Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 240554 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 154 AM EDT TUE MAR 24 2015 .SYNOPSIS...
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A DISTURBANCE PASSES SOUTH OF NEW ENGLAND THIS MORNING. HIGH PRESSURE BRINGS DRY AND COLD CONDITIONS TODAY...THEN MOVES OFFSHORE WEDNESDAY ALLOWING MORE SEASONABLE AIR TO RETURN. A WARM FRONT MOVES THROUGH THE REGION WEDNESDAY NIGHT. A COLD FRONT THEN SWEEPS ACROSS THE REGION THURSDAY NIGHT. A SECOND COLD FRONT MOVES THROUGH ON FRIDAY FOLLOWED BY BLUSTERY AND COLDER WEATHER FOR THE WEEKEND.
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&& .NEAR TERM /THROUGH TODAY/...
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THROUGH 8 AM/12Z... HIGH PRESSURE CENTERED OVER ONTARIO COVERS THE NORTHEAST USA AND TRENDS SOUTHEAST. INVERTED SURFACE TROUGH MOVING ACROSS THE CENTRAL APPALACHIANS TRENDING EAST. THE TROUGH IS CAUSING SNOW OVER SOUTHWEST PA AND NORTHERN WEST VIRGINA...BUT JUST MID CLOUDS FARTHER NORTH. THE MOVEMENT OF THE HIGH SHOULD BLOCK THE PRECIP FROM MOVING INTO OUR AREA...BUT WILL ALLOW MID AND HIGH CLOUDS OVER THE REGION DURING THE NIGHT. THERE HAS BEEN A CONCERN ABOUT OCEAN EFFECT CLOUDS REACHING INTO CAPE COD FROM THE GULF OF MAINE. THE EXISTING CLOUD SHIELD IS WELL EAST OF CAPE COD AND MOVING EAST. A NARROW AREA OF CLOUDS DOES EXTEND WEST FROM THE CLOUD SHIELD BUT TERMINATES EAST OF THE OUTER CAPE. SURFACE WINDS 010 DEGREES AT PROVINCETOWN WITH 10-15 KNOT SPEEDS ACROSS STELLWAGEN BANK...BUT LESS THAN 10 KNOTS FARTHER WEST. WATER TEMPS GENERALLY 2-4C WHILE 00Z CHH SOUNDING SHOWS -10C ALOFT. THUS THE WINDS AND TEMPS ARE MARGINAL FOR OCEAN EFFECT CLOUDS...MAINLY RIGHT ALONG THE OUTER CAPE AND MOSTLY TO THE EAST. IT IS POSSIBLE THE OUTER CAPE GETS CLIPPED BUT CONFIDENCE IS LOW. RADIATIONAL COOLING INLAND WITH DEWPOINTS IN THE SINGLE NUMBERS. WILL MAINTAIN MIN TEMPS IN THE TEENS WITH SINGLE NUMBERS IN NORTHWEST MASS. TODAY... HIGH PRESSURE WILL KEEP THE WEATHER DRY WITH A DIMINISHING NORTH WIND BECOMING LIGHT/VARIABLE. LINGERING MID CLOUDS IN THE MORNING MOSTLY SOUTH OF THE MASS PIKE BUT MOVING OFFSHORE BY AFTERNOON. MIXING REACHES TO AROUND 925 MB...WHERE TEMPERATURES SUPPORT AFTERNOON MAX SFC TEMPS IN THE 30S.
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&& .SHORT TERM /TONIGHT THROUGH 6 PM WEDNESDAY/...
