Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 281459 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 959 AM EST SAT FEB 28 2015 .SYNOPSIS... A FAST MOVING LOW PRESSURE SYSTEM WILL BRING ACCUMULATING SNOW TO THE REGION LATE SUNDAY INTO SUNDAY NIGHT...WITH THE HIGHEST AMOUNTS EXPECTED SOUTH OF THE MASSACHUSETTS TURNPIKE AND AWAY FROM THE IMMEDIATE SOUTH COAST. ANOTHER STORM IS LIKELY TUESDAY NIGHT INTO WEDNESDAY...WITH SNOW AND MIXED PRECIPITATION LIKELY CHANGING TO RAIN. COLD AND DRY CONDITIONS RETURN FOR THE END OF NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/...
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10 AM UPDATE... NO MAJOR CHANGES. ONLY MODIFICATIONS TO TEMPERATURES AND DEWPOINTS TO BRING THEM MORE IN-LINE WITH TRENDS. PREVIOUS DISCUSSION... HIGH PRESSURE OVERHEAD WILL ALLOW FOR SUNNY SKIES AND LIGHT WINDS. TEMPERATURESS SHOULD RECOVER INTO THE MIDDLE TO UPPER 20S IN MOST LOCATIONS...BUT THAT IS STILL AROUND 15 DEGREES BELOW NORMAL FOR THE LAST DAY OF FEBRUARY. HOWEVER...THE INCREASING LATE FEBRUARY SUN ANGLE AND LIGHT WINDS WILL MAKE IT SOMEWHAT MORE BEARABLE THAN OUR RECENT COLD WAVES. TONIGHT... HIGH PRESSURE OVERHEAD WILL ALLOW FOR ANOTHER EXCELLENT NIGHT OF RADIATIONAL COOLING. THE NORMALLY COLDEST OUTLYING LOCATIONS WILL DROP TO BETWEEN 5 AND 15 BELOW ZERO...WHILE MAINLY SINGLE DIGITS CAN BE EXPECTED FOR THE REST OF THE REGION. THE ONE FLY IN THE OINTMENT IS WE ARE EXPECTING SOME MID/HIGH CLOUDS TO INCREASE FROM THE WEST AFTER MIDNIGHT. IF THEY COME IN A BIT EARLIER THEN EXPECTED OUR TEMPERATURE FORECAST MIGHT BE TOO COLD.
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&& .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
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*** ACCUMULATING SNOW LATE SUNDAY AND ESPECIALLY SUNDAY NIGHT WITH THE HIGHEST AMOUNTS EXPECTED SOUTH OF THE MA TURNPIKE AND AWAY FROM THE IMMEDIATE SOUTH COAST *** A DIGGING SHORTWAVE WILL DROP TOWARDS THE GREAT LAKES ON SUNDAY. THIS WILL ALLOW FOR AN OVERRUNNING SETUP ACROSS SOUTHERN NEW ENGLAND. A NICE FRONTOGENESIS SIGNATURE WITH A DEVELOPING LOW LEVEL JET SHOULD RESULT IN A GOOD SLUG OF PRECIPITATION SUNDAY EVENING INTO SUNDAY NIGHT. MOST MODELS ARE SHOWING A WEAK SECONDARY LOW PRESSURE DEVELOPING NEAR THE SOUTH COAST. THIS WILL HELP TO BACK AND STRENGTHEN THE LOW LEVEL JET ALONG WITH SOME SURFACE CONVERGENCE RESULTING IN THE RISK FOR SOME HIGH PRECIPITATION TOTALS SOUTH OF THE MA TURNPIKE WHICH WILL EXPLAIN MORE BELOW. 