Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 240820 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 420 AM EDT THU JUL 24 2014 .SYNOPSIS...
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A COLD FRONT SLOWLY EXITS THE COASTAL WATERS TODAY. HIGH PRESSURE CENTERED OVER THE OHIO VALLEY WILL BUILD EASTWARD AND PROVIDE SUNNY SKIES FRIDAY. THE HIGH SHIFTS OFFSHORE SATURDAY. THEN UNSETTLED CONDITIONS LATE IN THE WEEKEND AND INTO NEXT WEEK. A WARM FRONT APPROACHES SUNDAY BRINGING WARM HUMID AIR. A COLD FRONT THEN SWINGS ACROSS THE REGION MONDAY AND TUESDAY...AND LINGERS OFF THE EAST COAST THE MIDDLE OF NEXT WEEK.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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4 AM UPDATE... WATER VAPOR IMAGERY SHOWS A WEAK SHORT WAVE MOVING THROUGH CENTRAL MA AT 4 AM. AHEAD OF IT THERE WAS A BATCH OF SHOWERS RACING NORTHEAST THROUGH SOUTHERN NH. THESE SHOWERS WILL BE LONG GONE BY DAYBREAK. FOG AND LOW CLOUDINESS HAS NOT BEEN AS WIDESPREAD AS THE MODELS INDICATED. SO FAR...ONLY NANTUCKET HAS VISIBILITY OF 1/2 MILE IN FOG. IN FACT...MOST OTHER PORTIONS OF SOUTHERN NEW ENGLAND HAD ONLY PARTIAL CLOUD COVER...SO MANY AREAS MAY START OUT PARTLY SUNNY AT DAYBREAK. AT THE SURFACE...THE COLD FRONT IS ALREADY ALONG THE COAST. THE UPPER TROUGH AXIS IS STILL TO OUR WEST AND AN UPPER LEVEL JET MAXIMUM IS FORECAST TO STRENGTHEN AS IT MOVES ACROSS OUR REGION THIS AFTERNOON. THIS IS LIKELY TO KEEP IT ON THE CLOUDY SIDE THROUGH THE MORNING AND EARLY AFTERNOON ESPECIALLY IN RI AND SOUTHEAST MA. THE FRONT WILL BE SLOW TO EXIT THE COASTAL WATERS SINCE A WEAK WAVE OF LOW PRESSURE WILL BE MOVING ALONG IT. WE ARE WATCHING A BATCH OF SHOWERS IN EASTERN PA BUT WITH DRIER DEWPOINTS FILTERING IN FROM THE NORTHWEST...ALREADY DOWN TO 57 AT KEENE...THINKING THAT THESE WILL ERODE. ALL MODELS RESTRICT ANY CHANCE OF SHOWERS TO MAINLY THE CAPE AND ISLANDS INTO THE EARLY AFTERNOON HOURS...SO HAVE CUT BACK ON POPS FOR TODAY. THE NORTHWEST TWO-THIRDS OF THE REGION SHOULD BECOME MOSTLY SUNNY AND PLEASANT IN THE AFTERNOON. HIGHS TODAY MAINLY UPPER 70S TO LOWER 80S.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
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A MOSTLY CLEAR NIGHT IS EXPECTED TONIGHT. THE ONLY EXCEPTION MAY BE ON THE ISLANDS WHERE MODELS ARE QUITE EMPHATIC ABOUT THE RETURN OF LOW CLOUDINESS AND FOG WITH LIGHT NORTHEASTERLY WIND FLOW AND DEWPOINT TEMPERATURES HANGING IN THE LOWER 60S. THE POSSIBILITY EXISTS FOR LOW VISIBILITIES ON NANTUCKET. LOWS WILL BE MUCH MORE COMFORTABLE...IN THE MID 50S TO LOWER 60S EXCEPT LOWER TO MID 60S ON THE ISLANDS. HIGH PRESSURE CENTERED OVER THE OHIO VALLEY WILL BUILD EASTWARD ON FRIDAY AND PROVIDE SUNNY SKIES TO SOUTHERN NEW ENGLAND WITH HIGHS REACHING INTO THE LOWER 80S...COOLER ON THE ISLANDS.
