Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 181945 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 245 PM EST THU DEC 18 2014 .SYNOPSIS...
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DRY AND SEASONABLE CONDITIONS WILL PREVAIL FRIDAY. AN UPPER LEVEL DISTURBANCE AND MOIST NORTHEAST FLOW MAY BRING SOME LIGHT SNOW SHOWERS SATURDAY INTO SUNDAY. LOW PRESSURE MAY IMPACT THE REGION TUESDAY...WITH A MUCH STRONGER STORM LIKELY BRINGING HEAVY RAIN AND WIND TO SOUTHERN NEW ENGLAND WEDNESDAY INTO WEDNESDAY EVENING. DRY BUT VERY WINDY CONDITIONS FOLLOW FOR CHRISTMAS DAY.
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&& .NEAR TERM /THROUGH TONIGHT/...
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LOW PRES MOVES NE FROM THE MARITIMES BUT CYCLONIC FLOW WILL PERSIST ALONG WITH SOME MOISTURE IN THE COLUMN WHICH WILL KEEP A FEW CLOUDS ACROSS THE REGION ALTHOUGH DRY WEATHER EXPECTED. WHILE GUSTY WINDS WILL DIMINISH TONIGHT...THERE IS ENOUGH PRESSURE GRADIENT TO KEEP THE WINDS UP SO TEMPS WILL NOT DROP OFF THAT QUICKLY. USED A BLEND OF AVAILABLE GUIDANCE WHICH SUGGESTS MIN TEMPS MOSTLY IN THE 20S...WITH LOWER 30S OVER THE OUTER CAPE/ISLANDS.
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&& .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
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FRIDAY... HIGH PRES BUILDS ACROSS THE GT LAKES WITH NW FLOW ACROSS NEW ENG. TRICKY CLOUD FORECAST AS NAM INDICATING LOW LEVEL MOISTURE TRAPPED BELOW INVERSION WITH WIDESPREAD LOW CLOUDS...WHILE GFS AND ECMWF ARE DRIER IN THE LOW LEVELS. GIVEN LOW LEVEL FLOW IS STILL NW...WE WILL LEAN MORE OPTIMISTIC THAN NAM WITH A MIX OF CLOUDS AND SUN EXPECTED. TEMPS WILL LIKELY BE 3-5 DEGREES COLDER THAN TODAY GIVEN COOLING AT 925 MB...WITH MAX TEMPS RANGING FROM NEAR 30 HIGHER TERRAIN IN NORTHERN AND WESTERN MA TO UPPER 30S IN THE COASTAL PLAIN. FRIDAY NIGHT... MID LEVEL SHORTWAVE MOVES INTO W NEW ENG TOWARD DAYBREAK...BUT FORCING IS WEAK THROUGH MOST OF THE NIGHT AND MOISTURE IS LIMITED SO EXPECTING A MAINLY DRY NIGHT. HOWEVER...AS HIGH PRES BUILDS EASTWARD ACROSS QUEBEC LOW LEVEL WINDS BECOME NE AND MODELS INDICATE INCREASING LOW MOISTURE BACKING IN ACROSS SE NEW ENG OVERNIGHT. DELTA T FROM SST TO THE TOP OF THE MIXED LAYER IS AROUND 13C WHICH IS MARGINAL FOR OCEAN EFFECT AND OCEAN INDUCED CAPES ARE NOT IMPRESSIVE...BUT LOW LEVEL LAPSE RATES ARE INCREASING. MODELS DO SHOW SOME LIGHT QPF DEVELOPING SO THERE MAY BE A FEW SNOW SHOWERS DEVELOPING OVER CAPE COD AND ACK OVERNIGHT AND WE HAVE SOME LOW CHC POPS.