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TONIGHT... HIGH PRESSURE OVERHEAD WILL BRING CLEAR SKIES AND LIGHT WIND. THIS WILL SET UP FAVORABLE RADIATIONAL COOLING. WITH DEWPOINTS IN THE TEENS AND LOWER 20S...EXPECT MIN TEMPS TO BE CLOSE TO THESE LEVELS. WEDNESDAY... HIGH PRESSURE MOVES OFFSHORE AND SETS UP A SOUTH-SOUTHWEST FLOW OF AIR. EVEN WITH THE COLD START...TEMPS SHOULD BE ABLE TO REBOUND BY THE AFTERNOON. MIXING WILL BE MORE SHALLOW...BUT TEMPS ALOFT WILL SUPPORT MAX AFTERNOON TEMPS IN THE 40S. MOISTURE PROFILES SHOW INCREASING CLOUDS THROUGH THE DAY. DURING THE MORNING THIS IS MOSTLY CIRRUS-LEVEL MOISTURE...BUT BY MID-LATE AFTERNOON THE PROFILES SHOW CLOUDS GETTING LOWER AND THICKER. AT 18Z THE LOW LEVEL JET AND ASSOCIATED LIFT IS AIMED AT WESTERN/CENTRAL NEW YORK. SO WE EXPECT ANY PCPN AT THAT TIME TO BE WELL TO OUR WEST. BY EVENING THE JET SHIFTS EAST AND WOULD SUPPORT PCPN ENTERING SOUTHERN NEW ENGLAND. TEMPERATURE PROFILES ARE WARM ENOUGH FOR RAIN. SO MOST OF THE DAY SHOULD BE DRY...WITH A CHANCE OF RAIN LATE AFTERNOON/EVENING.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
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HIGHLIGHTS * MILD THURSDAY AND THURSDAY NIGHT WITH SOME RAIN * COLD AGAIN FOR THE WEEKEND OVERVIEW... THE PNA REMAINS GENERALLY POSITIVE THROUGH THE PERIOD WHICH SUGGESTS BELOW NORMAL TEMPERATURES FOR AT LEAST MOST OF THE PERIOD. HOWEVER...SHORT WAVE ENERGY SEEMS TO BE ABLE TO SQUEEZE THROUGH THE WEST COAST RIDGE AND IN TURN INCREASES THE H5 HEIGHTS FOR A TIME IN THE EAST. ONE NOTABLE THRUST OF WARM AIR IS EXPECTED THURSDAY INTO THURSDAY NIGHT AS SECOND OF A COUPLE OF SHORT WAVE TROFS AND ASSOCIATED SURFACE LOW PASSES NW OF THE FORECAST AREA. THIS WILL OPEN THE DOOR TO MILD TEMPERATURES AND HIGH DEWPOINTS BEFORE THE NORTHERN STREAM TAKES OVER AND ANOTHER ANOMALOUSLY COLD AIR MASS RETURNS TO THE AREA IN TIME FOR THE WEEKEND. DETAILS... WEDNESDAY NIGHT...CLOUDS WILL LIKELY KEEP MINIMUM TEMPERATURES ABOVE FREEZING. THERE IS A CHANCE FOR SHOWERS BUT MOST OF THE FORCING LOOKS TO PASS NORTH OF THE AREA. THURSDAY AND THURSDAY NIGHT...MEDIUM RANGE MODELS ARE IN AGREEMENT OF SHORT WAVE TROF AND SURFACE WAVE ALONG A FRONT PASSING NW OF THE AREA. THERE ARE SOME TIMING AND TRACK DIFFERENCES BUT PROBABLY SIMILAR RESULT FOR SENSIBLE WEATHER. BOTH THE GFS AND ECMWF DEPICT STRONG LOW LEVEL JET 65 TO 75 KT AT 925 MB PASSING ACROSS SE NEW ENGLAND LATE THURSDAY/THURSDAY EVENING AND 850 MB TEMPERATURES THRUST ABOVE 10C. AN INVERSION AIDED BY SNOW COVER AND A RISK OF LOW CLOUDS BEING