Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 020915 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 415 AM EST MON MAR 2 2015 .SYNOPSIS...
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DRY AND BLUSTERY WEATHER FOLLOWS BEHIND THE PASSAGE OF A COLD FRONT EARLY THIS MORNING. LOW PRESSURE FROM NORTHERN CANADA AND ASSOCIATED LOW FORMING OVER THE PLAINS MONDAY WILL MERGE...THEN PASS WEST AND NORTH OF NEW ENGLAND. THIS WILL BRING ABOUT A WINTRY MIX...CHANGING TO RAIN LATE TUESDAY INTO WEDNESDAY. DRY AND COLD WEATHER RETURNS FOR THE END OF THE WEEK.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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TODAY... THE FAST MOVING LOW PRESSURE SYSTEM THAT BROUGHT LAST NIGHT/S SNOW HAS ALREADY EXITED THE REGION. A COLD FRONT WAS WORKING ACROSS THE REGION VERY EARLY THIS MORNING...BUT WITHOUT ANY PRECIPITATION. WINDS WILL PICKUP FROM THE WEST NORTHWEST SHORTLY AFTER SUNRISE. EXPECT IT TO BECOME WINDY BY LATE MORNING AND INTO THE AFTERNOON WITH WEST TO NORTHWEST GUSTS BETWEEN 30 AND 40 MPH. WE SHOULD SEE PARTIAL SUNSHINE...BUT ALSO A LOT OF STRATO-CUMULUS CLOUDS ESPECIALLY ACROSS THE INTERIOR. IT WILL BE DRY TODAY...OTHER THAN PERHAPS A PASSING FLURRY OR TWO ALONG THE EAST SLOPES OF THE BERKSHIRES. GIVEN THE INCREASING MARCH SUN ANGLE AND A WELL MIXED ATMOSPHERE...EXPECT HIGHS TO RECOVER INTO THE MIDDLE AND UPPER 30S. HOWEVER...IT WILL FEEL COLDER GIVEN THE WINDY CONDITIONS.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/...
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TONIGHT... A LARGE HIGH PRESSURE SYSTEM BUILDS IN FROM THE WEST. DIURNAL CUMULUS CLOUDS WILL DISSIPATE THIS EVENING...RESULTING IN MAINLY CLEAR SKIES. WINDS WILL ALSO GRADUALLY DIMINISH AND EVENTUALLY DECOUPLE IN THE TYPICAL LOCATIONS. THIS SHOULD ALLOW LOW TEMPS TO FALL WELL DOWN INTO THE SINGLE DIGITS TO EVEN BELOW ZERO IN THE NORMALLY COLDEST OUTLYING LOCATIONS. MEANWHILE...URBAN CENTERS OF DOWNTOWN BOSTON/PROVIDENCE WILL SEE LOW TEMPS IN THE MIDDLE TEENS. TUESDAY... HIGH PRESSURE WILL MOVE EAST OF THE REGION AS LOW PRESSURE TRACKS TOWARDS THE GREAT LAKES. PLENTY OF SUNSHINE IN THE MORNING WILL GIVE WAY TO MOSTLY CLOUDY SKIES TUE AFTERNOON. DRY WEATHER SHOULD PREVAIL EVERYWHERE THROUGH MID AFTERNOON...BUT WARM ADVECTION OVER THE COLD DOME SHOULD ALLOW LIGHT SNOW TO DEVELOP BY LATE AFTERNOON OR EARLY EVENING ACROSS WESTERN MA/NORTHERN CT. HIGH TEMPS AROUND 30 TO THE LOWER 30S...BUT WITH MUCH LESS WIND THEN TODAY.
