED TEMPS
DOWN TO THE 50TH PERCENTILE OF GUIDANCE, WHICH LOOK REASONABLE.
HIGHS WILL ROUGHLY BE AROUND SEASONABLE TEMPS. BETTER SHOT FOR
MILD TEMPS MID TO LATE IN THE WEEK AS FLOW SHIFTS TO THE S/SW.
THE GEFS/EPS INDICATING LOW (10-30) TO MODERATE (30-70) PROBS
OF 2M HIGH TEMPS AOA 80 DEGREES IN THE TUE-THU TIMEFRAME.
APPEARS THAT THE BEST SHOT AT THIS POINT IS ON WED.
COULD SEE A RETURN OF PRECIPITATION ON FRIDAY, BUT GUIDANCE ALL
OVER THE PLACE WITH THE AMPLITUDE AND TIMING OF A TROUGH DIGGING
IN FROM THE NORTHWEST. FOR NOW THINK THAT THE NBM SLIGHT CHANCE
TO CHANCES OF PRECIP LOOK REASONABLE.
AVIATION /14Z FRIDAY THROUGH TUESDAY/
FORECAST CONFIDENCE LEVELS:
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
TODAY...HIGH CONFIDENCE IN TRENDS, MODERATE IN TIMING.
MVFR CONDITIONS ALONG/SOUTH OF THE MA PIKE WITH DETERIORATION TO
IFR BY THIS AFTERNOON AS RAIN SPREADS IN. FURTHER NORTH WILL BE
VFR TO START, BUT GRADUALLY LOWERING TO MVFR LIMITS AS PRECIP
SPREADS IN. NE TO ENE WINDS AT 5-15 KTS. HIGHEST SPEEDS ACROSS
THE CAPE/ISLANDS. NOT OUT OF THE QUESTION THERE IS SOME EMBEDDED
THUNDER THIS AFTERNOON ACROSS CT, BUT HAVE NOT ADDED TO THE TAF
AT THIS POINT.
TONIGHT...MODERATE CONFIDENCE.
MVFR TO IFR CONDITIONS ACROSS PORTIONS OF CT, RI AND SE MA WITH
MAINLY VFR ACROSS FAR NORTHERN MA. RAIN FOCUS WILL SHIFT EAST
TO RI AND SE MA. WINDS OUT OF THE NNE TO NE AT 5-15 KTS.
SATURDAY...MODERATE CONFIDENCE.
CONDITIONS IMPROVING TO VFR FROM NW TO SE DURING THE MORNING.
SHOULD BE VFR REGION-WIDE DURING THE AFTERNOON. NE WINDS 10-15
KTS, BUT GUSTING TO 20-25 KTS ACROSS THE CAPE/ISLANDS.
KBOS TERMINAL...HIGH CONFIDENCE IN TAF TRENDS. MODERATE
CONFIDENCE IN EXACT TIMING OF DETERIORATION TO MVFR. THINKING
TIMING COULD BE AS EARLY AT 14-16Z.
KBDL TERMINAL...HIGH CONFIDENCE IN TAF TRENDS. MODERATE
CONFIDENCE IN TIMING WITH DETERIORATION.
OUTLOOK /SATURDAY NIGHT THROUGH TUESDAY/...
SATURDAY NIGHT: VFR. BREEZY. SLIGHT CHANCE SHRA.
SUNDAY THROUGH MONDAY: VFR. BREEZY.
MONDAY NIGHT THROUGH TUESDAY: VFR.
MARINE
FORECASTER CONFIDENCE LEVELS:
LOW - LESS THAN 30 PERCENT.
MEDIUM - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
GENERALLY EASTERLY WINDS THROUGH TONIGHT, THEN SHIFTING NE FOR
SATURDAY. GUSTS TO 20 KT TODAY, WITH 25 KT GUSTS POSSIBLE OVER
THE SOUTHERN WATERS LATE TONIGHT INTO SATURDAY. PERIODS OF RAIN
WITH REDUCED VISIBILITY DOWN TO 1-3 MILES AT TIMES. SMALL CRAFT
ADVISORIES REMAIN POSTED. ROUGH SEAS ACROSS THE SOUTHERN COASTAL
WATERS, THEN BUILDING ACROSS THE EASTERN OUTER COASTAL WATERS
FOR SATURDAY.
OUTLOOK /SATURDAY NIGHT THROUGH TUESDAY/...
SATURDAY NIGHT: MODERATE RISK FOR SMALL CRAFT ADVISORY WINDS
WITH LOCAL GUSTS UP TO 30 KT. AREAS OF ROUGH SEAS. CHANCE OF
RAIN SHOWERS.
SUNDAY: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH LOCAL
GUSTS UP TO 30 KT. AREAS OF ROUGH SEAS. SLIGHT CHANCE OF RAIN
SHOWERS.
SUNDAY NIGHT THROUGH MONDAY NIGHT: WINDS LESS THAN 25 KT. SEAS
UP TO 5 FT.
TUESDAY: WINDS LESS THAN 25 KT. AREAS OF SEAS APPROACHING 5 FT.
BOX WATCHES/WARNINGS/ADVISORIES
CT...NONE.
MA...NONE.
RI...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 1 AM TO 8 PM EDT SATURDAY FOR ANZ235.
SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 8 PM EDT
SATURDAY FOR ANZ237.
SMALL CRAFT ADVISORY FROM 8 AM TO 8 PM EDT SATURDAY FOR ANZ250.
SMALL CRAFT ADVISORY FROM 4 PM THIS AFTERNOON TO 8 PM EDT
SATURDAY FOR ANZ254.
SMALL CRAFT ADVISORY UNTIL 8 PM EDT SATURDAY FOR ANZ255-256.
SYNOPSIS...BELK/BL
NEAR TERM...BELK/KJC
SHORT TERM...BELK
LONG TERM...BL
AVIATION...BELK/BL
MARINE...BELK/BL
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