Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 181837 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 237 PM EDT THU SEP 18 2014 .SYNOPSIS... A WEAK COLD FRONT WILL CROSS THE AREA TODAY...BUT MOISTURE IS LIMITED SO IT WILL COME THROUGH DRY. COLD HIGH PRESSURE BUILDS INTO NEW ENGLAND TONIGHT AND FRIDAY...POSSIBLY BRINGING A TOUCH OF FROST TO THE INTERIOR. THE HIGH WILL MOVE OFFSHORE THROUGH THE WEEKEND RESULTING IN A WARMUP. A COLD FRONT MOVES THROUGH ON MONDAY...FOLLOWED BY COOLER WEATHER TUESDAY AND WEDNESDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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210 PM UPDATE... DRY COLD FRONT CONTINUES MOVE S OUT OF N NEW ENGLAND AT MIDDAY... CROSSING INTO N MA AT 18Z. NOTING A FEW SHOWERS DEVELOPING ACROSS THE MID HUDSON VALLEY FROM NEAR KALB TO KGFL WHICH ARE TENDING TO DRY OUT AS THEY SHIFT E TOWARD THE WESTERN VT/MA BORDER OVER THE LAST COUPLE OF HOURS AS SEEN ON LATEST NE REGIONAL MOSAIC RADAR LOOP. A BLEND OF DIURNAL AND FRONTAL CLOUDS HAVE MOVED IN AND DEVELOPED ACROSS CENTRAL AND NORTHERN AREAS THROUGH MIDDAY. LOOKING AT VISIBLE SATELLITE TRENDS...APPEARS THE SOUTHERN EXTENT OF THE FRONTAL CLOUDS ARE TENDING TO BREAK APART AS THEY SHIFT S WHILE THE DIURNAL CLOUDS HAVE TAKEN OVER. MORE CLOUDS WILL WORK S BEHIND THE FRONT. THESE ARE EXPECTED TO PUSH INTO S NH/N MA LATE THIS AFTERNOON/THIS EVENING. TEMPS HAVE RISEN TO THE MID 60S WELL INLAND TO LOWER-MID 70S ACROSS S RI/SE MA AS WITH LIGHT NW WINDS...WHICH ARE TENDING TO SHIFT TO A LIGHT SEA BREEZE ALONG THE E COAST GENERALLY FROM BOSTON SOUTHWARD. HAVE UPDATED GRIDS TO REFLECT CURRENT TRENDS AND INCORPORATED INTO THE REMAINDER OF THE NEAR TERM FORECAST.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... CLEARING WILL TAKE PLACE THIS EVENING FROM N TO S AS CANADIAN HIGH PRESSURE BUILDS ACROSS NEW ENGLAND AND SUBSIDENCE INCREASES BEHIND DEPARTING UPPER TROUGH. THIS WILL SET STAGE FOR A COLD NIGHT AS LOWS DROP BACK INTO 30S AND 40S...WITH TOUCH OF FROST POSSIBLE ACROSS PARTS OF NW MA AND SW NH. PER COLLABORATION WITH NEIGHBORING OFFICES THERE ARE A FEW CONCERNS WHICH MAY LIMIT WIDESPREAD FROST...INCLUDING HOW FAST CLEARING OCCURS AND DO WINDS DROP OFF ENOUGH TO ALLOW FROST FORMATION. GIVEN THESE CONCERNS WE WILL HOLD OFF ON ISSUING ADVISORIES AND ALLOW DAY SHIFT TO GET A BETTER LOOK. HIGH PRESSURE REMAINS IN CONTROL FRI. ONSHORE FLOW COMBINED WITH COOLER AIRMASS IN PLACE SHOULD KEEP AFTERNOON HIGHS IN 50S ALONG IMMEDIATE COAST AND HIGHER TERRAIN TO MID 60S ELSEWHERE. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... OVERVIEW AND MODEL PREFERENCES... LONG RANGE IS LIKELY TO BE DEFINED BY UPPER LVL LONGWAVE TROF AND ASSOCIATED CUTOFF LOW PRES EXTENDING OUT OVER HUDSON BAY AND BAFFIN ISLAND. INITIALLY...THIS TROF IS SHUNTED TO THE N OF NEW ENGLAND...AS MID LVL RIDGE MOVES TO THE E...YIELDING ZONAL FLOW. THIS IS THE WEEKEND TIMEFRAME...AND THE RISING HEIGHTS AND MODEST SW LOW LVL FLOW WILL LEAD TO MODERATE WARMING THROUGH SAT AND SUN. HOWEVER...STRONG COLD SHORTWAVE ASSOCIATED WITH CP AIRMASS NEAR ALASKA...WILL ONCE AGAIN DIG AND DEEPEN THE TROF ACROSS THE E EARLY MID NEXT WEEK...LEADING TO ANOTHER ROUND OF COOLER TEMPS ACROSS THE REGION. FOR THE MOST PART...THESE SYNOPTIC SCALE FEATURES ARE REASONABLY WELL AGREED UPON...AND THE 18.00Z GFS IS NOW MORE IN LINE WITH ECMWF TIMING OF THE COLD FRONT ASSOCIATED WITH THE EARLY WEEK WAVE. THEREFORE...FEEL A BLEND OF DETERMINISTIC GUIDANCE IS A GOOD STARTING POINT. DETAILS... FRI NIGHT THROUGH SUN... HIGH PRES WILL HOLD FAST ACROSS THE REGION...YIELDING AN INVERTED RIDGE AS THE CENTER SHIFTS OFFSHORE THANKS TO CONFLUENT ZONAL FLOW ALOFT. FRI NIGHT...WEAK PRES GRADIENT AND NEAR SKC SKIES MAY LEAD TO ENOUGH RADIATIONAL COOLING IN NW MA AND SW NH VALLEYS FOR FROST DEVELOPMENT. SOMETHING TO WATCH OVER THE NEXT 24-36 HOURS. FOR THE REST OF THE WEEKEND...MODEST RETURN FLOW AND WARM ADVECTION LEAD TO INCREASING H85 TEMPS FROM +11C SAT TO +14C SUN. THEREFORE...HIGHS RANGE IN THE LOW-MID 70S SAT...THEN MID 70S TO AROUND 80 ON SUN. PWAT VALUES LOOK TOO LOW AT THIS POINT TO SUPPORT THE LIGHT QPF GFS CONTINUES TO SHOW EACH AFTERNOON...AND WITH SUBSIDENCE IN PLACE BENEATH THE INVERTED RIDGE...WILL OPT TO MAINTAIN A DRY FORECAST THROUGH MOST OF THE DAY SUN. SUN NIGHT INTO MON... COLD FRONT IS EXPECTED TO CROSS THE REGION AS LOW PRES MOVES THROUGH SRN ON AND QC. MODEST PWAT VALUES AROUND 1.5 IN...RIGHT EQUATORWARD REGION OF UPPER LVL JET STREAK AND MODEST LOW LVL F-GEN ALL SUPPORT THE POSSIBILITY OF SHOWERS ACROSS THE REGION AS THIS FRONT MOVES THROUGH. MODELS STARTING TO LINE UP ON TIMING...MOVING IT THROUGH GENERALLY DURING THE AM HOURS MON. THIS TIMING WILL LIMIT CONVECTIVE POTENTIAL AND SOUNDINGS LOOK RELATIVELY STABLE...EVEN K VALUES REMAIN MOSTLY BELOW 30. THEREFORE...SUSPECT MAINLY JUST WIDESPREAD -SHRA ACTIVITY TO MOVE THROUGH DURING THE MORNING HOURS WITH GRADUAL IMPROVEMENT LATE DAY MON. THIS TIMING WILL ALSO KEEP COASTAL LOW PRES OFFSHORE...SO QPF VALUES SHOULD GENERALLY REMAIN BELOW A HALF INCH GIVEN CURRENT THINKING. TUE INTO THU... THIS COLD FRONT WILL ALLOW MODERATELY COOL AIRMASS TO BEGIN TO BUILD IN EARLY NEXT WEEK. IN FACT...GUIDANCE SUGGESTS THAT BY TUE...546DM THICKNESS VALUES MAY APPROACH THE NW CORNER OF THE FORECAST AREA ALONG WITH H85 TEMPS AROUND +2C. THEREFORE...UNDER THE COOL NW FLOW AND COLD ADVECTION...HIGHS TUE MAY STRUGGLE TO BREAK OUT OF THE 60S...WITH SOME 50S POSSIBLE. GRADUAL MODERATION IS EXPECTED INTO WED AND THU...BUT WITH TEMPS STILL LEANING SLIGHTLY BELOW NORMAL. THE HIGH MAY NOT CREST ACROSS THE REGION UNTIL WED...ONLY MOVING SLIGHTLY E BY THU...SO SUSPECT MAINLY DRY CONDITIONS PREVAIL. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/...