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&& .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
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OVERVIEW AND MODEL PREFERENCES... LONGWAVE E CANADIAN TROF REMAINS THE DOMINANT FEATURE DEFINING THE DAILY SENSIBLE WX ACROSS THE NORTHEAST. GIVEN AO/NAO REMAIN MOSTLY NEGATIVE AND PNA SHIFTS FROM NEGATIVE TO NEAR NEUTRAL..SUSPECT LITTLE CHANGE WITH THIS FEATURE AT LEAST THROUGH THE LONG TERM. THEREFORE...EXCEPT WHERE THE SRN STREAM DOMINATES COMING OUT OF A SPLIT ROW REGIME UPSTREAM..EXPECT MAINLY BELOW NORMAL TEMPERATURES THROUGH AT LEAST THIS COMING WEEKEND. THE ONE CAVEAT...A PHASING OF STREAMS AS NRN AND SRN STREAM WAVES MERGE IN THE MIDDLE OF THE WEEK IS A TRICKY FORECAST...AS THE MID LVL WARMING IS LIKELY TO OCCUR MUCH FASTER THAN LOW LVL WARMING THANKS TO ENTRENCHED COLD AIR AND A DEEP SNOWPACK ACROSS THE REGION ARE LIKELY TO SLOW WARM ADVECTION NEAR THE SFC. A MIXED PRECIP EVENT IS LIKELY...BUT NAM/GFS REMAIN COLDER WHILE ECMWF REMAINS THE MORE AMPLIFIED /STARTING COLDER...BUT ENDING WARMER/ THAN THE REST OF THE GUIDANCE. ECMWF HAS COOLED A BIT THOUGH...LENDING SOME CONFIDENCE TO THE FACT THAT A BLEND OF THE ENSEMBLES /COOLER THAN THE ECMWF BUT WITH SOME WEIGHT TOWARD A WARMER SOLUTION/ WOULD BE THE BEST STARTING POINT FOR THIS PARTICULAR FORECAST. THIS ENSEMBLE BLEND WORKS WELL FOR THE REMAINDER OF THE FORECAST AS WELL. DETAILS... TUE NIGHT INTO WED... OVERVIEW... WITH A MERGER OF THE NRN STREAM /COLD AIR/ AND THE SRN STREAM /MORE MOISTURE AND WARMER AIR/ AS WELL AS A ROBUST 50+ KT H92 LLJ WILL LEAD TO STRONG ISENTROPIC LIFT AND OVERRUNNING AS ATTENDANT LOW PRES PASSES N OF THE REGION. MOISTURE THROUGH THE COLUMN IS RATHER HIGH...PWATS 2+ STD DEVIATIONS ABOVE NORMAL ARE LIKELY GIVEN THE SRN STREAM CONNECTION. WITH COLD AIR TO START...H92 TEMPS START ABOUT -6C AND H85 TEMPS START ABOUT-8C TUE EVENING...WARM ADVECTIVE OVERRUNNING WILL START AS SHIELD OF MODERATE SNOWFALL..SLR/S WILL BE GRADUALLY BECOMING LOWER HOWEVER AS WARM AIR MOVES LIFTS THE DENDRITE ZONE OUT OF PEAK OMEGA. THE ONLY FIGHTING CHANCE THE SNOW WILL HAVE INITIALLY IS UPPER LVL INSTABILITY WHERE H7-H4 LAPSE RATES INCREASE. THIS MAY AID THE LIFT SOMEWHAT AND PRODUCE ENOUGH DYNAMIC COOLING TO OVERCOME THE WARMING INITIALLY...BUT IT APPEARS THE MID LVL WARM AIR WILL WIN EVENTUALLY. WHAT THIS ALL MEANS IS THAT MODERATE TO HEAVY PRECIP WILL START AS SNOW...AND GRADUALLY TRANSITION TO A WINTRY MIX OF SLEET AND FREEZING RAIN...FOLLOWED BY ALL RAIN INTO THE DAY ON WED AS MID LVL TEMPS WARM INTO THE POSITIVE DIGITS. TIMING... SNOW WILL BEGIN LATE TUE IN WRN MA AND CT...THEN SPREAD E THROUGH THE LATE AFTERNOON AND EVENING HOURS. NOT OUT OF THE QUESTION A PERIOD OF 1+ INCH/HOUR RATES ARE OBSERVED GIVEN THE LIFT. THE SNOW WILL BECOME HEAVIER AND WETTER AS TIME PROGRESSES THROUGH THE