Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 241057 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 657 AM EDT THU JUL 24 2014 .SYNOPSIS... 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. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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7 AM UPDATE... STILL A LOT OF CLOUDS BUT WITH SIGNS OF BREAKS. DRIER AIR TO THE NORTHWEST WITH DEWPOINTS IN THE 50S. WE ADJUSTED SKY COVER GRIDS TO REFLECT CURRENT OBSERVED COVER...BUT MAINTAINED THE CLEARING TREND AS BEFORE. WIND SHIFT LINE/COLD FRONT LOCATED ENTERING CAPE COD WITH NORTHWEST WINDS NORTHWEST OF THAT LINE. THIS SHOULD BRING IN THE DRIER AIR WITH CLEARING. THE CLEARING SHOULD ALLOW SOLAR HEATING ESPECIALLY IN OUR NORTHERN AND WESTERN LOCATIONS. TEMPS AT THE TOP OF THE MIXED LAYER WOULD SUPPORT SFC MAX TEMPS UPPER 70S/LOWER 80S. WILL NEED TO SEE IF WE CLEAR ENOUGH TO REALIZE THESE VALUES.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... 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. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... 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. && .AVIATION /12Z 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. AREA OF MVFR CIGS AROUND BOSTON...AND 200-500 FOOT CIGS NANTUCKET AND CHATHAM. EXPECT THESE CIGS TO BREAK UP...WITH VFR MOST PLACES THROUGH THE DAY. PLACES THAT AREN/T VFR ALREADY SHOULD TREND THAT WAY BY MIDDAY. 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... 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. && .EQUIPMENT... 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. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...WTB/GAF NEAR TERM...WTB/GAF SHORT TERM...GAF LONG TERM...WTB AVIATION...WTB/GAF MARINE...WTB/GAF EQUIPMENT...

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