Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 180927 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 427 AM EST THU DEC 18 2014 .SYNOPSIS...
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SCATTERED RAIN AND SNOW SHOWERS WILL QUICKLY COME TO AN END BY MID MORNING. OTHERWISE...HIGH PRESSURE SLOWLY BUILDING ACROSS EASTERN CANADA WILL RESULT IN DRY AND SEASONABLY CHILLY TEMPERATURES THROUGH FRIDAY. SCATTERED SNOW SHOWERS WILL DEVELOP SATURDAY NIGHT INTO SUNDAY WITH A LOW PRESSURE SYSTEM MOVING NEAR THE REGION TUESDAY. AN ANOMALOUS SYSTEM WILL IMPACT THE EASTERN UNITED STATES WEDNESDAY INTO THURSDAY.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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4 AM UPDATE... SHORTWAVE/COLD POOL ALOFT MOVES ACROSS SOUTHERN NEW ENGLAND THROUGH 12Z...TRIGGERING HIT AND MISS RAIN/SNOW SHOWERS. THE BEST MOISTURE/FORCING WILL BE ACROSS OUR NORTHERN/EASTERN ZONES...SO WILL HAVE THE HIGHEST POPS IN THOSE LOCATIONS. HOWEVER...ENOUGH FORCING IS AVAILABLE FOR A FEW BRIEF RAIN/SHOWERS ACROSS SOUTHWEST MA/CT AND RI. AS FOR PTYPE...COLD ENOUGH FOR SCATTERED SNOW SHOWERS ACROSS THE HIGHER TERRAIN. IN THE LOWER ELEVATIONS AND COASTAL PLAIN...BOUNDARY LAYER WILL BE MILD ENOUGH FOR SCATTERED RAIN SHOWERS INITIALLY. WET BULB PROCESSES MAY ALLOW FOR AN EVENTUAL MIXTURE OR CHANGE TO FLURRIES/SNOW SHOWERS. SPOTTY SNOW ACCUMULATIONS OF A COATING TO LESS THAN 1 INCH ARE POSSIBLE ACROSS PORTIONS OF THE HIGHER TERRAIN. MOST OF THE SCATTERED PRECIPITATION SHOULD EXIT EASTERN MA BY 8 OR 9 AM AS SHORTWAVE DEPARTS. OTHERWISE...EXPECT A MIXTURE OF CLOUDS AND SUN LATER THIS MORNING AND INTO THE AFTERNOON. LOW PRESSURE OVER THE CANADIAN MARITIMES AND HIGH PRESSURE ACROSS THE GREAT LAKES WILL RESULT IN GUSTY NORTHWEST WINDS. WIND GUSTS OF 25 TO 35 MPH ARE EXPECTED TO DEVELOP LATER THIS MORNING AND INTO THE AFTERNOON. HIGH TEMPS WILL MAINLY BE IN THE UPPER 30S TO THE MIDDLE 40S.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
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TONIGHT... LOW PRESSURE IN THE CANADIAN MARITIMES WILL CONTINUE TO LIFT NORTHEAST. THIS WILL ALLOW THE PRESSURE GRADIENT TO WEAKEN A BIT...BUT NOT ENOUGH FOR WINDS TO COMPLETELY DECOUPLE EVEN IN THE VALLEY LOCATIONS. THEREFORE...LOW TEMPS SHOULD MAINLY BE IN THE 20S TO AROUND 30 WITH PARTLY CLOUDY SKIES. FRIDAY... LARGE HIGH PRESSURE WILL OVER THE GREAT LAKES SHOULD PUSH EAST INTO QUEBEC. WHILE WERE NOT TOO COLD AT 850 MB...THIS HIGH PRESSURE SYSTEM SHOULD ALLOW SOME SHALLOW COLD AIR TOO OOZE SOUTH...KEEPING HIGH TEMPS IN THE 30S FOR MOST LOCATIONS. SHOULD SEE A MIXTURE OF CLOUDS AND SUN WITH LESS WIND THAN TODAY.
