Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 312115 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 415 PM EST SAT JAN 31 2015 .SYNOPSIS...
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BLUSTERY AND VERY COLD CONDITIONS TONIGHT AND INTO TOMORROW. A MAJOR WINTER STORM WILL AFFECT THE REGION VERY LATE SUNDAY NIGHT INTO MONDAY EVENING WITH HEAVY SNOW FOR MANY LOCATIONS. BITTERLY COLD WIND CHILLS FOLLOW LATER MONDAY NIGHT INTO TUESDAY MORNING. MODERATING TEMPS WEDNESDAY THEN VERY COLD CONDITIONS WILL RETURN TOWARD THE END OF THE WEEK. A COASTAL STORM WILL PASS WELL SOUTH OF NEW ENGLAND LATE IN THE WEEK BUT WILL HAVE TO BE MONITORED.
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&& .NEAR TERM /THROUGH SUNDAY/...
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430 PM UPDATE... FORECAST REMAINS ON TRACK FOR THE REMAINDER OF THE AFTERNOON. LOW PRESSURE WILL CONTINUE TO DEEPEN AS IT MOVE TOWARDS THE MARITIMES...ALLOWING FOR THE TIGHT PRESSURE GRADIENT TO CONTINUE. LATEST OBS AND BUFKIT SOUNDINGS SHOW THAT WIND GUSTS WILL BEGIN TO SLOWLY SUBSIDE THIS AFTERNOON...AND WITH MANY SITES BELOW ADV CONDITIONS PLAN ON LETTING THE ADV GO EXCEPT FOR THE CAPE AND ISLANDS. TONIGHT... DEEPENING LOW WILL MOVE WELL TOWARDS THE MARITIMES TONIGHT ALLOWING FOR WEAK MID-LEVEL RIDGING INTO THE REGION. STILL A DESCENT PRESSURE GRADIENT OVERNIGHT...ESP ACROSS THE EAST COAST SO ANTICIPATE WIND GUSTS TO REMAIN UP. HOWEVER ACROSS THE CT VALLEY REGION WINDS LOOK TO DECOUPLE OVERNIGHT SO EXPECT TEMPS TO DROP WELL INTO THE SINGLE DIGITS AND MAY BE CLOSE TO ZERO ESP AT ORE. HOWEVER WITH LIGHT WINDS...WIND CHILL ADV ARE NOT NEEDED. BIGGEST ISSUE WITH THESE COOLING TEMPS IS THE SKY COVER. AHEAD OF APPROACHING ARCTIC FRONT...MID TO HIGH LEVEL CLOUDS WILL BE MOVING IN FROM THE NORTH. THIS MAY LIMIT TEMPS...SO PLAYED THEM A TAD CONSERVATIVE. TOMORROW... 850MB ARCTIC FRONT WILL PUSH THROUGH THE REGION TOMORROW. HOWEVER TEMPS WILL BE WARMER THAN TODAY AS 925 MB TEMPS JUMP FROM -13C TO -8C. EXPECT TEMPS TO WARM INTO THE MID 20S TO PERHAPS THE LOW 30S ALONG THE COASTAL PLAIN. MID TO HIGH LEVEL MOISTURE WILL BE INCREASING THROUGHOUT THE DAY WHICH WILL INCREASE CLOUD COVER. OTHERWISE WINDS WILL BE CALMER AND DRY WEATHER WILL PREVAIL THROUGH MOST OF THE DAY.
