Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 252345 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 645 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 AND POSSIBLY FOLLOWED BY ADDITIONAL SNOW OR MIXED SNOW AND RAIN TUE NIGHT INTO WED. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... 645 PM UPDATE...MADE ONLY MINOR UPDATES TO THE FORECAST TO ACCOUNT FOR THE LATEST TRENDS. OTHERWISE...THE FORECAST IS ON TRACK. 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 /6 AM THURSDAY MORNING 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... * COLD AND MAINLY DRY FRIDAY THROUGH SUNDAY MORNING * CHANCE OF SNOW SUNDAY NIGHT INTO MONDAY * CHANCE OF SNOW POSSIBLY MIXING WITH RAIN TUESDAY NIGHT AND WEDNESDAY OVERVIEW... LARGE SCALE PATTERN CONTINUES TO FEATURE NORTHERN AND SOUTHERN STREAMS. WESTERN RIDGE RETROGRADES FOR A TIME BUT SEEMS TO BUILD BACK LATER IN THE FORECAST PERIOD...ALBEIT POSSIBLY NOT QUITE SO STRONGLY. A COUPLE OF SHORT WAVES DIG SOUTH ALONG THE WEST COAST AND EVENTUALLY WILL EJECT SHORT WAVES IN THE SOUTHERN STREAM FLOW. NORTHERN STREAM APPEARS TO REMAIN QUITE ACTIVE HOWEVER AND MAY BE THE DOMINANT FLOW FOR OUR REGION. A COLDER TREND IN THE MEDIUM RANGE MODELS FOR NEXT WEEK SUGGESTS A TREND TOWARD A SOMEWHAT MORE DOMINANT NORTHERN STREAM. NONETHELESS...THIS COULD CHANGE IN EITHER DIRECTION DEPENDING HOW MUCH ENERGY DROPS SOUTH ALONG THE WEST COAST AND HOW MUCH ENERGY REMAINS IN THE NORTHERN STREAM. THE OTHER FACTOR THAT COULD SIGNIFICANTLY IMPACT OUR SENSIBLE WEATHER IS TO WHAT DEGREE THERE IS ANY PHASING BETWEEN THE NORTHERN AND SOUTHERN STREAMS. GIVEN THE SENSITIVITY TO DEVELOPMENTS OVER WESTERN CANADA AND THE NORTHEAST PACIFIC OVER THE NEXT SEVERAL DAYS...CONFIDENCE IN OUTCOMES FROM SUNDAY NIGHT TO WEDNESDAY REMAIN ONLY MODERATE. DAY TO DAY... FRIDAY THROUGH SUNDAY MORNING...FAIRLY CONFIDENT OF DRY CONDITIONS THROUGH THIS PERIOD WITH THE POSSIBLE EXCEPTION OF SOME LINGERING OCEAN EFFECT SNOW SHOWERS OR FLURRIES ALONG OR JUST OFF THE OUTER CAPE AND NANTUCKET COAST DURING FRIDAY. ANTICIPATE A GRADUAL MODERATION IN DAYTIME TEMPERATURES BUT CHILLY TEMPERATURES BOTH FRIDAY NIGHT AND SATURDAY NIGHT GIVEN CLEAR SKIES AND A DEEP SNOWPACK. THERE REMAINS SOME NORTHWEST FLOW FRIDAY NIGHT SO SOME MIXING POSSIBLE. HOWEVER...THINK SOME INTERIOR VALLEYS WILL DECOUPLE COMPLETELY AND MAY SEE A FREE FALL IN TEMPERATURES. FOR SATURDAY NIGHT...ANTICIPATE SKIES TO REMAIN MOSTLY CLEAR EXCEPT FOR POSSIBLY SOME HIGH CLOUDS SPILLING OVER A FLAT UPPER RIDGE IN THE WEST. WINDS ARE EXPECTED TO BE STILL LIGHTER SATURDAY NIGHT AND SO EFFECTIVE RADIATIONAL COOLING IS LIKELY IF NOT TOO MANY HIGH CLOUDS MOVE IN. HAVE GONE A FEW DEGREES BELOW A MODEL CONSENSUS FOR BOTH FRIDAY AND SATURDAY NIGHTS WITH MANY INTERIOR LOCATIONS DROPPING BELOW ZERO BOTH NIGHTS. SUNDAY AFTERNOON THROUGH MONDAY...CLOUDS