Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 212020 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 319 PM EST FRI NOV 21 2014 .SYNOPSIS...
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AFTER A DRY BUT VERY COLD NIGHT...TEMPERATURES MODERATE SOME SATURDAY ON GUSTY SOUTHWEST WINDS. THIS WILL BE FOLLOWED BY A SIGNIFICANT WARM UP SUNDAY AND ESPECIALLY MONDAY...BUT WITH A PERIOD OF RAIN SUNDAY NIGHT AND MONDAY. QUIET FOR TUESDAY BUT CONDITIONS MAY CHANGE BY WEDNESDAY WITH THE THREAT OF A STORM SYSTEM. TURNING COLDER INTO THE END OF THE WEEK.
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&& .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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315 PM UPDATE... A RIDGE OF HIGH PRESSURE WILL BUILD INTO THE REGION FROM THE WEST. THIS WILL ALLOW WINDS TO GRADUALLY DIMINISH TONIGHT ALONG WITH MOSTLY CLEAR SKIES. THE EXCEPTION TO THAT WILL BE THE OUTER- CAPE...WHERE SOME OCEAN EFFECT CLOUDS MAY AFFECT THE REGION AT TIMES. OTHERWISE...GIVEN THE DRY AIRMASS IN PLACE...SHOULD BE A NICE SETUP FOR RADIATIONAL COOLING ONCE WINDS DECOUPLE. THIS WILL RESULT IN TEMPS WELL BELOW NORMAL FOR THIS TIME OF YEAR. LOW TEMPS SHOULD BOTTOM OUT AROUND 10 DEGREES ACROSS PORTIONS OF SOUTHWEST NH/NORTHWEST MA...TO MAINLY THE TEENS ELSEWHERE. THE URBAN HEAT ISLANDS OF DOWNTOWN BOSTON/PROVIDENCE WILL BE THE MILD SPOTS...WITH LOWS EXPECTED TO BE IN THE 20 TO 25 DEGREE RANGE.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
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SATURDAY... HIGH PRESSURE MOVES OFF THE MID ATLANTIC ALLOWING FOR STRONG MID LEVEL WARM ADVECTION TO DEVELOP. THE RESPONSE WILL BE AN INCREASE IN MID/HIGH LEVEL CLOUDINESS AS THE DAY WEARS ON...BUT IT WILL REMAIN DRY GIVEN THE LACK OF LOW LEVEL MOISTURE. DESPITE THE WARM ADVECTION ALOFT...IT WILL TAKE TIME FOR THAT TO BE COMPLETELY REALIZED AT THE SURFACE. WHILE IT WILL BE MILDER THAN TODAY...HIGH TEMPS WILL STILL BE BELOW NORMAL...MAINLY IN THE UPPER 30S AND LOWER 40S WITH SOME MIDDLE TO UPPER 40S ON THE CAPE AND ISLANDS. HOWEVER...EXPECTING SOUTHWEST WIND GUSTS OF 20 TO 30 MPH TO DEVELOP IN THE AFTERNOON AND PERHAPS A BIT STRONGER ALONG THE FAR SOUTHEAST NEW ENGLAND COAST. THIS WILL STILL MAKE IT FEEL RATHER CHILLY OUTSIDE FOR NOVEMBER STANDARDS. SATURDAY NIGHT... A MOISTURE STARVED SHORTWAVE WILL MOVE ACROSS THE REGION SAT NIGHT. THERE STILL SHOULD BE ENOUGH FORCING TO BRING A BRIEF PERIOD OF SCATTERED LIGHT PRECIPITATION. WHILE IT CERTAINLY WILL BE TOO WARM ALOFT FOR ANY SNOW...THE BIGGEST QUESTION IS WILL IT BE COLD ENOUGH AT THE SURFACE FOR SOME POCKETS OF SPOTTY LIGHT FREEZING RAIN ACROSS THE INTERIOR. ITS CERTAINLY POSSIBLE AND WILL NEED TO BE WATCHED...BUT ITS NOT AN IDEAL SETUP. THERE IS A LOT OF WIND OFF THE DECK AND PROBABLY ENOUGH TO PREVENT MOST AREAS FROM DECOUPLING. GIVEN WERE +4C AT 850 MB SOME OF THIS MILDER AIR WILL BE ABLE TO MIX DOWN. THIS SHOULD LIMIT THE OVERALL LIGHT ICING THREAT...BUT STILL CAN NOT RULE OUT SOME ISOLATED POCKETS IN THE DEEPER VALLEY LOCATIONS. LOW TEMPS WILL LIKELY BE IN THE UPPER 20S TO MIDDLE 30S DURING THE EVENING...BUT SHOULD RISE SOME OVERNIGHT.
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&& .LONG TERM /SUNDAY THROUGH FRIDAY/...