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&& .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
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HIGHLIGHTS... * MAJOR WINTER STORM VERY LATE SUN NIGHT INTO MON EVENING * HEAVY SNOWFALL EXPECTED FOR MUCH OF THE REGION * BIGGEST UNCERTAINTY SNOWFALL AMTS NEAR SOUTH COAST - PTYPE ISSUES * BITTERLY COLD AIR LATE MON NIGHT - WIND CHILLS 15 TO 25 BELOW ZERO DETAILS... A MAJOR WINTER STORM WILL AFFECT SOUTHERN NEW ENGLAND VERY LATE SUN NIGHT INTO MONDAY EVENING. ARCTIC HIGH PRESSURE ACROSS EASTERN CANADA WILL COMBINED WITH LOW PRESSURE APPROACHING FROM THE WEST. THE RESULT WILL BE STRONG SOUTHWEST FLOW ALOFT OVER RUNNING THE ARCTIC DOME AT THE SURFACE. THEN AS THE LOW DEEPENS...MUCH OF THE REGION WILL SEE SNOW ON THE BACKSIDE OF THE SYSTEM. BIGGEST UNCERTAINTY IS HOW MUCH OF THE REGION TRANSITIONS TO A PERIOD OF MIXED PTYPE DURING THE MIDDLE OF THE EVENT...CUTTING DOWN ON POSSIBLE SNOW ACCUMS. 1) TIMING AND UNCERTAINTY SNOW WILL LIKELY ARRIVE FROM SOUTHWEST TO NORTHEAST VERY LATE SUN EVENING IN OUR WESTERN ZONES AND AFTER MIDNIGHT ACROSS THE REST OF THE REGION. EXTREMELY TIGHT MID LEVEL THERMAL PACKING WILL ALLOW SNOW TO QUICKLY BECOME HEAVY. SNOW WILL FALL HEAVY MONDAY MORNING AT 1 TO 2 INCHES PER HOUR AND SIGNIFICANTLY IMPACT THE AM RUSH HOUR. THINGS THEN BECOME MORE UNCERTAIN LATER IN THE MORNING AND AFTERNOON. THE GFS IS MOST AGGRESSIVE IN SURGING WARM MID LEVEL AIR TO THE MA PIKE...RESULTING IN A CHANGE TO A PERIOD OF SLEET/FREEZING RAIN AND EVEN PLAIN RAIN ALONG THE FAR SOUTHEAST NEW ENGLAND COAST. THE NAM/ECMWF/GGEM APPEAR THE COLDEST KEEPING MOST AREAS HEAVY SNOW...EXCEPT FOR THE CAPE AND ISLANDS. THE UKMET APPEARS TO BE IN BETWEEN THE OTHER SOLUTIONS. GIVEN THE UNCERTAINTY WILL BLEND THE MODELS. RIGHT NOW WERE THINKING TRANSITION AREA MAY GET BRIEFLY NEAR OR PERHAPS JUST NORTH OF THE THE TAUNTON TO PROVIDENCE CORRIDOR...BEFORE COLLAPSING SOUTHEAST. REGARDLESS HOW FAR NORTH THE TRANSITION LINE GETS...MOST AREAS WILL CHANGE BACK TO SNOW MON EVENING. GIVEN CLOSED MID LEVEL CENTERS AND VERY COLD NORTHEAST FLOW...COULD BE SOME OCEAN ENHANCEMENT ACROSS EASTERN NEW ENGLAND FOR A TIME BEFORE SNOW ENDS. BULK OF SNOW SHOULD WIND DOWN AFTER MIDNIGHT ALTHOUGH THE GGEM IS A BIT SLOWER. 2) SNOWFALL ACCUMULATIONS AND HEADLINES WE ARE PRETTY CONFIDENT IN A HEAVY SNOWFALL FOR MUCH OF THE REGION...EXCEPT FOR AREAS NEAR THE SOUTH COAST WHERE PTYPE ISSUES MAYBE MORE PROBLEMATIC. 8 TO 14 INCHES EXPECTED FOR MUCH OF THE REGION. HAVE UPGRADED ALL AREAS FROM PROVIDENCE TO TAUNTON NORTHWARD TO WINTER STORM WARNING/S WITH HIGH CONFIDENCE ON CRITERIA BEING MET. AREAS SOUTHEAST OF THAT LINE...THERE IS SOME MORE UNCERTAINTY ESP CAPE/ISLANDS. IF A LOT OF MIXING OCCURS THESE AREAS MAY STRUGGLE TO REACH WARNING CRITERIA...BUT ITS STILL CERTAINLY POSSIBLE DEPENDING ON MODEL TRENDS. THEREFORE...WE HAVE HELD THE WINTER STORM WATCH FOR THE SOUTH COAST AND THE ISLANDS. 3) STRONG WINDS AND BLOWING AND DRIFTING SNOW NORTHEAST WIND GUSTS OF 35 TO 50 MPH EXPECTED ALONG THE COAST MONDAY INTO MONDAY NIGHT AS STORM INTENSIFIES AND PRESSURE GRADIENT INCREASES. THIS WILL LIKELY RESULT IN POOR VISIBILITY ALONG WITH BLOWING AND DRIFTING SNOW. ITS POSSIBLE THAT A FEW LOCATIONS ALONG THE COAST COULD SEE NEAR BLIZZARD CONDITIONS FOR A VERY SHORT TIME...BUT STORM DOESN/T SEEM TO WARRANT THOSE TYPE OF HEADLINES. 4) BITTERLY COLD AIR MONDAY NIGHT INTO EARLY TUESDAY MORNING. TEMPS WILL LIKELY PLUNGE BELOW ZERO TO 5 ABOVE ZERO IN MANY LOCATIONS BY EARLY TUE MORNING. THIS WILL RESULT IN WIND CHILLS VALUES BETWEEN 15 AND 25 BELOW ZERO. WIND CHILL ADVISORIES WILL LIKELY BE NEEDED.
