AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 838 PM EDT FRI JUL 8 2011 .SYNOPSIS... SHOWERS AND THUNDERSTORMS WILL CONTINUE PARTICULARLY SOUTH OF THE MASS PIKE THROUGH THIS EVENING. THESE WILL MOVE EAST OF OUR AREA BY SATURDAY MORNING. HIGH PRESSURE THEN BUILDS FAIR AND LESS HUMID AIR OVER NEW ENGLAND FOR THE WEEKEND. A COLD FRONT WILL MOVE SLOWLY THROUGH THE REGION LATE MONDAY THROUGH TUESDAY...BRINGING A CHANCE OF SHOWERS AND THUNDERSTORMS. HIGH PRESSURE RETURNS WEDNESDAY INTO THE END OF THE WEEK. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... 830 PM UPDATE...HAVE ISSUED A DENSE FOG ADVISORY FOR THE SOUTH COAST OF RI AND MA...THE CAPE AND THE ISLANDS THROUGH 10 AM SATURDAY. VISIBILITIES HAVE FALLEN TO A QUARTER MILE OR LESS AND IS EXPECTED TO REMAIN THERE. IF RAIN SHOWERS WORK THEIR WAY OVER THIS AREA...THERE MAY BE PERIODS OF HIGHER VISIBILITIES...BUT OVERALL EXPECT VISIBILITIES TO REMAIN AT A QUARTER MILE OR LESS. 7 PM UPDATE...NUMEROUS SHOWERS AND THUNDERSTORMS MOVING ACROSS SOUTHERN NEW ENGLAND THIS EVENING. INSTABILITY IS WANING WHICH HAS DECREASED THE INTENSITY OF THESE STORMS. NONETHELESS...EXPECT THEM TO CONTINUE FOR THE NEXT SEVERAL HOURS AT LEAST. MOVEMENT HAS BEEN QUITE SLOW AND FAIRLY CONTINUOUS OVER NORTHERN CONNECTICUT SO WE WILL CONTINUE WITH FLOOD ADVISORIES ACROSS THAT AREA. WE HAVE OPTED TO DROP THE SEVERE THUNDERSTORM WATCH FOR NORTHERN CONNECTICUT AS WELL WITH THE DECREASE IN INSTABILITY. MAIN CONCERN FOR THE REST OF THE EVENING WILL BE THE POTENTIAL FOR URBAN AND SMALL STREAM FLOODING. ANOTHER NOTE...ALBANY AND NEW YORK CITY RADARS ARE WAY OVERESTIMATING PRECIP. BOSTON RADAR IS OVERESTIMATING AS WELL BUT IS MUCH CLOSER TO REALITY. NAM AND GFS SHOW RIGHT ENTRANCE REGION OF UPPER JET OVER SOUTHERN NEW ENGLAND THIS EVENING. ACTUALLY THE GFS SHOWS A SECOND JET STREAK OVER SOUTHERN NEW ENGLAND. THE SURFACE INFLOW IN RESPONSE TO THIS FEATURE APPEARS TO BE GENERATING A ZONE OF FRONTOGENETIC FORCING ACROSS LONG ISLAND AND ALONG OUR SOUTHERN COAST. ALL OF THIS IS IN SUPPORT OF A WAVE ALONG THE STALLED FRONT TO OUR SOUTH AS WELL AS A WEAK COLD FRONT MOVING ACROSS FROM THE GREAT LAKES. UPPER SHORTWAVE MOVES ACROSS SOUTHERN NEW ENGLAND AROUND 06Z/2AM...SO THESE FEATURES SHOULD MOVE OFF TO OUR EAST BY SATURDAY MORNING. MID LEVEL LAPSE RATES REMAIN UNIMPRESSIVE...BUT THERE WILL BE SOME CAPE AND THE LIFTED INDEX REMAINS BELOW ZERO THROUGH THE NIGHT. SO CONVECTION IS EXPECTED. PRECIP WATER VALUES ARE AROUND 1.75 INCHES...SUPPORTING HEAVY DOWNPOURS. AFTER THE DOWNPOURS THAT SOUTHERN AREAS RECEIVED THIS MORNING...THERE IS POTENTIAL FOR LOCALIZED FLOODING IF ANY LATE AFTN AND EVENING CONVECTION MOVES OVER THESE AREAS. WE USED A BLEND OF MOS FOR OVERNIGHT TEMPS/DEWPOINTS. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... SATURDAY AND SATURDAY NIGHT... HIGH PRESSURE BUILDS OVER THE REGION. EXPECT DRY WEATHER. 800 MB TEMPS ARE FORECAST AROUND 10-11C...FULLY MIXED THIS WOULD MEAN MAX TEMPS IN THE MID 80S. WE USED A BLEND THAT SHOWS MAX TEMPS IN THE LOW TO MID 80S. DEWPOINTS EXPECT TO FALL INTO THE 50S DURING THE DAY...SO NIGHTTIME MIN TEMPS SHOULD REACH THE 50S EXCEPT LOWER 60S IN SOME OF THE LARGER CITIES. && .LONG TERM /SUNDAY THROUGH FRIDAY/... * COLD FRONT BRINGS SHOWERS AND THUNDERSTORMS MON AFTN THROUGH TUE * HIGH PRESSURE MOVES IN BEHIND FOR THE REST OF THE WEEK MODEL PREFERENCES... BETTER THAN AVERAGE MODEL AGREEMENT THROUGHOUT THE LONG TERM. WE WILL START OFF THE PERIOD WITH HIGH PRESSURE THEN TURN TO A SLOW MOVING COLD FRONT THAT SHOULD MOVE THROUGH SOUTHERN NEW ENGLAND LATE MONDAY INTO TUESDAY. THERE ARE SOME SLIGHT TIMING DISCREPANCIES ASSOCIATED WITH THE COLD FRONT WITH THE 00Z ECMWF MOVING IT INTO THE AREA A FEW HOURS EARLIER THAN THE 12Z GFS. BOTH MODELS HAVE THE FRONT MOVING OFFSHORE BY 06Z WEDNESDAY. THIS FRONT WILL LIKELY BRING SHOWERS AND THUNDERSTORMS TO THE REGION. AFTER THE COLD FRONT MOVES THROUGH...A COOL DAY WEDNESDAY FOLLOWED BY MODERATING TEMPERATURES AND BUILDING HIGH PRESSURE. DETAILS... SUNDAY...QUIET WEATHER WITH HIGH PRESSURE MOVING ACROSS OR JUST SOUTH OF SOUTHERN NEW ENGLAND. MOSTLY SUNNY SKIES EXPECTED WITH MID AND HIGH CLOUDS BUILDING LATE SUNDAY NIGHT AHEAD OF A COLD FRONT. 850MB TEMPS IN THE 13 TO 14C RANGE WITH DECENT MIXING SHOULD YIELD HIGHS AT OR A FEW DEGREES ABOVE NORMAL. MONDAY AND TUESDAY...SHOULD START OUT WITH MOSTLY CLEAR SKIES AND QUIET WEATHER. CLOUDS MOVE IN AND THICKEN DURING THE AFTERNOON AND EVENING HOURS AS THE COLD FRONT NEARS SOUTHERN NEW ENGLAND. SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE AHEAD OF THE FRONT WITH DECENT INSTABILITY IN PLACE. LIMITING FACTOR WILL BE THE TIMING OF THE COLD FRONTS APPROACH WITH THE ECMWF BRINGING THE FRONT INTO WESTERN NEW ENGLAND BETWEEN 06 AND 12Z TUESDAY AND THE GFS NOT UNTIL AFTER 12Z TUESDAY. THIS TIMING /PARTICULARLY THE ECMWF TIMING/ WILL LIMIT THE AMOUNT OF INSTABILITY. BELIEVE TUESDAY WILL BE THE MORE LIKELY DAY FOR THUNDERSTORMS WITH THE FRONT MOVING ACROSS MUCH OF THE AREA DURING THE DAY. HOWEVER...THE LIMITING FACTOR HERE WILL BE THE CLOUD COVER THAT IS LIKELY TO BE IN PLACE AHEAD OF THE FRONT TUESDAY. THERE IS CERTAINLY SOME UNCERTAINTY WITH THIS PART OF THE FORECAST. REGARDLESS...THIS PERIOD HAS THE BEST CHANCE OF PRECIPITATION AND WILL CONTINUE CHANCE POPS IN THE FORECAST FOR THIS TIME. WEDNESDAY THROUGH FRIDAY...HIGH PRESSURE BUILDS INTO THE REGION WITH MOSTLY CLEAR TO CLEAR SKIES...QUIET WEATHER...AND TEMPERATURES RIGHT AT OR A FEW DEGREES