290
FXUS61 KBOX 290203
AFDBOX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOSTON/NORTON MA
1003 PM EDT SAT MAR 28 2020
SYNOPSIS
RAIN WILL CONTINUE TONIGHT INTO EARLY MONDAY MORNING AS A
SECONDARY LOW PRESSURE DEVELOPS JUST TO OUR SOUTH. WEATHER
PATTERN REMAINS UNSETTLED AND CLOUDY FOR MUCH OF THE UPCOMING
WEEK, WITH SEASONABLY COOLER TEMPERATURES. INTERVALS OF
SCATTERED RAIN AND/OR SNOW SHOWERS MONDAY INTO TUESDAY, WITH
LIGHT SNOW COATINGS POSSIBLE IN THE HIGHER TERRAIN. STILL
MONITORING A POTENTIAL COASTAL LOW WEDNESDAY INTO PART OF FRIDAY
WHOSE IMPACT TO SOUTHERN NEW ENGLAND WILL DEPEND ON STORM
TRACK. PERIODS OF RAIN/WET SNOW WOULD BE POSSIBLE, WITH LITTLE
IF ANY IMPACT IF THE STORM TRACKS FURTHER OFFSHORE.
NEAR TERM /UNTIL 6 AM SUNDAY MORNING/
10 PM UPDATE...
INCREASED PRECIPITATION CHANCES ALONG WITH WIND SPEEDS AND GUSTS
PER OBSERVATIONS. REST OF THE FORECAST REMAINS ON TRACK.
630 PM UPDATE:
RADAR AND OBS INDICATE INITIAL WARM-FRONTAL RAINS HAVE
OVERSPREAD A GOOD CHUNK OF SOUTHERN NEW ENGLAND, ROUGHLY
SOUTHWEST OF A FITCHBURG TO NORWOOD TO MARSHFIELD LINE AS OF
THIS UPDATE. PRIOR TO THE RAIN ARRIVING, IT HAD BEEN SO DRY
(T-TD SPREADS SOME 20-30 DEGREES IN MOST PLACES) THAT THE
INITIAL ONSET OF RAIN HAS CAUSED TEMPERATURES TO FALL VERY
QUICKLY AND DEWPOINTS/RELATIVE HUMIDITIES TO RISE. NORTH OF THAT
DESCRIBED LINE, TEMPERATURES AWAY FROM THE NORTHEAST COASTS
WERE IN THE LOW TO MID 50S, BUT HAVE FALLEN FROM HIGHS IN THE
50S INTO THE 40S IN AREAS THAT HAVE SEEN RAIN. SPOTTERS AND
SOCIAL MEDIA REPORTS FROM BELCHERTOWN AND CHESTER HAVE EVEN
REPORTED SOME SLEET/PELLETS AT TIMES DESPITE AIR TEMPS THAT ARE
WELL ABOVE FREEZING.
USED A BLEND OF THE HRRR AND THE HREF TO RE-SHAPE POPS THRU
MIDNIGHT, GENERALLY SPREADING CATEGORICAL-POP RAINS IN A COUPLE
HOURS SOONER. ALSO TRIED TO SHOW TEMPERATURES COOLING PRETTY
QUICKLY AND DEWPOINTS RISING AS RAIN OVERSPREADS. LOWS STILL
LOOK ON TRACK, HOWEVER.
PREVIOUS DISCUSSION FOLLOWS...
LOOKING AT A FAIRLY COMMON SPRING-TIME PATTERN DEVELOPING
TONIGHT. EXPECTING A CUTOFF MID LEVEL LOW TO MOVE FROM THE
NORTHERN PLAINS INTO THE GREAT LAKES OVERNIGHT. AT THE SURFACE,
HIGH PRESSURE MOVES FARTHER OFFSHORE, RESULTING IN AN ONSHORE
FLOW. IN BETWEEN THESE TWO FEATURES, AT LEAST SOME WEAK LIFT IS
FAVORED. THIS SHOULD LEAD TO A WIDESPREAD RAINFALL, EVENTUALLY.
ABUNDANT LOW LEVEL DRY AIR WILL NEED TO BE OVERCOME BEFORE ANY
RAINFALL REACHES THE GROUND. HAD SOME REPORTS EARLIER THIS
AFTERNOON OF SOME ICE PELLETS, DUE TO EVAPORATIONAL COOLING.
WITH SURFACE DEWPOINT DEPRESSIONS STILL ABOUT 20-30 DEGREES, IT
WILL BE A WHILE LONGER BEFORE APPRECIABLE RAINFALL REACHES THE
GROUND.