TRAPPED UNDER THE INVERSION WILL LIKELY TEMPER SURFACE TEMPERATURES TO AN EXTENT. NEVERTHELESS...ANTICIPATE THURSDAY AFTERNOON TEMPERATURES TO RISE TO AT LEAST THE MID 50S BACK FROM THE IMMEDIATE SOUTH COAST. NOTABLY...DEWPOINTS WILL LIKELY RISE TO NEAR 50 IF NOT WELL INTO THE LOWER 50S THURSDAY AFTERNOON/EVENING. THIS WILL LIKELY PROMOTE RATHER RAPID SNOWMELT...ESPECIALLY IF SOME OF THE STRONG WINDS ALOFT MIX TO THE SURFACE. THE HIGH DEWPOINT AIR PASSING OVER THE SNOW COVER COULD RESULT IN SOME AREAS OF DENSE FOG THURSDAY EVENING...BUT CONFIDENCE ON FOG DETAILS NOT HIGH THIS FAR OUT. HAVE GONE LIKELY POPS THURSDAY AFTERNOON AND EVENING. HAVE NOT GONE MUCH ABOVE 60 PERCENT FOR ANY ONE PERIOD DUE TO SOME TIMING UNCERTAINTIES. THERE COULD BE SUFFICIENT DEEP INSTABILITY TO SUPPORT AN ISOLATED THUNDERSTORM OR TWO LATE THURSDAY AFTERNOON OR EVENING. ALTHOUGH THERE COULD BE A BAND OR TWO OF HEAVY SHOWERS...THE DURATION OF ANY HEAVY RAIN DOES NOT LOOK AT THIS TIME TO BE ALL THAT LONG AND SO QPF GENERALLY IN THE HALF TO THREE-QUARTERS INCH RANGE. FROM A HYDRO PERSPECTIVE...ANTICIPATE A SIGNIFICANT INCREASE IN RUNOFF AND RISES IN AREA STREAMS FROM WHAT WILL LIKELY BE MAJOR SNOWMELT AND SOME RAINFALL THURSDAY AFTERNOON AND EVENING. AT THIS TIME...HOWEVER...DOES NOT LOOK LIKE THERE WILL BE ENOUGH RAINFALL CONTRIBUTION ON TOP OF THE SNOWMELT TO CAUSE STREAMS TO GO INTO FLOOD. THE HYDRO PERSPECTIVE WILL NEED TO BE MONITORED AND ADJUSTED IF FUTURE GUIDANCE SUGGESTS HIGHER QPF. FRIDAY...COLD AIR ADVECTION RETURNS TO THE AREA...BUT THE STRONGEST COLD AIR ADVECTION MAY NOT REALLY TAKE PLACE UNTIL A SECONDARY COLD FRONT PASSES THROUGH SOUTHERN NEW ENGLAND. HENCE...TEMPERATURES WILL PROBABLY REACH INTO THE UPPER 40S TO EVEN THE LOWER 50S IN SE NEW ENGLAND AND RESULT IN STILL FURTHER SNOWMELT. WEEKEND...RELATIVELY HIGH CONFIDENCE THAT COLD AIR WILL BE IN PLACE AND WILL EXPERIENCE BELOW...IF NOT WELL BELOW...NORMAL TEMPERATURES THROUGH THE WEEKEND. AT THIS TIME...IT LOOKS TO BE DRY...ALTHOUGH THE 12Z GFS OPERATIONAL RUN SHOWING A CLOSED ALBEIT WEAKENDING 500 MB LOW PASSING OVER OR JUST SOUTH OF NEW ENGLAND ON SATURDAY IS A BIT DISCONCERTING. THE OPERATIONAL RUN OF THE ECMWF DOES NOT SUPPORT THIS AND THE GFS ENSEMBLES SHOW QUITE A BIT OF SPREAD. FOR NOW HAVE GONE WITH A DRY BUT COLD FORECAST. TEMPERATURES SATURDAY MAY STRUGGLE TO REACH 40 AND PROBABLY NOT MUCH HIGHER THAN THE LOWER 40S ACROSS MANY AREAS ON SUNDAY. MONDAY...A NORTHERN STREAM SHORT WAVE TROF MAY INDUCE SCATTERED RAIN OR SNOW SHOWERS BUT AMOUNTS LOOK LIGHT AT THIS TIME.
