Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 270759 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 359 AM EDT WED MAY 27 2015 .SYNOPSIS...
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WARM AND MUGGY CONDITIONS WILL INCREASE THROUGH TOMORROW. SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED EACH DAY... WITH TODAY AND TOMORROW HAVING THE HIGHER POTENTIAL FOR STRONG STORMS.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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4 AM UPDATE... SOUTHERN NEW ENGLAND REMAINS IN THE WARM...MOIST AIRMASS EARLY THIS MORNING. TEMPS ARE STILL IN THE MID TO UPPER 60S WITH A FEW SITES STILL AT 70F AS OF 4AM! SOUTHWESTERLY FLOW WILL CONTINUE INTO THE MORNING ALLOWING FOR THE LOW LEVELS TO MOISTEN UP BRINGING IN STRATUS AND FOG. HAVE UPDATED THE FORECAST MAINLY FOR VSBYS AND FOG POTENTIAL AS IT IS NOT AS WIDESPREAD AS PREVIOUSLY ADVERTISED. IN FACT...ONLY THE VINEYARD SHOWS VSBYS BELOW 5 SM. OTHERWISE THE BULK OF THE FORECAST REMAINS ON TRACK. TODAY... WARM...MUGGY CONDITIONS CONTINUE FOR TODAY. SOUTHWESTERLY WINDS WILL GUST BETWEEN 20-30 KTS AS HIGH TEMPS WARM INTO THE UPPER 70S TO MID 80S. UPPER LEVEL RIDGE CONTINUES TO DOMINATE THE REGION THROUGH MUCH OF THE DAY AS A COLD FRONT SLOWLY WORKS IT WAY EASTWARD ACROSS THE GREAT LAKES. FEEL TODAY HAS THE BETTER POTENTIAL TO SEE A FEW STRONG THUNDERSTORMS WITHIN THE PRE-FRONTAL TROUGH AND MODEST SOUTHERLY FLOW...ESPECIALLY ACROSS CT AND WESTERN MA. ASIDE FROM THE ABUNDANT MOISTURE...CAPE VALUES WILL RANGE BETWEEN 1500-2000 J/KG WITH ABOUT 25 KTS OF SHEAR. PWAT VALUES WILL BE ABOUT 1.5 INCHES...COMBINED WITH A DESCENT SOUTHERLY LLJ AND WARM CLOUD PROCESSES PER BUFKIT SOUNDINGS...ANY THUNDERSTORM HAS THE POTENTIAL TO PRODUCE VERY HEAVY RAIN. HAVE CONTINUED ENHANCED WORDING TO THE FORECAST FOR HEAVY RAIN. COULD SEE SOME STRONG WINDS GUSTS AS WELL...ESP ACROSS FRANKLIN COUNTY. SHOWERS AND STORMS SHOULD DEVELOP BY THE LATE AFTERNOON AND LINGER INTO THE EVENING HOURS. SPC HAS THE PIONEER VALLEY IN A SLIGHT RISK FOR SEVERE THUNDERSTORMS. AN ISOLATED SEVERE WIND GUST CANNOT BE RULED OUT...BUT OVERALL FEEL IS THAT STORMS SHOULD REMAIN BELOW SEVERE LIMITS WITH THE POTENTIAL FOR HEAVY RAINFALL. THE QUESTION FOR THIS EVENING IS HOW FAR EAST THE CONVECTION WILL GET. BELIEVE THAT THE MARINE INFLUENCE AND PROXIMITY OF THE UPPER RIDGE WILL MOST LIKELY WEAKEN THE STORMS CONSIDERABLY AS THEY MOVE NEAR THE CENTRAL HILL OF WORCESTER COUNTY. IN FACT BELIEVE PRECIP WILL STRUGGLE AFTER 3/4Z. AREAS OF FOG ARE EXPECTED TO DEVELOP ALONG THE SOUTH COAST BY THE EVENING HOURS LIMITING VISIBILITIES. DENSE FOG ADVISORY MAY BE NEEDED.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
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TONIGHT... MUGGY CONDITIONS WILL CONTINUE OVERNIGHT...WITH THE POTENTIAL FOR AREAS OF FOG ESPECIALLY ACROSS THE SOUTH COAST/CAPE AND ISLANDS. SOME LOCATIONS COULD SEE LOCALLY DENSE FOG. POPS DO SLOWLY INCREASE TO LOW CHANCE FOR THE WESTERN PORTIONS OF THE REGION OVERNIGHT AS THE PRE-FRONTAL TROUGH REMAINS NEARBY AND ELEVATED INSTABILITY COULD PROMOTE DEVELOPMENT OF A FEW SHOWERS/STORMS. TOMORROW... UPPER LEVEL SHORTWAVE WILL PASS THROUGH NORTHERN NEW ENGLAND ON THURSDAY PUSHING A COLD FRONT ACROSS THE REGION. 00Z GUIDANCE SHOWS THE FRONT PUSHING THROUGH BY THE AFTERNOON/EVENING HOURS WHICH COULD BE A SOURCE OF LIFT FOR ANY CONVECTION. HOWEVER APPEARS THAT THE BETTER DYNAMICS WILL BE NORTH OF THE REGION...IN MAINE AND NEW HAMPSHIRE. STILL CANT RULE OUT A FEW SCT SHOWERS/THUNDERSTORMS AS GUIDANCE SUGGESTS A NARROW CORRIDOR OF HEATING WITH DESCENT SHEAR BETWEEN 25-30 KTS AND MARGINAL MID-LEVEL LAPSE RATES. PWAT VALUES ARE STILL HIGH...AROUND 1.6 INCHES WHICH MAY YIELD TO THE POTENTIAL FOR HEAVY RAINFALL WITHIN ANY STRONG THUNDERSTORM.
