Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 180542 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 142 AM EDT FRI APR 18 2014 .SYNOPSIS... UNSEASONABLY COOL WEATHER WILL PREVAIL THROUGH FRIDAY AS HIGH PRESSURE BUILDS OVER THE REGION. LOW CLOUDS AND PATCHY DRIZZLE WILL AFFECT COASTAL AREAS DUE TO THE ONSHORE FLOW. A WEAKENING FRONT WILL PUSH ACROSS THE REGION ON SATURDAY. HIGH PRESSURE RETURNS INTO MONDAY WITH MODERATING TEMPERATURES. LOW PRESSURE AND A COLD FRONT WILL CROSS THE REGION TUESDAY INTO WEDNESDAY WITH THE CHANCE FOR SHOWERS. DRY AND SEASONABLE CONDITIONS ARE FORECAST INTO LATE NEXT WEEK. && .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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1 AM UPDATE... MARINE STRATO-CU LAYER HAS DEVELOPED MAINLY S OF LONG ISLAND AND INTO CENTRAL NJ THIS EVENING BUT WITH HIGH CLOUDS ONLY JUST EXITING TO THE E IT HAS STRUGGLED TO MAKE HEADWAY EXCEPT ACK AND CAPE COD...AND EVEN THERE IT HAS BEEN SCT AT BEST. STILL WITH PREDOMINANT E-NE FLOW MODEL SOUNDINGS ACROSS THE BOARD STILL SUPPORT ANOTHER ROUND OF BKN SC DEVELOPING ALONG THE E AND SE COASTS AND SHIFTING INLAND BEFORE DISSIPATING LATER TODAY. WILL CONTINUE WITH THIS TREND...BUT LOWER OVERALL AREAL COVERAGE DUE TO RECENT UNCERTAINTY AND DIFFICULTY GUIDANCE HAS HAD WITH INITIALIZING THESE MARINE LAYERS. MAY MAKE FURTHER ADJUSTMENTS WITH LATER UPDATES AS MORE REFINED MESOSCALE GUIDANCE CATCHES UP. PREVIOUS DISCUSSION... MODEL CROSS SECTIONS SHOW A RATHER DEEP LAYER OF LOW LEVEL MOISTURE RETURNING TO COASTAL AREAS LATER TONIGHT...SO WE CONTINUED THEME OF LOW CLOUDS AND PATCHY DRIZZLE OVERNIGHT. FARTHER INLAND...SOME OF THIS MOISTURE SHOULD ALSO BE PREVALENT FOR A TIME OVERNIGHT. EXPECT TO SEE PATCHY LOW CLOUDS CENTERED AROUND DAYBREAK SAT... BUT LOW LEVELS SHOULD BE DRY ENOUGH TO PREVENT ANY FOG/DRIZZLE. TEMPERATURES WILL DROP OFF QUICKLY EARLY TONIGHT...ESPECIALLY ACROSS INTERIOR...BEFORE CLOUDS ARRIVE LATE. LOWS ARE A BLEND OF GFS/NAM MOS WHICH YIELDS 20S TO LOWER 30S.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/... HIGH PRESSURE BUILDS OVER SOUTHERN NEW ENGLAND FRI. LOW LEVEL MOISTURE SHOULD BE EASILY TRAPPED BENEATH SUBSIDENCE INVERSION... ESPECIALLY NEAR COAST PER MODEL CROSS SECTIONS. EXPECT EARLY MORNING CLOUDS TO SCOUR OUT ACROSS INTERIOR...BUT HOLD FIRM CLOSER TO COASTLINE WHERE MARINE LAYER SHOULD ALSO BE DEEP ENOUGH TO SUPPORT PATCHY MORNING DRIZZLE. CONTINUED E/NE WINDS WILL KEEP TEMPERATURES BELOW AVERAGE BUT A LITTLE MILDER THAN TODAY. USED BLEND OF BIAS-CORRECTED GFS/NAM MOS SINCE THEY HAVE BEEN RUNNING A LITTLE TOO COOL WHICH GIVES HIGHS IN 40S COAST TO 50S INTERIOR. COULD COME CLOSE TO 60 ACROSS CT VALLEY. FLOW TURNS MORE W/SW FRI NIGHT AS HIGH MOVES OFFSHORE. MODELS MAINTAIN LOW LEVEL MOISTURE EARLY ON NEAR COAST BUT ERODE IT OVERNIGHT AS MID/HIGH LEVEL MOISTURE STREAMS INTO REGION AHEAD OF WEAKENING COLD FRONT. EXPECT TO HAVE LOW CLOUDS/PATCHY FOG EARLY ESPECIALLY NEAR CAPE COD AND ISLANDS. THIS MAY THIN OUT AS THICKER MID/HIGH CLOUDS ARRIVE BUT CONFIDENCE IS LOW. SHOULD BE A BIT MILDER WITH LOWS MAINLY IN 30S. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... HIGHLIGHTS... * DRY AND SEASONABLE THROUGH MONDAY * SHOWERS FORECAST FOR TUESDAY INTO WEDNESDAY OVERVIEW AND MODEL PREFERENCES/CONFIDENCE... NOTING MEDIUM RANGE MODELS CONTINUE TO SIGNAL A FLAT...SPLIT FLOW SURFACE AND UPPER LEVEL REGIME ACROSS THE LOWER 48 INTO EARLY NEXT WEEK...KEEPING FAST MOVING WEAK SYSTEMS ACROSS THE NORTHERN TIER STATES. BY AROUND SUNDAY...MODELS ARE SIGNALING AN H5 CUTOFF LOW DEVELOPING OFF THE SE U.S...WHICH COULD BRING A CHANGE IN THE OVERALL UPPER LEVEL FLOW AROUND THE MIDDLE OF NEXT WEEK. SOME QUESTIONS AS TO THE TIMING OF THIS FEATURE AND WHEN IT WILL MOVE OFFSHORE. BY THE MIDDLE OF NEXT WEEK...LOOKS LIKE A MORE AMPLIFIED LONG WAVE PATTERN DEVELOPS AS AN H5 SHORT WAVE DIGS OUT OF CENTRAL CANADA AND THE GREAT LAKES. THIS LOOKS TO ARRIVE AROUND THE TUE- WED TIMEFRAME...WHICH SIGNALS A PERIOD OF UNSETTLED WEATHER FOR THE REGION. ANOTHER CUTOFF LOW ALSO LOOKS TO DEVELOP ACROSS THE NORTHERN ROCKIES LATE IN THE PERIOD...WHICH MAY LEAD TO A SLOWING OF THE PROGRESSION OF SYSTEMS. USED A BLEND OF THE ENSEMBLE MEANS AND PREVIOUS FORECAST...ALL OF WHICH ARE IN GOOD AGREEMENT FOR MOST OF THIS FORECAST PERIOD. DETAILS... SATURDAY... EXPECT A DRY...WEAK FRONT TO CROSS THE REGION DURING THE DAY. WENT WITH A DRY FORECAST...AS THERE IS LITTLE IF ANY MOISTURE ASSOCIATED WITH THIS FEATURE EMBEDDED IN THE DRY WESTERLY UPPER FLOW. WINDS WILL SHIFT TO NW DURING THE AFTERNOON BUT...WITH A LIGHT PRES GRADIENT...NOT EXPECT THEM TO BECOME TOO GUSTY. HIGHS WILL RANGE FROM THE MID 50S TO LOWER 60S. WITH MOSTLY CLEAR SKIES AND LIGHT N WINDS...EXPECT OVERNIGHT LOWS WILL DROP TO THE UPPER 20S ACROSS SW NH INTO N CENTRAL AND W MA... POSSIBLY AS FAR S AS THE SPRINGFIELD AREA...RANGING TO THE UPPER 30S TO AROUND 40 ALONG THE IMMEDIATE S COAST. THESE COLDER INTERIOR READINGS WILL RUN AROUND 5 DEGREES BELOW SEASONAL NORMALS. SUNDAY AND MONDAY... CONTINUED HIGH CONFIDENCE FOR DRY AND SEASONABLE CONDITIONS ACROSS THE REGION AS HIGH PRES BECOMES CENTERED ACROSS NEW ENGLAND. WILL BE SOMEWHAT COOLER ALONG E COASTAL AREAS AS THE ORIENTATION OF THE N-S RIDGE AXIS WILL KEEP AN E-NE WIND FLOW IN PLACE. IT WILL REMAIN RATHER CHILLY ALONG THE COAST ON SUNDAY WITH HIGHS ONLY IN THE LOWER- MID 50S...EVEN SOME UPPER 40S ON THE OUTER CAPE AND NANTUCKET...BUT WILL MODERATE SOMEWHAT BY MONDAY AS THE RIDGE NARROWS AS IT SETTLES S. HIGHS MONDAY WILL REMAIN COOLER ACROSS THE OUTER CAPE AND NANTUCKET TO THE IMMEDIATE S COAST...TOPPING OFF IN THE LOWER-MID 50S...BUT RANGING TO THE 60S ELSEWHERE. SOME HIGH CLOUDS MAY BEGIN TO FILTER IN LATER SUN NIGHT INTO MON ACROSS CENTRAL AND NORTHERN AREAS. MONDAY NIGHT THROUGH WEDNESDAY... MODELS CONTINUE