Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 030651 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 251 AM EDT TUE MAY 3 2016 .SYNOPSIS...
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RAIN REDEVELOPS EARLY THIS MORNING AS LOW PRES TRACKS SOUTH OF NEW ENGLAND. RAIN TAPERS OFF THIS AFTERNOON FROM WEST TO EAST...BUT IT WILL REMAIN RATHER CLOUDY AND COOL. ONE OR MORE WAVES OF LOW PRESSURE PASS SOUTH OF THE REGION LATE WEDNESDAY BRINGING MORE SHOWERS. A CLOSED UPPER LOW DEVELOPS OVER THE APPALACHIANS THURSDAY AND DRIFTS SOUTH OF NEW ENGLAND FRIDAY AND SATURDAY. A COLD FRONT SWINGS THROUGH NEW ENGLAND SUNDAY...FOLLOWED BY HIGH PRESSURE AND DRIER WEATHER MONDAY.
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&& .NEAR TERM /TODAY/...
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300 AM UPDATE ... *** A PERIOD OF STEADY RAIN THIS MORNING POSSIBLY HEAVY AT TIMES ALONG THE SOUTH COAST *** FRONTAL WAVE OVER THE MID ATLC REGION EARLY THIS MORNING WILL TRACK ENE TODAY IN THE DEEP SW FLOW ALOFT ALONG THE EASTERN SEABOARD. WITHIN THIS AIRSTREAM COPIOUS AMOUNTS OF MOISTURE AVAILABLE AS PWATS OF UP TO 1.5 INCHES CURRENTLY STREAMING NE ACROSS DE INTO SOUTHERN NJ. THIS DEEP LAYER MOISTURE WILL BE OVERSPREADING A FAIRLY BAROCLINIC ENVIRONMENT WITH GOOD THERMAL PACKING ACROSS SOUTHERN NEW ENGLAND. THIS WILL RESULT IN A LARGE RAIN SHIELD OVERSPREADING THE REGION EARLY THIS MORNING. AT 06Z RAIN ALREADY INTO PSF AND DXR...AND SHOULD BE IN THE BOSTON- PROVIDENCE CORRIDOR AROUND 4-6 AM AND THEN ACROSS CAPE COD AND NANTUCKET BY 8 AM. AS FRONTAL WAVE TRACKS SOUTH OF NEW ENGLAND LATER THIS MORNING MODELS SUGGEST INCREASING LOW LEVEL FRONTOGENESIS ACROSS THE SOUTH COAST OF MA AND RI. NOT VERY MAY-ISH BUT MORE LIKE A LATE WINTER/EARLY SPRING SYSTEM. SOME ELEVATED INSTABILITY TOO SO ISOLATED THUNDER POSSIBLE BUT THE GREATER IMPACT WILL BE THIS INSTABILITY TO ENHANCE THE RISK FOR BANDS OF MODERATE TO HEAVY RAIN ESPECIALLY ALONG THE SOUTH COAST OF MA AND RI 09Z TO 15Z FROM WEST TO EAST. MAIN IMPACTS HERE WOULD BE CONFINED TO MINOR LOCAL URBAN/POOR DRAINAGE FLOODING. ELSEWHERE EXPECTING LESS RAINFALL NORTH OF THE MASS PIKE TOWARD THE MA/NH BORDER. OTHERWISE SYSTEM IS FAIRLY PROGRESSIVE WITH RAIN TAPERING OFF THIS AFTERNOON FROM WEST TO EAST. LOW CLOUDS LIKELY PERSIST GIVEN WEAK RIDGING BUILDS DOWN FROM THE NORTHEAST. THIS SUBSIDENCE INVERSION COMBINED WITH LOW MOISTURE TRAPPED MAY YIELD SPOTTY LIGHT DRIZZLE LATER IN THE DAY. ANOTHER COOL DAY AHEAD GIVEN THE RAIN AND LIGHT ONSHORE WINDS. THIS WILL ONLY YIELD HIGHS IN THE U40S TO L50S...ABOUT 10-15 DEGS COOLER THAN NORMAL. THE COOLER 2 METER TEMPS SEEM MORE REASONABLE COMPARED TO THE MILDER MOS HIGHS.
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&& .SHORT TERM /TONIGHT THROUGH 6 PM WEDNESDAY/...
