Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 211128 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 728 AM EDT TUE OCT 21 2014 .SYNOPSIS... A LONG DURATION COASTAL STORM WILL BRING PERIODS OF RAIN THROUGH THURSDAY WITH LINGERING SHOWERS FRIDAY AS THE STORM SLOWLY PULLS AWAY FROM NEW ENGLAND. MAINLY DRY WEATHER EXPECTED THIS WEEKEND WITH SEASONABLE TEMPERATURES. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 7 AM UPDATE... ACCORDING TO LATEST MSAS/LAPS MASS FIELDS...LOW PRES NEAR THE GREAT LAKES IS SLOWLY BEGINNING TO TRANSFER ENERGY TO DEVELOPING COASTAL WAVE JUST OFF OF THE NJ COAST THIS MORNING. THIS SECONDARY FEATURE IS ASSISTED BY MODERATE LLJ WHICH IS CURRENTLY MANIFESTING ITSELF AS A REGION OF MOD-HEAVY RAINFALL WITH CONVECTIVE ELEMENTS CURRENTLY PASSING JUST TO THE S OF THE ISLANDS. THIS FEATURES IS EXPECTED TO BRUSH THE CAPE AND ISLANDS THIS MORNING BEFORE SHIFTING NE AS THE LOW PRES CONTINUES TO DEVELOP TO THE S. WHAT THIS MEANS IS SHOWERS FOR THE CAPE/ISLANDS THIS MORNING...WITH GRADUALLY INCREASING -SHRA ACTIVITY ELSEWHERE INTO THE EVENING/OVERNIGHT HOURS TONIGHT. TRIED TO REFLECT THIS IN THE MORNING TAF UPDATE. OTHERWISE...MUCH OF THE FORECAST IS ON TRACK THIS MORNING. PREVIOUS DISCUSSION... PER LATEST WATER VAPOR IMAGERY TROUGH AMPLIFICATION TAKING PLACE OVER THE OH VLY INTO PA AND NY STATE. IN RESPONSE TO THIS AMPLIFICATION WARM CONVEYOR BELT AND ASSOCIATED RAINS DEVELOPING OVER THE NORTHEAST INTO WESTERN MA INTO SOUTHWEST NH...ALONG WITH ANOTHER AREA RI...SOUTHEAST MA AND ADJACENT WATERS. THIS SECOND AREA SHOULD BECOME THE FOCUS FOR POTENTIALLY HEAVIER RAINFALL LATER THIS MORNING INTO THIS AFTERNOON...AS LOW LEVEL JET DEVELOPS AND INCREASES IN MAGNITUDE ACROSS THIS AREA. THIS DIFFERENTIAL WARM AIR ADVECTION WILL YIELD ELEVATED INSTABILITY INCREASING THE RISK OF EMBEDDED CONVECTION WITHIN THE WARM CONVEYOR BELT RAINS ACROSS CAPE COD AND THE ISLANDS LATER THIS MORNING INTO THIS AFTERNOON. THE 00Z GUID INCLUDING THE LATEST RAP13/W-ARW/HRRR AND THE 03Z SREF ARE ALL IN GOOD AGREEMENT ON ANY HEAVIER RAINBANDS AND EMBEDDED CONVECTION TO TRACK OVER THE CAPE AND ISLANDS...AND POSSIBLY OFFSHORE. THUS HAVE CONFINED CHANCE OF HEAVY RAIN AND THUNDER TO THE REGION. RISK OF HEAVY RAIN WILL BE FROM ABOUT 15Z TO 21Z TODAY AND CONFINED TO CAPE COD AND THE ISLANDS. ELSEWHERE NOT MUCH APPRECIABLE RAINFALL TODAY. MAINLY PERIODS OF RAIN AND FOR THE MOST PART ON THE LIGHT SIDE. AS FOR TEMPS...ON THE MILD SIDE WITH HIGHS IN THE LOW TO MID 60S ACROSS MUCH OF RI AND SOUTHEAST MA AS WARM SECTOR OVERSPREADS THIS REGION. FARTHER INLAND COOLER WITH HIGHS IN THE 50S. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... TONIGHT... DRY SLOT OVERSPREADS THE REGION. THIS WILL RESULT IN PERIODS OF DRIZZLE AS LOW LEVEL MOISTURE BECOMES TRAPPED BENEATH DRY AIR ALOFT. FARTHER INLAND ACROSS SOUTHERN NH AND WESTERN MA A STEADIER RAIN IS POSSIBLE AS COMMA HEAD RAINS MAY CLIP THIS REGION WHILE BULK OF RAIN IS CONFINED TO CENTRAL AND NORTHERN NEW ENGLAND. AS FOR TEMPS...NOT MUCH OF A DROP OFF GIVEN ONSHORE FLOW/CLOUDS AND LIGHT PRECIP. WEDNESDAY... TRAILING SHORT WAVE ENERGY ROUNDS THE BASE OF THE TROUGH AND THEN TAKES AIM AT SOUTHERN NEW ENGLAND LATER IN THE DAY. STRONG SYNOPTIC SCALE FORCING WITH THIS FEATURE AND RESULTS IN COASTAL LOW OFF NJ COAST TO INTENSIFY. THUS SLUG OF HEAVY RAIN LIKELY TO MOVE ONSHORE INTO SOUTHERN NEW ENGLAND LATE IN THE DAY. IN ADDITION AS DRY SLOT APPROACHES THETA-E LAPSE RATES BEGIN TO DECREASE. THUS EMBEDDED CONVECTION POSSIBLE AND WOULD ENHANCE HEAVY RAINFALL POTENTIAL. THIS WILL INCREASE THE RISK URBAN/POOR DRAINAGE FLOODING AND MAY IMPACT THE EVENING COMMUTE. TEMPS SIMILAR AS TODAY WITH HIGHS IN THE L60S OVER SOUTHEAST MA AND COOLING INTO THE 50S ELSEWHERE. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... OVERVIEW AND MODEL PREFERENCES... WITH FAIRLY GOOD MODEL AGREEMENT THROUGH THE MID TERM REGARDING A SLOW MEANDERING AND STACKED LOW PRES SYSTEM MOVING JUST TO THE S OF SRN NEW ENGLAND...A GENERAL CONSENSUS BLEND WILL BE USED AS A BASELINE FOR THIS FORECAST. FOR THE REMAINDER...TOWARD THE END OF THE WEEK...THE OPERATIONAL ECMWF CONTINUES TO EXHIBIT A BIT OF A HIGHER AMPLIFICATION BIAS /SOMEWHAT TYPICAL OF THIS MODEL/. WHILE OTHER OPERATIONAL MODELS AND SEVERAL OF IT/S OWN ENSEMBLES ARE MORE PROGRESSIVE WITH A SECONDARY KICKER WAVE AND HIGH PRES. THEREFORE...WILL ADD LESS WEIGHT TO THE ECMWF BY THE LATE WEEK AND WEEKEND-EARLY NEXT WEEK TIME FRAME. AS MENTIONED ABOVE THE KEY FEATURE INITIALLY IS A SLOW MOVING CUTOFF LOW PRES WITH ATTENDANT OCCLUDING SFC LOW THROUGH LATE IN THE WEEK. IT/S NOT UNTIL A KICKER WAVE /DEEPENING WAVE EJECTING OUT OF THE CANADIAN W/ MOVES IN ON SAT THAT THE LOW PRES MOVES FULLY INTO THE MARITIMES AND ALLOWS DRIER AIR TO FULLY BUILD IN. THEREFORE...EXPECT THE WET/GRAY CONDITIONS TO CONTINUE THROUGH FRI WITH GRADUAL IMPROVEMENT FROM THEN INTO EARLY NEXT WEEK. DETAILS... WED NIGHT INTO THU... AT THIS POINT ALL FEATURES LINE UP FOR THE POTENTIALLY WETTEST PERIOD OF THE FORECAST. IN ESSENCE A REINFORCING LLJ /ABOUT 40+ KT MAINLY N OF THE BOX CWA/ MOVES IN COMBINED WITH UPPER LVL DRY SLOT AND NEAR 6.0+ C/KM LAPSE RATES. THEREFORE...LOOKS LIKE A DECENT SETUP FOR CONVECTIVE ELEMENTS WITH THIS LLJ PARTICULARLY BETWEEN 