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&& .AVIATION /05Z TUESDAY THROUGH SATURDAY/...
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FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. HIGH CONFIDENCE THROUGH WEDNESDAY. VFR THROUGH THE PERIOD. CLOUDS LOWER AND THICKEN WEDNESDAY AFTERNOON AND EVENING WITH MVFR CIGS/VSBYS POSSIBLE WEDNESDAY EVENING ESPECIALLY IN THE CT VALLEY. KBOS TAF...HIGH CONFIDENCE. KBDL TAF...HIGH CONFIDENCE. OUTLOOK...WEDNESDAY NIGHT THROUGH SATURDAY...MODERATE TO HIGH CONFIDENCE WEDNESDAY NIGHT THROUGH THURSDAY MORNING...GENERALLY VFR CONDITIONS EXCEPT POSSIBLY MVFR CIGS ALONG SOUTH COAST WEDNESDAY NIGHT INTO THE THURSDAY MORNING. THURSDAY AFTERNOON AND NIGHT...WIDESPREAD MVFR CIGS AND VSBYS IN SHOWERS WITH AREAS OF IFR CIGS/VSBY IN FOG. FRIDAY THROUGH SATURDAY...VFR CONDITIONS LIKELY.
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&& .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. HIGH CONFIDENCE THROUGH TUE NIGHT. WINDS AND SEAS ARE SLOWLY DIMINISHING. LINGERING 5 FOOT SEAS EAST OF MASS BUT EXPECTED TREND IS LOWER BELOW 5 FEET OVERNIGHT. TUE/TUE NIGHT...QUIET BOATING WEATHER WITH LIGHT WINDS AND SEAS AS HIGH PRES MOVES OVER THE WATERS. OUTLOOK...WEDNESDAY THROUGH SATURDAY... MODERATE TO HIGH CONFIDENCE WEDNESDAY THROUGH FRIDAY. MODERATE CONFIDENCE FRIDAY NIGHT INTO SATURDAY. CONDITIONS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY CONDITIONS WEDNESDAY THROUGH THURSDAY MORNING. STRONG SW WINDS DEVELOP ALOFT THURSDAY AFTERNOON AND EVENING BUT ANTICIPATE ONLY SOME OF THE WINDS MIXING TO THE SURFACE. WILL PROBABLY EXPERIENCE WINDS AND SEAS IN THE SMALL CRAFT ADVISORY RANGE EVEN THOUGH GALE FORCE OR STRONGER WINDS WILL LIKELY EXIST WITHIN A 1000 FEET OF THE SURFACE. TEMPERED BACK THE WAVE WATCH GUIDANCE A LITTLE FOR THIS PERIOD DUE TO THE LOW LEVEL INVERSION. AREAS OF DENSE FOG MAY BE A SIGNIFICANT HAZARD THURSDAY AFTERNOON AND EVENING...ESPECIALLY ALONG THE SOUTH COASTAL WATERS. THERE IS A LOW RISK THAT JUST ENOUGH COLD AIR ADVECTION WITH NORTHERLY WINDS FRIDAY NIGHT AND SATURDAY COULD CAUSE A PERIOD NEARING SMALL CRAFT ADVISORY WIND GUSTS...BUT CURRENTLY LOOKS MORE LIKELY THAT GUSTS WILL NOT EXCEED 20 KT. && .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...NONE. MA...NONE. RI...NONE. MARINE...NONE.
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&& $$ SYNOPSIS...WTB/THOMPSON NEAR TERM...WTB/THOMPSON SHORT TERM...WTB LONG TERM...THOMPSON AVIATION...WTB/THOMPSON MARINE...KJC/THOMPSON

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