Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 062113 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 413 PM EST SAT FEB 6 2016 .SYNOPSIS...
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HIGH PRESSURE BRINGS DRY WEATHER ALONG WITH MODERATING TEMPERATURES TONIGHT AND SUNDAY. AN OCEAN STORM MAY BRING A PLOWABLE SNOWFALL TO SOUTHEAST MASACHUSETTS INCLUDING CAPE COD AND THE ISLANDS MONDAY AND MONDAY NIGHT. PERIODS OF SNOW ARE LIKELY FOR THE REMAINDER OF THE REGION TUE...WED AND POSSIBLY LINGERING INTO THU. AN ARCTIC COLD FRONT BRINGS BITTERLY COLD CONDITIONS THE END OF THE WEEK INTO NEXT WEEKEND.
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&& .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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4 PM UPDATE... TONIGHT... CONFLUENT FLOW ALOFT PROVIDES DRY WEATHER TONIGHT ALONG WITH HIGH PRES AT THE SURFACE JUST SOUTH OF NEW ENGLAND. THIS WILL RESULT IN SW PRES GRADIENT/SURFACE WINDS AND YIELDING TEMPS NOT AS COLD AS LAST NIGHT AS DEW PTS CLIMB INTO THE 20S.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
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SUNDAY ... NOT MUCH CHANGE WITH CONFLUENT FLOW ALOFT AND HIGH PRES AT THE SURFACE. THUS EXPECTING A DRY COLUMN SUPPORTING LOTS OF SUNSHINE AND LIGHT WINDS...WHICH WILL MAKE TEMPS IN THE L40S FEEL EVEN MILDER. SUNDAY NIGHT ... 1035 QUEBEC SURFACE HIGH ADVECTS SHALLOW ARCTIC AIR SOUTHWARD INTO SOUTHERN NEW ENGLAND. MEANWHILE MID LEVEL SOUTHERN STREAM TROUGH OVER THE GULF STATES THIS AFTERNOON INDUCES CYCLOGENESIS OFF THE EAST COAST OF FL THIS EVENING AND THEN RAPIDLY INTENSIFYING INTO A SUB 980 MB LOW/GALE CENTER WELL EAST OF THE NC COAST SUN NIGHT. 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. THUS SNOW COMES ONSHORE 06Z-12 MON AND WILL LIKELY HAVE SOME OCEAN EFFECT SNOW /OES/ COMPONENT GIVEN NE WINDS AND SHALLOW ARCTIC AIR BLEEDING IN FROM THE NORTH. BIG DIFFERENCES WITH MODEL QPF WITH NAM/ARW/NMM MOST ROBUST. EC/GFS AND RGEM MORE MODEST SO FOLLOWED A MODEL BLEND GIVEN UNCERTAINTY.
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&& .LONG TERM /MONDAY THROUGH SATURDAY/... BIG PICTURE... LONGWAVE PATTERN SHOWS RIDGE WEST/TROUGH EAST AS BEFORE...WITH INCREASING AMPLITUDE EARLY WEEK AND DECREASING AMPLITUDE LATE WEEK. OVERALL A COLD AND UNSETTLED PATTERN FOR SOUTHERN NEW ENGLAND. AT SHORTER WAVE SCALES WE SEE THREE SHORTWAVES AFFECTING THE PATTERN. THE FIRST IS IN THE LOWER MISS RIVER VALLEY AND GENERATES COASTAL LOW PRESSURE OFF THE CAROLINAS SUNDAY. THIS SWINGS WIDE OF OUR AREA...CROSSING ABOUT 4 DEGREES SOUTH OF THE 40N/70W BENCHMARK...AND THEN SWEEPS NORTHEAST JUST SOUTH OF NOVA SCOTIA. THE SECOND SHORTWAVE IS MOVING ASHORE IN THE PACIFIC NORTHWEST AND WILL CARVE A DEEP COLD TROUGH OVER THE EASTERN USA DURING THE EARLY WEEK. THE THIRD SHORTWAVE IS ALONG THE ARCTIC OCEAN COASTLINE AND WILL