Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 192226 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 526 PM EST FRI DEC 19 2014 .SYNOPSIS... A WEAK DISTURBANCE AND ONSHORE FLOW WILL RESULT IN A PERIOD OF LIGHT SNOW/RAIN SHOWERS MAINLY ACROSS EASTERN NEW ENGLAND THIS WEEKEND INTO EARLY NEXT WEEK. LOW PRESSURE WILL PASS SOUTH OF NEW ENGLAND...BRINGING ANOTHER PERIOD OF PRECIPITATION. A MUCH STRONGER STORM PASSING WEST OF NEW ENGLAND WILL BRING HEAVY RAINFALL...GUSTY WINDS AND COASTAL FLOODING CONCERNS TO THE REGION WEDNESDAY INTO WEDNESDAY EVENING. DRY BUT VERY WINDY CONDITIONS FOLLOW FOR CHRISTMAS DAY INTO FRIDAY. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... PARTIAL CLEARING PUSHING SOUTH ACROSS NE MA THIS AFTERNOON AS LOW LEVEL DRIER AIR MOVES IN FROM THE N. NAM IS HANDLING THIS LOW LEVEL DRY AIR FAIRLY WELL AND SHOWS DRIER AIR OVERSPREADING MUCH OF CENTRAL AND WESTERN ZONES TONIGHT WHICH SHOULD LEAD TO SOME CLEARING. HOWEVER...LOW LEVEL MOISTURE WILL REMAIN LOCKED IN ACROSS CAPE COD AND BACK IN ACROSS SE MA OVERNIGHT. IT LOOKS MOSTLY DRY THROUGH THE NIGHT. MIN TEMPS MOSTLY IN THE 20S...WITH LOWER 30S OUTER CAPE/ACK. TEMPS COULD DROP INTO THE TEENS N AND W MA IF THERE IS SUFFICIENT CLEARING. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... HIGH PRES BUILDS ACROSS N MAINE AND THE MARITIMES WITH LOW LEVEL FLOW VEERING TO THE E WHILE SFC WINDS MOSTLY NE. THIS WILL RESULT IN LOW CLOUDS EXPANDING WEST ACROSS SNE DURING SAT AS LOW LEVEL MOISTURE INCREASES. NOT REALLY LOOKING AT A PURE OCEAN EFFECT SITUATION AS INSTABILITY IS MARGINAL. HOWEVER...HI-RES GUIDANCE PICKING UP ON A DEVELOPING COASTAL FRONT ACROSS CAPE COD VICINITY WITH E WINDS TO THE E OF THE BOUNDARY AND N/NE WINDS TO THE WEST. LOW LEVEL FORCING COMBINED WITH DEEPENING MOISTURE AS MID LEVEL SHORTWAVE MOVES IN FROM THE WEST WILL RESULT IN RAIN/SNOW SHOWERS EXPANDING WEST FROM CAPE COD INTO EASTERN HALF NEW ENG. WHILE SOME LIGHT PRECIP IS POSSIBLE IN THE MORNING...ESPECIALLY CAPE COD...BULK OF PRECIP OCCURS LATER SAT INTO SAT NIGHT ASSOCD WITH DEEPER MOISTURE AND LOW LEVEL LIFT FROM THE COASTAL FRONT/INVERTED TROF. PTYPE/SNOW ACCUM... LOOKING AT MOSTLY RAIN FOR CAPE/ISLANDS AND POSSIBLY INTO SE COASTAL PLYMOUTH COUNTY WHERE E WINDS WILL SUFFICIENTLY WARM THE BOUNDARY LAYER KEEPING TEMPS IN THE MID/UPPER 30S. HOWEVER...JUST INLAND AND NORTH FROM THE IMMEDIATE SE COAST AND WEST OF THE COASTAL FRONT WHERE WINDS ARE FORECAST TO BE MORE NORTHERLY...EXPECT MOSTLY SNOW ALTHOUGH THERE COULD BE A MIX AT THE START. FREEZING