TO SIGNAL THIS TO BE AN UNSETTLED PERIOD AS BROAD LOW PRES AND ITS ASSOCIATED COLD FRONT WORK OUT OF THE GREAT LAKES. SOME QUESTION AS TO THE ARRIVAL OF PRECIP...LOOKS TO BE A BIT SLOWER THAN PREVIOUSLY FORECAST. MAY SEE SCT SHOWERS MOVE INTO S NH/NW MA WELL AFTER MIDNIGHT MON NIGHT. BEST SHOT OF PRECIP WILL BE THE TUESDAY INTO WEDNESDAY MORNING TIMEFRAME AS THE FRONT TENDS TO SLOW DOWN AS IT MOVES ACROSS THE REGION...IN RESPONSE TO CUTOFF LOW PRES TRYING TO EXIT OFF THE SE U.S. COAST. MIGHT SEE BEST QPF VALUES INTO THE TUE NIGHT TIMEFRAME AS MODELS ARE TRYING TO SIGNAL A WEAK WAVE MOVING ALONG THE FRONT... POSSIBLY BRINGING A DECENT SHOT OF PRECIP INTO CENTRAL AND EASTERN AREAS. SOME DISPARITY AS TO WHERE THIS WILL OCCUR. KEPT POPS ON HIGH END CHANCE CATEGORY...BUT FEEL HIGHEST WILL BE MAINLY ACROSS CENTRAL AND EASTERN MA INTO RI FOR NOW. EXPECT HIGHS ON TUESDAY TO BE MAINLY IN THE 60S...EXCEPT 50S ALONG IMMEDIATE S COAST...BUT ONLY IN THE 50S TO LOWER 60S DURING WED WITH CLOUD COVER AND PRECIP. CURRENT TIMING SUGGESTS BACK EDGE OF PRECIP SHOULD START TO SHIFT INTO WESTERN AREAS DURING WED AFTERNOON. WEDNESDAY NIGHT-THURSDAY... SOME TIMING ISSUES ON THE OPERATIONAL MODEL RUNS...BUT LOOKS TO BE DRYING OUT FROM W-E EARLY WED NIGHT...THEN HIGH PRES BUILDS IN OUT OF CENTRAL CANADA FOR THURSDAY. SOMEWHAT LOWER CONFIDENCE DURING THIS TIMEFRAME DUE TO TIMING. && .AVIATION /05Z FRIDAY THROUGH TUESDAY/...
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LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. MODERATE CONFIDENCE THROUGH TONIGHT...HIGHER CONFIDENCE INTO SAT... THERE IS THE CHANCE OF ANOTHER ROUND OF MVFR CIGS WRAPPING INTO AREAS S AND E OF A WST-PVD-BOS LINE. LOWER CONFIDENCE ON EXACTLY HOW DEEP IT GETS...BUT ONCE IT OCCURS IT WILL LIKELY LINGER INTO AT LEAST THE EARLY AFTERNOON AS NE WINDS VEER TO THE E. OUTSIDE OF THIS LINE...MAINLY VFR IS EXPECTED. BY LATE THIS AFTERNOON...WINDS W OF THE LINE SHIFT FROM THE S TO W AND WINDS E OF THE LINE BEGIN TO SHIFT TO THE S...SO ANY LINGERING MVFR CIGS SHOULD BEGIN TO SCT OUT. AFTER THAT MAINLY VFR IS EXPECTED OVERNIGHT INTO SAT ALTHOUGH WITH INCREASING HIGH AND MID CLOUDS DURING THE OVERNIGHT AND EARLY MORNING HOURS. ALTHOUGH THERE IS THE LOW PROBABILITY OF SOME MVFR/IFR FOG BEFORE WINDS SHIFT TO THE W AT COASTAL TERMINALS EARLY SAT MORNING. WINDS THEN SHIFT TO THE W SAT MORNING WITH WNW WIND GUSTS AROUND 20 KT BY MID DAY SAT. KBOS TERMINAL...MODERATE CONFIDENCE. MAIN ISSUE IS WHETHER AND FOR HOW LONG MVFR CIGS REMAIN IN PLAY LATER THIS MORNING. KBDL TERMINAL...HIGH CONFIDENCE. OUTLOOK...SATURDAY NIGHT THROUGH TUESDAY... SATURDAY NIGHT THROUGH MONDAY...HIGH CONFIDENCE. VFR. MONDAY NIGHT AND TUESDAY...MODERATE CONFIDENCE. VFR TO START. MAY SEE LOCAL MVFR IN SCT SHOWERS MOVING INTO S NH AND CENTRAL-W MA AFTER MIDNIGHT. WILL SEE AREAS OF LOW END MVFR CIGS/VSBYS THROUGH TUESDAY AS FRONT SLOWLY CROSSES THE REGION.
