Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 252036 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 336 PM EST WED FEB 25 2015 .SYNOPSIS... HIGH PRESSURE WILL BUILD TO THE NORTH TONIGHT BRINGING DRY AND COLD CONDITIONS. A COASTAL STORM WILL TRACK WELL SOUTH OF NEW ENGLAND THURSDAY AND WILL BRING A PERIOD OF SNOW WITH MINOR ACCUMULATIONS TO COASTAL SECTIONS...ESPECIALLY THE CAPE AND ISLANDS. A REINFORCING SURGE OF COLD BUT DRY WEATHER RETURNS THURSDAY NIGHT THROUGH FRIDAY NIGHT. TEMPS SLOWLY MODERATE SAT AS HIGH PRES BUILDS INTO THE REGION...THEN A FRONTAL SYSTEM MAY BRING SOME SNOW LATE SUN INTO MON. && .NEAR TERM /THROUGH TONIGHT/... SFC RIDGING FROM ARCTIC HIGH PRES OVER THE PLAINS EXTENDS INTO SE CANADA TONIGHT. GUSTY WEST WINDS WILL DIMINISH THIS EVENING THEN TURN NORTHERLY LATE TONIGHT BRINGING COLD AND DRY CONDITIONS. CLEAR SKIES THIS EVENING WILL GIVE WAY TO INCREASING MID/HIGH CLOUDS OVERNIGHT AHEAD OF NEXT SHORTWAVE LIFTING NE TO THE MID ATLC COAST. THERE WILL BE A PERIOD OF GOOD RADIATIONAL COOLING THIS EVENING WITH DIMINISHING WIND AND CLEAR SKIES WHICH WILL ALLOW TEMPS TO DROP OFF QUICKLY BEFORE LEVELING OFF OVERNIGHT. USED A BLEND OF AVAILABLE MOS/MODEL GUIDANCE FOR MIN TEMPS WHICH YIELDS MINS IN THE TEENS ALONG THE COAST AND SINGLE NUMBERS AWAY FROM THE COAST. THERE IS A CHANCE OF A FEW LOCATIONS IN W MA DROPPING TO NEAR ZERO. && .SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/... THURSDAY... THERE IS CLUSTERING AMONG THE GUIDANCE WITH COASTAL LOW TRACKING WELL SOUTH OF THE BENCHMARK. NORMALLY A SUPPRESSED STORM TRACK LIKE THIS WOULD NOT PRODUCE ANY SNOW BUT THIS IS WINTER 2015 AND WE HAVE A FEW FACTORS THAT SUGGEST OTHERWISE. MODELS INDICATE DEEPENING MOISTURE THROUGH THE COLUMN WITH NEAR SATURATION AND WEAK OMEGA IN THE SNOW GROWTH REGION ASSOCD WITH MODEST LARGE SCALE FORCING AHEAD OF SHORTWAVE. THIS WILL LIKELY BRING SOME LIGHT SNOW TO THE REGION...ESPECIALLY NEAR THE COAST. THE UNCERTAINTY IS QPF AND SNOW AMOUNTS OVER THE CAPE/ISLANDS. ECMWF AND SREF BRING 0.25" TO ACK WITH 0.10" TO FAR SE MA WHILE NAM IS JUST A BIT LESS. GFS/GGEM ARE MUCH LIGHTER WITH QPF. WE HAVE ENOUGH CONFIDENCE THAT AT LEAST SOME MINOR ACCUM ARE LIKELY FOR THE CAPE/ISLANDS SO POPS WERE INCREASED HERE. USED A BLEND OF NAM/SREF/ECMWF/GFS QPF TO DERIVE SNOW ACCUM WHICH RESULTS IN 1-2 INCHES FOR CAPE COD AND UP TO 3 INCHES FOR ACK. A COATING TO AN INCH ELSEWHERE...MAINLY SOUTH OF THE MASS PIKE. SO NOT EXPECT ANY ACCUM TO THE NORTH ALTHOUGH SOME LIGHT FLURRIES IS POSSIBLE. OF PARTICULAR CONCERN IS THE HIRESWRF WHICH BRINGS 0.25" TO THE CAPE COD CANAL AND 0.50" TO ACK. WE ARE NOT READY TO JUMP ON THIS NOW BUT IT SHOWS POTENTIAL FOR HIGHER ACCUM AND WILL HAVE TO CLOSELY MONITOR TRENDS IN THE GUIDANCE. IT WILL BE A COLD DAY WITH TEMPS IN THE UPPER TEENS AND LOWER 20S...WITH MID/UPPER 20S CAPE/ISLANDS. THURSDAY