Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 250249 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 948 PM EST TUE FEB 24 2015 .SYNOPSIS... FAST MOVING LOW PRESSURE WILL BRING A PLOWABLE SNOWFALL TO RHODE ISLAND AND EASTERN MASSACHUSETTS LATE TONIGHT INTO VERY EARLY WEDNESDAY MORNING. A REINFORCING SURGE OF COLD BUT DRY WEATHER RETURNS WEDNESDAY NIGHT THROUGH FRI 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 /UNTIL 6 AM WEDNESDAY MORNING/... *** PLOWABLE SNOW ACROSS EASTERN MA/RI LATE TONIGHT BUT SHOULD BE OVER FOR MOST BY THE WEDNESDAY MORNING COMMUTE *** 945 PM UPDATE... VERY LIGHT SNOW SHOWERS AND FLURRIES HAS BROKEN OUT ACROSS MUCH OF THE REGION. LOOKS LIKE SOME SHALLOW LIFT OVER THE ARCTIC DOME AT THE SURFACE WITH EVEN SOME OCEAN EFFECT ON SOUTH WINDS THE RESULT. NOT REALLY EXPECTING MUCH MORE THAN A COATING OR SO FROM THIS ACTIVITY. THE MAIN UNCERTAINTY ARE THE RADAR RETURNS BLOSSOMING SOUTH OF LONG ISLAND. THE HRRR/RAP HAVE VERY LITTLE SNOW MAKING IT NORTHWEST OF EVEN THE CAPE COD CANAL. THIS CERTAINLY IS CONCERNING...BUT WE ARE NOT READY TO COMPLETELY BITE ON THOSE SOLUTIONS BASED ON BLOSSOMING RADAR. THE REST OF THE GUIDANCE HAS ABOUT 0.10 TO 0.20 INCHES OF QPF ALONG THE BOS TO PVD CORRIDOR POINTS SOUTH AND EAST. GIVEN A PERIOD OF GOOD LIFT IN THE SNOW GROWTH REGION RESULTING IN DECENT RATIOS...COULD EASILY TRANSLATE TO 1 TO 4 INCHES OF SNOW. HOWEVER...IF THINGS END UP SHIFTING EAST BY 20 OR SO MILES AT THE LAST SECOND MUCH OF THE ADVISORY AREA WOULD BE LOOKING AT JUST A COATING TO 1 INCH. ALL IN ALL...BASED ON THE LATEST RADAR TRENDS AND 00Z NAM NOT PLANNING TO MAKE ANY CHANGES TO THE GOING FORECAST. IF WE START TO SEE THE RADAR RETURNS TAKE A MORE EASTERLY TRAJECTORY AND THE OTHER 00Z GUIDANCE BACK OFF AS WELL...WILL HAVE TO LOWER SNOW ACCUMS. HOWEVER...JUST NOT ENOUGH CONFIDENCE TO MAKE CHANGES AT THIS TIME ESPECIALLY WITH THOSE IMPRESSIVE RETURNS LIGHTING UP SOUTH OF LONG ISLAND. PREVIOUS DISCUSSION... SYNOPTIC OVERVIEW... IMPRESSIVE NORTHERN STREAM SHORT WAVE TRAVERSING THE GREAT LAKES PER LATEST WATER VAPOR IMAGERY. GOOD MODEL AGREEMENT ON STRONG SYNOPTIC SCALE FORCING /MID LEVEL Q-VECTOR CONVERGENCE/ WITH THIS FEATURE AS IT CROSSES THE AREA TONIGHT...CENTERED ON 06Z. THE SHORT WAVE TROUGH HAS SUFFICIENT AMPLITUDE TO THE BACK THE MID LEVEL ENOUGH TO CAPTURE SOUTHERN STREAM MOISTURE SOUTH OF NEW ENGLAND. IN TURN THIS INDUCES AN INVERTED TROUGH OVER THE AREA EXTENDING FROM A SOUTHERN STREAM SYSTEM TRACKING WELL SOUTH OF NEW ENGLAND. THIS IS AN INDICATION OF THE STRONG FORCING FOR ASCENT FROM THIS NORTHERN STREAM SHORT WAVE. TIMING...SNOW