BELOW NORMAL. && .AVIATION /01Z SATURDAY THROUGH WEDNESDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT MODERATE...30 PERCENT TO 60 PERCENT HIGH...GREATER THAN 60 PERCENT TONIGHT... GENERALLY MVFR CEILINGS WITH PATCHY IFR IN SHOWERS. IFR CIGS AND VSBYS IN FOG...MAINLY CAPE AND ISLANDS AND SOUTH COAST OF MA/RI AND SHOWERS/TSTMS...MAINLY NORTHERN CONNECTICUT. HIGH CONFIDENCE. SATURDAY AND SATURDAY NIGHT... HIGH PRESSURE BUILDS OVER THE REGION. EXPECT VFR CONDITIONS. POSSIBLE LINGERING IFR IN FOG ON CAPE COD AND ISLANDS SATURDAY MORNING...BUT THIS SHOULD LIFT DURING THE MORNING. HIGH CONFIDENCE. KBOS TERMINAL...HIGH CONFIDENCE IN FIRST 6 HOURS OF THE TAF. MVFR TO BRIEF IFR CONDITIONS ARE POSSIBLE LATE TONIGHT/EARLY SATURDAY MORNING THEN IMPROVING TO VFR SATURDAY MORNING. OUTLOOK...SUNDAY THROUGH WEDNESDAY... SUNDAY THROUGH MONDAY MORNING...HIGH CONFIDENCE. VFR. MONDAY AFTERNOON THROUGH TUESDAY...MEDIUM CONFIDENCE. MAINLY VFR WITH PERIODS OF MVFR/IFR CONDITIONS IN SHOWERS AND THUNDERSTORMS. WEDNESDAY...HIGH CONFIDENCE. VFR. && .MARINE... TONIGHT... WINDS AND SEAS REMAIN BELOW SMALL CRAFT LEVELS. POOR VSBYS FROM DENSE FOG ESPECIALLY AROUND CAPE COD AND THE ISLANDS. TSTMS MAY PRODUCE HEAVY RAIN AND GUSTY WINDS. SATURDAY AND SATURDAY NIGHT... SEAS MAY BUILD TO 5-6 FEET ON THE SOUTHERN WATERS...MOSTLY A SOUTH-SOUTHWEST SWELL. A SMALL CRAFT ADVISORY HAS BEEN ISSUED. OUTLOOK...SUNDAY THROUGH WEDNESDAY... SUNDAY...SEAS ON THE OUTER WATERS AROUND 5 FEET SLOWLY DIMINISH AS HIGH PRESSURE MOVES OVER THE WATERS. MONDAY...WINDS AND SEAS REMAIN BELOW SCA CRITERIA. NICE BOATING WEATHER. TUESDAY...SEAS BUILD TO 5 TO 6 FEET ON THE OUTER WATERS WITH GUSTY SOUTHERLY WINDS SHIFTING TO THE WEST DURING THE AFTERNOON/EVENING HOURS AS A COLD FRONT MOVES OVER THE WATERS. WINDS MAY GUST TO NEAR 25 KTS AT TIMES. WEDNESDAY...NORTHWEST WINDS AND SEAS DIMINISH GRADUALLY AS HIGH PRESSURE BUILDS OVER THE WATERS. && .HYDROLOGY... MORNING RAINFALL IN TSTMS WAS HIGHEST OVER COASTAL SOUTHEAST MASS WITH BETWEEN 1 AND 1.5 INCHES FROM TIVERTON RI THROUGH NEW BEDFORD TO CHATHAM. BULK OF RAINFALL THIS EVENING HAS BEEN ACROSS NORTHERN CONNECTICUT. FLASH FLOOD GUIDANCE IS GENERALLY AT 2-3 INCHES PER HOUR AND 3.5 TO 4.5 IN 3 HOURS. NOT EXPECTING FLASH FLOODING TONIGHT BUT COULD BE LOCAL URBAN/SMALL STREAM/POOR DRAINAGE FLOODING IN THESE AREAS IF ADDITIONAL HEAVY DOWNPOURS MOVE ACROSS THIS EVENING AND TONIGHT. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...DENSE FOG ADVISORY UNTIL 10 AM EDT SATURDAY FOR MAZ020>024. NH...NONE. RI...DENSE FOG ADVISORY UNTIL 10 AM EDT SATURDAY FOR RIZ006>008. MARINE...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 7 AM SATURDAY TO 5 AM EDT SUNDAY FOR ANZ235-254>256. && $$ SYNOPSIS...WTB/RLG