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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 FRIDAY NIGHT/...HIGH CONFIDENCE. THROUGH 00Z...VFR. WILL SEE SCT-BKN CLOUDS AT 4500-6000 FT THROUGH 00Z MAINLY FROM THE MASS PIKE NORTHWARD...THOUGH WILL PUSH S TOWARD SUNSET /AROUND 23Z/ AS THE WEAK COLD FRONT MOVES ACROSS. LOCAL SEA BREEZES ALONG THE E COAST WILL BECOME NE BY 22Z-23Z. MAY SEE BRIEF LOCAL SPRINKLES AS FRONT PASSES MAINLY ACROSS THE INTERIOR. NOT EXPECTING WET RUNWAYS. TONIGHT...VFR. CLEARING SKIES FROM N-S AS FRONT PUSHES OFFSHORE. N-NE WINDS MAY GUST TO 20-25 KT ALONG E COAST FROM BOSTON S TO CAPE COD AND THE ISLANDS OVERNIGHT. FRIDAY-FRIDAY NIGHT...VFR. NE WINDS GUSTING TO 20 KT EARLY FRI ACROSS CAPE COD AND THE ISLANDS THEN DIMINISHING. E WINDS 10 KT OR LESS LATE FRI...SHIFTING TO S-SE FRI NIGHT. KBOS TERMINAL...HIGH CONFIDENCE IN TAF. SEA BREEZE THROUGH 22Z-23Z. KBDL TERMINAL...HIGH CONFIDENCE IN TAF. OUTLOOK...SATURDAY THROUGH MONDAY... SATURDAY AND SUNDAY...HIGH CONFIDENCE. MAINLY VFR THROUGH THE PERIOD ALTHOUGH SOME GROUND FOG IS POSSIBLE SAT MORNING AND SUN MORNING AT TYPICALLY PRONE AIRPORTS. WINDS MAINLY S-SW...WITH GUSTS AROUND 20 KT POSSIBLE SUN. SUN NIGHT INTO MON...MODERATE CONFIDENCE. COLD FRONT CROSSES THE REGION DURING THE MORNING HOURS MON. SHOWERS AND POSSIBLY MVFR/IFR CONDITIONS MAY MOVE THROUGH WITH THIS FRONT. OTHERWISE...IMPROVING BACK TO VFR BY LATE DAY MON.
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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 FRIDAY/...HIGH CONFIDENCE. THROUGH 00Z...WEAK COLD FRONT CROSSES THE WATERS THIS AFTERNOON. EXPECT NW WINDS WILL SHIFT TO N-NE. LONG GROUND SWELLS OF 3 TO 4 FT CONTINUE FROM DISTANT HURRICANE EDOUARD. MAY SEE BRIEF SWELLS TO 5 FT ON THE OUTER WATERS S AND E OF CAPE COD AND NANTUCKET WHICH SHOULD SLOWLY SUBSIDE. TONIGHT...WILL SEE PRESSURE SURGE WORKING DOWN FROM THE N ACROSS THE WATERS BEHIND THE COLD FRONT. EXPECT WIND GUSTS UP TO AROUND 25 KT...HIGHEST ACROSS THE EASTERN WATERS. SMALL CRAFT REMAINS IN EFFECT FOR ALL WATERS EXCEPT BOSTON HARBOR...NARRAGANSETT BAY AND BLOCK ISLAND SOUND. FRIDAY...WINDS AND SEAS DIMINISH AS HIGH PRESSURE BECOMES CENTERED OVER GULF OF MAINE...BUT WILL MAINTAIN SCA FOR OUTER WATERS WHERE SEAS WILL TAKE TIME TO DROP BELOW 5 FT. OUTLOOK...SATURDAY THROUGH MONDAY...MODERATE CONFIDENCE. SATURDAY-SUNDAY...WINDS SWING AROUND TO SOUTHWEST WITH DAYTIME GUSTS AROUND 20 KNOTS...POSSIBLY NEAR 25 KNOTS SUNDAY. SEAS WILL REMAIN 2-4 FEET. A COLD FRONT APPROACHES LATE SUNDAY WITH A CHANCE OF SHOWERS SUNDAY NIGHT. MONDAY... A COLD FRONT CROSSES THE WATERS EARLY IN THE DAY. WEST WINDS BEHIND THE FRONT WILL REMAIN LESS THAN 20 KNOTS. SEAS WILL BUILD TO 5-7 FEET ON THE OUTER AND EXPOSED WATERS...AS A SOUTH SWELL INCREASES TO 3-5 FEET. SMALL CRAFT ADVISORIES MAY BE NEEDED.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 6 AM EDT FRIDAY FOR ANZ231>235-251-256. SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 6 PM EDT FRIDAY FOR ANZ250-254-255. && $$ SYNOPSIS...DOODY/JWD NEAR TERM...EVT SHORT TERM...JWD LONG TERM...WTB AVIATION...DOODY/EVT MARINE...DOODY/EVT

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