AS FOR TIMING, IT WILL REALLY DEPEND UPON WHERE ONE IS LOCATED.
THE WESTERN HALF OF SOUTHERN NEW ENGLAND SHOULD SEE RAINFALL
DEVELOPING BETWEEN NOW AND 7 PM, WITH THE EASTERN HALF OF
SOUTHERN NEW ENGLAND SEEING THE RAIN DEVELOP BETWEEN 7 PM AND
MIDNIGHT SUNDAY.
ABOVE NORMAL LOW TEMPERATURES EXPECTED WITH THE CLOUDS ALREADY
IN PLACE, AND ONLY GETTING LOWER AND THICKER.
SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/
CUTOFF LOW SHOULD MOVE FROM THE GREAT LAKES TO NEW ENGLAND
DURING THIS TIME. MOST OF THE 28/12Z GUIDANCE SUGGESTS A
SECONDARY SURFACE LOW PRESSURE DEVELOPS JUST TO OUR SOUTH, THEN
LINGERS SUNDAY NIGHT INTO MONDAY. WHILE THIS SHOULD MEAN PLENTY
OF ASCENT TO GENERATE RAINFALL, THE AMOUNT OF AVAILABLE MOISTURE
IS NOT SO CERTAIN. PRECIPITABLE WATER VALUES START OUT 3-4
STANDARD DEVIATIONS ABOVE NORMAL SUNDAY, THEN DROP OFF TO NEAR
NORMAL SUNDAY NIGHT. EXPECTATION IS FOR WIDESPREAD RAIN TO
BECOME MORE SHOWERY IN NATURE, WITH PERHAPS A PERSISTENT
DRIZZLE DEVELOPING BENEATH THE DRIER AIR ALOFT.
LOW RISK FOR AN ELEVATED THUNDERSTORM TOWARDS THE SOUTH COAST OF
NEW ENGLAND SUNDAY AFTERNOON INTO SUNDAY NIGHT WITH THE
DEVELOPMENT OF THE SECONDARY LOW PRESSURE. LAPSE RATES WILL BE
MARGINAL, AND IT IS NOT A FAVORED TIME OF DAY.
STEADY EASTERLY WIND WILL LEAD TO TEMPERATURES NOT MOVING MUCH
DURING THIS TIME. STILL NEAR TO SLIGHTLY BELOW NORMAL FOR LATE
MARCH THOUGH DURING THE DAY. NIGHT-TIME TEMPERATURES MORE LIKELY
TO BE ABOVE NORMAL.
LONG TERM /MONDAY THROUGH SATURDAY/
HIGHLIGHTS...
* COOL AND CLOUDY WITH SCATTERED SHOWERS (SOME MIXED WITH GRAUPEL)
ON MONDAY. SOME SNOW COATINGS POSSIBLE IN THE HILLY TERRAIN
MONDAY NIGHT.
* CONTINUE TO MONITOR POTENTIAL MID TO LATE-WEEK COASTAL SYSTEM.
CONSENSUS TRACK REMAINS SOUTH OF SOUTHERN NEW ENGLAND, BUT COULD
BRING RAIN/WET SNOW IF IT TRACKS CLOSER TO THE COAST.
* BRIEF BREAK FRIDAY NIGHT - EARLY SATURDAY BEFORE A COLD FRONT
ARRIVES LATER SATURDAY.
* COOLER THAN NORMAL TEMPS (ESPECIALLY HIGHS) THROUGH MIDWEEK, THEN
TRENDING CLOSER TO NORMAL BY LATE WEEK/EARLY WEEKEND.
DETAILS...
OVERALL A FAIRLY UNSETTLED AND (MORE OFTEN THAN NOT) CLOUDIER
WEATHER PATTERN IN STORE THRU LATE WEEK. OTHER THAN IN CLOUD BREAKS,
SUNSHINE PROBABLY WILL BE HARD TO COME BY OVER THE NEXT HANDFUL OF
DAYS.
MONDAY:
UPPER LOW AND ITS COOL POCKET OF AIR ALOFT WILL MEANDER FROM ONTARIO
INTO INTERIOR NEW ENGLAND ON MONDAY. CONSIDERABLE LOW-LEVEL MOISTURE
SUPPORTS MOSTLY CLOUDY CONDITIONS WITH SCATTERED INSTABILITY-TYPE
SHOWERS. WHILE THE CONVECTIVE DEPTH IS PRETTY SHALLOW, STEEP LOWER-
LEVEL LAPSE RATES ASSOCIATED WITH COOLER POCKET OF AIR ALOFT AND LOW
FREEZING LEVELS COULD SUPPORT GRAUPEL AT TIMES. BEST CHANCE FOR
SHOWERS DURING THE DAY IS NORTH AND WEST OF I-95. QPF AMOUNTS SHOULD
BE LIMITED TO A TENTH-INCH OR LESS, BUT JUST BE AWARE THAT YOU'LL
HAVE TO DODGE SOME SHOWERS AT TIMES.