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&& .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
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BIG PICTURE... MUCH OF THE UPPER FLOW REMAINS UNCHANGED THROUGH THE FORECAST PERIOD. DEEP RIDGES WILL EXTEND ACROSS WESTERN NORTH AMERICA AND THE WESTERN ATLANTIC. CLOSED LOW OVER NORTHERN QUEBEC ANCHORS A TROUGH OVER EASTERN NORTH AMERICA. SHORTWAVE EJECTING FROM THE PACIFIC NORTHWEST WILL PLOW OVER THE TOP OF THE WESTERN RIDGE...THEN MERGE WITH THE EASTERN NORTH AMERICA TROUGH OVER THE WEEKEND. THIS WILL DEEPEN THE TROUGH AND PULL ITS FEATURES FARTHER SOUTH. THE DEPTH OF THE TROUGH AND THE EXTENT OF THE RIDGES ON EITHER SIDE WILL MAKE STRAIGHT WEST-TO-EAST MOVEMENT DIFFICULT NEXT WEEK. THE MASS FIELDS AND THERMAL FIELDS OF THE GFS AND ECMWF LOOK SIMILAR IN OVERVIEW. SOME DIFFERENCES IN DETAILS EMERGE DURING THE FIRST HALF OF NEXT WEEK. THE SIMILARITY BUILDS CONFIDENCE IN THE OVERALL FLOW OF THE FORECAST. THE LONGER RANGE DIFFERENCES IN DETAIL SUPPORT USING A BLEND OF THE FORECAST DATA. THE DAILIES... FRIDAY NIGHT AND SATURDAY... THIS SHOULD BE A FAIR PERIOD BUT WITH SIGNS OF CHANGES TO COME. HIGH PRESSURE SHIFTS OFFSHORE AND THE SURFACE FLOW TURNS SOUTHWEST. ALSO INCREASING SOUTHWEST FLOW ALOFT WITH INCREASING MOISTURE AT THE CIRRUS LEVEL. CROSS SECTIONS DO SHOW SOME INCREASING MOISTURE TOWARD SATURDAY EVENING AROUND 5000 FEET AS WELL. EXPECT MOSTLY CLEAR SKIES AND LIGHT WINDS FRIDAY NIGHT. SKY COVER INCREASES SATURDAY BUT MOSTLY HIGH THIN CLOUDS UNTIL LATE IN THE DAY. TEMPS IN THE MIXED LAYER WILL BE 12-14C WHICH SUPPORTS MAX SFC TEMPS LOW TO MID 80S. SATURDAY NIGHT-SUNDAY... AS THE SHORTWAVE PHASES WITH THE EASTERN UPPER TROUGH...THE SUPPORTING UPPER JET EXTENDS EAST TOWARD NEW ENGLAND. MEANWHILE WEST TO SOUTHWEST LOW LEVEL WINDS WILL BRING INCREASING HUMIDITY. THIS WILL MEAN INCREASING CLOUDS AND AN INCREASING CHANCE OF SHOWERS/THUNDER OVERNIGHT INTO SUNDAY AS THE RESULTING WARM FRONT APPROACHES. EXPECT DEWPOINTS TO INCREASING DURING THIS TIME AND REACH 65-70. MONDAY-TUESDAY-WEDNESDAY... SURFACE LOW ASSOCIATED WITH THE SHORTWAVE PIVOTS OVER THE GREAT LAKES SUNDAY NIGHT/MONDAY AND SWINGS A COLD FRONT TOWARD THE EAST COAST. AT THIS SAME TIME...THE UPPER TROUGH DEEPENS AND TURNS THE UPPER FLOW OVER THE EAST COAST MORE SOUTH-SOUTHWEST. AS A RESULT OF THIS...THE COLD FRONT WILL SLOW ITS EASTWARD PROGRESS MONDAY AS IT BECOMES PARALLEL TO THE UPPER FLOW. WE WILL BE IN THE WARM SECTOR LEADING THE COLD FRONT MONDAY AND PROBABLY TUESDAY. THIS SHOULD SUPPORT A CHANCE OF SHOWERS/TSTMS EACH DAY...ALTHOUGH LESS CONFIDENCE IN THE AREAL COVERAGE OF CHANCE POPS TUESDAY. LONG RANGE GUIDENCE SUGGESTS DRY WEATHER WEDNESDAY EVEN WITH THE UPPER LOW OVER THE LAKES AND BROAD CYCLONIC FLOW OVER NEW ENGLAND. WE WENT ALONG WITH THIS IDEA FOR NOW...BUT WITH LOW CONFIDENCE.
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&& .AVIATION /08Z THURSDAY THROUGH MONDAY/...