00Z AND 12Z ON THU. WITH MODEST PWATS UP TO 1.5 INCHES /ABOUT 2+ STD DEVIATIONS ABOVE NORMAL/. COULD SEE POCKETS OF HEAVIER RAIN THROUGH THE PERIOD...GRADUALLY DIMINISHING INTO THE DAYLIGHT HOURS ON THU AS THE LLJ AND DRY SLOT SHIFT N. RIGHT NOW THE PRIMARY THREAT WOULD BE THE TYPICAL URBAN AREAS WHERE DRAINAGE IS POOR FOR ANY NUISANCE FLOODING...BUT WILL NEED TO KEEP AN EYE ON THIS OVER THE NEXT 24-36 HOURS. OTHERWISE...THE GRAY/DAMP CONDITIONS CONTINUE WITH ONSHORE FLOW AND PLENTY OF MOISTURE/CLOUD COVER. DUE TO THIS CLOUD COVER...SUSPECT THAT LOWS REMAIN MAINLY IN THE 50S AND HIGHS ONLY RISE INTO THE MID 50S AND LOW 60S. FRI... GRADUAL IMPROVEMENT AS THE UPPER LVL SHORTWAVE EJECTING OUT OF CANADA BEGINS TO FORCE THE UPPER LVL CUTOFF TO THE E AND WEAKENS IT. STILL ENOUGH UPPER LVL COOL AIR AND MOISTURE TO SUPPORT A FEW MORE SHOWERS. SO THE GRAY/WET CONDITIONS CONTINUE...BUT WITH A MORE N COMPONENT TO THE FLOW...THESE SHOWERS ARE LIKELY TO BE FEWER AND FARTHER BETWEEN. TEMPS A BIT WARMER...MAINLY UPPER 50S TO MID 60S. SAT AND SUN... SFC COLD FRONT ASSOCIATED WITH THE SHORTWAVE WILL BE MOVING THROUGH THE REGION...WHICH SHOULD FINALLY RELEASE THE REGION FROM THE GRIPS OF THE CUTOFF. AT THIS POINT WITH DRIER AIR MOVING IN...MAY ONLY SEE CLOUD COVER WITH THIS FRONTAL PASSAGE...BUT AN ISOLATED SHOWER IS NOT OUT OF THE QUESTION MAINLY SAT NIGHT INTO EARLY SUN. THE DIFFERENCES IN AMPLIFICATION BETWEEN MODELS MAKE IT DIFFICULT TO TELL EXACTLY HOW DEEP THE COLD AIR GETS SAT NIGHT INTO SUN...BUT WITH FULL MIXING HIGHS OF LOW-MID 60S ARE NOT OUT OF THE QUESTION WITH LOWS FALLING BACK INTO THE 40S. MON AND TUE... HIGH PRES BUILDS IN ACROSS THE AREA WITH DRIER AIR AND MOSTLY CLEAR CONDITIONS. TEMPS MAY BE NEAR SEASONAL NORMALS...IF NOT SLIGHTLY ABOVE DEPENDING ON HOW DEEP THE COOL AIR BECOMES AT THIS POINT. && .AVIATION /12Z TUESDAY THROUGH SATURDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH WEDNESDAY/... TODAY...MODERATE CONFIDENCE. MAINLY VFR THROUGH THE DAY TODAY ALTHOUGH WITH GRADUALLY LOWERING CIGS. THE MAIN CAVEAT HERE WILL BE THE POSSIBILITY OF SHOWERS /POSSIBLY HEAVY AT TIMES/ MAINLY FOR THE CAPE/ISLANDS THIS MORNING WITH MVFR /AND POSSIBLY BRIEF IFR/ CONDITIONS POSSIBLE. INCREASING THREAT FOR SHOWERS LATE. TONIGHT... MAIN AREA OF RAIN LIFTS NORTHWARD INTO CENTRAL NEW ENGLAND. SPOTTY LIGHT RAIN AND DRIZZLE WILL BE COMMON ACROSS SOUTHERN NEW ENGLAND TERMINALS WITH VFR/MVFR TRENDING TOWARD IFR LATE TONIGHT. WEDNESDAY... IFR/MVFR WITH MOST OF THE RAIN CONFINED TO THE INTERIOR. HOWEVER A NEW AREA OF RAIN SHOULD MOVE ONSHORE TO THE SOUTH COAST LATE IN THE DAY. E-NE WINDS WILL INCREASE