LATER MONDAY NIGHT, MODEST COOL ADVECTION MAY HELP TRANSITION RAIN
TO WET SNOW SHOWERS PARTICULARLY ACROSS THE HIGHER TERRAIN. COULD BE
SOME SPOTTY LIGHT COATINGS IN THESE AREAS (EAST SLOPES OF THE
BERKSHIRES, NORTHERN WORCESTER COUNTY AND POSSIBLY INTO A PART OF
THE MERRIMACK VALLEY), BUT OTHERWISE LOOKING AT A CLOUDY NIGHT WITH
COOL RAIN SHOWERS.
ABUNDANT CLOUDS AND LIMITED HEATING SUPPORTS HIGHS ON THE COOLER END
OF GUIDANCE
TUESDAY:
STILL UNSETTLED INTO TUESDAY, WITH A LINGERING INVERTED TROUGH ALOFT
INTERACTING WITH SOME ONSHORE MOISTURE SUPPORTING A PERIOD OF LIGHT
RAIN OR SNOW SHOWERS. AT THE SURFACE, A COOL WEDGE OF HIGH PRESSURE
BUILDS DOWN FROM ME/EASTERN NH ON NORTHEASTERLY FLOW. THIS WILL HELP
REINFORCE THE COOLER AIR. TEMPERATURES SHOULD TREND COOLER THAN
NORMAL, WITH HIGHS IN THE LOW TO MID 40S FOR MOST, THOUGH INTO THE
MID-UPPER 40S ACROSS TOLLAND AND HARTFORD COUNTIES.
TUESDAY NIGHT THROUGH THURSDAY NIGHT:
PATTERN CHANGE TOWARD ONE OF HIGH-LATITUDE BLOCKING REMAINS
ADVERTISED FOR MUCH OF THIS PERIOD, WITH GFS/ECMWF ENSEMBLE
TELECONNECTIONS INDICATING A NEGATIVE-PHASE AO/NAO. BY TUESDAY
NIGHT, THE UPPER-LEVEL LOW INITIALLY OVER NOVA SCOTIA AND
ADJACENT WATERS BEGINS TO RETROGRADE BACK TOWARDS THE NORTHEAST
US. TODAY'S 12Z GUIDANCE CONTINUES TO ADVERTISE A SOUTHERN-
STREAM TROUGH WHICH LEADS TO SURFACE LOW DEVELOPING OVER THE
LOWER MS VALLEY/DEEP SOUTH ON TUESDAY, WHICH PROGRESSES OFF THE
MID-ATLANTIC COAST WEDNESDAY. WHERE THIS COASTAL LOW EVOLVES
THEREAFTER REMAINS UNCERTAIN.
CURRENTLY, NEARLY ALL OF THE 12Z DETERMINISTIC MODEL GUIDANCE
TRAVERSES THIS COASTAL LOW EASTWARD SOUTH OF 40 DEG N LATITUDE, WITH
LITTLE IF ANY POLEWARD/NORTHWARD ADVANCE. LAST NIGHT'S 00Z CANADIAN
GEM OPERATIONAL RUN, HOWEVER, DID BRING A COASTAL STORM TO SOUTHERN
NEW ENGLAND. IT'S SOUTHERN STREAM DISTURBANCE WAS A LOT STRONGER
THAN THE GFS OR THE ECMWF DEPICTION. IT IS ALSO WORTH NOTING THIS
LONE 00Z CANADIAN GEM SOLUTION DIDN'T HAVE SUPPORT FROM THE
GFS/ECMWF ENSEMBLE AND EVEN ITS OWN GEM ENSEMBLE. IT HAS SINCE GONE
BACK ON THE 12Z RUN TOWARD THE CONSENSUS SUPPRESSED/SOUTHERN TRACK.
THE SOUTHERN-STREAM TROUGH RESPONSIBLE IS PROGGED TO COME ONSHORE
COASTAL CALIFORNIA LATER TONIGHT, AND WHILE THE MODEL CONSENSUS
CURRENTLY FAVORS LITTLE IMPACT IF ANY AT ALL (AT LEAST AN
ENHANCEMENT TO NE WINDS OVER THE SOUTHERN WATERS), ALL OUTCOMES
STILL REMAIN ON THE TABLE AND WILL NOT YET DOWNPLAY THIS SYSTEM.