DRIZZLE IS NOT LIKELY AS THE COLUMN MOISTENS LATE SAT INTO SAT NIGHT WITH TEMPS -10C IN THE MOIST LAYER WHICH IS COLD ENOUGH FOR ICE CRYSTAL PRODUCTION. NAM IS PICKING UP ON SOME ENHANCEMENT IN N PLYMOUTH COUNTY INTO NORFOLK COUNTY WITH QPF UP TO A THIRD OF AN INCH. THIS LIKELY ASSOCD WITH A 20-25 KT E/NE LOW LEVEL JET THAT THE NAM IS FORECASTING. HOWEVER...THIS MIGHT BE OVERDONE AS HI-RES WRF QPF IS LESS AND OTHER MODELS ARE WEAKER WITH THE LOW LEVEL NE FLOW. DONT WANT TO COMPLETELY IGNORE THE NAM AS IT SOMETIMES CAN PICK UP ON HEAVIER MESOSCALE PRECIP IN THESE SITUATIONS SO USED A BLEND OF NAM/GFS QPF TO TEMPER NAM OUTPUT. MAINLY LOOKING AT A COATING TO AN INCH FOR EASTERN NEW ENG...HIGHEST AMOUNTS ACROSS E MA AWAY FROM THE IMMEDIATE COAST. LOCALIZED AMOUNTS UP TO 2 INCHES POSSIBLE...ESPECIALLY JUST SW OF BOSTON. && .LONG TERM /SUNDAY THROUGH FRIDAY/... HIGHLIGHTS... * SCT SNOW/RAIN SHOWERS LINGER ON SUNDAY WITH SLIGHTLY BELOW NORMAL TEMPS * WEAK LOW PRES WILL PASS SOUTH OF NEW ENGLAND MONDAY NIGHT AND TUESDAY BRINGING LIGHT PRECIPITATION...AS WELL AS A WINTRY MIX TO THE INTERIOR * STRENGTHENING LOW PRES WILL WRAP UP AROUND ANOMALOUS VORTEX ACROSS THE GREAT LAKES...BRINGING HEAVY RAIN...GUSTY WINDS AND COASTAL CONCERNS TO THE REGION LATE WEDNESDAY INTO CHRISTMAS EVE OVERVIEW AND MODEL PREFERENCES... MEDIUM RANGE MODEL SUITE CONTINUES TO SIGNAL DEVELOPMENT OF AMPLIFIED UPPER LEVEL PATTERN ACROSS NORTH AMERICA THROUGH THIS FORECAST PERIOD. AN H5 CUTOFF VORTEX WILL DOMINATE ACROSS THE GREAT LAKES AND ITS EXTENDING LONG WAVE TROUGH WRAPPING AROUND TO THE EASTERN SEABOARD AS IT BECOMES NEGATIVELY TILTED. WITH OVERALL SW FLOW IN PLACE...WILL SEE WEAK SYSTEMS WORK TOWARD THE REGION EARLY IN THE PERIOD. A STRONGER LOW WILL DEVELOP NEAR OR JUST OFF THE SE U.S. COAST AROUND EARLY WED AND PASS W OF THE REGION WED NIGHT... BRINGING GUSTY WINDS...HEAVY RAINFALL WITH A FEW THUNDERSTORMS POSSIBLE AS WELL AS POSSIBLE COASTAL CONCERNS. WHILE THERE ARE STILL SOME TIMING AND TRACK VARIANCES WITH THE MID WEEK SYSTEM...MODELS AND ENSEMBLES REMAIN IN GOOD AGREEMENT WITH THE DEVELOPMENT OF THIS AMPLIFIED PATTERN...AS WELL AS THE UPPER LEVEL VORTEX ACROSS THE GREAT LAKES AND SURFACE SYSTEM THAT WILL MORE THAN LIKELY AFFECT THE REGION DURING THE WEDNESDAY-WEDNESDAY NIGHT TIMEFRAME. USED A BLEND OF AVAILABLE GUIDANCE AS WELL AS GFS/EC ENSEMBLE MEANS FOR THIS FORECAST WHICH SHOWED GOOD CONTINUITY TO THE PREVIOUS FORECAST. DETAILS... SUNDAY AND MONDAY...MODERATE TO HIGH CONFIDENCE. LEFTOVER MOISTURE WILL LINGER SUNDAY MORNING WITH