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&& .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
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HIGHLIGHTS... * SCT SNOW/RAIN SHOWERS SAT INTO SUNDAY WITH BELOW AVG TEMPS * WEAK WAVE OF LOW PRESSURE ON TUESDAY * ANOMALOUS SYSTEM ACROSS THE GREAT LAKES WILL BRING HEAVY RAIN...GUSTY WINDS AND COASTAL CONCERNS AROUND CHRISTMAS EVE OVERVIEW... OVERALL 00Z GUIDANCE IS IN AGREEMENT SYNOPTICALLY WITH ISSUES ON TIMING AND SMALLER SCALE FEATURES. AMPLIFIED PATTERN SET TO RETURN TO THE U.S. AS THE STRONG W PACIFIC JET TRANSLATES DOWNSTREAM THIS WEEKEND INTO THE PAC NW. BUILDING HEIGHTS OVER SE CANADA SHOULD ALSO HELP DIG THE TROUGH INTO THE OHIO VALLEY MIDWEEK AND LIKELY CLOSE OFF AS IT SWINGS INTO SOUTHERN CANADA ON CHRISTMAS DAY. MODELS/ENSEMBLES HAVE BEEN FAIRLY CONSISTENT IN RECENT RUNS ON THIS AMPLIFIED PATTERN AND THE MOST RECENT GEFS/ECMWF ENSEMBLE GUIDANCE SHOW GOOD CORRELATION TO NEXT THURSDAY. DURING THIS SYNOPTIC TRANSITION...HIGH PRESSURE AND UPPER LEVEL RIDGE WILL BE OVER THE NORTHEAST SATURDAY INTO SUNDAY. DIGGING TROUGH OVER THE CENTRAL CONUS WILL PUSH A SHORTWAVE ACROSS THE SE INTO THE MID-ATLANTIC. APPEARS THAT A WEAK COASTAL LOW WILL DEVELOP MOVING TOWARDS THE REGION MONDAY INTO TUESDAY. THE GFS BRINGS THIS LOW OVER THE BENCHMARK WHERE THE EC PUSHES WELL EASTWARD THANKS TO BUILDING HIGH PRESSURE OVER EASTERN CANADA. THIS SYSTEM IS WEAK SO COASTAL REGIONS HAVE THE BEST SHOT FOR PRECIP. AS THIS SYSTEM DEPART APPEARS ANOMALOUS LOW OVER THE GREAT LAKES WILL DEVELOP A SECONDARY LOW CLOSER TO NEW ENGLAND. THE GFS IS STILL A TAD FASTER COMPARED TO THE EC BUT OVERALL EXCELLENT MODEL AGREEMENT 6+ DAYS OUT. DETAILS... SATURDAY INTO SUNDAY...HIGH CONFIDENCE. HIGH PRESSURE IN EASTERN CANADA WILL BUILD ACROSS THE REGION FRIDAY NIGHT INTO SATURDAY. HOWEVER IT APPEARS ON FRIDAY NIGHT INTO SATURDAY NORTHERLY FLOW MAY ALLOW FOR SOME OCEAN EFFECT CLOUDS/SNOW SHOWERS TO IMPACT THE CAPE. SURFACE TO 850 MB TEMP DIFFERENCE IS 14C WHICH IS UNSTABLE ENOUGH FOR SNOW SHOWERS ON SATURDAY FOR THE CAPE. AM NOT ANTICIPATE MUCH IN THE WAY OF ACCUMULATIONS BUT A DUSTING CANNOT BE RULED OUT. WEAK WAVE WILL MOVE THROUGH THE FLOW ON SATURDAY NIGHT AND WITH HIGH PRESSURE SHIFTING EASTWARD EXPECT ONSHORE EASTERLY FLOW. GUIDANCE CONTINUES TO SHOW QPF MOVING ONSHORE AND WITH MOISTURE AND THE LIFT COULD SEE SNOW SHOWERS MOVING INLAND SATURDAY NIGHT INTO SUNDAY. BIGGEST