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&& .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
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HIGHLIGHTS... * COLD PATTERN CONTINUES THRU NEXT WEEKEND * CLIPPER LOW APPEARING MORE LIKELY THAN COASTAL LOW WED/THU GOOD AGREEMENT AMONG 12Z DETERMINISTIC...12Z GEFS AND 00Z ECENS ENSEMBLES THAT THE POLAR JET WILL DOMINATE THE NORTHERN TIER STATES INCLUDING NEW ENGLAND THIS PERIOD. THIS COMBINED WITH STREAMS EXPECTED TO REMAIN UNPHASED WILL SUPPORT MAINLY DRY WEATHER THIS PERIOD. ONE CAVEAT WILL BE CLIPPER LOW ENTERING THE NORTHEAST WED/WED NIGHT. EARLIER MODEL RUNS SUGGESTED SECONDARY DEVELOPMENT ALONG THE TRAILING COLD FRONT SOUTHWEST OF NEW ENGLAND...WITH POSSIBLE COASTAL-OCEAN STORM IMPACTING OUR REGION AROUND THU. HOWEVER LATEST GUID INCLUDING ENSEMBLES SUGGEST MID LEVEL TROUGH WILL LACK SUFFICIENT AMPLITUDE TO BACK THE FLOW FOR A SECONDARY LOW TO IMPACT THE REGION. THEREFORE LEANING TOWARD A MORE OFFSHORE TRACK AND JUST A PERIOD OF LIGHT SNOW POSSIBLE WED/WED NIGHT. HOWEVER AT THIS TIME RANGE CAN/T BE TOO DETERMINISTIC. THUS WON`T TOTALLY DISCOUNT CLOSER SECONDARY DEVELOPMENT. AS FOR TEMPS...BITTERLY COLD TUE BEHIND DEPARTING MON NGT COASTAL LOW. THEN COLD EASES WED AHEAD OF APPROACHING CLIPPER LOW FOLLOWED BUT YET ANOTHER ARCTIC BLAST LATE IN THE WEEK BEHIND THE CLIPPER. AS FOR INTO NEXT WEEKEND ENSEMBLE TRENDS SUGGEST TEMPS COLDER THAN NORMAL.
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&& .AVIATION /21Z SATURDAY THROUGH THURSDAY/...
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FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM.../THROUGH SUNDAY/...HIGH CONFIDENCE. BEFORE 00Z...VFR WITH NW GUSTS TO 30-40 KT DIMINISHING AFTER SUNSET. AFTER 00Z...VFR WITH GRADUAL DIMINISHING WIND. SUNDAY...MAINLY VFR...BUT LOW PROB FOR AREAS OF MVFR CIGS DEVELOPING IN THE AFTERNOON. SUNDAY NIGHT INTO MONDAY NIGHT...HIGH CONFIDENCE IN TRENDS BUT LOWER CONFIDENCE IN TIMING. VFR SUNDAY EVENING DETERIORATES TO IFR-LIFR CIGS/VSBYS IN MODERATE TO HEAVY SNOW BY DAYBREAK MON AND CONTINUES AT TIMES INTO MONDAY EVENING. PTYPE MAY TRANSITION TO A PERIOD OF SLEET/FREEZING RAIN/RAIN NEAR AND SOUTHEAST OF A PROVIDENCE TO TAUNTON LINE. NORTHEAST WIND GUSTS OF 30 TO 45 KNOTS EXPECTED ALONG THE COAST. KBOS TAF...HIGH CONFIDENCE. KBDL TAF...HIGH CONFIDENCE. OUTLOOK /TUESDAY THROUGH THURSDAY/... TUESDAY INTO WEDNESDAY...MODERATE CONFIDENCE. MAINLY VFR ON TUESDAY. COULD SEE SOME MVFR CIGS IN SCT SNOW SHOWERS ON WEDNESDAY. THURSDAY...MODERATE CONFIDENCE. MAINLY VFR. LOW RISK OF MVFR ALONG SOUTHEAST MASS DEPENDING ON TRACK OF CLIPPER LOW.