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*/ HIGHLIGHTS... - TURNING WARMER AND WET MONDAY - A POSSIBLE MIDWEEK STORM...ESPECIALLY FOR SE NEW ENGLAND - LOOKING COLDER INTO THANKSGIVING */ OVERVIEW AND MODEL CONSENSUS... TRENDING +AO/NAO WITH NEAR-NEUTRAL PNA SUGGESTS A MORE PROGRESSIVE PATTERN AND MILD. NO SURPRISE TO SEE A LACK OF DEEP CLOSED-LOW H5 DISTURBANCES...THOUGH AN ACTIVE PATTERN WITH ABUNDANCE OF PACIFIC- ORIGIN WAVES MAINTAINING TROUGHING BETWEEN SECTORS OF ABOVE-AVERAGE OCEAN TEMPERATURES OVER THE NE-PACIFIC AND NW-ATLANTIC. SOME OF THOSE WAVES ARE WELL OUT IN THE PACIFIC AND HAVE NOT EVEN BEEN SAMPLED. THE WAVE ASSOCIATED WITH THE WINTER-STORM POTENTIAL FOR THE MIDWEEK / THANKSGIVING PERIOD IS JUST S OF THE FURTHEST E ALEUTAIN ISLANDS OF ALASKA. NOTING THIS...HAVE HIGHEST CONFIDENCE THROUGH EARLY-NEXT WEEK WITH THE FORECAST...BUT LOW CONFIDENCE FOR A POTENTIAL MIDWEEK STORM. WILL HIT UP THE DETAILS BELOW. SO FOR SUNDAY... CLOUDS AND LIGHT SHOWERS ASSOCIATED WITH A WEAK TROUGH DISTURBANCE. DISSIPATING BENEATH A MID-UPPER LEVEL RIDGE / SUBSIDENCE. BENEATH THE WARM-SECTOR AND RETURN S-FLOW ROUND THE HIGH PUSHING OFF INTO THE ATLANTIC...H925 TEMPERATURES NEARLY +10C...MAY SEE HIGHS WARM WELL INTO THE 50S WITH ANY SUNSHINE. AS FOR SUNDAY NIGHT... WARM-FRONT AND ACCOMPANYING BROADSCALE LIFT AHEAD OF A DEEPENING LOW ACROSS THE C-CONUS THROUGH THE GREAT LAKES REGION BECOMES THE FOCUS FOR RAIN ACROSS THE REGION. NON-DIURNAL WARMING TREND OVERNIGHT. ALL- RAIN EVENT. MAIN CONCERNS ARE WITH BOTH WINDS AND RAIN. WITH WINDS: STRONG LOW-LEVEL JET CENTERED AROUND MONDAY MORNING WITH WINDS 1-2 KFT AGL MODEL-CONSENSUS AVERAGING AROUND 50 MPH /45 KTS/. SUGGESTED BOUNDARY-LAYER DECOUPLING BENEATH MUCH WARMER AIR BETWEEN H925-85. BUT IF 2M TEMPERATURES ARE WARMER AS FORECAST FOR SUNDAY COULD BE WARMER SUNDAY NIGHT AIDING IN LOW-LEVEL MIXING. ALSO NEED TO CONSIDER ANY HEAVY RAIN WHICH COULD ALSO AID WITH DRAGGING FASTER MOMENTUM TO THE SURFACE. OVERALL: MAIN CONCERN ACROSS SE NEW ENGLAND AND HIGH TERRAIN ABOVE 1 KFT. WIND ADVISORIES MAY BE NECESSARY. CIPS ANALOG GUIDANCE HAS JUST ABOVE 50-PERCENT FOR WINDS > 35 MPH. WITH RAIN: BROADSCALE ASCENT OF THE WARM-CONVEYER-BELT WITH PWATS UP TO 1.5-INCHES AND ANOMALOUS HIGH-THETAE AIR. CONVERGENCE ALONG THE NOSE OF THE LOW-LEVEL JET TO THE PARENT WARM-FRONT. EXPECT A BROAD NW-SE BAND OF RAIN WITH PERHAPS AN EMBEDDED LINE OF HEAVIER RAIN. IT MOVES THROUGH NOTABLY QUICK. MODEL-CONSENSUS AVERAGE RAIN AMOUNTS ARE AROUND 0.50 - 0.75 INCHES. AM NOT EXPECTING ANY FLOOD ISSUES. INTO MONDAY... RAINS FOR THE MORNING...IMPROVING AFTERNOON. IF WE CLEAR AS H925 TEMPERATURES WARM TO +14C THEN WE COULD POSSIBLY SEE HIGHS INTO THE MID- TO UPPER-60S /+18C/ POSSIBLY TO NEAR 70. MODEL-CONSENSUS H925 WINDS AVERAGE AROUND 45 MPH /40 KTS/ AND WITH WARMER CONDITIONS COULD SEE THE POTENTIAL FOR MIXING OUT TO H9 AND MOMENTUM MIX-DOWN. WILL HINT AT THIS IN THE FORECAST...BUT MODERATE CONFIDENCE. MONDAY NIGHT THROUGH TUESDAY NIGHT... WILL GO WITH A FEW LINGERING SHOWERS...BUT THE MAIN PUMP OF MOISTURE SHOULD BE WELL OFFSHORE. OTHERWISE THE MAIN COLD FRONT ATTENDANT TO THE DEEPENING LOW