DROP SOUTH INTO THE USA MIDWEEK. OPERATIONAL GUIDANCE MASS FIELDS ARE SIMILAR ON THE BROAD SCALE MOST OF THE PERIOD. BUT THERE ARE DIFFERENCES IN THE DETAILS...ESPECIALLY REGARDING THE SECOND SHORTWAVE AND ITS DEVELOPING COASTAL SYSTEM TUESDAY. THIS SECOND SHORTWAVE WAS JUST COMING ASHORE AT MEASUREMENT TIME LAST NIGHT. THE 12Z SATURDAY MODELS SHOULD HAVE A BETTER READ ON THE SHORTWAVE AND ITS EFFECTS. WE CONTINUE TO FAVOR A MODEL BLEND ESPECIALLY USING THE GFS AND ECMWF. THE DAILIES... SUNDAY NIGHT-MONDAY... COASTAL STORM PASSES WELL OFFSHORE...SOME 4 DEGREES SOUTH OF THE BENCHMARK. NORMALLY THAT WOULD MEAN A SWING AND A MISS FOR STRIKE THREE. BUT HIGH PRESSURE BUILDS SOUTH FROM QUEBEC AND ESTABLISHES A PRESSURE GRADIENT THAT SHOULD BRING A NORTHEAST MARINE FLOW WITH DELTA OF 13-15C. THIS SHOULD AT LEAST BRING INCREASING CLOUDS OVERNIGHT AND MONDAY. LESS CONFIDENCE ON PCPN GIVEN MEDIOCRE FORCING AND CHANGING RUN-TO-RUN AMOUNTS. MODELS HAVE BACKED OFF ON QPF DURING MONDAY WITH MAIN FOCUS ON CAPE AND ISLANDS...POSSIBLY EASTERN MASS. WE HAVE BACKED OFF ONSET OF POPS UNTIL 06-12Z MONDAY AND VALUE OF POPS BY ABOUT 20 PERCENT. THIS STILL BRINGS POTENTIAL FOR SEVERAL INCHES IN EASTERN MASS WITH HIGHEST AMOUNTS CAPE COD/PLYMOUTH CO AREA. MONDAY NIGHT-TUESDAY... SECOND SHORTWAVE DIGS OVER THE MIDWEST WITH SURFACE LOW REDEVELOPMENT ALONG THE MID ATLANTIC COAST. THIS NEW COASTAL LOW THEN MOVES PAST NEW ENGLAND. BETTER DYNAMICS AND RESULTING LIFT SHOULD BE IN PLACE AND WITH DEEPER MOISTURE WOULD EXPECT THIS TO BE A BETTER CHANCE OF PCPN THAN THE MONDAY OFFSHORE SYSTEM. BUT THE RESPONSIBLE SHORTWAVE IS JUST NOW MOVING ASHORE AS NOTED ABOVE. SO STILL SOME UNCERTAINTY WITH THIS SYSTEM AND ITS POTENTIAL. WE WILL BRING A PERIOD OF LIKELY POPS AS THE SYSTEM MOVES THROUGH. WEDNESDAY THROUGH FRIDAY... UPPER TROUGH WITH ITS COLD POOL ALOFT AND CLOUD SHIELD LINGER WEDNESDAY. THE ARCTIC SHORTWAVE THEN SWINGS THROUGH ON THURSDAY. EXPECT QUITE A FEW CLOUDS DURING THIS PERIOD WITH A CHANCE OF SNOW SHOWERS. CLIPPER LOW THEN DROPS SOUTHEAST FROM NORTHERN ONTARIO FRIDAY AND BRINGING MORE CLOUDS AND SCATTERED SNOW SHOWERS. MIXED LAYER REACHES EITHER SIDE OF 925 MB EACH DAY...A LITTLE HIGHER THURSDAY BEHIND THE ARCTIC SHORTWAVE AND SURFACE FRONT. TEMPS ALOFT AT THE TOP OF THE LAYER SUPPORT 30S WEDNESDAY...20S WEST/32 EAST THURSDAY...AND 20S TO NEAR 30 FRIDAY. AS NOTED EARLIER...COLD AND UNSETTLED. && .AVIATION /20Z 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 NIGHT/... THRU TONIGHT ... HIGH FORECAST CONFIDENCE FOR VFR/DRY AND LIGHT SW WIND. WINDS MAY GUSTS UP TO 15-20 KT CAPE COD AND ISLANDS THIS EVENING. SUNDAY ... HIGH CONFIDENCE FOR VFR. LIGHT AND VARIABLE WINDS BECOMING NE TOWARD SUNSET. SUNDAY NIGHT ... VFR AND DRY THRU ABOUT MIDNIGHT. THEN LOWERING TO MVFR WITH INCREASING CHANCES OF SNOW OR MIX RAIN/SNOW TOWARD DAYBREAK MON. NE WINDS GUSTING UP TO 