Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 261956 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 356 PM EDT THU MAR 26 2015 .SYNOPSIS...
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AN APPROACHING COLD FRONT WILL BRING PERIODS OF SHOWERS INTO FRIDAY MORNING. WEAK LOW PRESSURE MAY BRING SCATTERED SNOW SHOWERS FRIDAY NIGHT INTO SATURDAY. HIGH PRESSURE WILL PUSH SOUTH OF NEW ENGLAND SUNDAY. ANOTHER BATCH OF PRECIPITATION IS POSSIBLE LATE SUNDAY NIGHT INTO MONDAY AHEAD OF A COLD FRONT.
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&& .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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***PERIODS OF SHOWERS WITH BRIEF LOCALIZED HEAVY RAINFALL TONIGHT*** NUMEROUS SHOWERS WITH BRIEF LOCALLY HEAVY RAINFALL WILL CONTINUE INTO EARLY THIS EVENING IN ASSOCIATION WITH A MID LEVEL SHORTWAVE. MARGINAL ELEVATED INSTABILITY WILL RESULT IN AN EMBEDDED THUNDERSTORM OR TWO. THERE THEN MAY BE A BIT OF A LULL IN THE ACTIVITY...BUT COLD FRONT DROPPING DOWN INTO SOUTHERN NEW ENGLAND WILL ALLOW ADDITIONAL SHOWERS TO RE-DEVELOP. BRIEF LOCALLY HEAVY RAINFALL MAY RESULT IN TYPICAL POOR DRAINAGE NUISANCE STREET FLOODING...BUT NO SIGNIFICANT FLOODING PROBLEMS ARE EXPECTED. THERE IS A PRETTY GOOD BAND OF MID LEVEL FRONTOGENESIS BEHIND THE ACTUAL SURFACE COLD FRONT. THEREFORE...EXPECT RAIN TO PERSIST RIGHT THROUGH THE OVERNIGHT HOURS ACROSS MUCH OF THE REGION. IN FACT...COLDER AIR WILL BEGIN TO WORK INTO THE REGION FROM THE NORTHWEST. IF PRECIPITATION INTENSITY IS ENOUGH...DYNAMIC COOLING MAY ALLOW RAIN TO CHANGE TO A BRIEF PERIOD OF WET SNOW ACROSS THE HIGH TERRAIN OF INTERIOR MASS TOWARD DAYBREAK. MOST OF THE GUIDANCE SUGGESTS JUST A DUSTING TO LESS THAN 1 INCH OF SNOW...WHICH IS IN LINE WITH OUR CURRENT THINKING. HOWEVER... THE NAM MODEL IS MOST ROBUST WITH IT ACTUALLY SHOWING THE POTENTIAL FOR A NARROW SWATH OF 2 TO 3 INCHES OF SNOW ACROSS THE WORCESTER HILLS. GIVEN THAT BOUNDARY LAYER IS MARGINAL...FEEL THAT IS A LOW PROBABILITY BUT WE CAN NOT COMPLETELY RULE IT. FINALLY...WE ISSUED A DENSE FOG ADVISORY FOR THE SOUTH COAST/CAPE AND ISLANDS THROUGH MIDNIGHT. SOUTH TO SOUTHWEST WINDS AND RELATIVELY HIGH DEWPOINT AIR BLOWING OVER THE COLD OCEAN WILL ALLOW FOR AREAS OF DENSE FOG AT TIMES ACROSS THIS REGION. THE LOSS OF DAYTIME HEATING MAY ALSO ALLOW THIS TO EXPAND A BIT...SO FELT IT WAS WORTH AN ADVISORY. WINDS SHIFT TO THE NORTH BEHIND THE COLD FRONT AFTER MIDNIGHT...SO VISIBILITIES SHOULD THEN IMPROVE.
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&& .SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/...
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FRIDAY... MID LEVEL FRONTOGENESIS BEHIND THE ACTUAL COLD FRONT WILL ALLOW FOR RAIN TO CONTINUE ACROSS EASTERN NEW ENGLAND FRIDAY MORNING. AS WE MENTIONED IN THE PREVIOUS SECTION...IT MAY BECOME JUST COLD ENOUGH ACROSS THE HIGHER TERRAIN OF MASS FOR A CHANGE TO WET SNOW BEFORE PRECIPITATION ENDS. THINGS SHOULD DRY OUT FOR MOST OF THE REGION BY AFTERNOON AS BEST FORCING DEPARTS...BUT SOME LINGERING SHOWERS WILL REMAIN POSSIBLE OVER THE SOUTHEAST NEW ENGLAND COAST. ACROSS THE REST OF THE REGION...PLENTY OF CLOUDS WILL LINGER EVEN THOUGH THE RAIN WILL HAVE COME TO AN END. HIGH TEMPS MAINLY IN THE 40S.
