Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 271821 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 121 PM EST SAT DEC 27 2014 .SYNOPSIS...
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HIGH PRESSURE MOVING OFF THE ATLANTIC COAST WILL CONTINUE MOVING TO THE EAST TONIGHT. A COLD FRONT WILL BRING RAIN SHOWERS SUNDAY. CANADIAN HIGH PRESSURE THEN BUILDS OVER THE NORTHEAST USA AND BRINGS COLDER WEATHER FOR MUCH OF THE WEEK.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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THROUGH 7 PM... HIGH PRESSURE IN CONTROL SURFACE AND ALOFT. SKIES SHOW PATCHY CIRRUS OVER MOST OF SOUTHERN NEW ENGLAND. STILL A PATCH OF LOWER STRATOCU OVER NORTHWEST MASS PRIMARILY ADAMS-ROWE. AMADAR SOUNDINGS SHOW POTENTIAL MIXING TO 925 MB...BOSTON AND MANCHESTER SOUNDINGS SUGGEST 900 MB. TEMPS AT THESE LEVELS WOULD SUPPORT MAX SFC TEMPS AROUND 50 OR THE LOW 50S. COULD BE A FEW DEGREES COOLER IN THE NORTHWEST DUE TO THE EXISTING CLOUDS. THE AIR THEN COOLS WITH SUNSET. TONIGHT... CLOUDS OVER THE GREAT LAKES/OHIO VALLEY AREA WILL SPREAD EAST TONIGHT. LOW CLOUDS OVER THE EASTERN GREAT LAKES MAY BREAK UP AS THEY APPROACH THIS EVENING...BUT THE MORE SUBSTANTIAL CLOUDS OVER OHIO/KENTUCKY SHOULD HOLD TOGETHER. PER SATELLITE IMAGERY...THESE LATER CLOUDS EXTRAPOLATE INTO NEW ENGLAND AROUND/AFTER MIDNIGHT. LOW PRESSURE IN THE GREAT LAKES WILL PASS NORTH OF NEW ENGLAND LATER TONIGHT. IN THE PROCESS IT WILL SWING A COLD FRONT INTO NORTHERN AND WESTERN NEW ENGLAND TOWARD MORNING. WE ARE EXPECTING A FEW SHOWERS OUT AHEAD OF THIS FRONT LATE TONIGHT WITH THE BEST CHANCE IN THE HILLS WEST OF THE CT RIVER. FAIR SKIES WILL ALLOW TEMPS TO COOL THIS EVENING. AS CLOUDS MOVE IN THE COOLING WILL END AND TEMPS SHOULD RISE A LITTLE. WE FOLLOWED THIS NON DIURNAL TREND FOR HOURLY TEMPS.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY NIGHT/...
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OVERVIEW...TROUGH DIGS OVER THE WESTERN USA MAKING ROOM FOR COLD AIR TO MOVE SOUTH INTO THE WESTERN USA. SHORTWAVE NORTH OF THE GREAT LAKES MOVES EAST...WITH THE SHORTWAVE AXIS CROSSING NEW ENGLAND SUNDAY NIGHT. THE UPPER FLOW REMAINS GENERALLY WESTERLY THROUGH THE PERIOD. SUNDAY...COLD FRONT MOVES ACROSS SOUTHERN NEW ENGLAND SUNDAY. MODEL CROSS SECTIONS SHOW DEEP MOISTURE DURING THE DAY WITH PRECIPITABLE WATER VALUES BRIEFLY RISING TO AROUND 1 INCH. THERE IS SUFFICIENT LIFT AND MOISTURE TO SUPPORT SHOWERS. WE HAVE BUMPED POPS UP TO 50-60 PERCENT. BEHIND THE FRONT...WINDS SHIFT TO WEST- NORTHWEST. VERTICAL PROFILES SUGGEST POTENTIAL MIXING OF 20 KNOT WINDS TO THE SURFACE IN GUSTS. TEMPS IN THE MIXED LAYER WOULD SUPPORT MAX SFC TEMPS IN THE 40S...MAYBE AROUND 50 ALONG THE SOUTH COAST. DEPENDING ON HOW FAST THE COLDER AIR MOVES IN IT IS POSSIBLE THAT EXTREME NW MASS MAY STAY IN THE 30S. SUNDAY NIGHT...THE LAST OF THE SHOWERS SHOULD MOVE SOUTH OF THE SOUTH COAST AND ISLANDS. DRIER AIR WILL MEAN A CLEARING TREND OVERNIGHT. WITH DEWPOINTS IN THE 20S AND LIGHT NORTHWEST WINDS...EXPECT TEMPS AWAY FROM THE COAST TO DIP BELOW FREEZING.