OVERNIGHT. IT APPEARS...EVEN IN THE COLDER SOLUTIONS THAT A GRADUAL TRANSITION TO SLEET THEN FREEZING RAIN OCCURS MAINLY 10PM TO 4AM WED. HOWEVER...WITH DEEP SNOW...ANY RAIN COULD FREEZE ON CONTACT AS SFC TEMPS ARE LIKELY TO STAY A BIT COLDER THAN 2M TEMPS. THEREFORE...COULD SEE ICE ACCRETION EVEN AS OBSERVED TEMPS SHIFT INTO THE MID-UPPER 30S...AND LINGER INTO MORNING HOURS WED. HOWEVER...DRIER AND COOLER AIR WILL BE ATTEMPTING TO SHIFT IN DURING THE DAY AS A TRANSITION TO STRAIGHT RAIN OCCURS...SUCH THAT A LULL IN PRECIP IS POSSIBLE BY AFTERNOON. OTHERWISE...EXPECT MAINLY RAIN DURING THE MORNING WED. PRECIP TYPE/TOTALS... THE INITIAL SNOWFALL IS LIKELY TO BE MAINLY MODERATE...WITH PERIODS APPROACHING AN INCH/HOUR AND WELL END FIRST ALONG THE S COAST AND LAST AT THE MA/NH BORDER IN THE EARLY MORNING HOURS WED. SUSPECT THAT HIGHEST TOTALS WILL BE IN NW MA WHERE OROGRAPHIC LIFT ENHANCES SNOWFALL RATES. ACCUMS OF ADVISORY LVL LOOK LIKELY AS 0.25-0.5 INCHES OF QPF ARE LIKELY BEFORE THE CHANGE. INITIALLY A CHANGE TO SLEET IS EXPECTED IN HIGHER RETURNS...WITH A GRADUAL SHIFT TO FREEZING RAIN. ICE AMOUNTS ARE TRICKY...AS 2M TEMPS ARE LIKELY TO SKEW DATA. WITH DEEP SNOWPACK IN PLACE...WILL LIKELY SEE SOME ICE ACCRETION APPROACHING T-0.1 INCHES IN SPOTS...ESPECIALLY ON TOP OF THE AREA SNOWS. GRADUALLY...THE WARMING WILL LIKELY SHIFT INTO THE 40S /ESPECIALLY AFTER DAYLIGHT WED/ AND FURTHER ACCRETION WILL BECOME LIMITED. OTHER IMPACTS TO CONSIDER... THE LOWER SLR /HEAVIER-WETTER/ NATURE OF THE SNOW WILL EXACERBATE ROOF LOADING...AND IT ONLY GET/S WORSE WITH THE POTENTIAL FOR SOME HEAVY ICE ON TOP AND SOME LIQUID WATER GETTING INTO THE SNOWPACK. THEREFORE...THERE IS THE RISK FOR FURTHER ROOF COLLAPSES IF NOT TAKEN CARE OF. ALSO...AS A TRANSITION TO RAIN OCCURS...WILL LIKELY SEE A FAIR AMOUNT OF ROADWAY PONDING AND NUISANCE POOR DRAINAGE FLOODING ESPECIALLY DURING THE MORNING WED AS SOME SNOWMELT OCCURS AND DRAINS CLOG. NOT EXPECT MUCH IN THE WAY OF RIVERINE OR STREAM FLOODING AS THE SNOWPACK SHOULD EASILY HANDLE THE 1.00 INCHES OF TOTAL QPF EXPECTED. STAY TUNED FOR FURTHER DETAILS AS WE APPROACH. WED NIGHT INTO THU... ANOTHER PERIOD TO WATCH. THE LEFTOVER COLD FRONTAL BOUNDARY SHIFTS OFFSHORE LEADING TO A LULL WED AFTERNOON INTO WED EVENING. HOWEVER...MODELS CONTINUE TO HINT AT REASONABLY ROBUST ANAFRONTAL LOW PRES WAVE TRAVERSING THE FRONT LATE WED NIGHT INTO THU. THIS IS SOMEWHAT ATYPICAL TO SEE ONE OF THIS STRENGTH...BUT GIVEN THE UPPER LVL SHORTWAVE WILL BE ROTATING OVER FROM THE W AND DEEPENING SOME...IT CAN/T BE RULED OUT. THE BIG QUESTION HERE IS WHAT THE TEMPS WILL BE BY THIS TIME. WED COULD BE VERY WARM ESPECIALLY IF ANY SUNNY BREAKS ARE OBSERVED AND W WINDS ARE EXPECTED BY THE AFTERNOON. HOWEVER...BY THE OVERNIGHT PERIOD...COLD ADVECTION WILL HAVE BEGUN ALOFT...LOWERING THE DENDRITE ZONE. THEREFORE...YET ANOTHER ROUND