Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 132030 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 430 PM EDT SAT SEP 13 2014 .SYNOPSIS...
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LOW PRESSURE SYSTEM WILL MOVE FROM THE SAINT LAWRENCE RIVER REGION NORTHEAST INTO SOUTHEAST QUEBEC TONIGHT. ANOTHER LOW SOUTH OF LONG ISLAND WILL PASS EAST OF NANTUCKET OVERNIGHT. THESE TWO SYSTEMS WILL BRING LIGHT RAIN TO SOUTHERN NEW ENGLAND BEFORE MIDNIGHT. HIGH PRESSURE WILL BRING SUNNY SKIES AND CLEAR NIGHTS SUNDAY INTO MONDAY WITH SLIGHTLY BELOW NORMAL TEMPERATURES. A COLD FRONT WILL LIKELY BRING A PERIOD OF SHOWERS LATE MONDAY NIGHT INTO TUESDAY. MAINLY DRY WEATHER EXPECTED NEXT WEDNESDAY THROUGH FRIDAY WITH SLIGHTLY BELOW NORMAL TEMPERATURES CONTINUING.
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&& .NEAR TERM /UNTIL 6 AM SUNDAY/...
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4 PM UPDATE... LIGHT RAIN HAD OVERSPREAD SOUTHERN NH...WESTERN AND CENTRAL MA... AND WESTERN CT. THERE WERE A FEW PATCHES OF MODERATE RAIN EMBEDDED IN THIS AREA. THE RAIN AREA WILL OVERSPREAD MOST OF THE REGION THIS EVENING. AM EXPECTING A FEW TENTHS OF AN INCH OF RAINFALL. MODELS ARE EMPHATIC AT LINKING MOISTURE FROM THE LOW SOUTH OF THE REGION WITH THIS BAND OF MOISTURE WHEN IT GETS OVER SOUTHEAST MA. WE STILL HAVE NOT SEEN ANY INCREASE TO OUR SOUTH HOWEVER. WE ARE NOT EXPECTING THE CONVECTION OVER THE SYRACUSE NY AREA TO REACH SOUTHERN NEW ENGLAND. EAST WINDS WILL TURN TO THE NORTH AND NORTHWEST ONCE THE LOW PASSES EAST OF NANTUCKET OVERNIGHT. SKIES ARE FORECAST TO CLEAR OUT FROM WEST TO EAST AFTER MIDNIGHT BUT THERE COULD BE SOME SCATTERED FOG PATCHES DEVELOPING DUE TO THE EARLIER RAINFALL. TOWARD DAYBREAK...WINDS MAY BRIEFLY GUST TO 20 TO 25 MPH ESPECIALLY NEAR THE COAST. OVERNIGHT LOWS WILL RANGE FROM THE MID 40S IN SW NH AND NW MA...TO THE UPPER 50S NEAR THE CAPE AND ISLANDS.
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&& .SHORT TERM /6 AM SUNDAY THROUGH 6 AM MONDAY/...
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SUNDAY...NORTHWEST WINDS MAY GUST TO 20 TO 25 MPH IN RI AND EASTERN MA EARLY IN THE MORNING FOR A FEW HOURS DUE TO THE GRADIENT BEHIND DEPARTING LOW PRESSURE AND ADVANCING STRONG HIGH PRESSURE...THEN WINDS WILL DROP OFF. OTHERWISE...A BRIGHT SUNNY DAY IS IN STORE WITH HIGH TEMPERATURES 65 TO 70 EXCEPT 60 TO 65 IN SOUTHERN NH. SUNDAY NIGHT...CRYSTAL CLEAR SKIES WILL ALLOW FOR GOOD RADIATIONAL COOLING. OVERNIGHT LOWS WILL MAINLY BE IN THE 40S BUT COULD DIP INTO THE UPPER 30S IN SOUTHWEST NH. THERE IS A VERY LOW PROBABILITY THAT SOME FROST COULD FORM IN SOUTHWEST NH.
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&& .LONG TERM /MONDAY THROUGH SATURDAY/...