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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 /THROUGH MONDAY NIGHT/... HIGH CONFIDENCE THROUGH SUNDAY AFTERNOON. TONIGHT...STRONG LOW PRESSURE PULLS FARTHER AWAY WITH WINDS DIMINISHING BELOW GALE AFTER 06Z...BUT GUSTS 25-30 KT WILL CONTINUE OVERNIGHT. MODERATE FREEZING SPRAY LIKELY CONTINUING...ESPECIALLY E MA COASTAL WATERS. SUNDAY...WINDS AND SEAS GRADUALLY DIMINISH THROUGH THE DAY. WINDS AND SEAS WILL SLOWLY DIMINISH THROUGHOUT THE DAY BUT EXPECT SCA WAVES TO REMAINS THROUGH THE PERIOD. LIGHT FREEZING SPRAY WILL PERSIST. SUNDAY NIGHT INTO MONDAY...MODERATE TO HIGH CONFIDENCE. ***STRONG GALE FORCE WIND GUSTS/HIGH SEAS AND THE RISK OF HEAVY FREEZING SPRAY MONDAY INTO MONDAY NIGHT*** WINDS/SEAS QUICKLY RAMP UP VERY LATE SUN NIGHT INTO MON AS LOW PRESSURE INTENSIFIES NEAR THE SOUTH COAST. GALE WATCHES ISSUED FOR EXPECTED 40+ KNOT NORTHEAST WIND GUSTS BY MON MORNING ALONG WITH SEAS BUILDING TO 15+ FEET ACROSS OUR EASTERN WATERS BY LATE MON AFTERNOON/EVENING. IN ADDITION...BITTERLY COLD AIR MOVING OVER THE WATERS MONDAY NIGHT WILL RESULT IN THE POTENTIAL FOR HEAVY FREEZING SPRAY. HAVE ALSO ISSUED A FREEZING SPRAY WATCH. OUTLOOK /TUESDAY THROUGH THURSDAY/...MODERATE TO HIGH FORECAST CONFIDENCE. TUESDAY...NW GALES LIKELY ALONG WITH FREEZING SPRAY...POSSIBLY MODERATE TO HEAVY. MAINLY DRY WITH GOOD VSBY EXCEPT FAR OFFSHORE WHERE SNOW SHOWERS WILL BE COMMON. WED...WINDS EASE AND BECOME SOUTHWEST AS CLIPPER LOW ENTERS THE GREAT LAKES AND NY STATE. NOT AS COLD SO FREEZING SPRAY UNLIKELY. VSBY MAY BRIEFLY LOWER IN A PERIOD OF LIGHT SNOW. THU...ARCTIC FRONT WITH NW GALES BEHIND FRONTAL PASSAGE. MODERATE TO HEAVY FREEZING SPRAY POSSIBLE.
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&& .TIDES/COASTAL FLOODING...
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*** MINOR TO PERHAPS ISOLATED AREAS OF MODERATE COASTAL FLOODING POSSIBLE MON/MON NIGHT EASTERN MA COASTLINE *** GOOD MODEL AGREEMENT ON SURFACE LOW TRACKING SOMEWHERE BETWEEN NANTUCKET AND THE 40N/70W BENCHMARK WITH NAM THE FASTEST AND GFS FARTHEST NORTHWEST. ECMWF SPLITS THE DIFFERENCE. MODEL CONSENSUS BRINGS STRONGEST ONSHORE WINDS BETWEEN 18Z AND 00Z...CLOSE TO LOW TIDE. IF THIS TIMING HOLDS UP WORST CASE SCENARIO WOULD BE MINOR COASTAL FLOODING. THE FIRST TIDE CYCLE OF CONCERN IS THE MONDAY MID MORNING. HOWEVER ALL WAVE GUID SUGGEST SEAS LESS THAN 10 FT AT HIGH TIDE GIVEN ARRIVAL OF STRONGEST WINDS LATER DURING THE AFTERNOON. THIS ALSO YIELDS SURGE VALUES OF A FOOT OR LESS. AS FOR THE MONDAY EVENING HIGH TIDE CYCLE...ASTRO TIDES ARE ABOUT A 1 FT LOWER. HOWEVER A STORM SURGE OF 1.5 TO 2.5 FT IS POSSIBLE. ESTOFS AND ETSS ARE LOWER...SO I BLENDED THE TWO GUID SOURCES AND ADDED 50 PERCENT TO COME UP WITH SURGE VALUES OF 1.5 TO 2.5 FT. IN ADDITION...SEAS WILL LIKELY BUILD TO 15 TO 20 FT DURING THE EVENING HIGH TIDE. ALL OF THESE FACTORS YIELD A MODERATE RISK OF MINOR COASTAL FLOODING WITH A LOW RISK OF ISOLATED MODERATE FLOODING. WHILE WINDS...SEAS AND STORM SURGE WILL BE LESS THAN THE PREVIOUS COASTAL STORM THERE COULD STILL BE SOME MODEST IMPACT ESPECIALLY FOR THOSE COMMUNITIES SUCH AS MARSHFIELD MA THAT WERE HIT HARD EARLIER THIS WEEK WHERE COASTAL STRUCTURES SUCH AS SEAWALLS WERE DAMAGED. GIVEN THE LOW TRACK IS CLOSE TO NANTUCKET THE GREATEST RISK OF COASTAL FLOODING WILL BE FARTHER NORTHWARD FROM CAPE COD TO CAPE ANN WITH PERHAPS THE HIGHEST RISK FROM HULL/COHASSET/SCITUATE/ MARSHFIELD/PLYMOUTH TO SANDWICH HARBOR. /DUXBURY GIVEN IT APPEARS MARGINAL FOR SIGNIFICANT COASTAL FLOODING AND STILL 48-60 HRS OUT IN TIME WILL HOLD OFF ON A COASTAL FLOOD WATCH.