OF LIGHT TO MODERATE SNOW IS POSSIBLE...WITH ACCUMS POSSIBLY REACHING ADVISORY LVL ON TOP OF THE SNOW AND ICE FROM THE PREVIOUS 24 HOURS. QPF VALUES OF 0.3-0.5 ARE PROGGED...WHICH WOULD SUGGEST EASY ACCUMS TO ADVISORY LVL. IT APPEARS THE PEAK WOULD BE MAINLY ALONG THE S COAST...AT LEAST THAT/S WHERE F-GEN AND MOISTURE SEEM TO BE MOST COINCIDENT. THU NIGHT INTO FRI... STRONG ARCTIC HIGH PRES MAKES A TRIUMPHANT RETURN TO THE REGION AS 1040+HPA IN THE MASS FIELDS COMBINE WITH -20C H85 TEMPS. EXPECT ANOTHER PERIOD OF COLD WITH POTENTIAL FOR SUB-ZERO NIGHTS AND HIGHS WELL BELOW NORMAL. IN FACT...CAN/T RULE OUT THE POTENTIAL NEED FOR WIND CHILL HEADLINES THU NIGHT AS THIS IS WHEN PRES GRADIENT APPEARS STRONG ENOUGH TO SUPPORT IT. NEXT WEEKEND... LOOKS MAINLY DRY AS HIGH PRES REMAINS IN CONTROL COULD SEE A WEAK UPPER DISTURBANCE AND ATTENDANT COLD FRONT ATTEMPT TO MAKE A PASSAGE. HOWEVER...VERY DRY AIRMASS IN PLACE COULD PREEMPT ANY PRECIPITATION ATTEMPTS. EARLY NEXT WEEK... HINTS AT ANOTHER POTENTIAL MODERATE LOW PRES WITH PRECIP IN TOW...HOWEVER LOTS OF UNCERTAINTY AS TO TIMING OR P-TYPES AT THIS TIME.
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&& .AVIATION /09Z MONDAY THROUGH FRIDAY/...
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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 TUESDAY/... TODAY...HIGH CONFIDENCE. LINGERING IFR CONDITIONS ACROSS CAPE/ISLANDS SHOULD IMPROVE TO VFR BY 11 OR 12Z. OTHERWISE...EXPECT VFR CONDITIONS TODAY DESPITE A SCATTERED TO EVEN BROKEN DECK OF STRATO-CUMULUS CLOUDS. WEST TO NORTHWEST WIND GUSTS OF 25 TO 35 ARE EXPECTED TO DEVELOP LATER THIS MORNING AND CONTINUE INTO THE AFTERNOON. TONIGHT...HIGH CONFIDENCE. WINDS GRADUALLY DIMINISH THIS EVENING WITH VFR CONDITIONS CONTINUING. TUESDAY...MODERATE TO HIGH CONFIDENCE. VFR CONDITIONS THROUGH AT LEAST MID AFTERNOON. MVFR-IFR CONDITIONS MAY DEVELOP BY LATE TUE AFTERNOON OR EARLY TUE EARLY EVENING ACROSS WESTERN MA/NORTHERN CT AS LIGHT SNOW DEVELOPS. KBOS TAF...HIGH CONFIDENCE. NORTHWEST WIND GUSTS OF 25 TO 35 KNOTS DEVELOP LATER THIS MORNING AND CONTINUE INTO THE AFTERNOON. KBDL TAF...HIGH CONFIDENCE. NORTHWEST WIND GUSTS OF 25 TO 35 KNOTS DEVELOP LATER THIS MORNING AND CONTINUE INTO THE AFTERNOON. OUTLOOK...TUESDAY NIGHT THROUGH FRIDAY... TUE NIGHT INTO WED...HIGH CONFIDENCE. PERIODS OF IFR AND OCCASIONAL IFR POSSIBLE. SNOW TO START...TRANSITIONING TO SLEET THEN FREEZING RAIN...THEN STRAIGHT RAIN THROUGH THE OVERNIGHT AND EARLY MORNING HOURS. SNOW ACCUMS GENERALLY 1-4 INCHES...ICE ACCUMS A TRACE TO A TENTH OF AN INCH POSSIBLE. SOUTHERLY WINDS WITH LLWS LIKELY. WED NIGHT INTO THU...MODERATE CONFIDENCE. AFTER A LULL IN PRECIP EARLY WED...A PERIOD OF RAIN TRANSITIONING TO SNOW IS POSSIBLE...ESPECIALLY TOWARD THE SOUTH COAST. VFR LIKELY NORTH...IFR LIKELY IN SNOWFALL. FRI...HIGH CONFIDENCE. CONDITIONS IMPROVE. VFR LIKELY.
