Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 190613 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 113 AM EST FRI DEC 19 2014 .SYNOPSIS... DRY AND SEASONABLE CONDITIONS WILL PREVAIL FRIDAY. AN UPPER LEVEL DISTURBANCE AND MOIST NORTHEAST FLOW WILL BRING SOME LIGHT PRECIPITATION SATURDAY INTO SUNDAY. LOW PRESSURE WILL LIKELY PASS WELL SOUTH OF THE REGION TUESDAY...BUT STILL COULD BRING A PERIOD OF LIGHT PRECIPITATION. A MUCH STRONGER STORM IS LIKELY TO BRING HEAVY RAIN AND WIND TO SOUTHERN NEW ENGLAND WEDNESDAY INTO WEDNESDAY EVENING. DRY BUT VERY WINDY CONDITIONS FOLLOW FOR CHRISTMAS DAY. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... 110 AM UPDATE... AN ABUNDANCE OF LOW CLOUDS REMAIN IN PLACE ACROSS MOST OF THE REGION VERY EARLY THIS MORNING...TRAPPED BELOW THE SHALLOW INVERSION. LITTLE CHANGE EXPECTED THROUGH DAYBREAK. LOW TEMPS SHOULD BOTTOM OUT IN THE 20S TO THE LOWER 30S. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/... FRIDAY... HIGH PRES BUILDS ACROSS THE GRT 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. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... HIGHLIGHTS... * SCT LIGHT SNOW/RAIN SHOWERS SAT INTO SUN...WITH A PERIOD OF DRIZZLE/FREEZING DRIZZLE POSSIBLE SAT NIGHT INTO SUN MORNING * WEAK WAVE OF LOW PRESSURE WILL PASS WELL OFFSHORE TUE BUT COULD STILL SEE LIGHT PRECIP * ANOMALOUSLY STRONG STORM SYSTEM WILL BRING HEAVY RAIN...GUSTY WINDS AND COASTAL CONCERNS AROUND CHRISTMAS EVE OVERVIEW AND MODEL PREFERENCES... MEDIUM RANGE MODELS CONTINUE IN PRETTY GOOD AGREEMENT ON LARGE SCALE AND UPPER LEVEL FEATURES THROUGH MOST OF THE FORECAST PERIOD. MODELS AND ENSEMBLES CONTINUE TO SIGNAL WEAK SHORT WAVES THAT TRANSLATE ACROSS THE REGION EARLY IN THIS PERIOD...WITH A RATHER POTENT BUT FAST MOVING ONE FOR SAT NIGHT/SUN TIMEFRAME WHICH IS AIDED WITH LOW LEVEL ONSHORE MOISTURE...WITH A SECOND WEAK LOW FOR LATE MON INTO TUE BRINGING ANOTHER PERIOD OF LIGHT PRECIP. STILL QUITE A FEW PLACEMENT AND TIMING ISSUES WITH THE EVOLUTION OF AN ANOMALOUSLY DEEP H5 CUTOFF LOW DEVELOPING ACROSS THE WESTERN GREAT LAKES AROUND THE MON-TUE TIMEFRAME...THEN ROTATES NE SOMEWHERE ACROSS S CENTRAL CANADA ON CHRISTMAS DAY. BIG IMPLICATIONS WITH THE ASSOCIATED LONG WAVE TROUGH. GUIDANCE CONTINUES TO INDICATE THE TROUGH BECOMING NEGATIVELY TILTED ACROSS THE MID ATLC OR SE U.S. LATE IN THIS PERIOD. SECONDARY/ TRIPLE POINT LOW FORMS ON SURFACE FRONT OVER THE EASTERN GULF AROUND TUESDAY...THEN WORKS UP ACROSS EASTERN PORTIONS OF THE SE AND MID ATLC STATES. QUESTION IS IF THIS LOW APPROACHES WESTERN PORTIONS OF NEW ENGLAND WED NIGHT. STILL SEE THE SIGNALS FOR A FAST MOVING STORM WITH MULTIPLE IMPACTS POSSIBLE...INCLUDING PERIOD OF HEAVY RAINFALL AND STRONG WIND GUSTS...FIRST FROM THE SOUTH THEN SHIFTING TO THE WEST. COULD EVEN SEE SOME COASTAL IMPACTS DURING THE HIGH TIDE CYCLE DURING WED. TIMING REMAINS AN ISSUE...AS ONE WOULD EXPECT THIS FAR OUT. MODEL GUIDANCE STILL DOING A RATHER GOOD JOB HANDLING