Area Forecast Discussion
Issued by NWS Boston, MA

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021 FXUS61 KBOX 071539 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 1039 AM EST SUN FEB 7 2016 .SYNOPSIS... HIGH PRESSURE WILL BRING DRY WEATHER WITH MILD TEMPERATURES TODAY. ALTHOUGH WE WILL BE ON THE WESTERN FRINGE OF A STRONG OCEAN STORM PASSING FAR TO THE SOUTHEAST OF THE REGION...OCEAN-EFFECT ENHANCEMENT MAY BRING A PLOWABLE SNOWFALL TO MUCH OF THE EASTERN HALF OF SOUTHERN NEW ENGLAND MONDAY AND MONDAY NIGHT. AN ADDITIONAL COASTAL LOW WILL BRING SNOW TO THE REGION ON TUESDAY...WITH LINGERING SNOW SHOWERS WEDNESDAY. AN ARCTIC COLD FRONT WILL CROSS THE REGION THURSDAY...FOLLOWED BY DRY AIR AND COLDER THAN NORMAL TEMPERATURES TO FINISH THE WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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1030 AM UPDATE... *** INCREASING RISK FOR HEAVY SNOW MONDAY RI AND EASTERN MA WITH NEAR BLIZZARD CONDITIONS POSSIBLE SOUTH OF BOSTON TO CAPE COD *** 12Z NAM HAS COME IN QUITE ROBUST WITH HEAVY SNOW THREAT INTO EASTERN CT...RI AND EASTERN MA WITH NEAR BLIZZARD CONDITIONS. 12Z RGEM NOT AS BIG AS NAM BUT TRENDING HEAVIER. DESPITE THE SYSTEM TRACKING SO FAR OFFSHORE...THE INTENSE SURFACE LOW /975MB!/ AND LARGE MID LEVEL CIRCULATION WILL ALLOW THE MOIST WARM CONVEYOR BELT/TROWAL/FIREHOSE TO PIVOT CYCLONICALLY MUCH FARTHER WEST THAN A TYPICAL STORM TRACK SOUTHEAST OF THE 40N/70W BENCHMARK. IN ADDITION THE 12Z NAM IS MOST SKILLFUL INSIDE 36 HRS. WILL WAIT TO EVALUATE ALL 12Z GUID BUT AS OF NOW LEANING TOWARD THE 12Z NAM. THIS WILL TRANSLATE TO HEAVY SNOW THREAT WESTWARD INTO EASTERN CT- WORCESTER HILLS ALL OF EASTERN MA /INCLUDING CAPE COD AND ISLANDS/ AND RI. STRONG LOW LEVEL JET OF UP TO 65 KT OVER NANTUCKET COMBINED WITH HEAVY SNOW MAY YIELD NEAR BLIZZARD CONDITIONS AT TIMES ACROSS COASTAL PLYMOUTH COUNTY...CAPE COD AND THE ISLANDS. SNOW INITIALLY WILL BE WET AND HEAVY OVER SOUTHEAST MA THEN TRANSITIONING TO DRIER/POWDERY SNOW. HOWEVER THIS WILL RESULT IN A RISK FOR DOWN TREE LIMBS AND POWER OUTAGES ACROSS SOUTHEAST MA. LOOKS LIKE A COASTAL FRONT WILL SETUP ACROSS EASTERN MA THAT WILL ENHANCE SNOWFALL BUT ALSO WITH A SHARP CUTOFF ON THE WESTERN EDGE AS SHALLOW COLD/DRY ARCTIC AIRMASS BLEEDS SOUTHWARD. THIS ARCTIC AIRMASS WILL YIELD OES ENHANCEMENT FIRST ACROSS CAPE ANN AREA AND EVENTUALLY BLEED SOUTHWARD