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&& .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH FRIDAY NIGHT/...HIGH CONFIDENCE. NE WINDS WILL DIMINISH THROUGH THIS EVENING. SEAS WILL TAKE THEIR TIME TO SUBSIDE HOWEVER GIVEN PERSISTENT NE FLOW THROUGH FRI. EXTENDED SCA PRIMARILY FOR SEAS MAINLY ON OUTER WATERS. THIS WILL ALSO RESULT IN LOW CLOUDS/PATCHY DRIZZLE ON WATERS LATER TONIGHT INTO FRI MORNING. SHOULD SEE MORE IN WAY OF FOG DEVELOPMENT FRI NIGHT...ESPECIALLY ON S COASTAL WATERS AS FLOW BECOMES MORE W/SW BUT IS LIGHT. SEAS SHOULD REMAIN ABOVE 5 FT ON OUTER WATERS. OUTLOOK...SATURDAY THROUGH TUESDAY... SATURDAY...EXPECT W-NW WINDS AT 15 KT OR LESS. SEAS REMAIN AOA 5 FT MAINLY OVER THE OPEN WATERS. SUNDAY...NE WINDS RETURN ACROSS THE WATERS AS HIGH PRES BUILDS TO THE N. GUSTS UP TO 20 KT EARLY. SEAS LINGER AROUND 5 FT ON THE EASTERN OUTER WATERS...THOUGH MAY SUBSIDE SUN NIGHT. MONDAY AND TUESDAY...EXPECT WINDS TO SHIFT FROM SE TO S-SW BUT REMAIN LIGHT...GENERALLY 15 KT OR LESS THROUGH THIS TIMEFRAME. MAY SEE SOME GUSTS UP TO 20 KT LATER TUESDAY. SEAS BELOW SMALL CRAFT CRITERIA. && .HYDROLOGY... MINOR FLOODING CONTINUES ALONG PORTIONS OF THE MAIN STEM CT RIVER. CREST HAS REACHED NORTHAMPTON AND IS FORECAST TO REACH THOMPSONVILLE THIS AFTERNOON AND HARTFORD TONIGHT. MODERATE FLOODING IS FORECAST ON LOWER REACHES NEAR MIDDLE HADDAM. FLOOD WARNINGS REMAIN POSTED ALONG CT RIVER AT... MONTAGUE NORTHAMPTON THOMPSONVILLE HARTFORD MIDDLE HADDAM THE STAGES ON THE PAWCATUCK RIVER WERE NEARING CREST. THE STAGE AT WESTERLY APPEARS TO BE CRESTING LATE THIS AFTERNOON...WHILE CLOSE TO CRESTING AT WOOD RIVER JUNCTION. && .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT EARLY THIS MORNING FOR ANZ235-237-251. SMALL CRAFT ADVISORY UNTIL 6 AM EDT SATURDAY FOR ANZ250-254- 255. SMALL CRAFT ADVISORY UNTIL 2 PM EDT THIS AFTERNOON FOR ANZ256.
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&& $$ SYNOPSIS...EVT/JWD NEAR TERM...DOODY/JWD SHORT TERM...JWD LONG TERM...EVT AVIATION...DOODY/EVT/JWD MARINE...EVT/JWD HYDROLOGY...

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