LIFTING THROUGH THE GREAT LAKES REGION SWEEPS ACROSS NEW ENGLAND. EXPECTING DRY AND COOLER WEATHER FOR TUESDAY... PERHAPS CONTINUING INTO TUESDAY NIGHT. WEDNESDAY AND BEYOND... JUST TOO EARLY TO SAY. LOTS OF UNCERTAINTY AS ENSEMBLE MEMBERS VARY CONSIDERABLY WITH SURFACE LOW CENTERS AROUND THE ENSEMBLE MEAN WHICH KEY UPON A LOW SE OF THE 40N / 70W BENCHMARK AROUND WEDNESDAY NIGHT. HAVE CONCERNS FOR SE NEW ENGLAND WHICH COULD SEE THE GREATEST IMPACT WHILE NOTING A RIDGE OF HIGH PRESSURE OVER S-CANADA /WITH THE CENTER OVER THE C-CONUS/. THE GFS-UPGRADED /T1534/ IS A FAR OUTLIER AND IS NOT CONSIDERED WITH THIS FORECAST. EVALUATING SYNOPTICS...THIS DOES NOT APPEAR TO BE A COASTAL STORM BUT MORE OF A WAVE LOW ALONG THE OFFSHORE STALLED FRONT. AS BEEN THE CASE THIS YEAR...COLD AIR HAS BEEN PLUNGING INTO THE CENTRAL CONUS BUT ITS TRUE BITE REMAINS MAINLY N/W OF OUR REGION. DO HAVE SOME CONFIDENCE THAT THE WAVE LOW WILL HUG CLOSER TO THE COAST. THEN IT COMES TO BREAKING DOWN TIMING / ASSOCIATED DYNAMICS / THERMAL FIELDS WHICH RIGHT NOW ARE AGAIN TOO EARLY TO DIAGNOSE. THERE HAS BEEN A CONSISTENT SIGNAL. STORM BEARS WATCHING. EXPECTING A RETURN OF ARCTIC AIR BEHIND WHATEVER MIDWEEK SYSTEM THAT MAY EMERGE. DAY 6-8 CIPS ANALOGS HAVE HIGH PROBABILITIES FOR BELOW- NORMAL TEMPERATURES FOR THE SE-CONUS INTO THE OHIO-RIVER VALLEY CENTERED AROUND THE LATE-THANKSGIVING WEEK PERIOD. EC ENSEMBLES AT H85 HAVE THE FREEZING MARK PLUNGING TO NEARLY THE GULF COAST...WITH -10C AIR INTO NEW ENGLAND BY NEXT WEEKEND.
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&& .AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
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FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. 315 PM UPDATE... TONIGHT...HIGH CONFIDENCE IN VFR WITH GRADUALLY DIMINISHING WIND. SATURDAY...HIGH CONFIDENCE IN VFR. SOUTHWEST WIND GUSTS OF 20 TO 30 KNOTS DEVELOP BY AFTERNOON...PERHAPS UP TO 35 KNOTS BY EARLY EVENING ACROSS PORTIONS OF THE CAPE/ISLANDS. SATURDAY NIGHT...MAINLY VFR CONDITIONS. HOWEVER...A BRIEF PERIOD OF MVFR CONDITIONS ARE POSSIBLE IN A FEW BRIEF PASSING SHOWERS. ISOLATED POCKETS OF LIGHT FREEZING RAIN CAN NOT BE RULED OUT ACROSS PORTIONS OF THE INTERIOR. SOUTHWEST WIND GUSTS OF 20 TO 30 KNOTS CONTINUE ON THE COASTAL PLAIN DURING THE EVENING...PERHAPS UP TO 35 KNOTS ACROSS PORTIONS OF THE CAPE AND ISLANDS. KBOS TERMINAL...HIGH CONFIDENCE IN VFR THROUGH SATURDAY AFTERNOON. KBDL TERMINAL...HIGH CONFIDENCE IN VFR THROUGH SATURDAY AFTERNOON. OUTLOOK...SUNDAY THROUGH WEDNESDAY. SUNDAY...MODERATE CONFIDENCE. INITIAL -SHRA EARLY SUNDAY WITH LOW-END VFR FOLLOWED BY SOME BRIEF IMPROVEMENT. WINDS TURNING S. SUNDAY NIGHT INTO MONDAY...MODERATE CONFIDENCE. CONDITIONS DETERIORATE MVFR-LIFR SUNDAY NIGHT INTO MONDAY MORNING WITH +RA AND STRONG S-WINDS WITH GUSTS AROUND 30 KTS POSSIBLE... OTHERWISE LLWS IMPACTS WITH 50 KT S-WINDS 2 KFT AGL. CONDITIONS IMPROVE BY MIDDAY...BUT COULD SEE CONTINUED SW-WINDS AROUND 25 KTS. MONDAY NIGHT THROUGH TUESDAY...MODERATE CONFIDENCE. W-FLOW WITH MAINLY VFR. WEDNESDAY...LOW CONFIDENCE. AN OFFSHORE STORM SYSTEM COULD BRING SIGNIFICANT IMPACTS ESPECIALLY TO THE SE-TERMINALS.