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&& .LONG TERM /SATURDAY THROUGH THURSDAY/... HIGHLIGHTS... * SCT SNOW/RAIN SHOWERS SAT INTO SUNDAY WITH BELOW AVG TEMPS * WEAK WAVE OF LOW PRESSURE ON TUESDAY * ANOMALOUS SYSTEM ACROSS THE GREAT LAKES WILL BRING HEAVY RAIN...GUSTY WINDS AND COASTAL CONCERNS AROUND CHRISTMAS EVE OVERVIEW... OVERALL 00Z GUIDANCE IS IN AGREEMENT SYNOPTICALLY WITH ISSUES ON TIMING AND SMALLER SCALE FEATURES. AMPLIFIED PATTERN SET TO RETURN TO THE U.S. AS THE STRONG W PACIFIC JET TRANSLATES DOWNSTREAM THIS WEEKEND INTO THE PAC NW. BUILDING HEIGHTS OVER SE CANADA SHOULD ALSO HELP DIG THE TROUGH INTO THE OHIO VALLEY MIDWEEK AND LIKELY CLOSE OFF AS IT SWINGS INTO SOUTHERN CANADA ON CHRISTMAS DAY. MODELS/ENSEMBLES HAVE BEEN FAIRLY CONSISTENT IN RECENT RUNS ON THIS AMPLIFIED PATTERN AND THE MOST RECENT GEFS/ECMWF ENSEMBLE GUIDANCE SHOW GOOD CORRELATION TO NEXT THURSDAY. DURING THIS SYNOPTIC TRANSITION...HIGH PRESSURE AND UPPER LEVEL RIDGE WILL BE OVER THE NORTHEAST SATURDAY INTO SUNDAY. DIGGING TROUGH OVER THE CENTRAL CONUS WILL PUSH A SHORTWAVE ACROSS THE SE INTO THE MID-ATLANTIC. APPEARS THAT A WEAK COASTAL LOW WILL DEVELOP MOVING TOWARDS THE REGION MONDAY INTO TUESDAY. THE GFS BRINGS THIS LOW OVER THE BENCHMARK WHERE THE EC PUSHES WELL EASTWARD THANKS TO BUILDING HIGH PRESSURE OVER EASTERN CANADA. THIS SYSTEM IS WEAK SO COASTAL REGIONS HAVE THE BEST SHOT FOR PRECIP. AS THIS SYSTEM DEPART APPEARS ANOMALOUS LOW OVER THE GREAT LAKES WILL DEVELOP A SECONDARY LOW CLOSER TO NEW ENGLAND. THE GFS IS STILL A TAD FASTER COMPARED TO THE EC BUT OVERALL EXCELLENT MODEL AGREEMENT 6+ DAYS OUT. DETAILS... SATURDAY INTO SUNDAY...HIGH CONFIDENCE. HIGH PRESSURE IN EASTERN CANADA WILL BUILD ACROSS THE REGION FRIDAY NIGHT INTO SATURDAY. HOWEVER IT APPEARS ON FRIDAY NIGHT INTO SATURDAY NORTHERLY FLOW MAY ALLOW FOR SOME OCEAN EFFECT CLOUDS/SNOW SHOWERS TO IMPACT THE CAPE. SURFACE TO 850 MB TEMP DIFFERENCE IS 14C WHICH IS UNSTABLE ENOUGH FOR SNOW SHOWERS ON SATURDAY FOR THE CAPE. AM NOT ANTICIPATE MUCH IN THE WAY OF ACCUMULATIONS BUT A DUSTING CANNOT BE RULED OUT. WEAK WAVE WILL MOVE THROUGH THE FLOW ON SATURDAY NIGHT AND WITH HIGH PRESSURE SHIFTING EASTWARD EXPECT ONSHORE EASTERLY FLOW. GUIDANCE CONTINUES TO SHOW QPF MOVING ONSHORE AND WITH MOISTURE AND THE LIFT COULD SEE SNOW SHOWERS MOVING INLAND SATURDAY NIGHT INTO SUNDAY. BIGGEST QUESTION IS WILL THE MOISTURE SATURATE ENOUGH TO -6C. IF NOT THEN THE POTENTIAL FOR