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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/...MODERATE CONFIDENCE. MVFR CIGS WERE SCATTERED THROUGHOUT SOUTHERN NEW ENGLAND SHORTLY BEFORE DAYBREAK EXCEPT LOW IFR ON NANTUCKET WITH LOCALLY DENSE FOG. EXPECT SKIES TO DAWN PARTLY SUNNY. THERE IS A SLIGHT CHANCE OF SHOWERS TODAY IN SOUTHEASTERNMOST MA INCLUDING CAPE COD AND THE ISLANDS. SKIES SHOULD BECOME VFR ACROSS THE NORTHWEST TWO-THIRDS OF THE REGION BY MID AFTERNOON. VFR WITH MOSTLY CLEAR SKIES EXPECTED MOST AREAS TONIGHT. THE ONLY EXCEPTION MAY BE ON THE ISLANDS WHERE MODELS ARE QUITE EMPHATIC ABOUT THE RETURN OF LOW CLOUDINESS AND FOG WITH LIGHT NORTHEASTERLY WIND FLOW AND DEWPOINT TEMPERATURES HANGING IN THE LOWER 60S. THE POSSIBILITY EXISTS FOR LOW VISIBILITIES ON NANTUCKET. VFR WITH ABUNDANT SUNSHINE EXPECTED REGION-WIDE ON FRI. LOCAL SEA BREEZES IN THE AFTERNOON. KBOS TAF...MODERATE CONFIDENCE. KBDL TAF...MODERATE CONFIDENCE. OUTLOOK...FRIDAY NIGHT THROUGH MONDAY...MODERATE CONFIDENCE. FRIDAY NIGHT THROUGH SATURDAY...VFR. LOCAL IFR POSSIBLE IN EARLY MORNING FOG/LOW CLOUDS. SATURDAY NIGHT-SUNDAY-MONDAY... VFR BUT WITH AREAS OF MVFR IN SHOWERS/TSTMS.
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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/...MODERATE CONFIDENCE. WINDS AND SEAS ARE FORECAST TO BE BELOW SMALL CRAFT ADVISORY THRESHOLDS THROUGH FRIDAY. NORTHWEST TO NORTHEAST WINDS ARE FORECAST FOR TODAY...GRADUALLY SHIFTING TO THE SOUTHWEST BY FRIDAY AFTERNOON. LOCAL SEA BREEZES ARE EXPECTED ON FRIDAY. LOCALLY DENSE FOG AT TIMES TODAY AND TONIGHT...ESPECIALLY OVER THE WATERS SOUTHEAST OF MA WITH VISIBILITIES 1 MILE OR LESS AT TIMES. OUTLOOK...FRIDAY NIGHT THROUGH MONDAY...MODERATE CONFIDENCE. FRIDAY NIGHT-SATURDAY... LIGHT SOUTHWEST WINDS FRIDAY NIGHT INCREASE ON SATURDAY BUT SHOULD REMAIN BELOW 25 KNOTS. SEAS ALSO BUILD BUT SHOULD REMAIN BELOW 5 FEET. SATURDAY NIGHT-SUNDAY...A WARM FRONT APPROACHES THE WATERS WITH WARMER MORE HUMID AIR AND WITH CLOUDS/SHOWERS/TSTMS. INCREASING SOUTHWEST WINDS WITH GUSTS NEAR 25 KNOTSD SUNDAY AFTERNOON AND SEAS BUILD TO 5-6 FEET ON THE EXPOSED WATERS. A SMALL CRAFT ADVISORY MAY BE NEEDED. MONDAY...WARM HUMID AIR OVER THE WATERS WITH SOUTHWEST WINDS GUSTING 20-22 KNOTS. THIS SHOULD KEEP SEAS AT 5-7 FEET ON THE EXPOSED WATERS. THE POTENTIAL FOR SMALL CRAFT ADVISORY WILL CONTINUE.
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&& .EQUIPMENT...
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THE BLUE HILL NOAA WEATHER RADIO TRANSMITTER IS TEMPORARILY OUT OF SERVICE DUE TO A PHONE COMPANY ISSUE. THIS IS BEING WORKED ON AND IS EXPECTED TO BE RESOLVED TODAY.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...NONE.
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&& $$ SYNOPSIS...GAF/WTB NEAR TERM...GAF SHORT TERM...GAF LONG TERM...WTB AVIATION...GAF/WTB MARINE...GAF/WTB EQUIPMENT...GAF

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