Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 310218 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 1018 PM EDT SAT AUG 30 2014 .SYNOPSIS...
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HIGH PRESSURE OFFSHORE BRINGS SOUTH WINDS TO NEW ENGLAND. THESE WINDS WILL BRING WARMER AND MORE HUMID CONDITIONS OVERNIGHT AND SUNDAY. AN APPROACHING COLD FRONT WILL BRING SHOWERS AND THUNDERSTORMS WITH TORRENTIAL DOWNPOURS POSSIBLE LATE SUNDAY AFTERNOON AND EVENING ESPECIALLY OVER THE INTERIOR. SCATTERED ON LABOR DAY THE SHOWERS AND STORMS WILL BE FOCUSED ACROSS CT/RI AND SOUTH OF THE MASS PIKE. ANOTHER COLD FRONT APPROACHES LATER TUESDAY. WARM BUT LESS HUMID WEATHER WILL THEN FOLLOW FOR MID WEEK.
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&& .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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NO SIGNIFICANT CHANGES WITH THIS FORECAST. DEWPOINTS CONTINUE TO SLOWLY RISE WITH VALUES EITHER SIDE OF 60. DEWPOINTS IN THE MID 60S TO LOW 70S HAVE REACHED WESTERN NY THROUGH THE CHESAPEAKE BAY REGION AND ARE MOVING NORTHEAST. THE INFLOW OF MOIST AIR...OVER THE AIRMASS IN PLACE OVER US RIGHT NOW...WILL SUPPORT DEVELOPING CLOUDS OVERNIGHT OVER OUR AREA. THE MOIST LAYER WILL BE RELATIVELY SHALLOW BUT COULD BRING SOME FOG AND DRIZZLE LATER TONIGHT ESPECIALLY ALONG THE SOUTH COAST. WITH DEWPOINTS AROUND 60 AND TRENDING HIGHER...EXPECT MIN SFC TEMPS TO BE IN THE 60S.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... *** POTENTIAL FOR A FEW STRONG T-STORMS SUN AFTN AND EVENING ACROSS NORTHERN MA AND SOUTHWEST NH *** SUNDAY...MERIDIONAL FLOW ACROSS THE MS VLY INTO THE GREAT LAKES IS YIELDING A PLUME OF TROPICAL MOISTURE WITH PWATS +3 STD STREAMING NORTHEAST TOWARD NEW ENGLAND. 12Z ECMWF MUCAPE CLIMBS TO ABOUT 1100J/KG AT 18Z SUNDAY ACROSS THE INTERIOR. EVEN THE LOW RES 12Z GEFS ENSEMBLES SUGGEST 400-600J/KG OF MEAN CAPE INLAND SUN AFTN. THUS SHOULD BE SUFFICIENT INSTABILITY ALONG WITH SURFACE CONVERGENCE ALONG A PREFRONTAL TROUGH TO INITIATE CONVECTION ACROSS THE INTERIOR SUNDAY AFTERNOON. 0-6KM SHEAR IS INITIALLY WEAK AT 25KT 18Z SUNDAY BUT INCREASES TO 35- 45 KT BY 00Z ACROSS NORTHERN MA AND SOUTHERN NH. THUS THIS IS SUFFICIENT FOR A LOW RISK FOR A FEW STRONG T-STORMS SUN AFTN AND EVENING WITH THE HIGHEST RISK ACROSS NORTHERN MA AND SOUTHWEST NH. THE MAIN HAZARDS WILL BE TORRENTIAL DOWNPOURS WITH LOCALIZED FLASH FLOODING GIVEN THE ANOMALOUS PWATS /DEW PTS NEAR 70 TOO/ AND STRONG WINDS GIVEN THE INCREASING SHEAR. GIVEN THE RECENT DRY WEATHER AND RESULTING HIGH FFG /3.5-4" IN 6 HRS/ GREATEST RISK OF FLASH FLOODING IS THE URBAN AREAS. NOT EXPECTING A COMPLETE WASHOUT AS THERE WILL BE DRY PERIODS OF WEATHER TOMORROW. ONCE MORNING FOG BURNS OFF SHOULD SEE PARTIAL SUNSHINE AND DRY WEATHER FROM MID MORNING INTO AT LEAST EARLY IF NOT MID AFTERNOON...AS CONVECTION FIRST FIRES NORTHWEST AREAS THEN SLIDES TOWARD THE COAST BY 00Z. IT WILL BE WARMER AND MORE HUMID THAN TODAY WITH HIGHS IN THE L80S AND DEW PTS IN THE MU60S TO AROUND 70. SUNDAY NIGHT... SCATTERED SHOWERS AND T-STORMS LINGER INTO THE EARLY EVENING ALONG WITH THE THREATS OF HEAVY RAINFALL/LOCALIZED FLASH FLOODING POSSIBLY ALONG WITH