FREEZING DRIZZLE IS POSSIBLE. FOR NOW BELIEVE THAT THERE IS ENOUGH MOISTURE SO A QUICK HALF INCH TO AN INCH IS POSSIBLE PER SOUNDINGS EAST OF THE WORCESTER HILLS. MONDAY INTO TUESDAY...MODERATE CONFIDENCE. WEAK COASTAL LOW PRESSURE SYSTEM WILL DEVELOP AND MOVE SOMEWHERE BETWEEN THE BENCHMARK AND WELL OFFSHORE. BELIEVE A SOLUTION FATHER OUT TO SEA IS POSSIBLE DUE TO STRONG HIGH PRESSURE IN EASTERN CANADA. REGARDLESS A ROUND OF SHOWERS WILL MOVE ACROSS THE REGION WITH THE COASTAL AREAS HAVING THE BEST SHOT TO SEE PRECIP. THERMAL PROFILES WILL ALLOW FOR SNOW AT NIGHT AND RAIN DURING THE DAY. TEMPERATURES WILL SLOWLY BEGIN TO WARM AS SOUTHERLY FLOW BECOMES DOMINATE OUT AHEAD OF STRONGER SYSTEM TO THE EAST. TUESDAY HIGH TIDE WILL BE 11.6 IN BOSTON DURING THE LATE MORNING AND WITH ANY EASTERLY FLOW MAY ALLOW FOR MINOR COASTAL FLOODING. WEDNESDAY INTO THURSDAY...HIGH CONFIDENCE IN SYSTEM LOW CONFIDENCE ON DETAILS. STRONG ANOMALOUS SYSTEM WILL STRENGTHEN OVER THE GREAT LAKES...DEVELOPING A SECONDARY SURFACE LOW JUST WEST OF SOUTHERN NEW ENGLAND. STILL A LOT OF DETAILS TO WORK OUT AS THIS SYSTEM IS STILL 6 DAYS AWAY...HOWEVER ENSEMBLES SHOW THAT THIS SYSTEM IS AROUND 2 TO 3 STANDARD DEVIATIONS ALLOWING FOR INCREASING CONFIDENCE THAT A POTENT STORM WILL OCCUR. LATEST 00Z GUIDANCE SHOWS THAT MOST PRECIP WILL BE LIQUID WITH A DEEP SUBTROPICAL CONNECTION BACK ACROSS MEXICO... PW ANOMALIES FORECAST TO RISE TO BETWEEN +1 TO +3 /OR HIGHER/...AND TEMPERATURES WELL ABOVE AVERAGE. IN FACT WE MAY BE CLOSE AT BREAKING RECORD HIGH TEMPS IF TEMPS WARM TO 60F OR ABOVE ON CHRISTMAS EVE. AS THE SYSTEM WRAPS UP INTO CANADA...COLD AIR ADVECTION SHOULD CIRCULATE AROUND AND BEGIN A TRANSITION FROM SOUTHWEST TO NORTHEAST IN TURNING P-TYPE TO SNOW. THIS SYSTEM IS QUITE STRONG SO WE WILL NEED TO WATCH FOR POSSIBLE URBAN FLOODING ISSUES AS WELL AS WIND ISSUES. GUIDANCE RIGHT NOW IS SHOWING A 40 TO 50 KT JET AT 925 MB WHICH MAY WARRANT WIND ADVISORIES BUT THIS SYSTEM COULD STRENGTHEN EVEN MORE SO A STRONGER JET IS POSSIBLE. LASTLY COASTAL FLOODING ISSUES WILL NEED TO BE ADDRESS AS HIGH TIDE ON WED AND THUS ARE 11.7 AND 11.5 RESPECTIVELY. ANY ONSHORE COMPONENT WILL PUSH THE TIDE ABOVE FLOOD SO COASTAL FLOODING IS POSSIBLE AS WELL AS BEACH EROSION. && .AVIATION /19Z 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 /TODAY THROUGH FRIDAY NIGHT/... THROUGH 00Z...LOW VFR/MVFR CIGS AROUND 3000-3500 FT. TREND SHOULD BE FOR CLOUD DECK TO BECOME SCT TOWARD 