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&& .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... OVERVIEW AND MODEL PREFERENCES... TO START OFF...MEDIUM RANGE MODELS AND ENSEMBLES KEEP OVERALL UPPER LEVEL PATTERN IN PLACE ACROSS THE LOWER 48...WITH RIDGING ALONG OR JUST E OF THE EASTERN SEABOARD AND TROUGHING ACROSS THE ROCKIES INTO THE SOUTHWEST. MODEL TRENDS CONTINUE TO SIGNAL SLOW DEAMPLIFICATION OF THE UPPER PATTERN GOING INTO THIS WEEKEND...WITH RIDGE AXIS FLATTENING OUT ACROSS THE NORTHEAST AS A SURFACE FRONT THAT TRIES TO WORK ACROSS THE REGION WASHES OUT DURING FRIDAY. BERMUDA HIGH RE- ESTABLISHES FOR EARLY THIS WEEKEND WHILE ANOTHER FRONT WORKS SE OUT OF QUEBEC. THIS FRONT LOOKS STRONG ENOUGH TO WORK SLOWLY SE AS THE WESTERN ATLC RIDGE SHIFTS S AND UPPER TROUGHING TAKES OVER ACROSS THE NORTHERN STREAM. BIG QUESTION WILL BE WHETHER THE FRONT WILL CLEAR OFF THE S COAST EARLY NEXT WEEK OR WILL IT STALL CLOSER TO OR OVER SOUTHERN AREAS. USED A BLEND OF AVAILABLE GUIDANCE FOR THIS FORECAST PACKAGE... THOUGH DID LEAN TOWARD MORE TOWARD THE ENSEMBLES FROM THIS WEEKEND ONWARD DUE TO TIMING DIFFERENCES WITH THE APPROACHING FRONT. FOR THE LATTER TIMEFRAME...LEANED CLOSER TO THE SLOWER ECMWF AND ECENS MEANS. DETAILS... THURSDAY...WILL SEE LEFTOVER SCT SHOWERS/TSTMS ACROSS WESTERN AREAS THU MORNING WITH PWATS ON ORDER OF AROUND 1.5 INCHES. THE FRONT SHIFTS S TAKING THE HIGHER PWAT AIR WITH IT...SO EXPECT THE PRECIP TO TEND TO WEAKEN THOUGH WILL LINGER WHERE MILDER TEMPS ARE THANKS TO DIURNAL INFLUENCES. INSTABILITY ALSO SHIFTS OFFSHORE AND WEAKENS SO EXPECT ANY THUNDERSTORMS TO TAPER OFF BY AROUND MIDDAY. BEST SHOT FOR PRECIP WILL BE FROM THE MERRIMACK VALLEY SE ACROSS CENTRAL MA TO THE MID AND LOWER CT VALLEY. CAN NOT RULE OUT A FEW QUICK DOWNPOURS THROUGH MIDDAY WITH THE HIGHER PWAT AIRMASS. WILL SEE AREAS OF FOG...LOCALLY DENSE...DEVELOP ACROSS S COASTAL AREAS THU NIGHT INTO FRI MORNING. FRIDAY...MODELS STARTED TO SIGNAL DRIER AIR WORKING IN ON MONDAY... BUT MOST OF THE MODEL SUITE HAS HIGH PRES RIDGE BUILDING S OUT OF QUEBEC SO EXPECT A DRY BUT MILD DAY. DEWPTS DROP A BIT...DOWN TO THE 50S...BUT WILL BEGIN TO RISE AGAIN FRI NIGHT. WILL SEE A LIGHT E-SE WIND FLOW SO WILL BE COOLER ALONG THE COAST...HIGHS MAINLY IN THE 70S EXCEPT 65-70 ACROSS COASTAL AREAS...RANGING TO THE LOWER TO MID 80S ACROSS THE CT VALLEY. SATURDAY...HIGH PRESSURE REPOSITIONS OFF THE EASTERN SEABOARD SO SW WINDS KICK IN AGAIN BRINGING A RETURN TO MORE HUMID AIR. ANOTHER COLD FRONT START TO APPROACH OUT OF GREAT LAKES AND WESTERN QUEBEC. ALSO NOTING INCREASING INSTABILITY PARAMETERS AHEAD OF THE FRONT... WITH K INDICES RISING TO THE LOWER-MID 30S AND