Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 292036 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 435 PM EDT FRI MAY 29 2015 .SYNOPSIS... A MAINLY DRY...WARM AND SOMEWHAT HUMID AFTERNOON IS IN STORE FOR MOST THE REGION FOR SATURDAY. A COLD FRONT WILL SLOWLY MOVE ACROSS THE REGION SUNDAY...THEN STALL SOUTH OF NEW ENGLAND EARLY NEXT WEEK. THIS WILL BRING A CHANCE OF SHOWERS AND A FEW THUNDERSTORMS SUNDAY...AND A PERIOD OF RAIN EARLY NEXT WEEK. HIGH PRESSURE BRINGS DRY WEATHER FOR THE LATTER PART OF THE WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... A VERY TRICKY FORECAST TONIGHT IN REGARDS TO LOW CLOUD POTENTIAL. LOW CLOUDS HAVE BEEN SITTING JUST OFF THE EASTERN MA COAST MUCH OF THE AFTERNOON. HOWEVER...SOLAR HEATING HAS KEPT THEM BASICALLY JUST OFFSHORE...EXCEPT AFFECTING PORTIONS OF COASTAL PLYMOUTH COUNTY AND THE OUTER-CAPE FOR A TIME. GIVEN EASTERLY WINDS ARE EXPECTED TO BECOME SOUTHERLY THIS EVENING...DO NOT EXPECT THESE LOW CLOUDS TO REALLY MOVE INLAND. ITS POSSIBLE THAT THEY MAKE IT ONSHORE FOR AN HOUR OR TWO TOWARDS SUNSET...ESPECIALLY ACROSS THE NORTH SHORE WITH SURFACE WINDS TURNING SOUTH BUT PROBABLY SHORT LIVED. OTHERWISE...THE FOCUS OF LOW CLOUDS/FOG WILL TURN TO THE SOUTH COAST/CAPE AND ISLANDS. SATELLITE IMAGERY SHOWS LOW CLOUDS SITTING SOUTH OF LONG ISLAND AND AS WINDS TURN SOUTHERLY AND BOUNDARY LAYER COOLS...SHOULD SEE THEM ADVECT NORTHWARD. LOW CONFIDENCE ON HOW FAR NORTH THESE LOW CLOUDS ADVECT...BUT PROBABLY AFFECT THE SOUTH COAST AND PERHAPS AS FAR NORTH AS THE MA PIKE. SOME FOG IS ALSO EXPECTED AND CAN/T RULE OUT A PERIOD OF DENSE FOG ACROSS SOUTHEAST NEW ENGLAND...BUT CONFIDENCE ON THAT IS LOW. OTHERWISE...A DRY NIGHT OTHER THAN PERHAPS A BIT OF MIST TOWARD DAYBREAK ALONG WITH THE FOG ACROSS THE SOUTHEAST NEW ENGLAND COAST. LOW TEMPS MAINLY IN THE UPPER 50S TO THE LOWER 60S. && .SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY NIGHT/... ***A WARM AND SOMEWHAT HUMID SATURDAY AFTERNOON IS ON TAP INLAND FROM THE SOUTH COAST*** HIGH PRESSURE MOVING OFF THE COAST WILL ALLOW A WARMER AND MORE HUMID AIRMASS TO OVERSPREAD SOUTHERN NEW ENGLAND ON SATURDAY. LOW CLOUDS THAT FORM SOUTH OF MA PIKE SHOULD SCOUR OUT BY SATURDAY AFTERNOON IF NOT EARLIER FOR MOST OF THE REGION. HOWEVER...LOW CLOUDS AND FOG PATCHES MAY LINGER ACROSS THE IMMEDIATE SOUTH COAST/CAPE/ISLANDS. OTHERWISE...HIGH TEMPS SHOULD REACH INTO THE MIDDLE TO UPPER 80S TO THE NORTHWEST OF A BOSTON TO PROVIDENCE LINE. THE WARMEST OF THOSE READINGS SHOULD BE FOUND IN THE MERRIMACK VALLEY. TO THE SOUTHEAST OF A BOSTON TO PROVIDENCE LINE...GUSTY SOUTHWEST