00Z..ESPECIALLY NEAR THE COAST. W/NW GUSTS TO 25-30 KT. TONIGHT...MODERATE CONFIDENCE. MAINLY VFR...BUT LINGERING MVFR CIGS POSSIBLE IN THE WEST. DIMINISHING WIND. FRIDAY...LOW CONFIDENCE DUE TO UNCERTAINTY WITH EXTENT OF ANY MVFR CIGS. WE HAVE MAINLY VFR IN THE TAFS WITH POCKETS OF MVFR...BUT IT IS POSSIBLE MVFR CIGS COULD BE MORE EXPANSIVE IF LOW LEVEL MOISTURE BECOMES TRAPPED BELOW THE INVERSION. LATER FORECASTS WILL NEED TO REEVALUATE THIS. FRIDAY NIGHT...MODERATE CONFIDENCE. MAINLY VFR...BUT MVFR CIGS FROM THE OCEAN EXPANDING WEST ACROSS E MA. LOW PROB FOR SOME OCEAN EFFECT SNOW SHOWERS OVER CAPE COD AND ACK AFTER MIDNIGHT. KBOS TERMINAL...MODERATE CONFIDENCE. MAINLY VFR...BUT LOW PROB FOR MVFR CIGS FRIDAY. KBDL TERMINAL...MODERATE CONFIDENCE. SHOULD SEE MVFR CIGS SCATTER OUT THIS EVENING. MVFR CIGS MAY RETURN FRI BUT THIS IS UNCERTAIN. OUTLOOK...SATURDAY THROUGH MONDAY... SATURDAY INTO SUNDAY...HIGH CONFIDENCE. MOSTLY VFR WITH MVFR CONDITIONS ANY SCT SNOW/RAIN SHOWERS. MONDAY...LOW CONFIDENCE. VFR CONDITIONS.
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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 FRIDAY NIGHT/...HIGH CONFIDENCE. TONIGHT...W/NW GUSTS 25-30 KT WILL LINGER OVER THE WATERS INTO THIS EVENING BEFORE DIMINISHING OVERNIGHT. SCA HEADLINES WILL CONTINUE TONIGHT. FRIDAY...NW WINDS WILL BE BELOW SCA THRESHOLDS...BUT HAZARDOUS SEAS WILL CONTINUE THROUGH THE MORNING OVER THE OUTER EASTERN WATERS...BEFORE SUBSIDING BELOW SCA. WILL LIKELY NEED TO EXTEND THE SCA FOR SEAS INTO FRI MORNING. FRIDAY NIGHT...N/NW WINDS AND SEAS BELOW SCA. OUTLOOK...SATURDAY INTO MONDAY...MODERATE TO HIGH CONFIDENCE. FRIDAY NIGHT INTO SUNDAY...ANTICIPATE DIMINISHING WINDS AND SEAS SUBSIDING LATE THU NIGHT INTO SATURDAY LEADING TO BELOW SMALL CRAFT ADVISORY LEVELS. MONDAY...EXPECT NE WINDS GUSTING UP TO 20 KT. LOW PROB OF 25 KT GUSTS AS WELL AS 5 FT SEAS.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...NONE. MA...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 1 AM EST FRIDAY FOR ANZ231-232-251. SMALL CRAFT ADVISORY UNTIL 11 PM EST THIS EVENING FOR ANZ233>235-237. SMALL CRAFT ADVISORY UNTIL 10 PM EST THIS EVENING FOR ANZ230- 236. SMALL CRAFT ADVISORY UNTIL 6 AM EST FRIDAY FOR ANZ250-254>256.
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&& $$ SYNOPSIS...KJC NEAR TERM...KJC SHORT TERM...KJC LONG TERM...DUNTEN AVIATION...KJC/DUNTEN MARINE...KJC/DUNTEN

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