INCREASE SUNDAY AFTERNOON IN ADVANCE OF AN APPROACHING UPPER TROF AND ARCTIC FRONT. ONE OR MORE WEAK WAVES MAY DEVELOP ALONG THIS FRONTAL BOUNDARY AND PRODUCE A LIGHT TO POSSIBLY MODERATE SNOWFALL EPISODE ACROSS SOUTHERN NEW ENGLAND. COLD AIR ADVECTION TAKES HOLD DURING MONDAY BUT PROBABLY NOT BEFORE SURFACE TEMPERATURES HAVE AN OPPORTUNITY TO RISE INTO THE MID 30S...HELPED ALONG BY A HIGHER SUN ANGLE SHOULD CLOUDS BREAK IN TIME. MONDAY NIGHT THROUGH TUESDAY...THIS TIME PERIOD LOOKS TO BE DRY WITH BELOW NORMAL TEMPERATURES AS A RELATIVELY STRONG HIGH PRESSURE AREAS DRIFTS ACROSS ONTARIO AND QUEBEC. TUESDAY NIGHT THROUGH WEDNESDAY...MEDIUM RANGE MODELS HAVE BEEN CONSISTENT OVER THE PAST FEW DAYS IN ADVERTISING A SOUTHERN STREAM SYSTEM APPROACHING NEW ENGLAND FROM THE SOUTHWEST. A THEME HAS BEEN FOR THE OPERATIONAL MODELS TO DEPICT A PRIMARY SYSTEM MOVING UP THE OHIO VALLEY WITH SECONDARY DEVELOPMENT ALONG A WARM FRONT NEAR THE MID ATLANTIC COAST. THERE HAS BEEN A TENDENCY TOWARD A COLDER SOLUTION IN RECENT RUNS...LIKELY REFLECTING A MORE DOMINANT NORTHERN STREAM FLOW...AND THE 12Z ECMWF GOES SO FAR AS TO SUPPRESS THE PRECIPITATION SHIELD JUST SOUTH OF NEW ENGLAND. GIVEN VARIATIONS IN MODEL SUCCESSIVE RUNS...CONFIDENCE IS NOT PARTICULARLY HIGH FOR THIS TIME PERIOD. FOR NOW...HAVE CHANCE POPS THROUGHOUT THE FORECAST AREA FOR MOST OF TUESDAY NIGHT AND WEDNESDAY AND HAVE LEANED TOWARD MORE SNOW THAN RAIN FOR THE FORECAST AREA. WE ARE LIKELY...HOWEVER...TO SEE A NUMBER OF DIFFERENT ITERATIONS IN SUBSEQUENT OPERATIONAL AND EVEN ENSEMBLE MODEL RUNS. && .AVIATION /00Z THURSDAY 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/... TONIGHT...HIGH CONFIDENCE. VFR. W WIND GUSTS 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...FRIDAY THROUGH MONDAY... FRIDAY THROUGH SUNDAY...HIGH CONFIDENCE FOR VFR CONDITIONS. SUNDAY NIGHT THROUGH MONDAY. MODERATE CONFIDENCE. MVFR CONDITIONS LIKELY DEVELOPING IN SNOW SUN NIGHT WITH AREAS OF IFR CIGS AND VSBYS POSSIBLE PERSISTING INTO MON MORNING. CONDITIONS IMPROVING TO VFR MON AFTERNOON. && .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 MONDAY... MODERATE TO HIGH CONFIDENCE. WINDS ARE EXPECTED TO BE MOSTLY UNDER SMALL CRAFT ADVISORY CONDITIONS THROUGH SUNDAY ALTHOUGH SEAS ACROSS THE OUTER WATERS MAY REMAIN NEAR OR A LITTLE ABOVE 5 FEET FRIDAY. NORTHWEST WINDS WILL LIKELY GUST ABOVE SMALL CRAFT ADVISORY THRESHOLDS MONDAY AND PERHAPS EVEN APPROACH MINIMAL GALE GUSTS LATE IN THE DAY. THERE IS ALSO A CHANCE OF FREEZING SPRAY OVER SOME OF THE WATERS MONDAY EVENING. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. RI...NONE. MARINE...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/THOMPSON NEAR TERM...KJC/RLG SHORT TERM...KJC LONG TERM...THOMPSON AVIATION...KJC/RLG/THOMPSON MARINE...KJC/THOMPSON

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