DOWN THE EASTERN MA COASTLINE. SNOWFALL...POTENTIAL 6-12" ACROSS MUCH OF EASTERN MA /INCLUDING CAPE COD AND ISLANDS/ RI...POSSIBLY WESTWARD INTO EASTERN CT AND NORTHWARD INTO THE WORCESTER HILLS. LOW RISK OF 18+ ACROSS COASTAL PLYMOUTH COUNTY TO THE UPPER CAPE AS OES AND LAND/SEA CONVERGENCE IS MAXIMIZED OVER THIS REGION. STAY TUNED...MUCH MORE TO COME THIS AFTERNOON. THOUGH START PLANNING FOR MAJOR IMPACT TO MORNING COMMUTE INTO THE AFTERNOON ACROSS RI AND EASTERN MA.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... TONIGHT... 1035 QUEBEC SURFACE HIGH ADVECTS SHALLOW ARCTIC AIR SOUTHWARD INTO SOUTHERN NEW ENGLAND. MEANWHILE MID LEVEL SOUTHERN STREAM TROUGH OVER THE GULF STATES INDUCES CYCLOGENESIS OFF THE EAST COAST OF SC THIS EVENING AND THEN RAPIDLY INTENSIFIES INTO A SUB 980 MB LOW/GALE CENTER WELL EAST OF THE NC COAST TONIGHT. TYPICALLY THIS TRACK IS TOO FAR OFFSHORE TO YIELD ACCUMULATING SNOW TO SOUTHEAST MA. HOWEVER THIS CYCLONE HAS A VERY LARGE CIRCULATION/WCB/FIREHOSE IN ADDITION TO 1035 MB SURFACE HIGH OVER QUEBEC...AND AS INDICATED BELOW...WE ARE EXPECTING OCEAN-EFFECT ENHANCEMENT. LIGHT SNOW SHOULD MOVE ONSHORE FROM THE SOUTH BEFORE DAYBREAK MONDAY. MONDAY... HAVE EXPANDED THE WINTER STORM WATCH TO INCLUDE MUCH OF EASTERN MA INCLUDING WORCESTER AND BOSTON METROPOLITAN AREAS...AND TO THE NORTHEAST HALF OF RI. CONTINUED THE WINTER STORM WATCH FOR SOUTHEASTERN MA...ALTHOUGH CONFIDENCE HAS INCREASED ALMOST TO THE POINT OF WARNINGS THERE BUT WILL LET THE DAY SHIFT GIVE A FINAL ASSESSMENT. ALTHOUGH WE WILL BE ON THE WESTERN FRINGE OF A STRONG OCEAN STORM PASSING FAR TO THE SOUTHEAST OF THE REGION...OCEAN-EFFECT ENHANCEMENT IS EXPECTED TO BE THE KEY TO THE FORECAST. WITH WATER TEMPERATURES RUNNING ABOUT +5C TO +6C...WE WOULD TYPICALLY BEGIN TO SEE OCEAN EFFECT WITH A DIFFERENTIAL OF ABOUT 13 DEGREES C BETWEEN THE OCEAN SURFACE AND 850 MB...OR ABOUT -7C. ALL MODELS INDICATE THAT THIS WILL HAPPEN...AND THE GFS AND ECMWF HAVE -10C AIR AT 850 MB EXTENDING ALONG THE EASTERN MA COAST MON AFTERNOON INTO MON NIGHT. WITH STRONG NE WINDS...GUSTING TO 40+ MPH AT THE COAST...THE SNOW SHOULD EXTEND WELL INLAND. THERE IS INCREASING CONSENSUS IN MODEL QPF BUT STILL SOME BIG DIFFERENCES. THE UKMET HAS BETWEEN 0.5 AND 1.2 INCHES OF LIQUID EQUIVALENT ACROSS EASTERN MA WITH THE HIGHEST ON CAPE COD AND NANTUCKET. THE GFS HAS INCREASED SINCE THE PREVIOUS RUN. THE 