WINDS WILL HOLD HIGH TEMPS IN THE 70S TO NEAR 80. IN FACT...SOUTHWEST WIND GUSTS OF 20 TO 30 MPH ARE EXPECTED FOR MOST OF THE REGION SATURDAY AFTERNOON WITH GOOD MIXING. UPPER LEVEL RIDGING SHOULD RESULT IN MAINLY A DRY DAY ACROSS THE REGION. BEST FORCING/INSTABILITY AND DYNAMICS WILL BE WELL TO OUR NORTHWEST WITH AN APPROACHING COLD FRONT. JUST A LOW RISK OF A SPOT SHOWER/THUNDERSTORM LATE SATURDAY AFTERNOON/EARLY EVENING ACROSS NORTHWEST MA. SATURDAY NIGHT... A COLD FRONT WILL BE SLOWLY APPROACHING OUR REGION FROM THE WEST. A SOUTHWEST LOW LEVEL JET WILL RESULT IN A MILD NIGHT...WITH LOW TEMPS ONLY DROPPING TO BETWEEN 60 AND 65. DRY WEATHER SHOULD DOMINATE THE FIRST PART OF THE NIGHT...BUT WE MAY SEE SOME SCATTERED SHOWERS AND PERHAPS AN EMBEDDED THUNDERSTORM OR TWO DEVELOP OVERNIGHT. THIS IS RESPONSE TO LOW LEVEL JET AND A BURST OF INSTABILITY. ACTIVITY WILL PROBABLY BE HIT AND MISS THROUGH DAYBREAK SUNDAY...WITH THE BULK OF IT TO THE NORTHWEST OF I-95. BULK OF LOW CLOUDS SHOULD BE CONFINED TO THE SOUTHEAST NEW ENGLAND COAST. ENOUGH WIND IN THE BOUNDARY LAYER MAY PREVENT A LOT OF FOG FROM DEVELOPING...BUT STILL CAN NOT RULE OUT SOME DEVELOPING. && .LONG TERM /SUNDAY THROUGH FRIDAY/... BIG PICTURE... CHANGEABLE PATTERN THROUGH THE WEEK. UPPER RIDGE MOVES OFFSHORE SUNDAY. UPPER TROUGH SLOWLY CROSSES THE NORTHEAST USA EARLY WEEK. UPPER RIDGE FROM THE WESTERN USA THEN SHIFTS EAST OVER THE EASTERN USA LATE WEEK. DIFFERENCES AMONG THE MODELS REGARDING TIMING WITH THE UPPER TROUGH EARLY WEEK WITH THE GGEM THE FASTEST AND ECMWF SLOWEST. WE USED A MODEL CONSENSUS IN TIMING. THE DAILIES... SUNDAY THROUGH TUESDAY... COLD FRONT EITHER OVER OR JUST NORTH OF NORTHERN MASS SUNDAY MORNING WILL MOVE SOUTH ACROSS THE REGION DURING THE DAY. PRECIPITABLE WATER VALUES ALONG AND AHEAD OF THE FRONT WILL BE 1.50 TO 1.75 INCHES WHICH IS AROUND 2 STD DEV ABOVE NORMAL. TOTALS OF 47-49 AND SHOWALTERS OF 0 TO -2. ALL OF THIS SUGGESTS SUFFICIENT MOISTURE FOR SHOWERS AND ENOUGH INSTABILITY OVER THE LOW LEVEL CONVERGENCE TO SUPPORT A FEW THUNDERSTORMS. DIFFERENCES AMONG THE MODELS ON TIMING THE FROPA BUT ALL MOVE IT SOUTH OF THE COAST BY SUNDAY EVENING. THE FRONT IS THEN ALIGNED WITH THE UPPER FLOW AND STALLS. SHORTWAVE MOVING THROUGH THE GREAT LAKES IS FORECAST TO GENERATE A WAVE ALONG THE FRONT WHICH CROSSES THE APPALACHIANS MONDAY AND PASSES SOUTH OF NEW ENGLAND TUESDAY. THIS ALONG WITH HIGH PRESSURE IN EASTERN CANADA SHOULD BRING A COOL NORTHEAST FLOW TO THE REGION MONDAY AND TUESDAY. MEANWHILE A SOUTHWEST FLOW CONTINUES ABOVE 5OOO FEET AGL AND SUPPIES LIFT AND MOISTURE OVER THE