ACCUMULATIONS...UNCERTAINTY AND HEADLINES... GOOD MODEL AGREEMENT ON SNOW COMING ONSHORE TO THE SOUTH COAST OF MA AND RI BETWEEN 10 PM AND MIDNIGHT...THEN QUICKLY OVERSPREADING THE REMAINDER OF THE AREA AFTER MIDNIGHT. HEAVIEST SNOW FALLS APPROXIMATELY 2 AM TO 5 AM FROM SW TO NE AND THEN TAPERS OFF BY 6-7 AM. THIS SYSTEM REMAINS VERY PROGRESSIVE AND TYPICALLY WOULD NOT PRODUCE MUCH SNOWFALL. HOWEVER AS NOTED BY PREVIOUS FORECASTERS THERE ARE SEVERAL ATTRIBUTES THAT SUPPORT A 2-4" SNOWFALL FOR MUCH OF RI AND EASTERN MA. THIS INCLUDES BRIEF BUT STRONG SYNOPTIC SCALE FORCING...MODEST MID LEVEL FGEN COLLOCATED WITH AN AREA OF WEAK INSTABILITY /-EPV/ AND RELATIVELY HIGH SLR PER GOOD LIFT IN THE SNOW GROWTH REGION. SO WHILE HEAVIEST QPF /0.20-0.35/ IS OVER CAPE COD AND THE ISLANDS...WARMING BLYR WILL YIELD LOWER SLR AND POSSIBLY RAIN MIXING IN FOR A TIME AT NANTUCKET. FARTHER INLAND SPECIFICALLY THE I-95 CORRIDOR OF RI AND EASTERN MA INCLUDING THE BOS-PVD CORRIDOR...MLVL FGEN/MESOSCALE SNOW BAND AND HIGHER SLR WILL LIKELY RESULT IN HIGHER SNOWFALL THAN MODEL QPF SUGGEST. IN FACT HIGHEST SNOW TOTALS LIKELY OCCUR SOMEWHERE ALONG THE I-95 CORRIDOR SOUTHEAST TO THE CAPE COD CANAL PER MID LEVEL BANDING SIGNATURE AND GOOD SNOW GROWTH. THUS OUR SNOW GRAPHIC HAS A LARGE AREA OF 2-4" SNOWFALL FROM BOS-PVD SOUTHEAST TO THE CAPE. IF ALL PARAMETERS ABOVE COME TOGETHER YIELDING A MORE ROBUST MESOSCALE SNOW BAND THERE IS A LOW RISK FOR A FEW LOCATIONS COMING CLOSE TO 5 OR 6". HOWEVER THE MORE LIKELY SCENARIO IS FOR 2-4". THUS NO CHANGE FROM PREVIOUS HEADLINES. CHARACTER OF THE SNOW WILL BE DRY/FLUFFY EXCEPT A BIT WETTER/HEAVIER FOR THE OUTER CAPE AND ISLANDS. THERE WILL BE A SHARP CUTOFF TO THE WEST SPECIFICALLY NW OF BOS-PVD AND VERY LITTLE IF ANY SNOW WEST OF I-91/CT RVR VLY. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... WEDNESDAY... ANY SNOW AT SUNRISE WILL BE CONFINED TO EXTREME EASTERN MA AND WILL EXIT OFFSHORE BY 7 AM...PERHAPS 8 AM FOR OUTER CAPE COD AND CAPE ANN. BEHIND THE DEPARTING SHORT WAVE NW WINDS PICK UP TO 20-30 MPH BY MIDDAY AND CONTINUE INTO THE AFTERNOON. SO DESPITE TEMPS CLIMBING INTO THE U20S AND L30S...A GUSTY NW WIND WILL PROVIDE A BIT OF A WIND CHILL. ALTHOUGH NOT NEARLY AS COLD AS WE HAVE EXPERIENCED RECENTLY. SUNSHINE DEVELOPS BY MID TO LATE MORNING. WED NIGHT... A TRAILING SHORT WAVE TROUGH BRINGS A REINFORCING SURGE OF COLD AIR TO THE REGION...ALTHOUGH NOT NEARLY AS COLD AS RECENT DAYS. MIN TEMPS BY SUNRISE THU WILL BE IN THE SINGLE DIGITS INLAND...AROUND 10 BOSTON AND PROVIDENCE TO TEENS ALONG THE SOUTH COAST...CAPE COD AND ISLANDS. && .LONG TERM /THURSDAY THROUGH TUESDAY/... 