Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 192030 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 330 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. LOW PRESSURE WILL PASS NEAR THE REGION ON TUESDAY...BRINGING A PERIOD OF PRECIPITATION. A MUCH STRONGER STORM IS LIKELY TO BRING HEAVY RAIN...WIND AND COASTAL FLOODING CONCERNS TO SOUTHERN NEW ENGLAND WEDNESDAY INTO WEDNESDAY EVENING. DRY BUT VERY WINDY CONDITIONS FOLLOW FOR CHRISTMAS DAY. && .NEAR TERM /THROUGH TONIGHT/... 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 /SATURDAY 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 SUNDAY WITH AVG TEMPS * WEAK WAVE OF LOW PRESSURE MON NIGHT/TUESDAY COULD BRING WINTRY MIX TO INTERIOR * 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. AN AMPLIFIED MID-UPPER LEVEL TROUGH AND PCPN FOCUSING LEAD SURFACE LOW/FRONTAL SYSTEM DEVELOPS OVER THE CENTRAL US BY EARLY NEXT WEEK. THE SUPPORTING AND INCREASINGLY NEG-TILT TROUGH ALOFT WORKS OVER THE ERN US AND OUT THROUGH THE NERN STATES INTO DAYS 5/6 WED/THU. 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 NIGHT BEFORE DEPARTING LATE SUNDAY. LONGWAVE DIGGING TROUGH OVER THE CENTRAL CONUS WILL PUSH A FEW SHORTWAVES THROUGH THE FLOW. FIRST ONE DEVELOPS A WEAK COASTAL LOW MOVING TOWARDS THE REGION LATE MONDAY INTO TUESDAY. THERE IS STILL SOME UNCERTAINTY WITH THE LOCATION OF THIS SYSTEM BUT APPEARS THAT THERE WILL BE SNOW/WINTRY MIX IN THE INTERIOR. AS THIS SYSTEM DEPARTS APPEARS AN ANOMALOUS LOW OVER THE GREAT LAKES WILL DEVELOP A SECONDARY LOW /DOUBLE BARREL LOW/ CLOSER TO NEW ENGLAND...PER ENSEMBLE GUIDANCE. STILL A GOOD AMOUNT OF SPREAD BUT IF THIS DOUBLE LOW DOES DEVELOP THEN THE RAIN AND WIND ASPECT OF THE SYSTEM INCREASES...DETAILS BELOW. STILL SOME UNCERTAINTY WITH THIS PARTICULAR SYSTEM BUT WITH 2 TO 3 SD AWAY AND GENERAL MODEL AGREEMENT HAVE HIGHER CONFIDENCE THIS SYSTEM WILL IMPACT SOUTHERN NEW ENGLAND. DETAILS... MONDAY INTO TUESDAY...MODERATE CONFIDENCE. WEAK COASTAL LOW PRESSURE SYSTEM WILL DEVELOP AND MOVE CLOSE TO THE SOUTHERN NEW ENGLAND COASTLINE. THERE IS STILL DESCENT MODEL SPREAD ON THE EXACT LOW TRACK BUT APPEARS THAT IT DOES WEAKEN AS IT APPROACHES FROM THE MID-ATLANTIC. REGARDLESS THERE COULD ALLOW FOR SHALLOW COLD AIR FROM THE DEPARTING TO HIGH TO STAY TRAP AND WITH WARM AIR ALOFT MOVING INTO THE REGION...COULD SEE SNOW OR WINTRY PRECIP ESP ACROSS THE HIGHER TERRAIN LATE MONDAY INTO TUESDAY MORNING. BECAUSE OF THE MODEL SPREAD STILL HAVE DETAILS TO WORK OUT BUT SOMETHING TO WATCH CLOSELY. TEMPERATURES WILL SLOWLY BEGIN TO WARM ON TUESDAY AS SOUTHERLY FLOW BECOMES DOMINATE OUT AHEAD OF STRONGER SYSTEM TO THE EAST. EASTERLY FLOW WILL CONTINUE TO DOMINATE AT THE SURFACE WITH A EASTERLY LLJ STRENGTHEN ABOUT 20-30KTS. TUESDAYS HIGH TIDE AT BOSTON WILL BE 11.6 DURING THE LATE MORNING...AND WITH PERSISTENT EASTERLY WINDS ANTICIPATE AT LEAST MINOR COASTAL FLOODING. IF THIS SURFACE LOW STRENGTHENS AND THE EASTERLY FLOW INCREASES THEN THE MASS EAST COASTLINE WILL HAVE TO BE WATCHED CLOSELY DURING THE TUESDAY HIGH TIDE. WEDNESDAY INTO THURSDAY...HIGH CONFIDENCE IN SYSTEM LOW CONFIDENCE ON DETAILS. STRONG ANOMALOUS SYSTEM WILL STRENGTHEN OVER THE GREAT LAKES...DEVELOPING A POTENTIAL SECONDARY SURFACE LOW JUST WEST OF SOUTHERN NEW ENGLAND. STILL A LOT OF DETAILS TO WORK OUT AS THIS SYSTEM IS STILL 5+ 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. HOWEVER LATEST GUIDANCE DOES SHOW A QUICK MOVING DRY SLOT SO SNOWFALL WILL STRUGGLE DUE TO LACK OF MOISTURE. THIS SYSTEM IS QUITE POTENT SO WE WILL NEED TO WATCH FOR POTENTIAL HAZARDS. CURRENTLY THINK THAT WE COULD SEE POSSIBLE URBAN FLOODING ISSUES AS WELL AS WIND ISSUES. GUIDANCE RIGHT NOW IS SHOWING A 45 TO 55 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 FOR BOSTON. ANY EASTERLY COMPONENT WILL PUSH THE TIDE ABOVE FLOOD SO COASTAL FLOODING IS POSSIBLE AS WELL AS BEACH EROSION. THE SOUTH COASTLINE WILL ALSO HAVE TO BE WATCH CLOSELY. A VERY STRONG SOUTHERLY JET WILL DEVELOP WED INTO THURSDAY AND WITH ASTRONOMICAL HIGH TIDE 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 MOVES INTO SOUTHERN CANADA...EXPECT A RATHER FAST UPPER W FLOW IN PLACE. MAY SEE LEFTOVER SNOW SHOWERS BUT TEMPS WILL FALL BACK CLOSE TO SEASONAL NORMS. && .AVIATION /19Z FRIDAY 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 TUESDAY... SUNDAY...HIGH CONFIDENCE. MAINLY VFR ACROSS CENTRAL AND WESTERN AREAS. E OF ORH MAY SEE MVFR CONDITIONS IN SNOW SHOWERS. MONDAY-TUESDAY...MODERATE CONFIDENCE. MAINLY VFR. MAY SEE LOCAL MVFR IN WIDELY SCT RAIN/SNOW SHOWERS MON NIGHT/TUE. && .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 TUESDAY...MODERATE TO HIGH CONFIDENCE. SUNDAY THROUGH MONDAY...WINDS AND SEAS BELOW SMALL CRAFT CRITERIA. MONDAY NIGHT AND TUESDAY...EXPECT E-NE WINDS GUSTING UP TO 25 KT WITH SEAS BUILDING UP TO 5-7 FT...HIGHEST ON THE EASTERN OUTER WATERS FROM COASTAL LOW. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...KJC NEAR TERM...KJC SHORT TERM...KJC LONG TERM...DUNTEN AVIATION...KJC/DUNTEN MARINE...KJC/DUNTEN

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