GENERAL FEATURES OF THIS SYSTEM AT THIS POINT. USED A BLEND OF THE AVAILABLE GUIDANCE ALONG WITH WPC GUIDANCE. DETAILS... SATURDAY INTO SUNDAY...HIGH CONFIDENCE. HIGH PRES AT THE SURFACE AND ALOFT MOVES ACROSS QUEBEC INTO THE MARITIMES DURING THIS WEEKEND...THEN TENDS TO SLOW ITS EASTWARD PROGRESS WITH BLOCKING OVER THE WESTERN ATLC. RATHER POTENT SHORT WAVE UNDERNEATH THE UPPER SYSTEM MOVES ACROSS THE REGION...AIDED BY A LOW LEVEL E-NE WIND IN PLACE. A LOT OF LOW LEVEL MOISTURE IN PLACE AS SEEN ON BUFKIT MODEL SOUNDINGS...SO WILL SEE SOME LIGHT RAIN/SNOW SHOWERS DEVELOP FROM E-W DURING SATURDAY. EXPECTING LITTLE IF ANY SNOW ACCUMULATIONS DURING SAT. HOWEVER...AS TEMPS FALL BACK SAT NIGHT...ALONG WITH THE DEEP LOW LEVEL MOISTURE FEED...WILL ALSO SEE AREAS OF DRIZZLE DEVELOP. BIG PROBLEM WILL BE JUST AWAY FROM THE COAST WHERE TEMPS FALL BELOW FREEZING WHICH MAY MEAN FREEZING DRIZZLE. DOES NOT TAKE MUCH TO GET GLAZING ESPECIALLY ON UNTREATED SURFACES. WILL NEED TO MONITOR THIS CLOSELY FOR POSSIBLE WINTER WEATHER HEADLINES ACROSS INTERIOR E MA INTO RI...POSSIBLY EVEN FURTHER W. WITH THE LIGHT SNOW...MIGHT SEE UP TO 1/2 INCH ACCUMULATIONS SAT NIGHT INTO SUN MORNING. ON SUNDAY...DRIZZLE WILL TAPER OFF DURING THE MORNING...THOUGH LEFTOVER RAIN/SNOW SHOWERS WILL LINGER THOUGH TEND TO TAPER OFF DURING THE AFTERNOON. MONDAY INTO TUESDAY...MODERATE CONFIDENCE. ANOTHER COASTAL LOW LOOKS TO DEVELOP OFF THE SE U.S. COAST AND...AS UPPER LEVEL TROUGH BEGINS TO DIG ACROSS THE CENTRAL U.S...WILL SHIFT TO THE E-NE UNDERNEATH THE UPPER RIDGE. THE MARITIMES SURFACE HIGH REMAINS PRETTY MUCH IN PLACE...WHICH WILL HELP SHIFT THE MAIN EFFECTS OF THIS LOW WELL OFFSHORE /SE OF THE 40N/70W BENCHMARK/. HOWEVER...MODELS CONTINUE TO SIGNAL LIGHT PRECIP REACHING THE COAST MAINLY MON NIGHT INTO TUE. EXPECT MAINLY MIXED RAIN/SNOW SHOWERS WITH SPOTTY BRIEF PERIODS OF FREEZING PRECIP AROUND DAYBREAK TUE ACROSS N CT/N RI INTO S CENTRAL MA. EXPECT HIGH TEMPS ON TUE TO RUN ABOUT 5 DEGS ABOVE SEASONAL NORMS AS WINDS BEGIN TO SHIFT MORE S- SE...THOUGH SOME TIMING ISSUES IN PLACE FOR WIND SHIFT AMONGST OP MODELS. ONCE THE LOW EXITS LATE TUE...WILL ALREADY START TO SEE MOISTURE FEED UP THE COAST FROM THE DEVELOPING GULF LOW...SO NOT MUCH OF A BREAK IN THE PRECIP BETWEEN SYSTEMS. TUESDAY/S LATE MORNING HIGH TIDE WILL RUN UP TO 11.6 FT IN BOSTON AND...WITH ANY EASTERLY WIND FLOW...THIS MAY CAUSE MINOR COASTAL FLOODING. WILL MONITOR THIS ASPECT. WEDNESDAY AND CHRISTMAS DAY...HIGH CONFIDENCE IN SYSTEM...LOW CONFIDENCE ON DETAILS. SECONDARY LOW FROM THE PARENT OVER THE NORTHERN GREAT LAKES DEEPENS AS IT SHIFTS N. MODELS TRY TO PUSH THIS SYSTEM CLOSE TO OR JUST INTO WESTERN NEW ENGLAND LATE WED/WED NIGHT...THOUGH STILL TIMING ISSUES IN PLACE. AT THIS POINT...WILL SEE HEAVIEST SLUG OF PRECIP MOVING ACROSS LATE WED INTO WED EVENING. GOOD TROPICAL CONNECTION CONTINUES WITH PWATS FROM 1.25 TO 1.4 INCHES...RUNNING ABOUT +2SD TO +3SD ABOVE NORMAL FOR LATE DECEMBER. GOOD