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&& .LONG TERM /MONDAY THROUGH SATURDAY/...
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HIGHLIGHTS... * MAINLY DRY AND COLD THROUGH THE PERIOD OVERVIEW... MEDIUM RANGE MODELS IN FAIRLY GOOD AGREEMENT THROUGH THIS FORECAST PERIOD...AND FORECAST CONFIDENCE IS MODERATE TO HIGH. OVER THE NEXT WEEK...A SPLIT FLOW PREVAILS ACROSS NORTH AMERICA AS ENERGY DIVES TO THE SW USA WHILE EASTERN CANADA AND THENORTHEAST USA ARE DOMINATED BY A BROAD TROF. THIS OPENS THE DOOR TO AN INTRUSION OF ARCTIC AIR INTO NEW ENGLAND FOR MOST OF THE WEEK AND A DRY W TO NW LOW LEVEL FLOW. BEYOND THIS FORECAST PERIOD...THERE IS WIDER DISPARITY IN HOW THE MODELS HANDLE THE EJECTION OF THE ENERGY FROM THE SW AND THE EVENTUAL IMPACT ON SOUTHERN NEW ENGLAND DURING THE FOLLOWING WEEKEND. DAY TO DAY... MON-TUE...COLD AIR MOVES INTO REGION BEHIND THE COLD FRONT WHICH STALLS S OF NEW ENGLAND. THE MEDIUM RANGE MODELS HAVE SIGNALED THE LIKELIHOOD OF ONE OR TWO WEAK WAVES MOVING ALONG THE FRONT IN THE MON TO TUE TIME FRAME. MORE THAN LIKELY THESE WAVES WILL BE SUPPRESSED ENOUGH TO KEEP ANY PRECIPITATION OFFSHORE. HOWEVER...THERE REMAINS A SMALL CHANCE OF FLURRIES OR VERY LIGHT SNOW GLANCING THE ISLANDS AND CAPE COD AND SO HAVE KEPT SLIGHT CHANCE POPS THERE. DID NOTE THAT THE SREF DEPICTS A 50 PERCENT CHANCE OF 12 HOUR QPF REACHING .25 INCHES NEARLY AS FAR NORTH AS THE MASS PIKE BUT THIS PRODUCT IS HEAVILY INFLUENCED BY THE NAM RUNS WHICH HAVE A FAIRLY TRACK RECORD BEYOND 36 OR 48 HOURS. TUE NIGHT THROUGH FRI...LOOKS TO BE DRY WITH BELOW NORMAL TEMPERATURES AS ARCTIC AIR SETTLES INTO THE REGION. HAVE DROPPED TEMPERATURES A FEW DEGREES TUE NIGHT AND WED NIGHT FROM THE CONSENSUS GUIDANCE...WHICH HAS A TENDENCY TO BE A LITTLE TOO CONSERVATIVE IN THESE SITUATIONS. WE SHOULD HAVE CLEAR SKIES AND LOW DEWPOINTS TUE AND WED NIGHTS BUT SOME QUESTION ON WHETHER THE LOW LEVEL WIND WILL FULLY DECOUPLE. COULD SEE SOME WED AM AND THU AM LOWS BELOW 10 DEGREES IN NW MA. ANTICIPATE A LITTLE MODERATION IN TEMPERATURES BY FRI.