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 MODELS ARE IN FAIRLY GOOD AGREEMENT THROUGH THE WEEKEND. THEN THEY DIVERGE A BIT...PARTICULARLY WITH A LOW PRESSURE SYSTEM EXPECTED TO IMPACT SOUTHERN NEW ENGLAND ON TUESDAY. HIGH PRESSURE BUILDS INTO SOUTHERN NEW ENGLAND FROM THE MIDWEST THROUGH SATURDAY. THEN THE HIGH PRESSURE MOVES OFFSHORE...ALLOWING LOW PRESSURE TO MOVE THROUGH QUEBEC AND BRING A COLD FRONT THROUGH SOUTHERN NEW ENGLAND LATE SUNDAY. THIS WILL BRING A PERIOD OF WINTRY WEATHER TO THE REGION. THEN HIGH PRESSURE BUILDS BACK IN BRIEFLY LATE MONDAY. THE MODELS DIFFER ON THE STRENGTH...DEVELOPMENT...AND TRACK OF A LOW PRESSURE SYSTEM EXPECTED TO AFFECT SOUTHERN NEW ENGLAND TUESDAY. THE ECMWF HAS THE MORE TYPICAL PATTERN OF A LOW MOVING THROUGH THE GREAT LAKES AND A SECONDARY LOW DEVELOPING OFF THE COAST OF NEW JERSEY AND TRACKING ACROSS THE 40/70 BENCHMARK. THE GFS KEEPS THE LOW PRESSURE AS AN INSIDE RUNNER...TRACKING UP THROUGH PENNSYLVANIA AND NEW YORK STATE. THESE TWO DIFFERENT SOLUTIONS WILL AFFECT EVERYTHING FROM TEMPERATURES TO PRECIPITATION TYPES. BUT THIS IS 7-8 DAYS OUT SO WE EXPECT THINGS TO CHANGE QUITE A BIT BETWEEN NOW AND THEN. THURSDAY AND FRIDAY...HIGH PRESSURE BUILDS INTO THE REGION. LOW PRESSURE SYSTEMS TRACKING WELL SOUTH OF SOUTHERN NEW ENGLAND MAY BRING SOME OCEAN EFFECT SNOW TO THE CAPE AND ISLANDS. SATURDAY...HIGH PRESSURE CENTERS OVER SOUTHERN NEW ENGLAND BRINGING DRY WEATHER AND MODERATING TEMPERATURES. SUNDAY AND MONDAY...HIGH PRESSURE MOVES OFFSHORE. LOW PRESSURE OVER HUDSON BAY WILL TRACK EASTWARD THROUGH QUEBEC BRINGING A COLD FRONT THROUGH SOUTHERN NEW ENGLAND. THIS WILL RESULT IN A PERIOD OF WINTRY PRECIP THROUGHOUT THE AREA. RIGHT NOW...THERMAL PROFILES INDICATE THAT THIS IS LIKELY TO BE IN THE FORM OF SNOW SHOWERS. A CHANGE IN THERMAL PROFILE COULD RESULT IN A WINTRY MIX OF PRECIP DURING THIS TIME. THE OTHER CONCERN DURING THIS TIME IS THE POTENTIAL FOR GUSTY WINDS. THE ECMWF INDICATES A RATHER STRONG LOW LEVEL JET DEVELOPING WHILE THE GFS KEEPS THE LOW LEVEL WINDS RATHER CALM. AT ANY RATE...EXPECT ADVISORY LEVEL WINDS WOULD BE THE MOST WE WOULD NEED TO BE CONCERNED ABOUT. WILL KEEP AN EYE ON THIS THROUGHOUT THE WEEK. TUESDAY...A COUPLE OF DIFFERENT SOLUTIONS FORECAST IN THE MODELS. THE ECMWF HAS A LOW PRESSURE SYSTEM MOVING THROUGH THE GREAT LAKES WITH A SECONDARY LOW FORMING OFF THE NEW JERSEY COAST AND PASSING JUST INSIDE THE 40/70 BENCHMARK. THE GFS HAS THE LOW TRACKING THROUGH PENNSYLVANIA AND NEW YORK BRINGING A WARM FRONT THROUGH SOUTHERN NEW ENGLAND. THESE TWO SOLUTIONS HAVE VASTLY DIFFERENT THERMAL PROFILES AND THIS WOULD AFFECT