QUESTION IS WILL THE MOISTURE SATURATE ENOUGH TO -6C. IF NOT THEN THE POTENTIAL FOR FREEZING DRIZZLE IS POSSIBLE. FOR NOW BELIEVE THAT THERE IS ENOUGH MOISTURE SO A QUICK HALF INCH TO AN INCH IS POSSIBLE PER SOUNDINGS EAST OF THE WORCESTER HILLS. MONDAY INTO TUESDAY...MODERATE CONFIDENCE. WEAK COASTAL LOW PRESSURE SYSTEM WILL DEVELOP AND MOVE SOMEWHERE BETWEEN THE BENCHMARK AND WELL OFFSHORE. BELIEVE A SOLUTION FATHER OUT TO SEA IS POSSIBLE DUE TO STRONG HIGH PRESSURE IN EASTERN CANADA. REGARDLESS A ROUND OF SHOWERS WILL MOVE ACROSS THE REGION WITH THE COASTAL AREAS HAVING THE BEST SHOT TO SEE PRECIP. THERMAL PROFILES WILL ALLOW FOR SNOW AT NIGHT AND RAIN DURING THE DAY. TEMPERATURES WILL SLOWLY BEGIN TO WARM AS SOUTHERLY FLOW BECOMES DOMINATE OUT AHEAD OF STRONGER SYSTEM TO THE EAST. TUESDAY HIGH TIDE WILL BE 11.6 IN BOSTON DURING THE LATE MORNING AND WITH ANY EASTERLY FLOW MAY ALLOW FOR MINOR COASTAL FLOODING. WEDNESDAY INTO THURSDAY...HIGH CONFIDENCE IN SYSTEM LOW CONFIDENCE ON DETAILS. STRONG ANOMALOUS SYSTEM WILL STRENGTHEN OVER THE GREAT LAKES...DEVELOPING A SECONDARY SURFACE LOW JUST WEST OF SOUTHERN NEW ENGLAND. STILL A LOT OF DETAILS TO WORK OUT AS THIS SYSTEM IS STILL 6 DAYS AWAY...HOWEVER ENSEMBLES SHOW THAT THIS SYSTEM IS AROUND 2 TO 3 STANDARD DEVIATIONS ALLOWING FOR INCREASING CONFIDENCE THAT A POTENT STORM WILL OCCUR. LATEST 00Z GUIDANCE SHOWS THAT MOST PRECIP WILL BE LIQUID WITH A DEEP SUBTROPICAL CONNECTION BACK ACROSS MEXICO... PW ANOMALIES FORECAST TO RISE TO BETWEEN +1 TO +3 /OR HIGHER/...AND TEMPERATURES WELL ABOVE AVERAGE. IN FACT WE MAY BE CLOSE AT BREAKING RECORD HIGH TEMPS IF TEMPS WARM TO 60F OR ABOVE ON CHRISTMAS EVE. AS THE SYSTEM WRAPS UP INTO CANADA...COLD AIR ADVECTION SHOULD CIRCULATE AROUND AND BEGIN A TRANSITION FROM SOUTHWEST TO NORTHEAST IN TURNING P-TYPE TO SNOW. THIS SYSTEM IS QUITE STRONG SO WE WILL NEED TO WATCH FOR POSSIBLE URBAN FLOODING ISSUES AS WELL AS WIND ISSUES. GUIDANCE RIGHT NOW IS SHOWING A 40 TO 50 KT JET AT 925 MB WHICH MAY WARRANT WIND ADVISORIES BUT THIS SYSTEM COULD STRENGTHEN EVEN MORE SO A STRONGER JET IS POSSIBLE. LASTLY COASTAL FLOODING ISSUES WILL NEED TO BE ADDRESS AS HIGH TIDE ON WED AND THUS ARE 11.7 AND 11.5 RESPECTIVELY. ANY ONSHORE COMPONET WILL PUSH THE TIDE ABOVE FLOOD SO COASTAL FLOODING IS POSSIBLE AS WELL AS BEACH EROSION.
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&& .AVIATION /10Z THURSDAY THROUGH MONDAY/...