00Z NAM IS IN LINE WITH THE GFS AND THE ECMWF. IN GENERAL...4 TO 6 INCHES IS A REAL POSSIBILITY IN THE I-95 CORRIDOR PERHAPS EVEN BACK TO WORCESTER AND NORTHEAST TO THE MERRIMACK VALLEY AND CAPE ANN. ONLY 2 OR 3 INCHES OUT IN HARTFORD/SPRINGFIELD AREAS AND THE CT RIVER VALLEY. HOWEVER...THE JACKPOT COULD BE SOUTHERN PLYMOUTH COUNTY AND PORTIONS OF CAPE COD WHERE 6 TO 10 INCHES ARE POSSIBLE. THE FORECAST IS VERY TRICKY FOR NANTUCKET WHERE WET BULB COOLING SHOULD MEAN ALMOST ALL SNOW. WE MAY NEED TO UP POTENTIAL SNOW AMOUNTS CONSIDERABLY. ONE CONCERN IS THE HIGHER RESOLUTION NAM AND THE LOWER RESOLUTION CANADIAN MODEL WHICH BOTH FORECAST MUCH HIGHER AMOUNTS IN SOUTHEAST MA. WITH THE WINDS NEAR 40 MPH AT TIMES...IT IS POSSIBLE THAT NEAR BLIZZARD CONDITIONS COULD OCCUR ALONG THE COAST...ESPECIALLY IN PLYMOUTH...BARNSTABLE...DUKES...AND NANTUCKET COUNTIES. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... BIG PICTURE... LONGWAVE SCALE SHOWS RIDGE OVER THE WESTERN USA AND TROUGH OVER THE EASTERN USA THROUGH THE FORECAST PERIOD. AT SHORTER SCALES...MODELS CONTINUE TO ADVERTISE THREE SHORTWAVES AFFECTING SOUTHERN NEW ENGLAND DURING EARLY TO MID WEEK. THE FIRST PASSES WELL OFFSHORE ON MONDAY AS NOTED IN THE SHORT TERM DISCUSSION. THE SECOND SHORTWAVE DIGS OVER THE MIDWEST INTO THE MEAN TROUGH POSITION AND GENERATES ANOTHER COASTAL LOW MONDAY NIGHT...THIS ONE ON THE MID ATLANTIC COAST. THE THIRD SHORTWAVE DIVES SOUTH FROM THE ARCTIC INTO THE EASTERN USA TROUGH...THEN SWEEPS ACROSS NEW ENGLAND THURSDAY. CLOSED UPPER LOW FROM BAFFIN ISLAND THEN DIVES SOUTH OVER EASTERN CANADA AND MAINTAINS THE EASTERN CYCLONIC FLOW AND LOW HEIGHTS INTO SATURDAY. THIS POINTS TO AN UNSETTLED PERIOD MUCH OF THE COMING WEEK WITH NEAR SEASONABLE TEMPS EARLY WEEK AND BELOW NORMAL TEMPS LATE WEEK. MODEL MASS FIELDS ARE SIMILAR THROUGH TUESDAY AND INDICATE THE SAME GENERAL PATTERN THROUGH SATURDAY. BUT THERE ARE ALSO DIFFERENCES IN DETAILS IN TIMING OF THE SHORTWAVES...ESPECIALLY STARTING TUESDAY. WE CONTINUE TO USE A BLEND OF MODEL DATA. CONFIDENCE IS LOW-MODERATE TUESDAY-WEDNESDAY AND MODERATE FOR THE LATE WEEK. THE DAILIES... MONDAY NIGHT... OFFSHORE LOW PRESSURE MOVES OFF SOUTH OF NOVA SCOTIA MONDAY NIGHT. ALTHOUGH UPPER DYNAMICS ARE MARGINAL...LOW LEVEL LIFT WILL DRAW UPON THE LINGERING NORTHEAST FLOW OFF THE GULF OF MAINE TO BRING SNOW TO THE REGION...ESPECIALLY AREAS EAST