LIGHT RAIN AND/OR SNOW SHOWERS MAINLY ACROSS E MA/RI THOUGH COULD SEE SOME ISOLD ACTIVITY FURTHER INLAND AS COASTAL FRONT WEAKENS. RIDGING WILL NOSE DOWN THE COAST FROM HIGH PRES OVER NORTHERN NEW ENGLAND AND QUEBEC SUN NIGHT INTO MONDAY...BRINGING A BRIEF DRY PERIOD THOUGH CLOUDS WILL LINGER WITH A CONTINUED ONSHORE WIND FLOW...ALBEIT WEAK. EXPECT TEMPS TO RUN NEAR OR SLIGHTLY BELOW NORMAL...THOUGH WILL BE A BIT MILDER ALONG THE S COAST DURING MON. BY LATE MONDAY...MAY START TO SEE SOME PRECIP WORK INTO THE LOWER CT VALLEY AS A WEAK LOW MOVES OFF THE MID ATLC COAST. MONDAY NIGHT-TUESDAY...MODERATE CONFIDENCE. WEAK COASTAL LOW WILL PASS OFF THE SOUTH COAST...BUT WILL BRING ENOUGH MOISTURE AND LIFT FOR PRECIP TO MOVE IN FROM S-N. TEMPS WILL STILL BE CHILLY THOUGH...ESPECIALLY INLAND THERE THE COLDER AIR WILL BE TRAPPED... SO WILL SEE SOME MIXED PRECIP /SLEET AND/OR FREEZING RAIN/. EVEN THOUGH QPF WILL BE LIGHT...COULD BE ENOUGH TO CAUSE SOME LIGHT GLAZING PROBLEMS LATE MON NIGHT INTO TUE MORNING. STILL SOME TIMING ISSUES AS WELL AS QUESTIONS WITH THERMAL PROFILES...BUT MAY NEED WINTER WX HEADLINES DURING THIS TIMEFRAME. SOMETHING TO MONITOR CLOSELY. BY TUE AFTERNOON...TEMPS SHOULD RECOVER WITH GRADUALLY INCREASING E-SE WINDS...SO WILL SEE ALL RAIN BY THEN. HIGHS ON TUE WILL RANGE FROM THE UPPER 30S ACROSS THE HIGHER INLAND TERRAIN TO THE MID AND UPPER 40S ALONG THE COAST. ONE OTHER ISSUE THAT MAY NEED ATTENTION WILL BE THE LONG EASTERLY FETCH AND INCREASING ASTRONOMICAL TIDES ON TUESDAY. BOSTON HARBOR/S HIGH TIDE OCCURS AT 1142 AM AT 11.6 FEET. SURFACE WINDS LOOK TO REMAIN AT 15 KT OR LESS BUT...WITH THE MAINLY EASTERLY WIND DIRECTION OVER SEVERAL DAYS...MAY SEE SOME GROUND SWELLS WORK IN WHICH COULD CAUSE SOME POSSIBLE SPLASHOVER DURING THE MIDDAY TIDE. WEDNESDAY AND THURSDAY...HIGH CONFIDENCE IN SYSTEM DEVELOPMENT AND EFFECTS...LOW TO MODERATE CONFIDENCE ON TIMING DETAILS. WILL SEE STRONG SURFACE SYSTEM AND ITS ASSOCIATED H5 CUTOFF VORTEX WILL BE INTENSIFYING DURING THIS TIMEFRAME...WHILE LONG WAVE TROUGHING WILL BECOME NEGATIVELY TILTED AROUND THE MID ATLC OR SE U.S. COAST. A SECONDARY LOW...WITH ENERGY AND TROPICAL MOISTURE WORKING IN FROM THE GULF OF MEXICO...WILL INTENSIFY DURING WED AS IT WRAPS AROUND THE LARGER UPPER LEVEL CIRCULATION. LOOKS LIKE THIS LOW WILL PASS W OF THE REGION...BUT WILL BE IN THE AREA OF BEST MOISTURE CONVERGENCE AND TRANSPORT UP THE EASTERN SEABOARD. THE 12Z GFS IS BULLISH IN BRINGING SLUG OF HEAVY QPF ACROSS THE REGION. BOTH THE 12Z EC AND GGEM ALSO SIGNAL THIS INFLUX