STRONG WINDS. CONVECTION WANES AS THE EVENING PROGRESSES. WARM AND HUMID CONDITIONS CONTINUE AND WILL LEAD TO ANOTHER ROUND OF FOG. && .LONG TERM /MONDAY THROUGH SATURDAY/... HEADLINES... * HEAVY SHOWERS/T-STORMS POSSIBLE MON...TUE EVENING INTO EARLY WED * BRIEF BREAK/DRY WEATHER TUESDAY * DRYING HIGH PRESSURE WED THROUGH FRIDAY OVERVIEW...THE OVERALL PATTERN HAS THE STATES CONTAINING A RIDGE IN THE EAST AND A TROUGH IN THE WEST. THE BOUNDARY IN BEWTEEN SHOULD THEN BRING IN MOISTURE ALONG A COLD FRONT. AFTER THE RAIN-CAUSING TROUGH MOVES THROUGH WEDNESDAY...A RIDGE BUILDS OVER THE REGION FOR THE REST OF THE WORK WEEK AS A COLD FRONT APPROACHES FROM THE WEST FOR SATURDAY. A NEGATIVE NAO FORMS BLOCKING UP THE PATTERN LATE WHILE A NEGATIVE PNA STAYS OVER THE UNITED STATES KEEPING THE RIDGE OVER THE EAST COAST. MODELS HAVE A GOOD AGREEMENT ON THE FIRST PART OF THE PERIOD...HOWEVER THE MAGNITUDE OF THE RIDGE OVER THE MIDWEST COMES INTO QUESTION EARLY WEDNESDAY AS THE ECMWF HAS A DIGGING TROUGH ON THE WEST COAST WHEREAS THE 6Z GFS HAS MORE OF A ZONAL FLOW PATTERN DURING THIS PERIOD. WITH THE QUICKER ZONAL FLOW PATTERN...THE 6Z GFS BRINGS THE COLD FRONT THROUGH QUICKER THAN THE ECMWF...WHICH IS ITS NORMAL BIAS...SO HAVE LEANED AGAINST THE 6Z GFS FOR THAT PERIOD. THE 6Z GFS IS LATER THAN THE ECMWF BRINGING THAT TROUGH DOWN INTO THE STATES AS WELL SO EXTRA INSTABILITY IS INTO THE REGION THURSDAY NIGHT VIA THE 6Z GFS. HAVE LEANED AGAINST THAT AS WELL AND MORE TOWARDS THE ECMWF...12Z GFS AND ENSEMBLES THAT HAVE A HIGH STILL OVER THE EAST COAST. DAILIES... MONDAY...SHORTWAVE MOVES THROUGH THE REGION WITH CONTINUED SOUTHWEST FLOW. THIS ALLOWS FOR PRECIPITATION AND WEAK INSTABILITY AS SHOWN BY PWATS 2 TO 3 SDS ABOVE NORMAL AND K-INDEX ABOVE 30 IN SOUTHERN PORTIONS OF THE REGION. MUCAPE IS ONLY JUST ABOVE 1000 J/KG. THE LOW LEVEL JET WILL BE DEPARTING THE REGION TO THE SOUTH SO SHEAR SHOULD STAY LOW HOWEVER WITH DECREASING 500 MB TEMPS CAN/T RULE OUT SOME CONVECTION. DEW POINTS WILL ALSO REACH THE 70S SO HUMIDITY WILL BE TROPICAL IN NATURE. WILL HAVE TO WATCH FOR FLOODING...BUT REGION HAS BEEN DRY FOR A WHILE SO LOCALIZED FLOODING MAY BE THE ONLY TYPE THAT IS OBSERVED. TUESDAY...POSSIBILITY OF FOG IN VALLEYS AND OTHER FOG PRONE AREAS. OTHERWISE AREAS OF ISENTROPIC DESCENSION...RISING HEIGHTS AND RISING 700 MB TEMPERATURES TO CLOSE TO 10C ALLUDE TO THE POSSIBILITY OF A LULL IN THE PRECIPITATION DURING THIS PERIOD. BELIEVE THAT OCCURS FROM EARLY MORNING TO EARLY AFTERNOON. DEW POINTS WILL AGAIN REACH THE 70S DURING THE DAY. THEN...A COLD FRONT PUSHES THROUGH OVERNIGHT INTO WEDNESDAY WITH A GERATER POSSIBILITY OF SHOWERS AND THUNDERSTORMS AHEAD OF IT ESPECIALLY OVER NORTHWESTERN MA. THIS IS WHERE NEGATIVE SHOWALTER VALUES AND BETTER SHEAR EXISTS. WEDNESDAY...AS THE COLD FRONT PUSHES THROUGH IN THE MORNING... EXPECT TO SEE ANY SHOWERS COME TO AN END AND DRIER AIR PUSH IN. A HIGH PRESSURE SYSTEM BEGINS TO TAKE CONTROL WITH NORTHWEST WINDS. THURSDAY AND FRIDAY...HIGH PRESSURE CONTINUES. CLEARING SKIES AND DRIER AIR WITH DEW POINTS INTO THE UPPER 50S. SATURDAY...HAVE TO WATCH FOR AN APPROACHING COLD FRONT FOR THIS TIME PERIOD. && .AVIATION /02Z SUNDAY THROUGH THURSDAY/...