OF THE CENTRAL HILLS. THE BEST CHANCE WILL BE IN SOUTHEAST MASS/CAPE COD WHERE THE EXPOSURE TO THE NORTHEAST FLOW IS STRONGEST. SNOW WILL TAPER OFF OVERNIGHT AS THE OFFSHORE LOW GETS FARTHER AWAY. TUESDAY-WEDNESDAY-THURSDAY... THE SECOND COASTAL LOW GEARS UP ALONG THE MID ATLANTIC COAST EARLY TUESDAY AND MOVES NORTHEAST PASSING JUST SOUTH OF THE 40N/70W BENCHMARK. THIS IS CLOSE ENOUGH...AND MODELS AGREE...TO BRING ANOTHER SURGE OF PRECIP INTO SOUTHERN NEW ENGLAND. THE STRONGEST LIFT TUESDAY MORNING IS FOCUSSED IN THE LOWER LEVELS...AOB 850 MB...WITH DEEPER LIFT TUESDAY EVENING AND NIGHT. THE MOST FAVORED AREAS FOR SNOW WILL BE ALONG THE SOUTH COAST...WITH DECREASING POPS FARTHER NORTH AND NORTHWEST. THE UPPER TROUGH AND COLD POOL WILL WORK INTO NEW ENGLAND WEDNESDAY WITH SUFFICIENT UPPER MOISTURE FOR CLOUDS...AND ENOUGH COOLING TEMPS ALOFT TO GENERATE SCATTERED SNOW SHOWERS. ONE MORE SHORTWAVE MOVING THROUGH THE TROUGH WILL MOVE THROUGH EITHER WEDNESDAY NIGHT OR THURSDAY...MODELS SHOW SOME TIMING DIFFERENCES. THIS SHORTWAVE COMES FROM NORTHERN CANADA...WILL SUPPORT AN ARCTIC COLD FRONT THAT WILL BRING ONE MORE CHANCE OF SNOW SHOWERS. FRIDAY-SATURDAY... COLDER AIR POURS IN BEHIND THE ARCTIC FRONT. LINGERING LOW LEVEL MOISTURE MAY SUPPORT DAYTIME CLOUDS BUT THE DEEPER COLUMN WILL BECOME DRY SUGGESTING AT LEAST SOME SUNSHINE. THE TOP OF THE MIXED LAYER SHOULD BE BETWEEN 900 AND 925 MB FRIDAY...AND 875 MB SATURDAY. TEMPS AT THESE LEVELS WOULD SUPPORT MAX SFC TEMPS IN THE 20S FRIDAY AND MID TEENS TO MID 20S SATURDAY. THIS COLD AIR ALONG WITH 15-25 KNOT WEST-NORTHWEST WINDS WILL GENERATE OCEAN EFFECT SNOW SHOWERS OFF THE COAST. THE FRIDAY WEST-TO-EAST FETCH WILL NEED TO BE MONITORED FOR POTENTIAL SNOW BANDS SOUTH OF NEW ENGLAND AFFECTING THE ISLANDS. THE SATURDAY NORTHWEST FETCH SHOULD MAINLY BE OFFSHORE. && .AVIATION /15Z SUNDAY 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 MONDAY/... TODAY...HIGH CONFIDENCE VFR. LIGHT AND VARIABLE WINDS BECOMING NE TOWARD SUNSET. TONIGHT...VFR AND DRY THROUGH ABOUT MIDNIGHT. THEN CEILINGS LOWERING TO MVFR WITH INCREASING CHANCES OF SNOW OR MIXED RAIN/SNOW TOWARD DAYBREAK MON ALONG THE SOUTH COAST. NE WINDS GUSTING UP TO 35 KT CAPE COD AND ISLANDS TOWARD DAYBREAK. MONDAY...IFR IN SNOW EASTERN MA AND RI. VISIBILITIES MAY BE REDUCED TO NEAR ZERO ALONG THE IMMEDIATE COAST WHERE HEAVY OCEAN EFFECT SNOW SQUALLS ARE LIKELY. MVFR