Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 180705 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 305 AM 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/... 305 AM UPDATE... SKIES REMAIN CLEAR ACROSS REGION EARLY THIS MORNING AND WILL REMAIN THAT WAY THROUGH SUNRISE. EXPECT PATCHY FOG IN LOW LYING AREAS DUE TO GOOD RADIATIONAL COOLING CONDITIONS. LOWS WILL BOTTOM OUT IN 40S AND 50S. WEAK COLD FRONT REMAINS DRAPED ACROSS ST LAWRENCE VALLEY AND WILL HEAD SE...CROSSING SOUTHERN NEW ENGLAND THIS MORNING. CROSS SECTIONS SHOW MOISTURE IS LIMITED WITH FRONT...SO ONLY EXPECTING A PERIOD OF CLOUDINESS AS IT MOVES THROUGH ESPECIALLY DUE TO PASSAGE OF UPPER TROUGH. COULD BE BRIEF SPRINKLE BUT RADAR TRENDS SUGGEST KEEPING FORECAST DRY. HIGHS WILL TOP OUT IN 60S AND LOWER 70S...WHICH IS BLEND OF MOS GUIDANCE. NAM MOS SEEMS A BIT TOO WARM WITH HIGHS REACHING MID 70S NEAR S COAST CONSIDERING EXPECTED CLOUD COVER. && .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/... BIG PICTURE... ZONAL FLOW FRIDAY WITH 500 MB HEIGHTS BUILDING FROM A LITTLE BELOW NORMAL TO A LITTLE ABOVE BY THE NIGHTTIME. UPPER RIDGE BUILDS OVER THE WESTERN STATES WHILE A SHORTWAVE IN THE FLOW DIGS OVER THE NORTHERN PLAINS AND GREAT LAKES OVER THE WEEKEND. THE TROUGH THEN MOVES OVER NEW ENGLAND EARLY NEXT WEEK. BEST CHANCE OF SHOWERS WOULD BE SUNDAY NIGHT-MONDAY AS THE TROUGH APPROACHES. EXPECT A WARMING TREND OVER THE WEEKEND FOLLOWED BY COOLING TEMPS EARLY NEXT WEEK AS THE TROUGH MOVES OVERHEAD. THE DAILIES... FRIDAY-SATURDAY-SUNDAY... HIGH PRESSURE CENTERED OVER NORTHERN NEW ENGLAND FRIDAY MOVES EAST OVER THE MARITIMES DURING THE WEEKEND. THE RIDGE AXIS HOLDS ACROSS SOUTHERN NEW ENGLAND INTO SATURDAY...THEN SHIFTS SOUTH SUNDAY. THIS SHOULD SUPPORT DRY WEATHER THROUGH THE PERIOD. THE ECMWF ACTUALLY BRINGS SHOWERS INTO OUR NORTHWEST AREAS SATURDAY NIGHT AND THEN AGAIN SUNDAY AFTERNOON. BUT BOTH GFS AND ECMWF SHOW A SIMILAR JET POSITION ENTERING THE ST LAWRENCE VALLEY...AND THE GFS IS DRY UNTIL SUNDAY NIGHT. ADDED TO THIS IS THE OVERALL DRY PATTERN FOR SOUTHERN NEW ENGLAND THE PAST FEW WEEKS AND WHICH FAVORS THE DRIER FORECAST. TEMPS AT THE TOP OF THE MIXED LAYER ARE FORECAST EQUIV TO A TEMP OF 0-1C AT 850 MB FRIDAY...WARMING TO 10-11C BY SUNDAY. THIS SUPPORTS MAX SFC TEMPS UPPER 50S-LOWER 60S FRIDAY...WARMING TO 75-80 SUNDAY. WINDS IN THE MIXED LAYER ARE FORECAST TO REACH NEAR 20 KNOTS SATURDAY AND 25 KNOTS SUNDAY. WE HAVE BUMPED UP THE MODEL GRIDS TO REFLECT THESE VALUES. SUNDAY NIGHT-MONDAY... UPPER SHORTWAVE MOVES INTO THE GREAT LAKES AND SWINGS A COLD FRONT THROUGH