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FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. 4 AM UPDATE... SHORT TERM /TODAY THROUGH FRIDAY/...HIGH CONFIDENCE. TODAY...VFR CONDITIONS MOST OF THE DAY. HOWEVER...BRIEF LOCALIZED MVFR CONDITIONS POSSIBLE THROUGH 12Z IN SCATTERED RAIN/SNOW SHOWERS ESPECIALLY NORTHERN AND EASTERN MA. BRIEF MVFR CIGS ALSO WILL BE POSSIBLE INTO THE AFTERNOON...BUT EXPECT VFR CONDITIONS TO DOMINATE. NORTHWEST WIND GUSTS OF 25 KNOTS EXPECTED TO DEVELOP LATER THIS MORNING INTO THE AFTERNOON. TONIGHT AND FRIDAY...MAINLY VFR CONDITIONS BUT BRIEF PERIODS OF MARGINAL MVFR CIGS POSSIBLE. KBOS TERMINAL...HIGH CONFIDENCE. LOW RISK OF BRIEF MVFR CONDITIONS IN A FEW RAIN/SNOW SHOWERS THROUGH 12Z. KBDL TERMINAL...HIGH CONFIDENCE. OUTLOOK...FRIDAY NIGHT THROUGH MONDAY... FRIDAY NIGHT INTO SUNDAY...HIGH CONFIDENCE. MOSTLY VFR WITH MVFR CONDITIONS ANY SCT SNOW/RAIN SHOWERS. MONDAY...LOW CONFIDENCE. VFR CONDITIONS.
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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 /TODAY THROUGH FRIDAY/...MODERATE TO HIGH CONFIDENCE. TODAY...SCA HEADLINES FOR ALL WATERS. HIGH PRESSURE OVER THE GREAT LAKES AND LOW PRESSURE OVER THE CANADIAN MARITIMES WILL RESULT IN A TIGHT PRESSURE GRADIENT. NORTHWEST WIND GUSTS OF 25 TO 30 KNOTS EXPECTED ACROSS ALL WATERS. A FEW GUSTS NEAR 35 KNOTS ARE POSSIBLE ACROSS OUR SOUTHERN AND EASTERN OUTER-WATERS...BUT DO NOT THINK THEY WILL BE WIDESPREAD ENOUGH FOR GALE WARNINGS. TONIGHT...SCA HEADLINES WILL CONTINUE FOR MOST OPEN WATERS. WINDS WILL DIMINISH SOME BUT STILL THINK WINDS WILL GUST UP TO 25 KNOTS FOR MUCH OF THE NIGHT. FRIDAY...HIGH PRESSURE BUILDING INTO QUEBEC WILL ALLOW THE PRESSURE GRADIENT TO WEAKEN. STILL EXPECT NORTHWEST WINDS TO GUST TO 20 KNOTS IN THE COLD AIR ADVECTION PATTERN...BUT BELOW SMALL CRAFT ADVISORY THRESHOLDS. LINGERING SMALL CRAFT SEAS ACROSS THE SOUTHEAST WATERS SHOULD DIMINISH BY LATE MORNING. OTHERWISE...NO HEADLINES ARE ANTICIPATED. OUTLOOK...FRIDAY NIGHT INTO MONDAY...MODERATE TO HIGH CONFIDENCE. FRIDAY NIGHT INTO SUNDAY...ANTICIPATE DIMINISHING WINDS AND SEAS SUBSIDING LATE THU NIGHT INTO SATURDAY LEADING TO BELOW SMALL CRAFT ADVISORY LEVELS. MONDAY...EXPECT NE WINDS GUSTING UP TO 20 KT. LOW PROB OF 25 KT GUSTS AS WELL AS 5 FT SEAS.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...NONE. MA...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 3 AM EST FRIDAY FOR ANZ232>235-237. SMALL CRAFT ADVISORY UNTIL 7 PM EST THIS EVENING FOR ANZ230- 236. SMALL CRAFT ADVISORY UNTIL 6 AM EST FRIDAY FOR ANZ231-250-251- 254>256.
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&& $$ SYNOPSIS...FRANK/DUNTEN NEAR TERM...FRANK SHORT TERM...FRANK LONG TERM...DUNTEN AVIATION...FRANK/DUNTEN MARINE...FRANK/DUNTEN

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