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UPDATED 330 AM ... TONIGHT ... COLUMN BEGINS TO DRY FROM TOP DOWN AS SUBSIDENCE INCREASES BEHIND DEPARTING FRONTAL WAVE. HOWEVER NOT EXPECTING SKIES TO CLEAR MUCH IF ANY GIVEN LOTS OF LOW LEVEL MOISTURE TRAPPED BENEATH SUBSIDENCE INVERSION. IN FACT THIS MAY YIELD PATCHY DRIZZLE/MIST OVERNIGHT. WEDNESDAY ... LONG WAVE TROUGH SHARPENS AS NORTHERN STREAM JET ENERGY DIVING SOUTHWARD FROM ONTARIO THRU THE GREAT LAKES FORMS A CLOSED LOW OVER THE OH VALLEY LATE IN THE DAY. THIS BACKS THE UPPER LEVEL FLOW ALONG THE EASTERN SEABOARD WITH A NEW FRONTAL WAVE AND PLUME OF MOISTURE SURGING NORTHWARD INTO SOUTHERN NEW ENGLAND BY DAYS END. SO THE WEATHER THEME FOR WED WILL BE A MAINLY DRY START /OTHER THAN MORNING MIST-DRIZZLE/ FOLLOWED BY INCREASING THREAT FOR RAIN ESPECIALLY LATE IN THE DAY FROM SOUTH TO NORTH. ANOTHER COOLER THAN NORMAL DAY WITH SURFACE RIDGE WEDGED FROM THE MARITIMES INTO NEW ENGLAND ALONG WITH CLOUDY SKIES AND LIGHT ONSHORE WINDS.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... BIG PICTURE... LONGWAVE SCALE SHOWS TROUGH EAST/RIDGE WEST FOR MUCH OF THE FORECAST PERIOD. PROGRESSIVE NORTHERN STREAM STAYS ACROSS CANADA MUCH OF THE WEEK WHILE FLOW ACROSS THE USA REMAINS BLOCKY WITH CLOSED LOWS OVER THE PACIFIC AND ATLANTIC COASTS AND A WEAKER RIDGE OVER THE PLAINS. SHORTWAVES MOVE THROUGH THE EASTERN USA CLOSED LOW. THEN OVER THE WEEKEND A SHORTWAVE IN THE NORTHERN STREAM DIGS INTO THE LONGWAVE TROUGH. THIS KICKS OUT THE ATLANTIC CLOSED LOW AND ESTABLISHES A NEW CLOSED LOW OVER THE MARITIMES. THIS REMAINS AN UNSETTLED PATTERN FOR NEW ENGLAND THROUGH THE WEEKEND A TREND TO DRIER WEATHER EARLY NEXT WEEK. THE DAILIES... TUESDAY NIGHT-WEDNESDAY... SOUTHWEST UPPER FLOW WITH SEVERAL JET STREAKS MOVING OVERHEAD OF NEW ENGLAND. STATIONARY FRONT REMAINS OFFSHORE. THIS IS THE RECIPE FOR ONE OR MORE SURFACE LOWS RIPPLING UP THE FRONT AND PASSING TO OUR SOUTH. LOW LEVEL FLOW SOUTH OF THE FRONT REMAINS DIRECTED OUT TO SEA...BUT IF ONE OF THESE LOWS BECOMES A LITTLE STRONGER THAN DEPICTED THEN IT IS CONCEIVABLE THAT IT COULD BRIEFLY PULL THE LOW LEVEL FLOW OUT OF THE SOUTH AND GENERATE SOME LOW LEVEL LIFT/OVERRUNNING ACROSS SOUTHERN NEW ENGLAND AS IT PASSES. MEANWHILE THE JET STREAKS ALOFT WILL GENERATE SOME UPPER VENTING. AT A MINIMUM THIS WOULD INDICATE CHANCE POPS FOR SHOWERS IN SOUTHERN NEW ENGLAND. IF ONE LOW BECOMES FOCUSSED ALONG THE FRONT THEN HIGHER POPS VALUES /ABOVE THE 55 PCT LIKELY THRESHOLD/ WOULD BE REASONABLE ALONG THE SOUTH COAST AND ISLANDS. THURSDAY THROUGH SATURDAY... CLOSED UPPER LOW TAKES SHAPE OVER THE APPALACHIANS AND DRIFTS SOUTH OF NEW ENGLAND. COLD POOL ALOFT ASSOCIATED WITH THE LOW WILL ADVECT OVER OUR AREA AND DESTABILIZE THE AIRMASS. THIS WILL SUPPORT SCATTERED SHOWERS THROUGH THE PERIOD. SUNDAY-MONDAY... NORTHERN SHORTWAVE DIVES SOUTHEAST THROUGH NEW ENGLAND SUNDAY. THIS DRIVES THE CLOSED LOW OFF TO THE EAST AND BRINGS A COLD FRONT THROUGH OUR AREA ON SUNDAY. WE SHOULD BE UNDER THE LEFT EXIT REGION OF THE NORTHWEST UPPER JET...PROVIDING ENOUGH VENTING TO SUPPORT SCATTERED SHOWERS. HIGH PRESSURE THEN BUILDS IN WITH DRIER WEATHER FOR MONDAY. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/...