SOUTHERN NEW ENGLAND LATE SUNDAY NIGHT OR MONDAY MORNING. THE ECMWF IS A LITTLE FASTER WITH FROPA...BUT WE STAYED CLOSER TO THE GFS. MUCH OF THE SYSTEM REMAINS TO OUR NORTH BUT SOUTHERN NEW ENGLAND REMAINS IN THE RIGHT ENTRANCE REGION OF THE SUPPORTING UPPER JET WHICH SHOULD PROMOTE SOME LIFT. WE WILL HOLD WITH CHANCE POPS FOR SHOWERS OVERNIGHT AND MONDAY. TUESDAY-WEDNESDAY... UPPER TROUGH AND COLD POOL MOVE OVERHEAD TUESDAY AND EAST OF US WEDNESDAY. SURFACE HIGH PRESSURE BUILDS IN BOTH DAYS. ENOUGH DESTABILIZING ALOFT AND CLOUD-LEVEL MOISTURE TO SUPPORT DIURNAL CLOUDS TUESDAY. OTHERWISE FAIR WEATHER BOTH DAYS. TEMPS IN THE MIXED LAYER SUPPORT MAX SFC TEMPS IN THE 60S BOTH DAYS. DEW POINTS IN THE UPPER 30S AND 40S WILL SUPPORT MIN SFC TEMPS IN THE 40S...POSSIBLY SOME UPPER 30S. && .AVIATION /07Z THURSDAY THROUGH MONDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT-TERM /THROUGH FRIDAY/...HIGH CONFIDENCE. PATCHY MVFR/IFR IN VALLEY FOG THROUGH SUNRISE...OTHERWISE VFR TODAY WITH SCT-BKN040-060 DEVELOPING AROUND MIDDAY. WEAK COLD FRONT BRINGS WIND SHIFT TO N/NE ACROSS MOST OF AREA BY LATE MORNING OR EARLY AFTERNOON. POSSIBILITY OF BRIEF SPRINKLE BUT PROBABLY NOT MUCH MORE THAN THAT AND NOT ENOUGH TO WET RUNWAYS. CLEARING SKIES TONIGHT. POSSIBILITY OF PATCHY FROST ACROSS VALLEYS OF NW MA AND SW NH. VFR FRI WITH E/NE FLOW. KBOS TERMINAL...HIGH CONFIDENCE IN TAF...INCLUDING TIMING OF WIND SHIFT TODAY. KBDL TERMINAL...HIGH CONFIDENCE IN TAF. OUTLOOK...SATURDAY THROUGH MONDAY...MODERATE TO HIGH CONFIDENCE. VFR THROUGH THE PERIOD. PATCHY IFR CIGS/VSBYS IN FOG SATURDAY AND SUNDAY EARLY MORNINGS. PATCHY MVFR IN SHOWERS SUNDAY NIGHT AND MONDAY. SOUTHWEST WINDS SATURDAY MAY GUST TO 20 KNOTS. SOUTHWEST WINDS SUNDAY MAY GUST 25 KNOTS...POSSIBLY A LITTLE HIGHER. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH FRIDAY/...HIGH CONFIDENCE. WEAK COLD FRONT CROSSES WATERS LATER THIS MORNING WITH WIND SHIFT TO N/NE. SWELL FROM OFFSHORE HURRICANE EDOUARD SHOULD BRING 3-4 FT SEAS TO OUTER WATERS BUT CONDITIONS EXPECTED TO REMAIN BELOW SCA. SHOULD SEE BRIEF SURGE IN N/NE WINDS TONIGHT AS COOLER AIR ARRIVES... MAINLY FROM MERRIMACK RIVER TO CAPE COD/ISLANDS WHERE 25KT GUSTS LIKELY AS SEEN ON FORECAST SOUNDINGS. SCA BEING POSTED FOR ALL WATERS EXCEPT BOSTON HARBOR... NARRAGANSETT BAY AND BLOCK ISLAND SOUND. WINDS AND SEAS DIMINISH FRI 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. && .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...JWD SHORT TERM...JWD LONG TERM...WTB AVIATION...DOODY/JWD MARINE...DOODY/JWD

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