Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 310750 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 350 AM EDT SUN AUG 31 2014 .SYNOPSIS... WARM HUMID FLOW OVER THE NORTHEAST USA. A UPPER SHORTWAVE FROM THE GREAT LAKES DRIVES EAST THROUGH NEW ENGLAND LATE AFTERNOON/EVENING BRINGING POTENTIAL THUNDERSTORMS WITH HEAVY DOWNPOURS AND STRONG WINDS. SHOWERS AND THUNDERSTORMS WILL LINGER INTO MONDAY...WITH THE BEST CHANCE 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. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... THROUGH 8 AM... WARMER MORE HUMID AIR CONTINUES TO FLOW INTO SOUTHERN NEW ENGLAND. AS OF 2 AM DEWPOINTS HAD CLIMBED INTO THE LOW TO MID 60S. EXPECT THESE VALUES TO SLOWLY INCREASE THROUGH MORNING. CLOUDS ARE FILLING IN OVER THE NORTHEAST...SO WE EXPECT MOSTLY CLOUDY SKIES THROUGH SUNRISE. TODAY... BACK EDGE OF THE CLOUD AREA IS SOUTHWEST OF PHILADELPHIA. THIS IS ABOUT WHERE DEWPOINTS ARE AROUND 70. THIS MEANS A CLOUDY START TO THE DAY...BUT POTENTIAL FOR THE SUN TO BREAK THROUGH LATER IN THE MORNING OR EARLY AFTERNOON. A SOUTHWEST UPPER FLOW AND SURFACE COLD FRONT IN THE GREAT LAKES SUGGESTS NO FROPA TODAY. THE UPPER SHORTWAVE PASSES ACROSS NORTHERN NEW ENGLAND...BUT CLOSE ENOUGH TO AFFECT SOUTHERN NEW ENGLAND. A PRE-FRONTAL TROUGH SUPPORTED BY AN UPPER SHORTWAVE IS A REASONABLE SCENARIO...WITH BEST CHANCE CLOSEST TO THE SHORTWAVE IN WESTERN/NORTHERN MASS AND IN SOUTHERN NH. AT THE LEAST THIS SHOULD BE A WARM VERY HUMID DAY. THE AIRMASS WILL CONTAIN DEEP TROPICAL MOISTURE WITH PRECIPITABLE WATER VALUES FORECAST AT 2.0 TO 2.30 INCHES...ABOVE 2 STD DEVIATIONS AND SO QUITE SIGNIFICANT. QUESTIONS OF THE DAY ARE POTENTIAL FOR CONVECTION AND POTENTIAL FOR DAMAGING CONVECTION. STABILITY PARAMETERS ARE FAVORABLE FOR TSTMS...LI AROUND -2 TO -4/TOTALS INTO THE MID 40S. UPPER WIND FIELDS SUGGEST SEVERE WIND POTENTIAL WITH 30 KNOTS AT 850 MB AND 40-50 KNOTS AT 500 MB. AFTERNOON/EVENING SHEAR VALUES LOOK SUFFICIENT TO PROVIDE ORGANIZATION TO SOME TSTMS. PUTTING IT ALL TOGETHER: POTENTIAL FOR AFTERNOON/EVENING STRONG THUNDERSTORMS WITH WIND AND HEAVY DOWNPOURS...AND A LOWER BUT REAL POTENTIAL FOR DAMAGING WIND GUSTS. FLASH FLOOD INDICES ARE ABOVE 3.5 INCHES... SO FLOODING PROBLEMS WILL BE ALONG THE LINES OF URBAN AND POOR DRAINAGE FLOODING. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... TONIGHT... CONVECTION LINGERS INTO AT LEAST THE START OF THE NIGHT. SIGNS IN THE MODEL DATA THAT THE SURFACE BOUNDARY MAY LINGER OVER SOUTHEAST MASS/RI/CT LATER AT NIGHT. THIS MAY PROVIDE A FOCUS FOR AT LEAST SCATTERED CONVECTION CONTINUING OVERNIGHT IN THIS AREA. NO AIRMASS CHANGE SO IT SHOULD BE A WARM AND HUMID NIGHT WITH DEWPOINTS AROUND 70...AND SO MIN TEMPS SHOULD BE AROUND 70 OR IN THE LOWER 70S. MONDAY... WARM HUMID AIRMASS LINGERS OVER THE REGION. PRECIP WATER VALUES CONTINUE ABOVE 2 INCHES SOUTH OF THE MASS PIKE AND 1.5 TO 2.0 INCHES NORTH. DYNAMICS WILL BE DIMINISHING...BUT SOUTHERN NEW ENGLAND WILL CONTINUE UNDER THE RIGHT ENTRANCE REGION OF THE DEPARTING UPPER JET FOR AT LEAST PART OF THE DAY. WE WILL CONTINUE WITH CHANCE POPS FOR SHOWERS/TSTMS...AND WITH LOCALLY HEAVY DOWNPOURS. && .LONG TERM /MONDAY NIGHT 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... 