WILL CONTINUE TO ADVERTISE LOWER CHANCE-LEVEL POPS WITH NONETHELESS
CONSIDERABLE CLOUDINESS AT LEAST GIVEN THE PRESENCE OF THE
RETROGRADING UPPER LOW AND RELATED MOISTURE.
WILL HAVE TO WATCH HOW CLOSE ANY WRAP-AROUND PRECIP GETS LATER WED
NIGHT INTO THURS NIGHT, WITH THE 12Z ECMWF/CANADIAN GEM AND TO
A LESSER EXTENT THE GFS INDICATING THIS POTENTIAL.
TEMPERATURES WED START OFF COOLER THAN NORMAL ON THE HIGHS (IN THE
MID TO UPPER 40S), AND NEAR NORMAL ON THE LOWS (IN THE 30S TUES THRU
THURS NIGHT). BY THURSDAY, HIGHS SHOULD START TO TREND CLOSER
TO NORMAL (UPPER 40S-MID 50S).
FRIDAY - SATURDAY:
THERE IS SOME LEVEL OF UNCERTAINTY IN THIS PERIOD ON SHOWER CHANCES
ON FRIDAY DEPENDING ON HOW CLOSE ANY WRAP-AROUND MOISTURE MAKES IT
FROM THE DISTANT COASTAL SYSTEM, WHICH LOOKS TO SLOW/STALL IN THE
WATERS SOUTH OF THE CANADIAN MARITIMES. BETTER CHANCES MAY BE
TOWARDS THE COAST THAN FURTHER INLAND, BUT WILL STAY CLOSE TO A
MODEL BLENDED APPROACH WHICH KEEPS CHANCES FOR SHOWERS GOING ACROSS
A LARGER PART OF SOUTHERN NEW ENGLAND.
NONETHELESS, EVEN IF DRIER WEATHER ULTIMATELY ENSUES FOR FRIDAY,
MOST MODELS SHOW A COLD FRONT PROGRESSING IN FROM THE GREAT LAKES/OH
VALLEY INTO SATURDAY, BRINGING ANOTHER CHANCE FOR SHOWERS.
SEASONABLE TO SLIGHTLY ABOVE NORMAL HIGHS IN THE UPPER 40S TO MID
50S WITH LOWS IN THE MID/UPPER 30S.
AVIATION /02Z SUNDAY THROUGH THURSDAY/
FORECASTER CONFIDENCE LEVELS...
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
00Z TAF UPDATE:
TONIGHT...HIGH CONFIDENCE IN THE TRENDS. MODERATE CONFIDENCE IN
TIMING.
GENERALLY DETERIORATING CONDITIONS TOWARD MVFR, GENERALLY SOONER
IN THE INTERIOR AS RAIN OVERSPREADS THE TAFS. AFTER MIDNIGHT THE
PROSPECTS FOR MVFR-IFR CEILINGS INCREASE IN THE INTERIOR AND
THE TERRAIN, WHILE STAYING CLOSER TO MVFR NEAR THE COAST. VISBYS
SHOULD BE GENERALLY VFR/MVFR, WITH HEAVIER RAINS BRINGING IN
THE LOWEST VISBYS.
SUNDAY AND SUNDAY NIGHT...MAINLY MVFR WITH AREAS IFR IN HEAVIER
RAINFALL.
KBOS TERMINAL...HIGH CONFIDENCE IN TAF TRENDS. MODERATE
CONFIDENCE IN TIMING.
KBDL TERMINAL...HIGH CONFIDENCE IN TAF TRENDS. MODERATE
CONFIDENCE IN TIMING.
OUTLOOK /MONDAY THROUGH THURSDAY/...
MONDAY: MVFR/IFR CONDITIONS POSSIBLE. BREEZY. SCATTERED SHRA,
PATCHY BR.
MONDAY NIGHT: MVFR/IFR CONDITIONS POSSIBLE. BREEZY. SCATTERED
SHRA, SCATTERED SHSN, PATCHY BR.
TUESDAY: MVFR/IFR CONDITIONS POSSIBLE. BREEZY. ISOLATED SHRA.
TUESDAY NIGHT: MAINLY VFR, WITH AREAS MVFR POSSIBLE. BREEZY.
WEDNESDAY: MAINLY VFR, WITH AREAS MVFR POSSIBLE. BREEZY. SLIGHT
CHANCE SHRA.
WEDNESDAY NIGHT: MVFR/IFR CONDITIONS POSSIBLE. BREEZY. SLIGHT
CHANCE SHRA, SLIGHT CHANCE SHSN.