IN LIGHTER SNOW IN WESTERN MA AND NORTHERN CT. NORTHEAST WINDS GUSTING TO 40 KT ALONG THE MA COAST...HIGHEST S OF BOSTON. KBOS TERMINAL...HIGH CONFIDENCE THROUGH THIS EVENING THEN MODERATE CONFIDENCE LATE TONIGHT REGARDING ARRIVAL TIME OF LOWERING CEILINGS AND ARRIVAL OF SNOW. MODERATE CONFIDENCE FOR MONDAY. KBDL TERMINAL...HIGH CONFIDENCE THROUGH MIDNIGHT. MODERATE CONFIDENCE ON THE TIMING OF THE ARRIVAL OF LOWER CEILINGS LATER TONIGHT AND ARRIVAL OF SNOW MONDAY. OUTLOOK /MONDAY NIGHT THROUGH THURSDAY/... MONDAY NIGHT THROUGH WEDNESDAY...IFR/LIFR CIGS/VSBYS IN PERIODS OF SNOW. NORTHEAST WINDS GUSTS TO 35 KNOTS ALONG THE COAST MONDAY NIGHT AND 20-25 KNOTS TUESDAY. CONDITIONS IMPROVE TO MVFR IN SNOW SHOWERS WEDNESDAY WITH WINDS SHIFTING WEST AND DIMINISHING. THURSDAY...COLD FRONT MOVES THROUGH THE REGION BRINGING A WIND SHIFT. WINDS PICK UP OUT OF THE NORTHWEST NEAR 30 KNOTS. BRIEF MVFR/IFR IN SNOW SHOWERS WITH THE FRONT.
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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/...HIGH CONFIDENCE. OVERNIGHT...W TO SW WINDS GUSTING TO 20-25 KT OVER THE EASTERN MA WATERS...GRADUALLY DIMINISHING TOWARD DAYBREAK. TODAY...TRANQUIL WIND AND SEAS ALONG WITH DRY WEATHER AND GOOD VSBY. TONIGHT...NE WINDS INCREASE TO GALE FORCE ACROSS THE RI AND SOUTHERN MA WATERS...AND POSSIBLY THE NORTHERN MA WATERS TOWARD DAYBREAK. GALE WARNINGS POSTED FOR ALL OF THE MA AND RI COASTAL WATERS. VSBY LOWERING IN SNOW LATE ALONG THE SOUTH COAST. SEAS WILL BUILD RAPIDLY WITH POWERFUL LOW PRES WELL OFF THE NORTH CAROLINA COAST COMBINING WITH A 1035 MB SURFACE HIGH OVER QUEBEC. MONDAY...GALE FORCE WINDS GUSTING TO 35-45 KTS OVER ALL COASTAL WATERS ALONG WITH VISIBILITIES REDUCED TO BELOW 1 MILE IN SNOW. LOCALLY NEAR ZERO VISIBILITY POSSIBLE IN HEAVIER SNOW SQUALLS. THE ONLY EXCEPTION IS OVER NARRAGANSETT BAY WHERE SMALL CRAFT ADVISORIES ARE POSTED FOR WIND GUSTS OF LESS THAN 30 KTS. VERY ROUGH SEAS BUILDING UP TO 14-18 FEET OFF THE MA COAST. OUTLOOK /MONDAY NIGHT THROUGH THURSDAY/...MODERATE CONFIDENCE... MONDAY NIGHT...MODERATE-HIGH CONFIDENCE. DIMINISHING NORTHEAST WINDS. GALES LINGERING NORTH AND EAST OF PROVINCETOWN EARLY IN THE NIGHT. ROUGH SEAS EARLY WITH HEIGHTS AROUND 15 FEET EASTOF MASSACHUSETTS...DIMINISHING TO 8-12 FEET BY MORNING. AS GALES COME DOWN...A SMALL CRAFT ADVISORY WILL BE NEEDED. TUESDAY-WEDNESDAY... DIMINISHING