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 /08Z SUNDAY THROUGH THURSDAY/... 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. TODAY...VFR SKY COVER WITH AREAS OF MVFR CIGS AROUND 2000 FEET. THE LOWER CIGS SHOULD IMPROVE TO VFR LATE MORNING AND AFTERNOON. DEVELOPING TSTMS AFTER NOON WITH BEST CHANCE AFTER 3 PM. BEST CHANCE WILL BE WESTERN/NORTHERN MASS AND SOUTHERN NH. MVFR/IFR CONDITIONS IN ANY STORMS WITH POTENTIAL FOR HEAVY DOWNPOURS AND STRONG WIND GUSTS...POSSIBLY A FEW DAMAGING WIND GUSTS. TONIGHT...CONVECTION CONTINUES INTO THE EARLY NIGHT BUT SHOULD DIMINISH AFTER SUNSET. MVFR/IFR CIGS AND VSBYS IN ANY THUNDERSTORMS. MVFR/IFR CIGS AND VSBYS IN FOG OVERNIGHT. MONDAY...MVFR CIGS/VSBYS IN SHOWERS AND SCATTERED TSTMS. IFR CIGS/VSBYS IN MORNING FOG. LOCALLY HEAVY DOWNPOURS STILL POSSIBLE. 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 NIGHT THROUGH WEDNESDAY... 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. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. MODERATE CONFIDENCE TODAY THROUGH MONDAY. TODAY... DRY WEATHER FOR MUCH OF THE DAY. POTENTIAL FOR SHOWERS/TSTMS AFTER 4 PM...EXCEPT AFTER 2 PM NORTH OF CAPE ANN. ANY STORMS WILL HAVE STRONG WIND GUSTS AS WELL AS POOR VISIBILITY IN HEAVY DOWNPOURS. SOUTHWEST WIND WILL GUST TO 20-22 KNOTS WHICH IS CLOSE TO SMALL CRAFT LEVELS. THE PERSISTANCE OF THE WIND WILL BUILD SEAS A TAD WITH 5 FOOT HEIGHTS MOVING INTO THE OUTER WATERS LATE IN THE DAY. A SMALL CRAFT ADVISORY HAS BEEN PUT IN EFFECT ON THE OUTER WATERS STARTING THIS EVENING. IT IS MAINLY FOR THE 5 FOOT SEAS...BUT WINDS WILL BE CLOSE TO THRESHOLD AND SO WE WILL KEEP THE HEADLINE NON-SPECIFIC. TONIGHT... THE POTENTIAL FOR 5 FOOT SEAS WILL EXTEND INTO RI SOUND ON THE SOUTHWEST WIND. GAVE SOME THOUGHT ABOUT SIMILAR POTENTIALS FOR BLOCK ISLAND SOUND AND BUZZARDS BAY...BUT PREFERED THE BETTER FETCH INTO RI SOUND WHERE A SMALL CRAFT ADVISORY WILL BE IN EFFECT. SHOWERS AND THUNDERSTORMS MAY MOVE ACROSS THE WATERS. BEST CHANCE ON TIMING OF THE STORMS WOULD BE THE FIRST PART OF TONIGHT...BUT CONDITIONS WILL REMAIN FAVORABLE THROUGH THE NIGHT. ANY STORMS WOULD HAVE STRONG WIND GUSTS EARLY TONIGHT AND POOR VISIBILITY IN HEAVY DOWNPOURS AT ANY TIME. MONDAY... WINDS AND SEAS DIMINISH BELOW SMALL CRAFT LEVELS. SMALL CRAFTS WILL LINGER OVER THE OUTER WATERS DURING THE MORNING. OUTLOOK...MONDAY NIGHT THROUGH WEDNESDAY... TUESDAY THROUGH THURSDAY...MODERATE CONFIDENCE. EXPECT WINDS AND SEAS BELOW SMALL CRAFT CRITERIA. SW WINDS WILL VEER TO NW LATE TUE NIGHT INTO WED. && .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 5 AM EDT MONDAY FOR ANZ250. SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 11 AM EDT MONDAY FOR ANZ254>256. SMALL CRAFT ADVISORY FROM 10 PM THIS EVENING TO 6 AM EDT MONDAY FOR ANZ235.
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&& $$ SYNOPSIS...WTB/NOCERA NEAR TERM...WTB/GAF SHORT TERM...WTB LONG TERM...NOCERA AVIATION...WTB MARINE...WTB/NOCERA

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