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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 /TODAY THROUGH TUESDAY/... TODAY AND TONIGHT...HIGH CONFIDENCE. A COLD FRONT CROSSES THE REGION EARLY THIS MORNING AND WINDS WILL PICKUP QUICKLY AFTER SUNRISE. NORTHWEST WIND GUSTS OF 35 TO 40 KNOTS WILL DEVELOP BY LATE MORNING AND CONTINUE INTO THE EVENING IN THE COLD AIR ADVECTION PATTERN. GALE WARNINGS POSTED FOR ALL WATERS. WINDS WILL BEGIN TO DIMINISH FOR THE SECOND HALF OF THE NIGHT AS HIGH PRESSURE BEGINS TO BUILD IN FROM THE WEST. IN ADDITION...WIDESPREAD LIGHT FREEZING SPRAY EXPECTED TONIGHT. TUESDAY...HIGH CONFIDENCE. WINDS WILL HAVE DROPPED BELOW SMALL CRAFT ADVISORY THRESHOLDS BY EARLY MORNING AS HIGH PRESSURE BUILDS ACROSS THE WATERS. HOWEVER...LEFT OVER SWELL WILL KEEP SMALL CRAFT SEAS GOING ACROSS THE OUTER-WATERS UNTIL AROUND NOON. OUTLOOK...TUESDAY NIGHT THROUGH FRIDAY..MODERATE CONFIDENCE. TUE NIGHT INTO WED... LOW PRES MOVES WELL INLAND...WITH A PERIOD OF SNOW RAPIDLY CHANGING TO SLEET THEN RAIN ACROSS THE WATERS OVERNIGHT TUE NIGHT. LOW VSBYS EXPECTED. SLY WINDS GUST TO AROUND 25 KT AT TIMES WITH SEAS INCREASING 5-8 FT BY WED MORNING ON THE OCEAN WATERS. SMALL CRAFT ADVISORIES LIKELY. WED NIGHT INTO THU NIGHT... ANOTHER WAVE OF LOW PRES MOVES ALONG A STALLED FRONTAL BOUNDARY OVER THE WATERS. PRECIP CONTINUES. NW WINDS CONTINUE TO GUST 25 KT. ALSO...SEAS REMAIN ELEVATED 5-8FT. SMALL CRAFT ADVISORIES LIKELY CONTINUE. FRI... CONDITIONS IMPROVE...SMALL CRAFT ADVISORIES MAY BE ABLE TO BE TAKEN DOWN.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...NONE. MA...NONE. RI...NONE. MARINE...GALE WARNING FROM 11 AM THIS MORNING TO 1 AM EST TUESDAY FOR ANZ231-232-250-251-254-255. GALE WARNING FROM 11 AM THIS MORNING TO 11 PM EST THIS EVENING FOR ANZ233>235-237-256. GALE WARNING FROM 11 AM THIS MORNING TO 8 PM EST THIS EVENING FOR ANZ230-236.
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&& $$ SYNOPSIS...FRANK/DOODY NEAR TERM...FRANK SHORT TERM...FRANK LONG TERM...DOODY AVIATION...FRANK/DOODY MARINE...FRANK/DOODY

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