THURSDAY: MAINLY VFR, WITH AREAS MVFR POSSIBLE. BREEZY. SLIGHT
CHANCE SHRA.
MARINE
TWEAKED THE TIMING OF SMALL CRAFT ADVISORIES ACROSS THE WATERS.
DID NOT HAVE ENOUGH CONFIDENCE TO ISSUE SUCH ADVISORIES FOR
BOSTON HARBOR AND NARRAGANSETT BAY, BUT IT IS NOT IMPOSSIBLE FOR
SOME GUSTS TO 25 KT ON THOSE WATERS SUNDAY. LOW RISK FOR GALE
FORCE GUSTS ACROSS THE EASTERN COASTAL WATERS LATE SUNDAY
AFTERNOON INTO SUNDAY EVENING. NOT ENOUGH CONFIDENCE IN THESE
GUSTS TO UPGRADE TO GALE WARNINGS. IT'S MARGINAL.
RAIN EXPECTED TO DEVELOP TONIGHT INTO SUNDAY AS A WARM FRONT
LIFTS THROUGH AND A SECONDARY LOW DEVELOPS ALONG THE SOUTH
COAST. SOME VISIBILITY REDUCTION AS FOG DEVELOPS, TOO. WINDS
WILL GRADUALLY SHIFT TO THE EAST TONIGHT AND SUNDAY, THEN
INCREASE. ON SUNDAY GUSTS WILL INCREASE TO 25- 30 KTS ALONG
WITH SEAS BUILDING TO 5-8 FEET ACROSS THE INTERIOR OCEAN WATERS,
WHILE THE OUTER WATERS SEE WAVES BUILD TO 7-10 FEET. CONFIDENCE
HAS INCREASED TO ISSUE A SMALL CRAFT ADVISORY ACROSS THE
MAJORITY OF OCEAN WATERS THROUGH SUNDAY.
THERE IS POTENTIAL FOR ISOLATED THUNDERSTORMS ACROSS THE OCEAN
WATERS SUNDAY EVENING.
WINDS DECREASE AND BECOME MORE VARIABLE ACROSS MOST OF THE
WATERS SUNDAY NIGHT AS A SECONDARY LOW PRESSURE DEVELOPS NEAR
CAPE COD.
OUTLOOK /MONDAY THROUGH THURSDAY/...
MONDAY: WINDS LESS THAN 25 KT. AREAS OF ROUGH SEAS. SCATTERED
RAIN SHOWERS, PATCHY FOG. LOCAL VISIBILITY 1 TO 3 NM.
MONDAY NIGHT: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH
GUSTS UP TO 25 KT. AREAS OF ROUGH SEAS. SCATTERED RAIN SHOWERS,
PATCHY FOG.
TUESDAY: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS UP
TO 25 KT. AREAS OF ROUGH SEAS. ISOLATED RAIN SHOWERS.
TUESDAY NIGHT: WINDS LESS THAN 25 KT. AREAS OF ROUGH SEAS.
SLIGHT CHANCE OF RAIN SHOWERS.
WEDNESDAY: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS
UP TO 25 KT. AREAS OF ROUGH SEAS. SLIGHT CHANCE OF RAIN
SHOWERS.
WEDNESDAY NIGHT: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH
GUSTS UP TO 25 KT. SEAS UP TO 5 FT. CHANCE OF RAIN SHOWERS.
THURSDAY: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS UP
TO 25 KT. LOCAL ROUGH SEAS. SLIGHT CHANCE OF RAIN SHOWERS.
BOX WATCHES/WARNINGS/ADVISORIES
CT...NONE.
MA...NONE.
RI...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 5 AM SUNDAY TO 2 AM EDT MONDAY FOR
ANZ232.
SMALL CRAFT ADVISORY FROM 5 AM TO 10 PM EDT SUNDAY FOR ANZ233-
234.
SMALL CRAFT ADVISORY FROM 8 AM SUNDAY TO 2 AM EDT MONDAY FOR
ANZ231.
SMALL CRAFT ADVISORY UNTIL 8 AM EDT MONDAY FOR ANZ235-237-255-
256.
SMALL CRAFT ADVISORY FROM 8 AM SUNDAY TO 8 AM EDT MONDAY FOR
ANZ250-251.
SMALL CRAFT ADVISORY FROM 5 AM SUNDAY TO 8 AM EDT MONDAY FOR
ANZ254.
SYNOPSIS...BELK/LOCONTO
NEAR TERM...BELK/BL/LOCONTO
SHORT TERM...BELK
LONG TERM...LOCONTO
AVIATION...BELK/LOCONTO
MARINE...BELK/LOCONTO
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