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FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. UPDATED 300 AM ... SHORT TERM /THROUGH WEDNESDAY/... BEFORE 12Z ... WIDE RANGE OF CONDITIONS EARLY THIS MORNING HOWEVER TREND WILL BE DOWN TOWARD IFR/LIFR AS RAIN OVERSPREADS ALL TERMINALS FROM WEST TO EAST. BANDS OF HEAVY RAIN WILL LIKELY EXIT NYC AREA AND COASTAL CT AND APPROACHING SOUTHERN RI AND MA TOWARD 12Z. HEAVY CONFIDENCE ON TRENDS BUT LOWER ON PRECISE DETAILS. AFTER 12Z ... RAIN OVER MOST OF THE AREA WITH BANDS OF MODERATE TO HEAVY RAIN ALONG THE SOUTH COAST OF MA AND RI. IFR AND MVFR PREVAIL. RAIN BEGINS TO PULL OUT OF THE REGION THIS AFTERNOON FROM WEST TO EAST. FORECAST CONFIDENCE HIGH ON TRENDS BUT LOWER ON EXACT DETAILS. TONIGHT ... IFR AND MVFR WITH IFR LIKELY OVER SOUTHEAST MA AND THE HIGHER TERRAIN. MVFR ELSEWHERE. SPOTTY DRIZZLE/MIST POSSIBLE IN IFR AREAS. OTHERWISE MAINLY DRY. FORECAST CONFIDENCE HIGH ON TRENDS BUT LOWER ON EXACT DETAILS. WED ... IFR LIKELY SOUTHEAST MA WITH MVFR ELSEWHERE. MAINLY DRY EARLY WITH JUST SPOTTY MIST/DRIZZLE. RAIN REDEVELOPS LATE IN THE DAY FROM SOUTH TO NORTH. LIGHT ENE WINDS. FORECAST CONFIDENCE HIGH ON TRENDS BUT LOWER ON EXACT DETAILS. KBOS TERMINAL ... MODERATE TO HIGH CONFIDENCE IN TAF. BULK OF HEAVY RAIN TODAY SHOULD SLIDE SOUTH OF LOGAN. KBDL TERMINAL ... MODERATE TO HIGH CONFIDENCE IN TAF. HEAVIEST RAIN TODAY IS FROM 09Z TO 15Z THEN TAPERING OFF. OUTLOOK /WEDNESDAY NIGHT THROUGH SATURDAY/...MODERATE CONFIDENCE WEDNESDAY NIGHT ...AREAS OF MVFR/IFR IN SHOWERS AND LOW CIGS. NORTHEAST WIND 15 KNOTS OR LESS. THURSDAY THROUGH SATURDAY...VFR WITH AREAS OF MVFR/IFR IN SCATTERED SHOWERS.
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&& .MARINE...
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FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. 3 AM UPDATE ... SHORT TERM /THROUGH WEDNESDAY/ ... HIGH CONFIDENCE. LIGHT TO MODEST ENE WINDS TODAY THRU WED. PERIOD OF STEADY RAIN THIS MORNING...HEAVY AT TIMES THEN TAPERING OFF THIS AFTERNOON. MIST/DRIZZLE AND FOG TONIGHT INTO WED MORNING. THEN ANOTHER WEAK FRONTAL WAVE SOUTH OF NEW ENGLAND BRINGS ANOTHER ROUND OF RAIN LATE WED. OUTLOOK /WEDNESDAY NIGHT THROUGH SATURDAY/...MODERATE CONFIDENCE... NORTHEAST WINDS 15 KNOTS OR LESS. SEAS 5 TO 7 FEET THROUGH THE PERIOD. SMALL CRAFT ADVISORY FOR SEAS MAY BE NEEDED...MOSTLY ON THE OUTER WATERS.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...NONE. MA...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 2 AM EDT EARLY THIS MORNING FOR ANZ250-254-255.
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&& $$ SYNOPSIS...WTB/FRANK NEAR TERM...WTB/FRANK/NOCERA SHORT TERM...FRANK LONG TERM...WTB AVIATION...WTB/FRANK/NOCERA MARINE...WTB/FRANK

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