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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...TONIGHT THROUGH SATURDAY NIGHT... TONIGHT...HIGH CONFIDENCE. NORTHWEST SMALL CRAFT WIND GUSTS WILL GRADUALLY DIMINISH AS THE NIGHT WEARS ON. THIS A RESULT OF A RIDGE OF HIGH PRESSURE BUILDING IN FROM THE WEST...DECREASING THE PRESSURE GRADIENT. SATURDAY AND SATURDAY NIGHT...MODERATE TO HIGH CONFIDENCE. HIGH PRESSURE MOVES OFF THE MID ATLANTIC ON SAT ALLOWING FOR A RETURN SOUTHWEST FLOW OF AIR OVER THE WATERS. THERE IS A PRETTY GOOD WEST TO SOUTHWEST LOW LEVEL JET AND GIVEN THE AIRMASS IS STILL RELATIVELY COLD EXPECT DECENT MIXING OVER THE OCEAN. THEREFORE...HAVE ISSUED A GALE WATCH FOR MOST OF OUR OPEN WATERS FROM MID AFTERNOON SAT INTO SAT NIGHT. THERE IS ENOUGH FOR AT LEAST THE POTENTIAL FOR A PERIOD OF 35 KNOT WIND GUSTS. SEAS WILL LIKELY BUILD TO BETWEEN 6 AND 9 FEET ACROSS THE SOUTHERN WATERS. THE NEXT SHIFT CAN EITHER UPGRADE TO STRONG SMALL CRAFTS OR LOW END GALE WARNINGS. OUTLOOK...SUNDAY THROUGH WEDNESDAY. SUNDAY...MODERATE CONFIDENCE. CONDITIONS IMPROVING AS SW-WINDS TURN S AND RELAX. WILL SEE WAVE ACTION DISSIPATE BELOW SMALL-CRAFT ADVISORY LEVELS. SUNDAY NIGHT INTO MONDAY...MODERATE CONFIDENCE. CONDITIONS DETERIORATE INTO MONDAY MORNING WITH RAIN OVER THE WATERS AND EMBEDDED HEAVIER SHOWERS. VISIBILITY IMPACTS POSSIBLE. WINDS INCREASING OUT OF THE S. GUSTS EXCEEDING GALE FORCE APPEAR LIKELY. WAVES SUBSEQUENTLY INCREASING TO 10 FEET ON THE OUTER WATERS. MONDAY NIGHT THROUGH TUESDAY...MODERATE CONFIDENCE. WINDS TURNING SW REMAINING BLUSTERY WITH GUSTS EXCEEDING 25 KTS. WAVES MAINTAINED WITH HEIGHTS OF 8 TO 10 FEET ON THE OUTER WATERS. WEDNESDAY...LOW CONFIDENCE. AN OFFSHORE STORM SYSTEM COULD BRING SIGNIFICANT IMPACTS TO THE WATERS YET DETAILS UNCERTAIN AT THIS TIME.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...GALE WATCH FROM SATURDAY AFTERNOON THROUGH LATE SATURDAY NIGHT FOR ANZ231>235-237-250-254>256. SMALL CRAFT ADVISORY UNTIL 1 AM EST SATURDAY FOR ANZ232>235- 237. SMALL CRAFT ADVISORY UNTIL 7 PM EST THIS EVENING FOR ANZ230- 236. SMALL CRAFT ADVISORY UNTIL 7 AM EST SATURDAY FOR ANZ231-251- 255-256. SMALL CRAFT ADVISORY UNTIL 10 AM EST SATURDAY FOR ANZ250-254.
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&& $$ SYNOPSIS...FRANK/SIPPRELL NEAR TERM...FRANK SHORT TERM...FRANK LONG TERM...SIPPRELL AVIATION...FRANK/SIPPRELL MARINE...FRANK/SIPPRELL

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