35 KT CAPE COD AND ISLANDS TOWARD 12Z MON. KBOS TERMINAL...HIGH CONFIDENCE THRU SUN EVENING THEN LOWERING LATE SUN NIGHT REGARDING ARRIVAL OF LOWER CIGS/VSBYS IN SNOW/RAIN. KBDL TERMINAL...HIGH CONFIDENCE IN TRENDS. OUTLOOK /MONDAY THROUGH THURSDAY/... TWO POTENTIAL STORMS DURING THIS PERIOD...EITHER COULD BRING IFR/LIFR CIGS AND VSBYS IN SNOW. THE FIRST CHANCE FOR THIS WILL BE MONDAY...WITH BEST CHANCE ON CAPE COD AND ISLANDS. NORTH-NORTHEAST WINDS WILL GUST TO 35 KNOTS ALONG THE EASTERN MASS COAST. THE SECOND CHANCE WILL BE MONDAY NIGHT AND TUESDAY WITH ALL OF SOUTHERN NEW ENGLAND UNDER THE GUN. CONDITIONS IMPROVE WEDNESDAY TO MVFR CIGS WITH SCATTERED SNOW SHOWERS.
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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 SUNDAY NIGHT/...HIGH CONFIDENCE. TONIGHT AND SUNDAY ... TRANQUIL WIND AND SEAS ALONG WITH DRY WEATHER AND GOOD VSBY. SUNDAY NIGHT ... NE WINDS LIKELY INCREASE TO GALE FORCE ACROSS THE RI AND SOUTHERN MA WATERS. THUS GALE WARNINGS POSTED. LOW PROBABILITY NORTH OF CAPE COD SO GALE WATCHES POSTED THERE. VSBY LOWERING IN SNOW LATE. SEAS WILL BUILD RAPIDLY WITH POWERFUL LOW PRES OFF THE NC COAST COMBINING WITH 1035 MB SURFACE HIGH OVER QUEBEC. OUTLOOK /TUESDAY THROUGH THURSDAY/...MODERATE CONFIDENCE... TUESDAY...A SECOND WEATHER SYSTEM WILL DEVELOP ALONG THE MID ATLANTIC COAST AND MOVE OUTSIDE NANTUCKET. THIS WILL BRING ANOTHER PERIOD OF NORTHEAST WINDS WITH GUSTS OVER 25 KNOTS. THERE REMAIN MANY QUESTIONS ABOUT THIS NEXT SYSTEM...AS WELL AS LOW POTENTIAL FOR WINDS REACHING 35 KNOTS. SEAS WILL REMAIN AT 7 TO 11 FEET. WEDNESDAY... WINDS DIMINISH AS THE SECOND COASTAL STORM MOVES OFF. WIND SPEEDS SHOULD GO BELOW 25 KNOTS. ROUGH SEAS WILL LINGER MUCH OF THE DAY ESPECIALLY ON THE SOUTHERN EXPOSED WATERS.
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&& .TIDES/COASTAL FLOODING...
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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 12-18 FT JUST OFFSHORE WILL YIELD A RISK OF MODERATE COASTAL FLOODING. ETSS WAS A BIT HIGHER THAN ESTOFS AND SEEMS REASONABLE. WIND FIELD DECREASES SUBSTANTIALLY 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.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...NONE. MA...COASTAL FLOOD WATCH FROM MONDAY MORNING THROUGH MONDAY AFTERNOON FOR MAZ019-022-024. WINTER STORM WATCH FROM MONDAY MORNING THROUGH MONDAY AFTERNOON FOR MAZ018-019-021>024. RI...NONE. MARINE...GALE WARNING FROM MIDNIGHT SUNDAY NIGHT TO 6 PM EST MONDAY FOR ANZ231>235-237-254>256. GALE WATCH FROM LATE SUNDAY NIGHT THROUGH MONDAY AFTERNOON FOR ANZ230-250-251.
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&& $$ SYNOPSIS...NOCERA NEAR TERM...NOCERA SHORT TERM...NOCERA LONG TERM...WTB AVIATION...WTB/NOCERA MARINE...WTB/NOCERA TIDES/COASTAL FLOODING...NOCERA

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