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&& .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/... HIGHLIGHTS... * SCT SNOW/RAIN SHOWERS ON SATURDAY * A WEAK COLD FRONT WILL MOVE THROUGH ON MONDAY BRINGING SCT SHOWERS * MODERATING SPRING-LIKE TEMPS INTO NEXT WEEK MODEL GUIDANCE... OVERALL AMPLIFIED TROUGH PATTERN WILL CONTINUE WITH 00Z GUIDANCE IN GOOD AGREEMENT. STILL SUBTLE DETAIL DIFFERENCES AT THE MESO LEVEL. BROAD UPPER TROUGH REMAINS OVER THE EAST COAST FRIDAY NIGHT INTO SATURDAY WITH THE TROUGH MOVING EAST OF THE REGION LATE SATURDAY NIGHT INTO SUNDAY. LOW PRESSURE SYSTEM WILL CROSS SRN CANADA AND BRING A TRAILING FRONT THROUGH THE AREA ON MONDAY. GUIDANCE STILL SHOWS PERSISTENT DIFFERENCES WITH SOUTHWARD EXTENT OF THE TRAILING FRONT AS THE GFS IS FARTHER SOUTH. GUIDANCE WAS SOMEWHAT CLOSER TO BEING EVENLY SPLIT 24 HRS AGO BUT THE PAST COUPLE UKMET/CMC RUNS TRENDED TO THE NRN CLUSTER AND EVEN THE 18Z/00Z GEFS MEANS HAVE STARTED TO TREND NWD OF THE OPERATIONAL GFS RUNS. SO TRENDED THIS PORTION TOWARDS THE EC/HPC. LASTLY THE DOMINATE NORTHERN STREAM FLOW BECOMES MORE PROGRESSIVE AS STRONG WESTERN RIDGE WEAKENS AS SEVERAL WAVES BEGIN TO MOVE THROUGH THE FLOW MIDDLE OF NEXT WEEK. THESE WILL NEED TO BE WATCHED CLOSELY FOR THE UPCOMING EASTER WEEKEND. DETAILS... * FRIDAY NIGHT INTO SATURDAY...MODERATE CONFIDENCE. COLD AIR WILL USHER ACROSS THE REGION FRIDAY NIGHT INTO SATURDAY BEHIND PASSING COLD FRONT. THE UPPER LEVEL TROUGH AXIS WILL BE OVERHEAD...COULD SEE SOME SCT SNOW SHOWERS DURING THE DAY ON SATURDAY. CONFIDENCE IS INCREASING COMPARED TO YESTERDAY AS MOST OF THE GUIDANCE SPITS OUT SOME QPF. SURFACE LOW PRESSURE WILL MOVE WELL SOUTH OF THE BENCHMARK FRIDAY NIGHT/SAT MORNING HOWEVER...GUIDANCE IS HINTING AT A WEAK SURFACE/INVERTED TROUGH OVER THE AREA ON SATURDAY. THIS COMBINED WITH LOW LEVEL MOISTURE AND VERY STEEP LAPSE RATES WILL ALLOW FOR SCT SNOW/RAIN SHOWERS TO DEVELOP. EXPECT MOSTLY CLOUDY SKIES SO TEMPS WILL STRUGGLE TO REACH INTO THE UPPER 30S...SO THINKING P-TYPE IS MORE SNOW. MODELS ARE ALSO HINTING AT POSSIBLE FRONTOGENESIS WHICH COULD INCREASE SNOWFALL RATES. LOW CONFIDENCE ON WHERE THIS MAY SET UP BUT WILL NEED TO WATCH FOR SOME AREA IN SOUTHERN NEW ENGLAND SEEING A SURPRISED 1-2 INCHES POSSIBLY. TEMPS OVERNIGHT WILL FALL WELL BELOW NORMALS WITH LOWS AROUND THE TEENS TO LOW 20S. TEMPS MAY BE SLIGHTLY COLDER AT WE COULD RADIATE OUT THANKS TO CLEARING SKIES AND LIGHT WINDS ACROSS THE INTERIOR. LOW PROBABILITY OF LINGERING OCEAN EFFECT SNOW ACROSS THE CAPE. * SUNDAY...HIGH CONFIDENCE. SUNDAY IS A TRANSITION DAY AS DEEP TROUGH BEGINS TO PULL OFFSHORE AND UPPER LEVEL RIDGE MOVES INTO THE