NORTH WINDS TUESDAY WILL BECOME NORTHWEST WEDNESDAY...WITH SPEEDS 20-25 KNOTS TUESDAY AND BELOW 20 KNOTS WEDNESDAY. SEAS WILL REMAIN ROUGH WITH 7-10 FOOT HEIGHTS TUESDAY AND 5-10 FOOT HEIGHTS WEDNESDAY. SMALL CRAFT ADVISORY WILL BE NEEDED. THURSDAY... AN ARCTIC COLD FRONT SWEEPS ACROSS THE WATERS WITH COLDER AIR MOVING IN. WINDS WILL SHIFT NORTHWEST WITH GUSTS UP TO 30 KNOTS. THESE WINDS WILL DRIVE 5-8 FOOT SEAS ESPECIALLY ON THE OUTER WATERS. SMALL CRAFT ADVISORY WILL BE NEEDED. THE COLD FRONT MAY BRING A FEW SNOW SHOWERS WITH BRIEFLY POOR VSBYS. THE ARCTIC COLD AIR BEHIND THE FRONT WILL START TO GENERATE OCEAN EFFECT SNOW SHOWERS WITH LOCAL POOR VSBYS LATER IN THE DAY ESPECIALLY EAST OF MASSACHUSETTS.
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&& .TIDES/COASTAL FLOODING... ASTRO TIDES LATE MON MORNING ARE HIGH WITH 11.2 FT AT BOSTON. STRONG NE WINDS UP TO 40 KT WILL YIELD A STORM SURGE OF 1.5 FT TO 2.0 FT AT THE TIME OF HIGH TIDE. THIS COMBINED WITH STRONG WAVE ACTION OF 14-18 FT JUST OFFSHORE WILL YIELD A RISK OF MODERATE COASTAL FLOODING. ETSS WAS A BIT HIGHER THAN ESTOFS AND SEEMS REASONABLE. WIND FIELD IS SOMEWHAT LOWER NORTH OF PLYMOUTH COUNTY. THUS THREAT OF COASTAL FLOODING IS LOWER FROM BOSTON NORTHWARD. THEREFORE HAVE CONFINED THE COASTAL FLOOD WATCH SOUTH OF BOSTON THRU PLYMOUTH TO CAPE COD AND NANTUCKET. OTHER CONCERN IS BEACH EROSION GIVEN THE HIGH WATER LEVELS...STRONG WAVE ACTION OVER MULTIPLE TIDE CYCLES. AGAIN APPEARS HIGHEST RISK WILL BE SOUTH OF BOSTON. HOWEVER WILL HAVE TO MONITOR LATER MODEL RUNS FOR POSSIBLE EXPANSION OF THE WATCH NORTHWARD. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...COASTAL FLOOD WATCH FROM MONDAY MORNING THROUGH MONDAY AFTERNOON FOR MAZ019-022-024. WINTER STORM WATCH FROM MONDAY MORNING THROUGH TUESDAY MORNING FOR MAZ005>007-012>024. RI...WINTER STORM WATCH FROM MONDAY MORNING THROUGH TUESDAY MORNING FOR RIZ001-002-004-005-007. MARINE...GALE WARNING FROM MIDNIGHT TONIGHT TO 6 PM EST MONDAY FOR ANZ231>235-237-254>256. GALE WARNING FROM 4 AM TO 6 PM EST MONDAY FOR ANZ230. SMALL CRAFT ADVISORY FROM 5 AM TO 7 PM EST MONDAY FOR ANZ236. GALE WARNING FROM 4 AM TO 10 PM EST MONDAY FOR ANZ250-251. && $$ SYNOPSIS...WTB/GAF NEAR TERM...NOCERA/EVT/GAF SHORT TERM...GAF LONG TERM...WTB AVIATION...WTB/GAF MARINE...WTB/GAF TIDES/COASTAL FLOODING...

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