1} TIMING AND PTYPE: DRY WEATHER SHOULD PREVAIL SUNDAY MORNING. MID LEVEL WARM ADVECTION SHOULD ALLOW LIGHT SNOW TO DEVELOP DURING THE AFTERNOON ACROSS THE INTERIOR...REACHING THE COASTAL PLAIN BY LATE AFTERNOON/EARLY EVENING. THE SNOW WILL INITIALLY BE LIGHT...BUT EXPECT THE SNOW TO PICKUP IN INTENSITY SUNDAY EVENING AND OVERNIGHT AS THE LOW LEVEL JET/FORCING INCREASE. MODEL SOUNDINGS SHOW A PERIOD OF DECENT OMEGA IN THE PRIME SNOW GROWTH REGION. SYSTEM IS FAIRLY PROGRESSIVE...SO THE SNOW SHOULD BE OVER EARLY MONDAY MORNING AND BEFORE RUSH HOUR STARTS. PTYPE WILL PROBABLY BE ALL SNOW FOR A LOT OF THE REGION. IT BECOMES MORE UNCERTAIN ACROSS SOUTHERN RI AND FAR SOUTHEAST MA. THE NAM MODEL IS AN OUTLIER AND MOST AGGRESSIVE IN BRINGING A SURGE OF WARM MID LEVEL AIR NORTHWARD...WHICH WOULD CHANGE PTYPE TO RAIN FOR JUST ABOUT ALL OF RHODE ISLAND AND SOUTHEAST MA SUN NIGHT. HOWEVER...MOST OF THE OTHER GUIDANCE KEEPS PTYPE SNOW EXCEPT FOR AREAS NEAR THE SOUTH COAST/CAPE/ISLANDS. SO FOR NOW WILL KEEP THE CHANGE OVER LINE JUST SOUTH OF THE TAUNTON TO PROVIDENCE CORRIDOR...BUT THIS MAY NEED TO BE ADJUSTED BASED ON LATEST MODEL DATA. 2)SNOW ACCUMULATIONS AND HEADLINES: THIS LOOKS TO BE A HIGH END WINTER WEATHER ADVISORY OR LOW END WARNING FOR MUCH OF THE REGION. WE ARE GENERALLY EXPECTING SNOWFALL AMOUNTS OF BETWEEN 3 AND 7 INCHES...AWAY FROM THE SOUTH COAST WHERE PTYPE ISSUES WILL BE MORE PROBLEMATIC. THE NAM IS HEAVIER ON QPF AND WE OPTED TO GO WITH A GFS/ECMWF BLEND. EVEN THESE MODELS STILL HAVE BETWEEN 0.40 TO 0.60 INCHES OF PRECIP FROM NEAR THE PIKE TO THE SOUTH COAST. THIS SEEMS TO BE IN RESPONSE TO A WEAK WAVE DEVELOPING NEAR THE SOUTH COAST...ALLOWING FOR A MORE BACKED LOW LEVEL JET AND BETTER SURFACE CONVERGENCE. WITH PRETTY GOOD OMEGA IN THE SNOW GROWTH REGION...SNOWFALL RATIOS MAY BE BETTER THAN 10 TO 1 RATIOS. WITH THAT SAID...FELT IT IS WORTH A WINTER STORM WATCH FROM NEAR THE PIKE TO AREAS INLAND FROM THE SOUTH COAST...WHERE PTYPE WILL PROBABLY END UP AS MAINLY SNOW. THIS IS FOR THE POTENTIAL OF 4 TO 7 INCHES OF SNOW. WE ARE FAIRLY CONFIDENCE IN WIDESPREAD 3 TO 4 INCH AMOUNTS...BUT CONFIDENCE IS LOWER ON WHETHER OR NOT WE SEE THE 6 TO 7 INCH AMOUNTS. HOWEVER...WE ONLY NEED 50 PERCENT CONFIDENCE IN THOSE HIGHER TOTALS OCCURRING TO ISSUE THE WATCH AND IT GIVES THE NEXT SHIFT SOME MORE OPTIONS. 3) FORECAST UNCERTAINTY: HOW MUCH SNOW WE ACTUALLY RECEIVE WILL HAVE A LOT TO DO WITH HOW QUICKLY THE SECONDARY WAVE OF LOW PRESSURE DEVELOPS AND HOW FAR NORTH THE RAIN/SNOW LINE GETS. THE NAM MODEL IS STRONGEST WITH THE DEVELOPMENT OF THIS WAVE AND HENCE HAS THE HIGHEST QPF...BUT DOES INTRODUCE MORE PTYPE ISSUES. MEANWHILE...THE GGEM IS THE WEAKEST WITH THIS DEVELOPMENT AND BARELY HAS ADVISORY LEVEL SNOW FOR THE REGION. CURRENTLY WE ARE LEANING TOWARDS A GFS/ECMWF COMPROMISE...RESULTING IN 3 TO 7 INCHES OF SNOW WITH THE HIGHEST AMOUNTS SOUTH OF PIKE AND AWAY FROM THE SOUTH COAST.