REGION. TEMPS ON SUNDAY WILL WARM INTO THE MID 40S TO LOW 50S AS WARM AIR ADVECTION ADVANCES. EXPECT MOSTLY CLEAR SKIES IN THE MORNING BUT THEY WILL BEGIN TO CLOUD UP DURING THE AFTERNOON AS THE NEXT SYSTEM APPROACHES FROM THE WEST. MONDAY INTO WEDNESDAY...LOW CONFIDENCE. NEXT UPPER LEVEL DISTURBANCE WILL IMPACT SOUTHERN NEW ENGLAND LATE SUNDAY INTO MONDAY. STILL A GOOD AMOUNT OF SPREAD AMONGST THE GUIDANCE AS MENTIONED ABOVE...BUT TRENDED TOWARDS THE EC/HPC ON THIS PORTION OF THE FORECAST. SURFACE LOW ACROSS THE GREAT LAKES WILL PASS JUST NORTH OF SNE...DRAGGING ASSOCIATED COLD FRONT WITH IT. TEMPS AT THE ONSET LOOK TO BE COOL THEN WARM UP DURING THE DAY ON MONDAY PRIOR TO FRONTAL PASSAGE. TIMING OF THE FRONT WILL BE AN ISSUE IMPACTING HIGH TEMPS. EC KEEPS THEM COOL WITH A FASTER PASSAGE COMPARED TO THE GFS WHICH IS SLOWER BUT WARMS TEMPS UP INTO THE 50S. AT THE ONSET OF PRECIP EXPECT A FEW SNOW SHOWERS...BUT THEN TRANSITIONING TO RAIN FAIRLY QUICKLY AS TEMPS WARM. A FEW QUICK MOVING SYSTEMS WILL MOVE THROUGH THE FLOW DURING THE UPCOMING WEEK. FIRST ONE IS LATE TUESDAY INTO WED FOLLOWED BY ANOTHER THUS/FRIDAY. AT THE SURFACE...HIGH PRESSURE WILL BUILD ON TUESDAY FOLLOWED BY WEAK LOW ON WEDNESDAY AND A WARM FRONT ON THURSDAY. && .AVIATION /20Z THURSDAY THROUGH TUESDAY/...
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FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM...THIS AFTERNOON THROUGH FRIDAY... THIS AFTERNOON AND TONIGHT...MODERATE CONFIDENCE. PERIODS OF SHOWERS ALONG WITH AN EMBEDDED THUNDERSTORM OR TWO EXPECTED THROUGH TONIGHT. MAINLY IFR CONDITIONS IN LOWER CLOUDS ALONG WITH AREAS OF FOG...ESPECIALLY ALONG THE SOUTH COAST WHERE IT MAY BE LOCALLY DENSE. LLWS IS ALSO EXPECTED GIVEN LOW LEVEL JET AROUND 60 KNOTS. FRIDAY...MODERATE TO HIGH CONFIDENCE. RAIN SHOWERS SHOULD COME TO AN END FOR MOST OF THE REGION DURING THE MORNING...ALTHOUGH MAY LINGER A BIT LONGER ACROSS THE FAR SOUTHEAST MA COAST. PTYPE MAY ACTUALLY CHANGE TO A BIT OF WET SNOW BEFORE ENDING ACROSS THE HIGHER TERRAIN...BUT ODDS OF ANY REAL ACCUMULATIONS ON RUNWAYS ARE RATHER LOW. OTHERWISE...CONDITIONS SHOULD IMPROVE TO MAINLY VFR BY AFTERNOON ALTHOUGH SOME MARGINAL MVFR CIGS MAY PERSIST AT TIMES. KBOS TAF...MODERATE CONFIDENCE IN TAF. KBDL TAF...MODERATE CONFIDENCE IN TAF OUTLOOK...SATURDAY THROUGH MONDAY...MODERATE CONFIDENCE. SATURDAY...CONDITIONS MAY DETERIORATE FROM EAST TO WEST ON SATURDAY IN SCT SNOW SHOWERS. LOW CONFIDENCE ON ANY ACCUMS ON RUNWAYS BUT FEEL BEST SHOT IS ORH. SATURDAY NIGHT INTO SUNDAY...VFR CONDITIONS LIKELY. SCT MVFR ACROSS THE CAPE IN OCEAN EFFECT SNOW SHOWERS. MONDAY...VFR DROPPING TO POSSIBLE MVFR IN SCT RAIN SHOWERS.