LATE IN THE DAY AS WELL. KBOS...HIGH CONFIDENCE IN TAF ON TRENDS BUT LOWER CONFIDENCE ON EXACT TIMING AND DETAILS. KBDL...HIGH CONFIDENCE IN TAF ON TRENDS BUT LOWER CONFIDENCE ON EXACT TIMING AND DETAILS. OUTLOOK...WEDNESDAY NIGHT THROUGH SATURDAY...MODERATE CONFIDENCE. WEDNESDAY NIGHT THROUGH THURSDAY... MAINLY IFR/MVFR WITH PERIODS OF HEAVY RAIN POSSIBLE. LOW CIGS AND VSBYS IN HEAVIER RAIN AND FOG. SLIGHT CHANCE OF THUNDER THROUGH THE PERIOD. CHANCE FOR LLWS ESPECIALLY OVERNIGHT INTO EARLY THU MORNING WITH UP TO 40 KT POSSIBLE AT AROUND 2KFT ESPECIALLY TERMINALS N OF THE MASS PIKE. FRIDAY AND SATURDAY... IMPROVING TO VFR. AREAS OF MVFR CIGS/VSBYS IN SHOWERS ON FRIDAY...WITH THE BEST CHANCE IN SOUTHERN NH AND EASTERN MASS. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /TODAY THROUGH WED/... TODAY... STRONGEST SOUTHEAST WINDS WILL OCCUR OVER THE EASTERN MA WATERS...WITH GUSTS UP TO 25 KT. THUS SCA POSTED FOR THAT AREA. HEAVY RAIN WITH LOW RISK OF T-STORMS ACROSS THIS AREA. ELSEWHERE LIGHTER WINDS AND SHOWERS. TONIGHT... EAST TO NORTHEAST WINDS. LOW RISK OF 25 KT OVER CAPE ANN WATERS. VSBY REDUCED IN AREAS OF FOG AND DRIZZLE. WEDNESDAY... HEAVY RAIN AND POSSIBLE EMBEDDED THUNDER MOVES SOUTHEAST TO NORTHWEST ACROSS THE WATERS AND THEN ONSHORE LATE IN THE DAY. NORTHEAST WINDS 15-20 KT. VSBY REDUCED IN AREAS OF FOG AND HEAVY RAIN LATE IN THE DAY. OUTLOOK...WEDNESDAY THROUGH SATURDAY...MODERATE CONFIDENCE. WED NIGHT INTO THU... MAINLY E-NE FLOW ALONG THE WATERS WED NIGHT INTO EARLY THU. THEN SHIFTING TO NW DURING THE AFTERNOON AND EVENING THU. A FEW WIND GUSTS MAY APPROACH GALE FORCE WED NIGHT MAINLY ACROSS THE N WATERS...WITH SMALL CRAFT ADVISORY LEVEL WINDS ELSEWHERE. THE WINDS DROP OFF AS THEY SHIFT THU...BUT THEN GUST AGAIN TO SMALL CRAFT ADVISORY LEVELS LATE DAY THU. OTHERWISE...SEAS BUILD WED NIGHT INTO THU MORNING WITH AT LEAST 5-9 FT SEAS POSSIBLE. SOME HEAVY RAIN POSSIBLE WED NIGHT INTO EARLY THU MORNING. FRI... LOW PRES MOVES FURTHER OFFSHORE...WINDS AND SEAS MAY STILL REACH SMALL CRAFT ADVISORY LEVELS DURING THE DAY FRI AND INTO FRI NIGHT...BUT EXPECT GRADUAL IMPROVEMENT. SATURDAY...WINDS AND SEAS SHOULD REMAIN BELOW SMALL CRAFT LEVELS. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY FROM NOON TODAY TO 8 AM EDT WEDNESDAY FOR ANZ250-254. SMALL CRAFT ADVISORY FROM 3 PM THIS AFTERNOON TO 8 AM EDT WEDNESDAY FOR ANZ251. SMALL CRAFT ADVISORY UNTIL 7 AM EDT WEDNESDAY FOR ANZ255-256. && $$ SYNOPSIS...NOCERA/DOODY NEAR TERM...NOCERA/DOODY SHORT TERM...NOCERA LONG TERM...DOODY AVIATION...NOCERA/DOODY MARINE...NOCERA/DOODY

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