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&& .LONG TERM /MONDAY THROUGH FRIDAY/...
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HIGHLIGHTS... * CONDITIONS IMPROVE MONDAY * ANOTHER STORM POSSIBLE TUE NIGHT INTO WED...WITH SNOW OR MIXED PRECIP LIKELY CHANGING TO RAIN * COLD AND DRY TOWARD THE END OF THE WEEK OVERVIEW AND MODEL PREFERENCES... ONE THING IS FOR CERTAIN...WITH LITTLE CHANGE IN THE NAO/AO AND THE PNA EXPECTED TO REBOUND FROM NEGATIVE VALUES BACK TOWARD A MORE NEUTRAL SOLUTION...THE COLD AIR AND LONGWAVE TROF LOOK TO REMAIN THROUGH THE LONG TERM FORECAST. THE ONLY CAVEAT WILL BE IN THE LOW LVLS ON WED...WHEN A ROBUST SW LLJ WILL ALLOW LOW-MID LVL TEMPS TO WARM CLOSER TO ABOVE CLIMATOLOGICAL NORMALS. HOWEVER... THE COLD AIR INITIALLY IN PLACE WILL LEAD TO P-TYPE ISSUES FOR THE MID WEEK SYSTEM. ECMWF DETERMINISTIC REMAINS THE MOST ROBUST OF THE OPERATIONAL MODELS...WITH HIGHER AMPLIFICATION IN THE FLOW PATTERN THAN THE GFS AND UKMET. IT STARTS MUCH COLDER...BUT ENDS MUCH WARMER. HOWEVER...DO NOTE THAT SOME OF THE GEFS AND ECENS ENSEMBLES AGREE WITH THE ECMWF. THEREFORE...WILL BE USING THE ENSEMBLE BLEND AS A BASELINE AS THIS TAKES INTO ACCOUNT BOTH THE MORE PROGRESSIVE /AND ULTIMATELY LESS ROBUST WITH THE THERMAL DIFFERENCES/ AND THE POTENTIAL FOR A MORE DYNAMIC SYSTEM. WILL USE THIS BLEND THROUGH THE REMAINDER OF THE FORECAST AS WELL. DETAILS... MONDAY... MORNING SNOWS COME TO AN END EARLY ACROSS E MA...AND FLURRIES DISSIPATE THROUGH THE BERKSHIRES AND LITCHFIELD HILLS AS DRY NW FLOW MOVES IN. BLUSTERY CONDITIONS EXPECTED...AND EVEN THROUGH HIGHS WILL STILL BE MAKING IT INTO THE LOW-UPPER 30S...NW WINDS WITH GUSTS 25-35 MPH AT TIMES WILL YIELD WIND CHILLS STRUGGLING INTO THE LOW 20S. MONDAY NIGHT INTO TUESDAY... HIGH PRES WILL MOVE ACROSS THE REGION. DRY CONDITIONS DOMINATE ALTHOUGH WITH TEMPS REMAINING BELOW NORMAL. TUESDAY NIGHT INTO THURSDAY... MODEL CONSENSUS IS NOW GENERALLY IN AGREEMENT THAT BOTH THE NRN AND SRN STREAMS PHASE IN SOME FASHION ACROSS THE CENTRAL CONUS WITH THE FORMATION OF LOW PRES WHICH IS EXPECTED TO SLIDE ACROSS SRN CANADA. WARM FRONT WILL APPROACH...BUT GIVEN DEEP SNOWPACK THE LOW LVL FRONT MAY ACTUAL STALL NEAR THE S COAST AS THE LOW MOVES