Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 140544 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 144 AM EDT SUN SEP 14 2014 .SYNOPSIS... HIGH PRESSURE OVER THE GREAT LAKES WILL BUILD INTO NEW ENGLAND OVERNIGHT BRINGING DRIER AIR TO THE REGION. THE HIGH SETTLES OVER THE NORTHEAST TODAY AND MONDAY PROVIDING SUNNY SKIES AND CLEAR NIGHTS WITH SLIGHTLY COOLER THAN 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. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... 130 AM UPDATE... SURFACE TROUGH AXIS/WIND SHIFT LINE HAS MOVED OFFSHORE AS OF 1 AM WITH WNW FLOW ADVECTING POST FRONTAL AIRMASS INTO NEW ENGLAND. DEW PTS FALLING INTO THE 40S FROM NORTHWEST CT/MA AND SOUTHWEST NH. SUFFICIENT MIXING TO PRECLUDE MUCH IF ANY FOG EARLY THIS MORNING. THE EXCEPTION IS ACROSS NASHUA NH AND SOME OTHER INTERIOR SPOTS. OTHERWISE AN UNEVENTFUL OVERNIGHT/PREDAWN HOURS. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM MONDAY/... 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. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... 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 ARCTIC 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 ENGLAND 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 THURSDAY 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. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. HIGH CONFIDENCE THRU MONDAY. TODAY...MVFR/IFR ACROSS RI/EASTERN MA AND SOUTHEAST NH WILL IMPROVE TO VFR BY 09Z. NNW WINDS MAY GUSTS UP TO 25 KT FROM 09Z TO 15Z THEN DIMINISH WITH AFTERNOON SEABREEZES POSSIBLE. TONIGHT...VFR ALONG WITH LIGHT WINDS. LOW RISK OF PATCHY MVFR INLAND IN FOG. MONDAY...VFR WITH LIGHT WINDS INTERIOR AND SEABREEZES ALONG THE COAST. KBOS TERMINAL...HIGH CONFIDENCE IN TAF EXCEPT FOR AFTERNOON WINDS. IFR/MVFR CONDITIONS IMPROVE TO VFR BY 09Z. SEABREEZE MAY DEVELOP THIS AFTERNOON BUT LOW CONFIDENCE. KBDL TERMINAL...HIGH CONFIDENCE IN TAF FOR VFR CONDITIONS. OUTLOOK...MONDAY NIGHT THROUGH THURSDAY...HIGH CONFIDENCE. MONDAY NIGHT...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. && .MARINE... 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. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY FROM 6 AM TO 11 AM EDT THIS MORNING FOR ANZ231-232-251-255. SMALL CRAFT ADVISORY FROM 6 AM THIS MORNING TO 4 PM EDT THIS AFTERNOON FOR ANZ250-254. && $$ SYNOPSIS...GAF/99 NEAR TERM...NOCERA SHORT TERM...GAF LONG TERM...99 AVIATION...NOCERA/99 MARINE...GAF/99

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