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FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THRU SUNDAY NIGHT/...HIGH CONFIDENCE IN TRENDS BUT LOWER CONFIDENCE IN PRECISE DETAILS AND TIMING. OVERNIGHT...VFR TO START. INCREASING SKY COVER WITH CIGS LOWERING TO MVFR AFTER MIDNIGHT. MVFR/IFR VSBYS IN PATCHY FOG POSSIBLE AFTER 2 AM. SUNDAY...MARGINAL MVFR-VFR. SHRA AND TSRA DEVELOPING AFTER 18Z WEST AND THEN SLIDING EAST TOWARD 00Z. ACTIVITY MOST WIDESPREAD ACROSS NORTHWEST CT-MA INTO SOUTHWEST NH. A FEW STRONG STORMS POSSIBLE WITH TORRENTIAL DOWNPOURS AND GUSTY WINDS POSSIBLE. SUNDAY NIGHT...MVFR DURING THE EVENING SLIPPING TO IFR. SHRA AND TSRA ESPECIALLY DURING THE EVENING. A FEW STRONG STORMS POSSIBLE WITH HEAVY RAINFALL AND GUSTY WIND. KBOS TERMINAL...HIGH CONFIDENCE IN TAF REGARDING TRENDS BUT LOWER CONFIDENCE ON PRECISE DETAILS AND TIMING. KBDL TERMINAL...HIGH CONFIDENCE IN TAF REGARDING TRENDS BUT LOWER CONFIDENCE ON PRECISE DETAILS AND TIMING. OUTLOOK...MONDAY THROUGH WEDNESDAY... MONDAY...MODERATE CONFIDENCE. MVFR-IFR CIGS/VSBYS IN AREAS OF SHOWERS. POSSIBLE TSRA ESPECIALLY INLAND. SW WINDS. TUESDAY...MODERATE CONFIDENCE. MAY SEE PATCHY FOG AFTER MIDNIGHT IN NORMALLY PRONE VALLEY AREAS IN THE MORNING. A WINDOW OF PRECIPITATION-FREE WEATHER EXPECTED SOMETIME DURING THIS PERIOD. OTHERWISE ANOTHER FRONT PUSHES ACROSS THE REGION TUE NIGHT. MVFR CONDITIONS IN SHOWERS AND STORMS. SW WINDS CONTINUE. WEDNESDAY AND THURSDAY...MODERATE CONFIDENCE. MAINLY VFR. LOCAL MVFR-IFR VSBYS FROM DEPARTING SHOWERS WEDNESDAY WILL IMPROVE BY MID MORNING WITH COLD FRONTAL PASSAGE. EVENTUAL CHANGE FROM SW WINDS TO NW WINDS WEDNESDAY. VFR CONDITIONS THURSDAY WITH HIGH PRESSURE OVERHEAD.
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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. TONIGHT... S-SE WINDS BECOME SW OVERNIGHT. GOOD VSBY SHOULD LOWER LATER TONIGHT PATCHY FOG AND DRIZZLE. SUNDAY... LOW CLOUDS/FOG AND DRIZZLE LIMIT VSBY EARLY BUT IMPROVING BY MIDDAY. DRY WEATHER THEREAFTER WITH RISK OF SHOWERS AND THUNDERSTORMS HOLD OFF UNTIL AT LEAST 5 PM AND POSSIBLY UNTIL AFTER DARK. SW WIND 15-20 KT WITH A FEW GUSTS CLOSE TO 25 KT NEAR SHORE ESPECIALLY ACROSS CAPE COD AND THE ISLANDS. SUN NIGHT... SCATTERED SHOWERS AND T-STORMS DURING THE EVENING. PATCHY FOG WILL LIMIT VSBY. SW WIND 15-20 KT. OUTLOOK...SUNDAY NIGHT THROUGH WEDNESDAY... MONDAY...MODERATE CONFIDENCE. WINDS BEGIN TO RELAX DURING THE DAY. SEAS ALSO RELAX FROM 5FT SWELL TO AROUND 3 TO 4 FT SWELL. COULD BE NEAR SCA FOR DECAYING 5FT SWELLS. TUESDAY THROUGH THURSDAY...MODERATE CONFIDENCE. EXPECT WINDS AND SEAS BELOW SMALL CRAFT CRITERIA. SW WINDS WILL VEER TO NW LATE TUE NIGHT INTO WED.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...NOCERA NEAR TERM...WTB/GAF SHORT TERM...NOCERA LONG TERM...NOCERA AVIATION...NOCERA MARINE...NOCERA

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