PRECIPITATION TYPES. WE HAVE AWHILE TO GO ON THIS STORM SO WILL ALLOW LATER RUNS TO BETTER RESOLVE THIS PARTICULAR STORM. && .AVIATION /02Z WEDNESDAY THROUGH SUNDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /TODAY THROUGH WEDNESDAY/... TONIGHT...DRY WEATHER THRU ABOUT 03Z THEN SNOW COMES ONSHORE TO THE SOUTH COAST OF MA AND RI BETWEEN 04Z-05Z...THEN OVERSPREADS THE REMAINDER OF RI AND EASTERN MA THEREAFTER. BRIEF MODERATE TO HEAVY SNOW 07Z-10Z OVER RI AND EASTERN MA THEN EXITS OFFSHORE 11Z/12Z. MVFR AND IFR CONDITIONS IN THIS AREA WITH 2-4" SNOWFALL FOR BOS/PVD/HYA/FMH AND ACK ALONG WITH NEIGHBORING TERMINALS. ELSEWHERE...VFR TO MVFR CIGS WITH LITTLE IF ANY SNOW. WED/WED NIGHT...VFR AND DRY WEATHER WITH MODEST NW WINDS. KBOS TAF...HIGH CONFIDENCE IN VFR CONDITIONS THRU 03Z/04Z. THEN BURST OF MODERATE TO EVEN BRIEFLY HEAVY SNOW EXPECTED BETWEEN 07Z AND 10Z WED. QUICKLY IMPROVING THEREAFTER. 2-4" SNOWFALL LIKELY. DRY/FLUFFY SNOW. KBDL TAF...HIGH CONFIDENCE IN TAF. BRIEF MVFR CONDITIONS POSSIBLE BETWEEN 04Z AND 08Z IN A BAND OF LIGHT SNOW. OUTLOOK...THURSDAY THROUGH SUNDAY... THURSDAY THROUGH FRIDAY...HIGH CONFIDENCE. VFR. LOW PROBABILITY OF MVFR/IFR CONDITIONS ON THE OUTER CAPE AND NANTUCKET IN OCEAN EFFECT SNOW SHOWERS. SATURDAY...HIGH CONFIDENCE. VFR. SUNDAY...MODERATE CONFIDENCE. MVFR/IFR CONDITIONS LIKELY IN SNOW SHOWERS. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/... TONIGHT...MODEST SOUTH WINDS BECOME NW TOWARD SUNRISE. SNOW LIMITS VSBY TO LESS THAN A MILE ROUGHLY 11 PM TO 5 AM. WED...NW WINDS 20-30 KT BEGINNING MID MORNING. ANY SNOW MOVES WELL OFFSHORE BY 8-9AM. WED NIGHT...NW WINDS DIMINISH AND BECOME NORTHERLY.OUTLOOK...THURSDAY THROUGH SUNDAY... OUTLOOK...THURSDAY THROUGH SUNDAY... MODERATE CONFIDENCE. SMALL CRAFT SEAS LINGER ON THE OUTER WATERS THURSDAY AND FRIDAY. HIGH PRESSURE STARTS BUILDING OVER THE WATERS THROUGH THE WEEKEND...KEEPING WINDS AND SEAS BELOW SMALL CRAFT CRITERIA. PERIODS OF OCEAN EFFECT SNOW THURSDAY AND FRIDAY NEAR THE CAPE AND ISLANDS MAY REDUCE VISIBILITIES AND MORE WIDESPREAD SNOW/RAIN WILL BE POSSIBLE LATE SUNDAY AS A COLD FRONT APPROACHES THE WATERS. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...WINTER WEATHER ADVISORY UNTIL 7 AM EST WEDNESDAY FOR MAZ006- 007-013>024. RI...WINTER WEATHER ADVISORY UNTIL 7 AM EST WEDNESDAY FOR RIZ002- 004>008. MARINE...SMALL CRAFT ADVISORY FROM 10 AM WEDNESDAY TO 1 AM EST THURSDAY FOR ANZ230>237-250-251-254>256. && $$ SYNOPSIS...NOCERA/RLG NEAR TERM...FRANK/NOCERA SHORT TERM...NOCERA LONG TERM...RLG AVIATION...NOCERA/RLG MARINE...NOCERA/RLG

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