OVER AS THE UPPER WARM FRONT SLIDES INTO CENTRAL NEW ENGLAND. THIS PRESENTS A GOOD OVERRUNNING SITUATION WITH STRONG 50-60 KT H92 LLJ OUT OF THE SW. GIVEN THAT THIS SYSTEM IS ASSOCIATED WITH THE SRN STREAM...IT ALSO CARRIES WITH IT A FAIR AMOUNT OF MOISTURE AS PWATS LOOK TO REACH 2-3 STD DEVIATIONS ABOVE NORMAL SO ALL IN ALL..PLENTY OF INGREDIENTS FOR HEAVY PRECIP ACROSS THE AREA. THE QUESTION WILL BE TYPE...ALL GUIDANCE BEGIN COLD ENOUGH FOR SNOW AT ONSET TUE NIGHT INTO EARLY WED. ECMWF WOULD SUGGEST MUCH MORE AND BETTER LIFT IN THE SNOW GROWTH REGION...SO THERE IS THAT TO CONSIDER. IN ANY CASE...WILL NEED TO AT LEAST WATCH FOR POTENTIAL WARNING LEVEL SNOWFALL BEFORE THE WARM AIR BEGINS TO BUILD IN FROM S TO N THROUGH THE DAY ON WED. EVEN THOUGH THE ECMWF STARTS THE COLDEST...IT ENDS AS THE WARMEST SOLUTION...BRINGING THE H92 +8C LINE ALL THE WAY INTO CENTRAL MA. SO WE DO EXPECT A GRADUAL SHIFT TO A WINTRY MIX INCLUDING SLEET AND FREEZING RAIN FOR A TIME GIVEN THE DEEP SNOWPACK ACROSS THE REGION. SOME AREAS OF WRN MA...AND THE HILLS OF NRN CT MAY ACTUALLY STAY AS A MIX OF SLEET FREEZING RAIN AND EVEN MAYBE SOME SNOW GIVEN THAT THE SFC WARM FRONT MAY STALL. WILL HAVE TO WATCH FOR ICY CONDITIONS WITH AS MUCH AS A QUARTER INCH OF ICE NOT OUT OF THE QUESTION WHERE IT DOESN/T SWITCH TO RAIN WITH MELTING /BEST CHANCE OF RAIN/MELT IS IN RI/CT AND PORTIONS OF MASS E OF I-495 AND S OF THE MASS PIKE/. HEAVY RAIN A THREAT TOO GIVEN UPPER LVL INSTABILITY AND ROBUST LLJ...SO WHERE MELTING AND HEAVY RAIN ARE OBSERVED...POOR DRAINAGE FLOODING IS A POSSIBILITY WHERE SNOW CLOGS AREA DRAINS. THIS HEAVY MIXED PRECIP EVENT COULD LINGER INTO THU...THE MORE AMPLIFIED ECMWF AND SEVERAL ECENS/GEFS MEMBERS SUGGEST THAT THE LEFTOVER COLD FRONT STALLS WITH YET ANOTHER WEAK WAVE OF LOW PRES MOVING THROUGH THU. OTHER SOLUTIONS ARE MORE PROGRESSIVE AND HAVE LESS QPF /SNOW POTENTIALLY/ ON THE BACK END. HOWEVER...BY THU AFTERNOON/EVENING...CONDITIONS SHOULD BE IMPROVING /ALTHOUGH WITH RAPID TEMPERATURE DROP/. LATE NEXT WEEK... EVEN THOUGH THERE IS UNCERTAINTY WITH HOW AMPLIFIED THE PATTERN IS BY LATE WEEK. IT APPEARS A PERIOD OF DRY BUT COLD WX IS LIKELY AS ARCTIC AIR ONCE AGAIN SHIFTS IN BEHIND THE EXITING MID WEEK SYSTEM.