NIGHT... COASTAL LOW PULLS AWAY WITH HIGH PRES BUILDING IN FROM THE WEST. MAINLY DRY CONDITIONS...BUT LOW LEVEL NORTHERLY FLOW AND STEEP LOW LEVEL LAPSE RATES OVER THE OCEAN WILL LIKELY RESULT IN SOME OCEAN EFFECT SNOW SHOWERS OVER CAPE COD. EXPECT LOTS OF CLOUDS AS MOISTURE IS FAIRLY ROBUST BELOW 700 MB. LOW LEVEL NORTHERLY FLOW TAPPING ARCTIC AIRMASS TO THE NORTH WILL RESULT IN ANOTHER COLD NIGHT WITH MINS IN THE SINGLE NUMBERS...WITH TEENS ALONG THE COAST. NEAR ZERO READING POSSIBLE IN W MA. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... HIGHLIGHTS... * OCEAN EFFECT SNOW POSSIBLE ON THE CAPE THURSDAY * HIGH PRESSURE EXPECTED THROUGH THE WEEKEND * COLD FRONT BRINGS WINTRY PRECIP SUNDAY INTO MONDAY * ANOTHER STORM POSSIBLE TUESDAY INTO WEDNESDAY OVERVIEW AND MODEL PREFERENCES... JUST SUBTLE ENOUGH OF A SHIFT IN THE OVERALL PATTERN TO SUPPRESS STORM TRACK BOTH TOO FAR SOUTH AND TOO FAR NORTH TO BRING ANY SIGNIFICANT STORMS TO NEW ENGLAND IN THE MID AND LONG TERMS. AO/NAO REMAIN PRIMARILY POSITIVE...SUGGESTING THAT THE PATTERN REMAINS PROGRESSIVE OFFSHORE. HOWEVER...NOW NOTE A NEGATIVE SHIFT IN THE PNA...WHICH HAS ALLOWED THE ATLANTIC RIDGE OF HIGH PRES JUST N OF THE EQUATOR TO RETROGRADE A BIT AND MORE STRONGLY INFLUENCE THE WX ACROSS SRN NEW ENGLAND. THIS SUPPRESSES THE FIRST COUPLE OF WAVES DIVING S FROM NRN QC BY STRETCHING THEM IN THE FAST FLOW CREATED BETWEEN THE RIDGE TO THE S AND THE LONGWAVE TROF OVER ERN CANADA. THIS PREVENTS THE RAPID DEEPENING OF MOST OF THESE SYSTEMS IN THE WEEKEND...SOMETHING EVEN THE ECENS/GEFS SHOW REASONABLE CLUSTERING ON. THE BIGGEST DIFFERENCES START EARLY NEXT WEEK AS THERE IS AN ATTEMPT TO JOIN THE SRN AND NRN STREAMS FROM THE GREAT LAKES INTO THE NE CONUS...WHICH COULD BETTER FEATURE LOW PRES EFFECTING THE REGION BEGINNING AS AN INSIDE RUNNER. DETAILS... SAT AND SUN... HIGH PRES REMAINS IN CONTROL CRESTING SAT NIGHT INTO EARLY SUN. MID AND UPPER LVL TEMPS REMAIN GENERALLY BELOW -10C UNTIL SUN...AT WHICH POINT SLIGHT WARM ADVECTION WILL ALLOW THEM TO REACH -6C OR SO. THEREFORE...MINS FRI AND SAT WILL BE GENERALLY IN THE NEGATIVE TO POSITIVE SINGLE DIGITS. HIGHS SAT WILL BE MAINLY BELOW NORMAL...BUT THEN CLOSER TO MAYBE EVEN SLIGHTLY ABOVE NORMAL ON SUN. SUN NIGHT INTO MON... LOW PRES PASSING WILL TO THE N WILL PUSH A COLD FRONT ACROSS THE REGION SUN NIGHT INTO MON. NOTING ENOUGH F-GEN WITH EVEN A POSSIBLE SUBTROPICAL MOISTURE CONNECTION. THEREFORE...EXPECT WIDESPREAD PRECIP ACROSS THE REGION. AT THIS TIME...IT APPEARS THE LOW-MID LVLS ARE COLD ENOUGH FOR SNOW...ESPECIALLY GIVEN DYNAMIC COOLING MAY BE ABLE TO OVERCOME DIURNAL WARMING MON MORNING. QPF VALUES REMAIN AT ISSUE GIVEN THAT SUBTROPICAL CONNECTION WHICH IS FEATURED IN SOME MODELS BUT NOT OTHERS. THEREFORE...SNOWFALL TOTALS COULD STAY BELOW OR JUST EXCEED ADVISORY LEVELS. TUE INTO WED... WILL NEED TO KEEP AN EYE ON YET ANOTHER