THOUGH NOT QUITE AS HIGH ON THE PRECIP AMTS. STILL NOTING PWATS AT 1.4 TO 1.5 INCHES...RUNNING 2-3SD ABOVE SEASONAL NORMALS AT ABOUT THE TIME OF THE HEAVIEST PRECIP LATE WED INTO WED EVENING. ON TOP OF THIS...SOME GOOD INSTABILITY MOVES ACROSS WITH K INDICES IN THE LOWER-MID 30S AND TOTAL TOTALS IN THE LOWER 50S. WOULD NOT BE SURPRISED TO SEE SOME ISOLD THUNDER SO MENTIONED IN THE FORECAST MAINLY DURING WED NIGHT...ALONG WITH HEAVY RAINFALL FROM THE CONVECTION. LOW LEVEL JET ON ORDER OF 40-55 KT AT H85 AND 50-60 KT AT H925...SO COULD ALSO SEE GUSTY WINDS ESPECIALLY WITH ANY STORMS. OH...ONE MORE THING...THERE WILL BE A BRIEF BURST OF MILDER AIR THAT WORKS IN WITH THIS SYSTEM. EXPECT TEMPS TO RISE TO THE MID 40S WELL INLAND TO THE MID 50S AT THE COAST...BUT WILL NOT TOP OFF UNTIL CLOSE TO MIDNIGHT WED NIGHT...WHICH WILL HELP SUPPORT THE INSTABILITY. MODELS CONTINUE TO SIGNAL FAST MOVEMENT OF THE SURFACE SYSTEM LATE WED NIGHT...WITH DRY SLOT WORKING ACROSS THE REGION AFTER MIDNIGHT WITH DRY CONDITIONS BY DAWN ON CHRISTMAS MORNING. WINDS WILL QUICKLY SHIFT AROUND TO W-SW AND WILL BECOME VERY GUSTY WITH THE LOW LEVEL JET IN PLACE AND COLDER AIR WRAPPING IN. MAY HAVE SOME COASTAL FLOODING ISSUES WITH HIGHEST ASTRONOMICAL TIDES OF THE MONTH OCCUR ON WED AND THU...UP TO 11.7 FT AND 11.5 FT RESPECTIVELY FOR BOSTON. ANY EASTERLY COMPONENT WILL PUSH THE TIDE ABOVE FLOOD...SO COASTAL FLOODING IS POSSIBLE AS WELL AS BEACH EROSION ON THE WED TIDE ALONG E FACING BEACHES. THE SOUTH COASTLINE WILL ALSO HAVE TO BE WATCH CLOSELY ON THU AS WINDS SHIFT TO W- SW...THOUGH E COASTAL AREAS COULD SEE PROBLEMS WITH CONTINUED E SWELLS. AS MENTIONED ABOVE...STRONG SOUTHERLY JET DEVELOPS WED INTO THU AND...WITH ASTRONOMICAL HIGH TIDES...COULD ALSO SEE MINOR TO MODERATE COASTAL FLOODING. ANOTHER ISSUE IS THE POTENTIAL PRESSURE FALLS IF THIS SYSTEM STRENGTHENS EVEN MORE...IT COULD ADD ANOTHER FOOT ONTO THE SURGE. FRIDAY...LOW CONFIDENCE. ONCE UPPER LOW AND SURFACE SYSTEM MOVES INTO SOUTHERN CANADA... EXPECT A RATHER FAST UPPER W FLOW IN PLACE. MAY SEE SOME LEFTOVER SNOW SHOWERS ACROSS THE E SLOPES OF THE BERKSHIRES. GUSTY W-SW WINDS CONTINUE AS TEMPS FALL BACK TO MORE SEASONABLE LEVELS. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /TODAY THROUGH SATURDAY/... THROUGH 00Z...LOW VFR AND MVFR CIGS WILL PERSIST...BUT BECOMING VFR ALONG THE E MA COAST AS CLEARING MOVES IN FROM THE N. TONIGHT...MODERATE CONFIDENCE. EXPECT PARTIAL CLEARING AND BECOMING VFR DURING THE NIGHT AS LOW LEVEL DRY AIR MOVES SOUTH ACROSS THE REGION. HOWEVER...LOW CLOUDS AND MVFR CIGS OVER THE OUTER CAPE WILL GRADUALLY BACK IN ACROSS SE MA OVERNIGHT. SATURDAY...MODERATE CONFIDENCE. MVFR CIGS ACROSS SE NEW ENG WILL EXPAND WEST ACROSS THE REST OF THE COASTAL PLAIN THEN INTO THE INTERIOR DURING THE AFTERNOON. CT VALLEY SHOULD REMAIN VFR. SCATTERED RAIN SHOWERS WILL DEVELOP OVER CAPE COD WITH SNOW SHOWERS INTO E MA BY LATE AFTERNOON. SATURDAY NIGHT...MODERATE CONFIDENCE. WIDESPREAD MVFR CIGS WITH POCKETS OF IFR E MA COAST. PERIODS OF LIGHT RAIN OVER CAPE COD WITH LIGHT SNOW FURTHER INLAND ACROSS E MA. MINOR ACCUM POSSIBLE ACROSS E MA JUST INLAND FROM THE IMMEDIATE COAST. KBOS TERMINAL...MODERATE CONFIDENCE IN TAF. EXPECT VFR TONIGHT...BEFORE MVFR CIGS DEVELOP SAT MORNING. KBDL TERMINAL...MODERATE CONFIDENCE IN TAF. OUTLOOK...SUNDAY THROUGH WEDNESDAY... SUNDAY...HIGH CONFIDENCE. MAINLY VFR ACROSS CENTRAL AND WESTERN AREAS. E MA/RI...MAY SEE LOCAL MVFR CONDITIONS IN RAIN/SNOW SHOWERS INTO THE AFTERNOON...THEN SLOW IMPROVEMENT FROM W-E. MONDAY...MODERATE CONFIDENCE. MAINLY VFR. MONDAY NIGHT-TUESDAY...MODERATE CONFIDENCE. DEVELOPING RAIN OR MIXED PRECIP FROM S-N MON NIGHT WITH MVFR CONDITIONS. MAY SEE -FZRA/-PL ACROSS CENTRAL AND WESTERN AREAS AROUND OR AFTER MIDNIGHT INTO TUE MORNING THEN SHOULD CHANGE TO RAIN AS TEMPS RISE. E-SE WINDS GUSTING TO 20-25 KT ALONG S COAST TUE. TUESDAY NIGHT-WEDNESDAY...MODERATE CONFIDENCE. MVFR-IFR CONDITIONS IN RAIN...HEAVY AT TIMES DURING WED. ISOLD THUNDER POSSIBLE WED AFTERNOON/EVENING. E WINDS SHIFTING TO SE-S LATE TUE NIGHT/WED WITH GUSTS UP TO 25-30 KT...HIGHEST ACROSS CAPE COD AND THE ISLANDS. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /TODAY THROUGH SATURDAY NIGHT/...HIGH CONFIDENCE. HIGH PRESSURE BUILDING EAST N MAINE AND THE MARITIMES WILL KEEP WINDS/SEAS BELOW SCA THRESHOLDS THROUGH SATURDAY NIGHT...WITH WIND SPEEDS LESS THAN 20 KT. NORTHERLY WINDS TONIGHT BECOMING NE SAT/SAT NIGHT. GUSTS UP TO 20 KT POSSIBLE SAT NIGHT ACROSS NE MA COASTAL WATERS. OUTLOOK...SUNDAY THROUGH WEDNESDAY...MODERATE TO HIGH CONFIDENCE. SUNDAY THROUGH MONDAY NIGHT...WINDS AND SEAS BELOW SMALL CRAFT CRITERIA. E WINDS GUSTING UP TO 20 KT MON NIGHT. TUESDAY-WEDNESDAY...E WINDS INCREASE...GUSTING TO 30 KT TUE THEN SHIFT TO SE GUSTING TO 30-35 KT WED HIGHEST ON THE OUTER WATERS. SEAS BUILD UP TO 7-11 FT BY WED. GALES ON THE OUTER WATERS LIKELY. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...KJC/EVT NEAR TERM...KJC SHORT TERM...KJC LONG TERM...EVT AVIATION...KJC/EVT MARINE...KJC/EVT

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