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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...TONIGHT AND FRIDAY... TONIGHT...MODERATE CONFIDENCE. SOUTH TO SOUTHWEST WIND GUSTS OF 20 TO 30 KNOTS EXPECTED THIS EVENING AHEAD OF AN APPROACHING COLD FRONT. HIGH DEWPOINT AIR WILL ALSO RESULT IN AREAS OF DENSE FOG. SEAS WILL BUILD TO BETWEEN 5 AND 9 FEET ACROSS THE OUTER-WATERS. WINDS SHIFT TO THE NORTH BEHIND THE COLD FRONT BETWEEN 6 AND 12Z. FRIDAY...MODERATE TO HIGH CONFIDENCE. NORTHERLY WINDS OF 10 TO 15 KNOTS WITH GUSTS TO 20 KNOTS EXPECTED BEHIND THE COLD FRONT. LEFT OVER SOUTH TO SOUTHEAST SWELL WILL KEEP SEAS ABOVE SMALL CRAFT THRESHOLDS ACROSS MOST OPEN WATERS THROUGH FRI AFTERNOON. OUTLOOK...FRIDAY NIGHT THROUGH MONDAY... MODERATE CONFIDENCE INTO MONDAY. FRIDAY NIGHT....WINDS INCREASE UP TO 25-30KTS BEHIND FRONTAL PASSAGE. SCA WILL BE NEEDED. SATURDAY AND SATURDAY NIGHT...EXPECT NW WINDS TO CONTINUE TO GUST TO SMALL CRAFT LEVELS WITH SEAS BUILDING UP TO 6-9 FT ON THE OUTER WATERS THROUGH SAT NIGHT. LOW PROB OF SCT SNOW/RAIN SHOWERS DURING THE DAY. SUNDAY THROUGH MONDAY...WINDS AND SEAS BRIEFLY SUBSIDE AS WINDS BACK TO SW SUN/SUN NIGHT...THOUGH SEAS MAY REMAIN AROUND 5 FT ON THE FAR OUTER WATERS. WINDS AND SEAS INCREASE AGAIN MONDAY AHEAD OF NEXT SYSTEM SO SMALL CRAFTS WILL LIKELY BE RENEWED.
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&& .HYDROLOGY...
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BASIN AVERAGE RAINFALL AMOUNTS WILL RANGE FROM 0.5 TO 1.25 INCHES ACROSS THE REGION THROUGH FRIDAY MORNING. NOHRSC MODELING ADDS 1 TO 2 INCHES OF WATER FROM MELTING SNOW DUE TO DEWPOINTS IN THE 40S TO NEAR 50. THIS WILL BRING RISES ON RIVERS AND STREAMS THROUGH FRIDAY...ESPECIALLY SMALLER ONES WHICH MAY APPROACH BANKFULL. HOWEVER...GIVEN RAINFALL HAS BEEN SPREAD OUT OVER A LONG DURATION WITH MANY DRY PERIODS DO NOT EXPECT ANY SIGNIFICANT FLOODING PROBLEMS. BRIEF HEAVY RAINFALL IN SHOWERS MAY RESULT IN TYPICAL NUISANCE POOR DRAINAGE STREET FLOODING TONIGHT...BUT AGAIN NOTHING SIGNIFICANT EXPECTED.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...NONE. MA...DENSE FOG ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR MAZ020>024. RI...DENSE FOG ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR RIZ005>008. MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT FRIDAY FOR ANZ232>234. SMALL CRAFT ADVISORY UNTIL 2 AM EDT FRIDAY FOR ANZ231-236. SMALL CRAFT ADVISORY UNTIL 8 PM EDT FRIDAY FOR ANZ235-237-250- 254>256.
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&& $$ SYNOPSIS...FRANK NEAR TERM...FRANK SHORT TERM...FRANK LONG TERM...DUNTEN AVIATION...FRANK/DUNTEN MARINE...FRANK/DUNTEN HYDROLOGY...FRANK

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