INSIDE RUNNER WHICH WILL FORCE THE COLD FRONT STALLING OFFSHORE FROM MON...TO SHIFT N AS A WARM FRONT. OVERRUNNING SITUATION GIVEN THE DEEP SNOWPACK REMAIN ACROSS THE REGION AND COLD AIR LOCKED IN WITH 1035 HIGH PRES NEAR NEW BRUNSWICK SUGGEST P-TYPE ISSUES WHICH WILL HAVE TO BE WATCHED. THIS SYSTEM IS STRONGER AND HAS AN EVEN BETTER CONNECTION TO SUBTROPICAL MOISTURE THAN DOES THE PREVIOUS SO THIS WILL LIKELY BE THE SYSTEM TO WATCH AS IT APPROACHES. && .AVIATION /20Z WEDNESDAY THROUGH MONDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /TODAY THROUGH WEDNESDAY NIGHT/... THROUGH TONIGHT...HIGH CONFIDENCE. VFR. W WIND GUSTS TO 25 KT THIS AFTERNOON...DIMINISHING THIS EVENING. THURSDAY...MODERATE CONFIDENCE. AREAS OF MVFR DEVELOPING IN LIGHT SNOW...ESPECIALLY NEAR THE COAST. AREAS OF IFR AND HEAVIER SNOW POSSIBLE CAPE/ISLANDS. THURSDAY NIGHT...MAINLY VFR...BUT AREAS OF MVFR CIGS ALONG WITH A CHANCE OF OCEAN EFFECT SNOW SHOWERS OVER THE CAPE/ISLANDS. KBOS TAF...LOWER CONFIDENCE WED IN THE POTENTIAL FOR BRIEF MVFR IN LIGHT SNOW. KBDL TAF...LOWER CONFIDENCE WED IN THE POTENTIAL FOR BRIEF MVFR IN LIGHT SNOW. OUTLOOK...THURSDAY NIGHT THROUGH SUNDAY... THU NIGHT AND FRI...HIGH CONFIDENCE. MAINLY VFR. ALTHOUGH PERIODS OF MVFR/IFR POSSIBLE MAINLY FOR CAPE COD TERMINALS IN OCEAN EFFECT SNOWS. SAT AND SUN...HIGH CONFIDENCE. MAINLY VFR. ALTHOUGH SOME SNOW IS POSSIBLE LATE SUN FROM W TO E WITH MVFR/IFR CONDITIONS POSSIBLE. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH THURSDAY NIGHT/...HIGH CONFIDENCE. TONIGHT...WINDS DIMINISH BELOW SCA THIS EVENING...BUT SCA SEAS WILL LINGER OVER THE OUTER WATERS FOR MUCH OF THE NIGHT. THURSDAY...NE WINDS INCREASE TO 15-20 KT AS OCEAN STORM TRACKS WELL S OF THE WATERS. A FEW G25 KT POSSIBLE OVER THE SOUTHERN WATERS. VSBYS REDUCED IN SNOW ESPECIALLY OVER THE WATERS EAST AND SOUTH OF CAPE COD. THURSDAY NIGHT...DIMINISHING N WINDS BUT LINGERING SCA SEAS PERSIST OVER THE OUTER WATERS. OUTLOOK...FRIDAY THROUGH SUNDAY... THU AND FRI...MODERATE CONFIDENCE. LEFTOVER AND LINGERING SWELL CAUSED BY LOW PRES MOVING WELL OFFSHORE MAY REQUIRE SMALL CRAFT ADVISORY HEADLINES ON THE OCEAN WATERS...WHERE WAVES COULD REACH 5-6FT AT TIMES. WINDS HOWEVER...OUT OF THE N...NE WILL REMAIN BELOW 25 KT. SAT AND SUN...MODERATE CONFIDENCE. A PERIOD OF MAINLY QUIET BOATING WEATHER EXPECTED AS HIGH PRES MOVES OVER THE WATERS. WINDS AND SEAS MAINLY BELOW SMALL CRAFT ADVISORY HEADLINES. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EST THIS EVENING FOR ANZ232>237. SMALL CRAFT ADVISORY UNTIL 10 PM EST THIS EVENING FOR ANZ230. SMALL CRAFT ADVISORY UNTIL 1 AM EST THURSDAY FOR ANZ231-251. SMALL CRAFT ADVISORY UNTIL 6 AM EST THURSDAY FOR ANZ250- 254>256. && $$ SYNOPSIS...KJC NEAR TERM...KJC SHORT TERM...KJC LONG TERM...DOODY AVIATION...KJC/DOODY MARINE...KJC/DOODY

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