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&& .AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
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FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /TODAY THROUGH SUNDAY NIGHT/... 15Z UPDATE...NO CHANGES. TODAY AND TONIGHT...HIGH CONFIDENCE. VFR. SUNDAY MORNING...MODERATE CONFIDENCE. VFR. INCREASING MID-LEVEL CLOUDS. SUNDAY AFTERNOON INTO MONDAY MORNING... SNOW OVERSPREADS THE REGION W-E. CIGS/VSBYS DETERIORATE TO MVFR- IFR BY EARLY EVENING...WIDESPREAD IFR-LIFR SUNDAY NIGHT. SN MAY MIX WITH OR CHANGE TO RA FOR A TIME ACROSS PORTIONS OF S RI AND FAR SE MA...ESPECIALLY IMMEDIATE S-COAST/CAPE AND ISLANDS. PRECIP SHOULD RAPIDLY END FROM W-E TOWARD DAYBREAK MONDAY....IMPROVING CONDITIONS. KBOS TAF...HIGH CONFIDENCE. VFR INTO SUNDAY MORNING. KBDL TAF...HIGH CONFIDENCE. VFR INTO SUNDAY MORNING. OUTLOOK...MONDAY THROUGH WEDNESDAY... MONDAY...HIGH CONFIDENCE. CONDITIONS IMPROVE EARLY FROM IFR/MVFR IN SNOWS AND LOW CIGS... WITH VFR EXPECTED EVERYWHERE BY AFTERNOON. NW WINDS IN THE AFTERNOON WITH GUSTS 25-30 KT. MON NIGHT INTO TUE...HIGH CONFIDENCE. MAINLY VFR. GRADUALLY LOWERING CIGS ON TUE. TUE NIGHT INTO WED...MODERATE CONFIDENCE. MIXED WINTRY PRECIP LIKELY STARTS AS ALL SNOW...TRANSITIONS TO A MIX OF SLEET AND FREEZING RAIN...THEN TO ALL RAIN DURING THE DAY ON WED. SOME SNOW AND ICE ACCUMULATIONS ARE LIKELY WITH IFR OR POTENTIALLY EVEN LIFR CONDITIONS AT TIMES.
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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. SHORT TERM /THROUGH SATURDAY NIGHT/...HIGH CONFIDENCE. 10 AM UPDATE...NO MAJOR CHANGES. HIGH PRESSURE NEARBY WILL KEEP WINDS/SEAS WELL BELOW SMALL CRAFT ADVISORY THRESHOLDS INTO SUNDAY MORNING. A WEAK WAVE OF LOW PRESSURE MOVES ACROSS THE WATERS LATE SUN INTO SUN NIGHT...BUT WEAK PRESSURE GRADIENT SHOULD KEEP WINDS/SEAS BELOW SMALL CRAFT THRESHOLDS. OUTLOOK...SUNDAY THROUGH WEDNESDAY... MONDAY INTO MONDAY NIGHT...HIGH CONFIDENCE. SW WINDS SHIFT TO THE NW DURING THE DAYLIGHT HOURS AS A COLD FRONT SWEEPS ACROSS THE WATERS. ONCE WINDS SHIFT NW IN THE AFTERNOON EXPECT GALE FORCE GUSTS 35-40KT. COLDER AIR TUE NIGHT COULD LEAD TO LIGHT FREEZING SPRAY. TUESDAY...MODERATE CONFIDENCE. WINDS GRADUALLY DIMINISH OUT OF THE W-NW BUT SEAS ARE LIKELY TO REMAIN ELEVATED 5-8FT ON THE OCEAN WATERS. SMALL CRAFT ADVISORIES WILL LIKELY BE NEEDED. TUESDAY NIGHT INTO WEDNESDAY...MODERATE CONFIDENCE. SNOW CHANGES TO RAIN TUE NIGHT WITH LOW VSBYS OVER THE WATERS. WINDS OUT OF THE S MAINLY AROUND 25-30 KT AT MOST. SEAS BUILD 12-15 FT BY DAYTIME ON WED ON SE OCEAN WATERS. SMALL CRAFT ADVISORIES WILL LIKELY BE NEEDED.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...WINTER STORM WATCH FROM SUNDAY AFTERNOON THROUGH LATE SUNDAY NIGHT FOR CTZ002>004. MA...WINTER STORM WATCH FROM SUNDAY AFTERNOON THROUGH LATE SUNDAY NIGHT FOR MAZ009-011>013-015>019. RI...WINTER STORM WATCH FROM SUNDAY AFTERNOON THROUGH LATE SUNDAY NIGHT FOR RIZ001>004. MARINE...NONE. LEFT OVER SMALL CRAFT SEAS ACROSS THE OUTER-WATERS WILL DIMINISH EARLY THIS MORNING. OTHERWISE...
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&& $$ SYNOPSIS...FRANK/DOODY NEAR TERM...FRANK/DOODY/SIPPRELL SHORT TERM...FRANK LONG TERM...DOODY AVIATION...FRANK/DOODY/SIPPRELL MARINE...FRANK/DOODY

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