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&& .AVIATION /18Z 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/... THIS AFTERNOON...HIGH CONFIDENCE. VFR WITH MOST AREAS HAVING AT WORST SOME SCATTERD CIRRUS AT 25K FEET. AREA OF LOWER CLOUDS OVER NORTHWEST MASS WITH CIGS AROUND 3500 FEET SHOULD LINGER AND THEN SLOWLY BREAK. TONIGHT...HIGH CONFIDENCE. MAINLY VFR. LOW PROBABILITY OF MVFR CIGS/LOCAL MVFR VSBYS IN SCATTERED SHOWERS ACROSS WESTERN MA AND NW CT WELL AFTER MIDNIGHT. SUNDAY...HIGH CONFIDENCE. GENERALLY VFR BUT WITH MVFR CEILINGS AND VSBYS POSSIBLE IN ANY RAIN SHOWERS. SW WINDS 10 TO 20 KT SHIFTING TO THE NW. SUNDAY NIGHT...HIGH CONFIDENCE. VFR WITH A LIGHT NORTHWEST WIND. KBOS TERMINAL...HIGH CONFIDENCE IN TAF. KBDL TERMINAL...HIGH CONFIDENCE IN TAF. OUTLOOK...MONDAY THROUGH WEDNESDAY... MODERATE TO HIGH CONFIDENCE OF MAINLY VFR CONDITIONS THROUGH THE PERIOD.
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&& .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH SUNDAY/...MODERATE TO HIGH CONFIDENCE. THIS AFTERNOON...WINDS AND SEAS BELOW SMALL CRAFT ADVISORY CRITERIA. W WINDS BECOME SW AND MAY GUST TO AROUND 15 KT AT TIMES. SEAS AT BUOY 44097 SOUTHEAST OF BLOCK ISLAND DROPPED TO 3 FEET AT 11Z. NOTED THAT MOST BUOYS ARE REPORTING A LONG PERIOD SWELL OF ABOUT 5 SECONDS. USED SWANNAM GUIDANCE WHICH IS HANDLING THE SEAS SOMEWHAT BETTER THAN THE WAVEWATCH HERE IN THE NEAR TERM PART OF THE FORECAST. TONIGHT... SW WINDS WILL INCREASE AHEAD OF AN APPROACHING COLD FRONT. SOUTHWEST WIND GUSTS COULD REACH 20 TO ALMOST 25 KT TOWARD DAYBREAK...ESPECIALLY OVER THE SOUTHERN WATERS. SUNDAY...A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE SOUTHERN AND EASTERN OUTER WATERS...AND FOR RHODE ISLAND SOUND. SEAS ARE EXPECTED TO BUILD TO 5 OR 6 FEET IN THOSE AREAS...AND THERE COULD BE WIND GUSTS TO 25 KT FROM THE SOUTHWEST AHEAD OF THE COLD FRONT. SCATTERED SHOWERS COULD CAUSE SOME VISIBILITY RESTRICTIONS. WINDS SHOULD SHIFT TO THE WEST LATE IN THE AFTERNOON BEHIND THE FRONT. OUTLOOK...SUNDAY NIGHT THROUGH THURSDAY...MODERATE TO HIGH CONFIDENCE. IN SPITE OF SURFACE COLD ADVECTION DURING THE PERIOD...WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY THRESHOLDS. HOWEVER...SHOULD A SURFACE WAVE OF LOW PRES PASS ON THE NW ENVELOPE OF POSSIBLE SOLUTIONS ON TUESDAY...THEN THE RESULTANT NE GRADIENT COULD BE ENOUGH TO CAUSE WIND GUSTS TO NEAR 25 KT AND SEAS TO NEAR 5 FEET S AND SE OF NANTUCKET. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY FROM 6 AM TO 6 PM EST SUNDAY FOR ANZ235- 250-254>256. && $$ SYNOPSIS...WTB/THOMPSON NEAR TERM...WTB/GAF/THOMPSON SHORT TERM...WTB LONG TERM...GAF/THOMPSON AVIATION...WTB/THOMPSON MARINE...GAF/THOMPSON

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