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&& .CLIMATE... WITH EXTREMELY COLD AIR MOVING IN BEHIND THE DEPARTING LOW MONDAY NIGHT...TEMPERATURES MAY FALL BACK CLOSE TO OR SURPASSING RECORD LEVELS EARLY TUESDAY MORNING. AND THAT IS NOT TAKING INTO ACCOUNT THE STRONG WINDS. HERE ARE THE RECORD LOWS FOR TUESDAY 2/3... BOSTON -5 SET IN 1881 PROVIDENCE -6 SET IN 1961 WORCESTER -7 SET IN 1931, 1955 AND 1971 WINDSOR LOCKS -3 SET IN 1955 BLUE HILL OBS -7 SET IN 1955 && .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...WINTER STORM WARNING FROM 9 PM SUNDAY TO 1 AM EST TUESDAY FOR CTZ002>004. MA...WINTER STORM WATCH FROM SUNDAY EVENING THROUGH LATE MONDAY NIGHT FOR MAZ020>024. WINTER STORM WARNING FROM 9 PM SUNDAY TO 1 AM EST TUESDAY FOR MAZ002>019-026. WIND ADVISORY UNTIL 9 PM EST THIS EVENING FOR MAZ022>024. RI...WINTER STORM WATCH FROM SUNDAY EVENING THROUGH LATE MONDAY NIGHT FOR RIZ005>008. WINTER STORM WARNING FROM 9 PM SUNDAY TO 1 AM EST TUESDAY FOR RIZ001>004. MARINE...GALE WATCH FROM MONDAY MORNING THROUGH TUESDAY MORNING FOR ANZ231>235-237. HEAVY FREEZING SPRAY WATCH FROM MONDAY EVENING THROUGH TUESDAY MORNING FOR ANZ231>235-237-250-251-254>256. FREEZING SPRAY ADVISORY UNTIL 8 AM EST SUNDAY FOR ANZ231-232- 250-251-254-255. GALE WARNING UNTIL 1 AM EST SUNDAY FOR ANZ231-232-250-251- 254>256. FREEZING SPRAY ADVISORY UNTIL 1 AM EST SUNDAY FOR ANZ233>235- 237. GALE WARNING UNTIL 10 PM EST THIS EVENING FOR ANZ233>235-237. GALE WATCH FROM MONDAY MORNING THROUGH LATE MONDAY NIGHT FOR ANZ230-236. GALE WARNING UNTIL 9 PM EST THIS EVENING FOR ANZ230. GALE WARNING UNTIL 6 PM EST THIS EVENING FOR ANZ236. GALE WATCH FROM LATE SUNDAY NIGHT THROUGH TUESDAY MORNING FOR ANZ250-251-254>256. FREEZING SPRAY ADVISORY UNTIL 8 PM EST THIS EVENING FOR ANZ256.
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&& $$ SYNOPSIS...FRANK/NOCERA/DUNTEN NEAR TERM...DUNTEN SHORT TERM...FRANK LONG TERM...NOCERA AVIATION...FRANK/DUNTEN/NOCERA MARINE...FRANK/NOCERA/DUNTEN TIDES/COASTAL FLOODING...NOCERA CLIMATE...STAFF

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