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HIGHLIGHTS... *SHOWERS POSSIBLE FROM COLD FRONTAL PASSAGE MON NIGHT/TUE *BELOW NORMAL TEMPS OBSERVED AFTER LATE WEEK FRONTAL PASSAGE *LESS HUMIDITY AS DEW POINTS ARE BELOW 60F FOR THE ENTIRE PERIOD OVERVIEW... THIS PERIOD IS CHARACTERIZED BY A RIDGE IN THE WEST AND A TROUGH IN THE EAST OR THE TYPICAL POSITIVE PNA PATTERN AT LEAST TO START. WITH THE UPPER LEVEL LOW PRESSURE SYSTEM DROPPING SOUTH OUT OF CANADA...EXPECT THE ARTIC OSCILLATION TO DROP MORE NEGATIVE. ALSO EXPECTING THE NAO TO DROP FROM POSITIVE TO MORE NEUTRAL INDICATING A SLOWING PATTERN. MODELS HANDLE THIS PERIOD FAIRLY WELL AND WITH ADEQUATE AGREEMENT ASIDE FROM THE HANDLING OF A SHORTWAVE THAT MOVES THROUGH THE REGION. THE 6Z GFS IS FASTER AND WEAKER WITH THE MOVEMENT OF THAT SHORTWAVE THROUGH THE REGION THAN THE ECMWF. THE LATTER HAS A STRONGER SHORTWAVE...WHICH FORMS A LOW PRESSURE SYSTEM SOUTH OF THE AREA. HAVE GONE WITH A BLEND OF THE MODELS TO ELIMINATE THE GFS BIAS TOWARDS QUICKER EVOLUTION THROUGH THE REGION AND THE HEAVIER PRECIPITATION FROM THE ECMWF. LATER IN THE PERIOD...A COLD FRONT PUSHES SOUTH THROUGH NEW ENGALND WITH MORE MODEL DISAGREEMENT. THE ECMWF ALLOWS FOR A LATER PASSAGE OF THE FRONT LATE THURSDAY NIGHT WHILE THE GFS PUSHES IT THROUGH LATE WEDNESDAY/EARLY THURSDAY. FOLLOWING THE ENSEMBLES AND WPC...HAVE GONE WITH AN EARLY THURSDAY FRONTAL PASSAGE. DAILIES... MONDAY...A HIGH PRESSURE SYSTEM MOVES FROM WEST TO EAST CHANGING WINDS TO THE SOUTHWEST AHEAD OF A SHORTWAVE FROM CANADA. WITH MIXING UP TO AROUND 850 MB THAT WOULD GIVE HIGH TEMPS IN THE MID TO UPPER 60S TUESDAY...EVEN WITH THE SOUTHWEST WARMING WINDS...THE HUMIDITY REMAINS LOW WITH PWATS ONLY AROUND 1 INCH AND THE TOTAL OF TOTALS ONLY AROUND 40. FEEL A LOWER END EVENT MAY OCCUR FROM THIS WITH THE QUICK MOVING LOW PRESSURE SYSTEM. HAVE LEANED AWAY FROM THE ECMWF...BUT FEEL THE GFS MAY BE TOO LOW. ALSO DON/T SEE MUCH IN THE WAY OF INSTABILITY FOR THUNDER. WEDNESDAY THROUGH FRIDAY...AREAS OF HIGH PRESSURE PINWHEEL AROUND THE UPPER LEVEL LOW IN SOUTHEASTERN CANADA. A COLD FRONT LOOKS TO PASS THROUGH EARLY THURSDAY WITH TEMPERATURES AS COLD AS JUST OVER 2 SDS BELOW NORMAL AT 850MB OR 1.5 KM INTO THE SKY. AM EXPECTING A FEW CUMULUS CLOUDS TO BE AROUND...BUT NOT OVERCAST AT ALL. BEST CHANCE TO SEE THURDSAY OVERNIGHT TEMPS DIP BELOW 40F AND WOULD THEREFORE HAVE TO WATCH FOR FROST IN THOSE AREAS...NAMELY NORTHWESTERN MA AND SOUTHEASTERN NH. SATURDAY...THE 6Z GFS IS SHOWING A COLD FRONT...BUT WITH THE NAO BEGINNING TO GO NEGATIVE AND INDICATING A SLOWING PATTERN...WILL STICK WITH WHAT THE ECMWF AND OTHER ENSEMBLE MODELS ARE SHOWING AND ALLOW HIGH PRESSURE TO SLOWLY EXIT THE REGION.
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&& .AVIATION /20Z SATURDAY THROUGH THURSDAY/...