SHOT OF MILD AIR WORKS IN ON SE-S WINDS. MODELS CONTINUE TO SIGNAL H925 AND H85 FROM 50-65 KT...AND AT LEAST SOME WILL MIX DOWN ESPECIALLY IF THE LOW PRES PASSES CLOSER /WITH RAPIDLY FALLING PRESSURE/. HAVE HIGHS ON WED UP TO THE LOWER 50S ACROSS EASTERN AND SOUTHERN AREAS...BUT COULD BE EVEN HIGHER WITH STRONG ONSHORE WINDS. CURRENT TIMING SUGGESTS THE DRY SLOT SHOULD WORK INTO THE REGION LATE WED NIGHT INTO CHRISTMAS MORNING...SO PRECIP SHOULD END. WILL STILL SEE GUSTY WINDS...THOUGH QUICKLY SHIFTING TO W-SW AND GUSTING UP TO 25-30 KT...HIGHEST ALONG THE S COAST. MAY NEED HEADLINES WITH THIS SYSTEM...WITH POSSIBLE URBAN/POOR DRAINAGE FLOODING IN HEAVY RAINFALL WED/WED NIGHT...STRONG WINDS BOTH WED AND THU...AND MAYBE EVEN FOR COASTAL CONCERNS. NOTING ASTRO HIGH TIDES CONTINUE /11.7 AND 11.5 FT AT BOSTON RESPECTIVELY/... THOUGH TIMING OF WIND SHIFT MAY COME INTO PLAY FOR CHRISTMAS EVE INTO CHRISTMAS MORNING. FRIDAY...LOW CONFIDENCE MAINLY FOR TIMING. ONCE UPPER LOW MOVES INTO SOUTHERN CANADA...EXPECT A RATHER FAST UPPER W FLOW IN PLACE. MAY SEE LEFTOVER SNOW SHOWERS ACROSS THE E SLOPES OF THE BERKSHIRES INTO THE MONADNOCKS. TEMPS WILL FALL BACK CLOSE TO SEASONAL NORMS. ANOTHER LOW MIGHT MOVE INTO W NY STATE FRI NIGHT. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /TODAY THROUGH SATURDAY/... TODAY AND TONIGHT...LOW TO MODERATE CONFIDENCE. A BROKEN DECK OF CLOUDS WILL PROBABLY REMAIN IN PLACE TODAY. OVERALL...OUR CONFIDENCE IN SKY COVER IS BELOW NORMAL BUT CEILINGS SHOULD VARY BETWEEN LOW END VFR TO MVFR THROUGH THE AFTERNOON. PERHAPS SOME OF THE CLOUDS SCATTER OUT THIS EVENING...BUT AGAIN THAT IS UNCERTAIN. OCEAN EFFECT CLOUDINESS WILL DEVELOP ACROSS THE CAPE/ACK AS WINDS TURN TO A MORE NORTHERLY DIRECTION. SATURDAY...MODERATE CONFIDENCE. MVFR CIGS OVERSPREAD THE COASTAL PLAIN AND EVENTUALLY EVEN INTO PORTIONS OF THE INTERIOR BY LATE AFTERNOON. SCATTERED OCEAN EFFECT LIGHT RAIN/SNOW SHOWERS WILL OVERSPREAD THE SOUTHEAST NEW ENGLAND COAST WITH NORTHEAST SURFACE WINDS. OUTLOOK...SATURDAY NIGHT THROUGH TUESDAY... SATURDAY NIGHT INTO SUNDAY...HIGH CONFIDENCE. MAINLY VFR ACROSS CENTRAL AND WESTERN AREAS. E MA INTO RI...AREAS MVFR CIGS/VSBYS IN ANY RAIN/SNOW SHOWERS...AREAS OF DRIZZLE SAT NIGHT INTO SUN MORNING. 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 FRIDAY NIGHT/...HIGH CONFIDENCE. 110 AM UPDATE... OVERNIGHT...NW WINDS CONTINUE TO GRADUALLY DIMINISH AS PRESSURE GRADIENT WEAKENS. LET SCA HEADLINES EXPIRE FOR SOUNDS AND BAYS...BUT THEY CONTINUE INTO THE MORNING FOR LEFT OVER SEAS. 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 THROUGH TUESDAY...MODERATE TO HIGH CONFIDENCE. SATURDAY 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. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EST EARLY THIS MORNING FOR ANZ250-254>256. && $$ SYNOPSIS...KJC/EVT NEAR TERM...FRANK SHORT TERM...KJC LONG TERM...EVT AVIATION...FRANK/EVT MARINE...FRANK/KJC/EVT

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