TOP. WE WILL MAINTAIN LIKELY POPS MONDAY DIMINISHING TO CHANCE POPS DURING THE DAY TUESDAY AS THE LOW MOVES EAST. WEDNESDAY THROUGH FRIDAY... HIGH PRESSURE BUILDS SURFACE AND ALOFT BRINGING DRY WEATHER TO SOUTHERN NEW ENGLAND. WITH THE DEMISE OF THE NORTHEAST MARINE FLOW...MIXING SHOULD RETURN WITH HEIGHTS REACHING AT LEAST 875 MB WEDNESDAY AND AT LEAST 850 MB THURSDAY AND FRIDAY. TEMPERATURES AT THE TOP OF THE MIXED LAYER EACH DAY SUGGEST MAX SFC TEMPS IN THE MID 60S TO LOW 70S WEDNESDAY...70S TO NEAR 80 THURSDAY...AND 75-85 FRIDAY. && .AVIATION /20Z FRIDAY THROUGH WEDNESDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. TONIGHT...LOW TO MODERATE CONFIDENCE. LOW CLOUDS SITTING JUST OFF THE EASTERN MA COAST LATE THIS AFTERNOON. WINDS ALONG THE EASTERN MA COAST TURN SOUTH SOUTHWEST THIS EVENING...SO THAT SHOULD LIMIT LOW CLOUDS COMING IN FROM THE EAST. THEREFORE...EVEN IF THEY DO GET INTO BOSTON THEY WILL BE SHORT LIVED AND MAY REMAIN JUST OFF THE COAST. THE BIGGER CONCERN THEN TURNS TO LOW CLOUDS/FOG PATCHES THAT MAY DEVELOP ALONG THE SOUTH COAST AND ESPECIALLY CAPE/ISLANDS. AGAIN...CONFIDENCE IS LOW SO WILL HAVE TO MONITOR CLOSELY. SATURDAY...MODERATE CONFIDENCE. ANY LOW CLOUDS/FOG PATCHES SOUTH OF PIKE PROBABLY SCOUR OUT BY LATE MORNING/EARLY AFTERNOON...EXCEPT CAPE/ISLANDS WHERE THEY MAY LINGER INTO THE AFTERNOON. DRY WEATHER EXPECTED...ALTHOUGH THERE IS A LOW RISK OF A SPOT SHOWER/THUNDERSTORM ACROSS NORTHWEST MA LATE IN THE AFTERNOON/EARLY EVENING. SATURDAY NIGHT...MODERATE CONFIDENCE. MAINLY VFR TO MARGINAL MVFR CIGS EXCEPT FAR SOUTHEAST NEW ENGLAND COAST WHERE IFR CIGS/VSBYS ARE POSSIBLE. SCATTERED SHOWERS AND PERHAPS A THUNDERSTORM OR TWO WILL BE POSSIBLE MAINLY ACROSS THE INTERIOR WITH THE HIGHER RISK DURING THE OVERNIGHT HOURS. KBOS TERMINAL...LOW CONFIDENCE IN TAF EARLY THIS EVENING. IFR CIGS SITTING JUST EAST OF THE TERMINAL AT LATE AFTERNOON. GIVEN WINDS TURNING SOUTH SOUTHWEST EARLY THIS EVENING...THEY MAY NEVER MAKE IT INTO THE TERMINAL. HOWEVER...ITS POSSIBLE THAT THEY DO FOR AN HOUR OR TWO SINCE THEIR SO CLOSE AND WILL HAVE TO CLOSELY MONITOR. KBDL TERMINAL...LOW TO MODERATE CONFIDENCE IN TAF. MVFR TO IFR CIGS MAY DEVELOP AFTER MIDNIGHT BUT UNCERTAIN. OUTLOOK...SUNDAY THROUGH WEDNESDAY...MODERATE CONFIDENCE. SUNDAY... COLD FRONT MOVES ACROSS SOUTHERN NEW ENGLAND FROM NORTH TO SOUTH. VFR CIGS/VSBYS WITH AREAS OF MVFR IN SHOWERS/THUNDERSTORMS. SOUTHWEST WINDS TO START...BECOMING NORTHEAST BY EVENING. WINDS AT 2000-3000 FEET AGL START SOUTHWEST 25-35 KNOTS AND BECOME NORTHEAST 25 TO 30 KNOTS BY EVENING. SOUTHWEST WINDS LINGER THROUGH THE DAY AT OR ABOVE 5000 FEET. THIS MAY CREATE SOME LOW LEVEL WIND SHEAR AT TIMES...DIRECTIONAL SHEAR IN THE VERTICAL IS LIKELY AND SPEED SHEAR POSSIBLY. MONDAY THROUGH TUESDAY... MVFR/IFR CIGS AND VSBYS WITH BEST CHANCE OVER THE COASTAL PLAIN AND EASTERN SLOPES OF THE WORCESTER HILLS. SHOWERS POSSIBLE THROUGH BOTH DAYS. WEDNESDAY... VFR WITH A NORTH-NORTHWEST WIND. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/... TONIGHT...MODERATE TO HIGH CONFIDENCE. WEAK PRESSURE GRADIENT WILL KEEP WINDS/SEAS BELOW SMALL CRAFT ADVISORY THRESHOLDS. HOWEVER...AREAS OF FOG MAY DEVELOP OVERNIGHT ACROSS OUR SOUTHERN WATERS BUT ITS UNCERTAIN IF IT WILL BECOME DENSE. SATURDAY...MODERATE TO HIGH CONFIDENCE. EXCELLENT MIXING OVER THE LAND WILL GENERATE NEAR SHORE SMALL CRAFT WIND GUSTS OF 25 TO 30 KNOTS SATURDAY AFTERNOON. IN ADDITION...SOUTHEAST SWELL WILL GENERATE 5 FOOT SEAS ACROSS THE OUTER-WATERS. THEREFORE...SMALL CRAFT HEADLINES POSTED FOR ALL WATERS. AREAS OF FOG MAY BE LOCALLY DENSE IN THE MORNING ALONG THE SOUTH COAST...SHOULD IMPROVE SOMEWHAT BY AFTERNOON. SATURDAY NIGHT...MODERATE TO HIGH CONFIDENCE. NEAR SHORE SMALL CRAFT WIND GUSTS SHOULD DIMINISH SATURDAY EVENING. HOWEVER...5 FOOT SWELL WILL CONTINUE ACROSS THE OUTER-WATERS. SOME FOG POSSIBLE SAT NIGHT...BUT PROBABLY NOT AS WIDESPREAD AS TONIGHT GIVEN SOME MORE BOUNDARY LAYER WIND. OUTLOOK...SUNDAY THROUGH WEDNESDAY...MODERATE CONFIDENCE. SUNDAY...SMALL CRAFT ADVISORY MAY BE NEEDED ON SOME OF THE WATERS. A COLD FRONT CROSSES THE EASTERN WATERS DURING THE DAY. THE FRONT CROSSES THE SOUTHERN WATERS SUNDAY EVENING. SHOWERS AND POSSIBLE THUNDERSTORMS ALONG AND AHEAD OF THE FRONT. EXPECTING SOUTHWEST GUSTS TO 20 KNOTS AHEAD OF THE FRONT. WINDS THEN SHIFT TO NORTHEAST AND EAST BEHIND THE FRONT WITH GUSTS TO 20 KNOTS FROM THAT DIRECTION. SEAS LINGER AROUND 5 FEET ON THE OUTER WATERS. MONDAY-TUESDAY...SMALL CRAFT ADVISORY MAY BE NEEDED ESPECIALLY ON THE EASTERN WATERS. NORTHEAST WINDS GUSTING 20 TO 25 KNOTS EACH DAY. SEAS 5 TO 8 FEET ON THE EASTERN MASS WATERS...AND 3 TO 5 FEET ON THE SOUTHERN WATERS. WEDNESDAY...A SMALL CRAFT ADVISORY MAY BE NEEDED...MAINLY ON THE EASTERN WATERS. DIMINISHING NORTHEAST TO NORTH WINDS. SEAS OF 5 FEET MAY LINGER ON THE EASTERN WATERS. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY FROM NOON TO 10 PM EDT SATURDAY FOR ANZ230>237-251. SMALL CRAFT ADVISORY FROM 2 PM SATURDAY TO 8 AM EDT SUNDAY FOR ANZ250-254>256. && $$ SYNOPSIS...FRANK/WTB NEAR TERM...FRANK SHORT TERM...FRANK LONG TERM...WTB AVIATION...FRANK/WTB MARINE...FRANK/WTB

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