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FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. CONFIDENCE IS MODERATE FOR TONIGHT...THEN HIGH FOR SUNDAY AND SUNDAY NIGHT. TONIGHT...LIGHT RAIN WITH EMBEDDED AREAS OF MODERATE RAIN. CEILINGS/VSBYS MAINLY IN THE MVFR RANGE BUT A FEW PLACES COULD HAVE IFR NEAR 3 MILES IN RAIN AND FOG. THE RAIN WILL END FROM WEST TO EAST IN THE 02Z TO 06Z TIME FRAME. MODELS SHOW SOME IFR CEILINGS POSSIBLE OVER NANTUCKET AND THE OUTER CAPE LATE TONIGHT. FOG PATCHES MAY REDEVELOP FOR A WHILE LATE TONIGHT BUT BELIEVE LOWERING DEWPOINTS AND MIXING IN THE NW GRADIENT WILL RESULT IN VFR CONDITIONS TAKING HOLD MOST AREAS LATE. WINDS COULD GUST TO 20 KT TOWARD DAYBREAK. SUNDAY AND SUNDAY NIGHT...VFR WITH CLEAR SKIES AND EXCELLENT VISIBILITY. KBOS TERMINAL...MODERATE TO HIGH CONFIDENCE. GENERALLY MVFR/VFR CONDITIONS. LIGHT RAIN MOVING INTO AROUND 22Z AND CONTINUING THROUGH ABOUT 02-03Z. CLEARING SKIES AFTER 06Z. NE WINDS SHIFTING TO THE NW AND GUSTING UP TO 22 KT AFTER 09Z. VFR WITH DIMINISHING WINDS SUNDAY. KBDL TERMINAL...MODERATE TO HIGH CONFIDENCE. GENERALLY MVFR/VFR CONDITIONS IN LIGHT TO OCCASIONALLY MODERATE RAIN THROUGH 02Z. SKIES CLEARING 03-05Z. VFR SUNDAY. OUTLOOK...MONDAY THROUGH THURSDAY...HIGH CONFIDENCE. MONDAY...VFR CONDITIONS EXPECTED. TUESDAY...SHOWERS BEGIN IN THE EARLY MORNING HOURS WITH MVFR CONDITIONS EXPECTED. THEN BECOMING VFR AS SHOWERS EXIT IN THE MID AFTERNOON HOURS. WEDNESDAY AND THURSDAY...VFR CONDITIONS EXPECTED.
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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. FORECAST CONFIDENCE IS MODERATE TONIGHT THROUGH SUNDAY NIGHT. TONIGHT...E WINDS 15 TO 20 KT WITH SOME HIGHER GUSTS ALONG THE COAST WILL SHIFT TO THE N AND NW WELL AFTER MIDNIGHT AS LOW PRESSURE SOUTH OF LONG ISLAND MOVES NE AND PASSES TO THE E OF NANTUCKET. A BAND OF LIGHT TO OCCASIONALLY MODERATE RAIN WILL PASS OVER THE WATERS AND MAY RESTRICT VISIBILITIES MAINLY TO 3 TO 5 MILES. SUNDAY...THE GRADIENT BETWEEN THE DEPARTING LOW PRESSURE AND ADVANCING STRONG HIGH PRESSURE MAY CAUSE A BRIEF PERIOD OF NW WIND GUSTS TO 25 KT WITHIN A FEW HOURS EITHER SIDE OF DAYBREAK SUNDAY. AS A RESULT A SMALL CRAFT ADVISORY HAS BEEN ISSUED FOR THE EASTERN MA COASTAL WATERS. THE WINDS SHOULD DIMINISH BY LATE MORNING...BUT SEAS COULD LINGER NEAR 5 FT OVER THE OUTER WATERS EAST OF MA...SO THE SMALL CRAFT ADVISORY EXTENDS INTO THE AFTERNOON FOR THOSE AREAS. SUNDAY NIGHT...WINDS AND SEAS BELOW SMALL CRAFT ADVISORY CRITERIA. OUTLOOK...MONDAY THROUGH THURSDAY... MONDAY INTO TUE MORNING...MODERATE TO HIGH CONFIDENCE. HIGH PRESSURE NEARBY WILL RESULT IN A WEAK PRESSURE GRADIENT KEEPING WINDS/SEAS BELOW SCA THRESHOLDS. TUESDAY AFTERNOON INTO WEDNESDAY...MODERATE CONFIDENCE. SWELLS BEGIN TO BUILD TO BETWEEN 5 AND 7FT BEHIND THE DEPARTING LOW PRESSURE SYSTEM AND COLD FRONT. THIS IS ABOVE SCA LEVELS AND THEREFORE A SCA MAY BE NEED. THURSDAY...AS NEXT HIGH PRESSURE SYSTEM APPROACHES WITH WEAKER PRESSURE GRADIENT...EXPECT SWELLS TO DIE DOWN DURING THE DAY TO BELOW SCA THRESHOLD.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY FROM 6 AM TO 11 AM EDT SUNDAY FOR ANZ231- 232-251-255. SMALL CRAFT ADVISORY FROM 6 AM TO 4 PM EDT SUNDAY FOR ANZ250- 254.
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&& $$ SYNOPSIS...FIELD/FRANK/HR NEAR TERM...FIELD SHORT TERM...FIELD LONG TERM...FRANK/HR AVIATION...FIELD/FRANK/HR MARINE...FIELD/FRANK/HR

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