TQ VALUES IN THE UPPER TEENS SO COULD SEE SOME ELEVATED CONVECTION WHICH COULD LAST INTO SAT NIGHT. BEST LIFT MOVES CLOSER DURING LATE SAT/SAT NIGHT SO WILL SEE SCT SHOWERS/THUNDERSTORMS DEVELOP. A PWAT SWATH OF 1.6 TO 1.75 INCHES PUSHES OUT AHEAD OF THE FRONT...SO MAY SEE SOME HEAVIER DOWNPOURS WITH ANY CONVECTION. WILL SEE QUITE A BIT OF SUNSHINE EARLY SATURDAY...SO TEMPS WILL REBOUND TO THE 80S FOR MOST LOCATIONS EXCEPT THE LOWER-MID 70S ALONG S COASTAL AREAS. SUNDAY...COLD FRONT SLOWLY ACROSS THE REGION SUNDAY MORNING...THEN REACHES THE S COAST BY SUNDAY NIGHT. EXPECT CHANCE SHOWERS AND THUNDERSTORMS. STILL SOME TIMING ISSUES BETWEEN THE GFS AND ECMWF BUT A BIT BETTER FOR THIS TIMEFRAME. WITH THE SLOW MOVEMENT OF THE FRONT...EXPECT SCT PRECIP TO CONTINUE THROUGH SUN NIGHT. MONDAY-TUESDAY...SOMEWHAT LOWER CONFIDENCE DUE TO TIMING AND PLACEMENT DIFFERENCES WITH THE FRONT AND WHETHER IT STALLS NEAR THE S COAST OR OFFSHORE. AT THIS POINT...KEPT CHANCE POPS ACROSS CENTRAL AND SOUTHERN AREAS THROUGH MIDDAY THEN SHOULD PUSH JUST OFFSHORE BUT MAY LINGER ACROSS THE ISLANDS THROUGH MOST OF THE DAY SUNDAY. MAY SEE SOME THUNDERSTORMS EARLY...THEN INSTABILITY WORKS OFFSHORE BUT COULD STILL SEE SOME SHOWERS WHILE HIGH PRES MOVES ACROSS NORTHERN NEW ENGLAND. HAVE KEPT SLIGHT CHANCE POPS GOING FOR SOUTHERN AREAS INTO TUESDAY AS FRONT LOOKS TO LINGER...THEN MAY TRY TO MAKE A RUN BACK NE AS THE HIGH PUSHES OFF INTO THE GULF OF MAINE. && .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
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FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. BEFORE 12Z...MODERATE CONFIDENCE. COULD SEE IFR CIGS AND VSBYS ACROSS THE SOUTH COAST...CAPE AND ISLANDS. OTHERWISE VFR AREA WIDE. TODAY...MODERATE CONFIDENCE. IFR/MVFR WILL DEVELOP ALONG THE SOUTH COAST WHILE THE REMAINDER OF THE REGION IS VFR. WESTERN SITES COULD DROP TO MVFR WITHIN ANY -SHRA/-TSRA THAT DEVELOPS. EXPECT SW WINDS TO GUST UP TO 20-30 KT AT TIMES MAINLY ACROSS RI/SE MA. TONIGHT...MODERATE CONFIDENCE. CONDITIONS DETERIORATE TO IFR ALONG THE SOUTH COAST...CAPE...AND ISLANDS AS MARITIME FOG AND STRATUS ROLL IN. THURSDAY...MODERATE CONFIDENCE. COLD FRONT WILL PASS ACROSS THE REGION SWITCHING THE SOUTHERLY WINDS TO THE WEST DURING THE DAY. IFR...FOG AND STRATUS IS POSSIBLE BEFORE FRONTAL PASSAGE ALONG SE TAF SITES. CANNOT RULE OUT A FEW SHOWERS/T-STORMS ALONG THE FRONT DROPPING CONDITIONS TO MVFR. OTHERWISE VFR WILL PREVAIL. KBOS TERMINAL...HIGH CONFIDENCE IN TAF. KBDL TERMINAL...HIGH CONFIDENCE IN TAF. COULD SEE CONDITIONS DROP TO MVFR WITHIN ANY THUNDERSTORM TODAY. OUTLOOK...THURSDAY NIGHT THROUGH SUNDAY...MODERATE CONFIDENCE. FRIDAY...VFR. MAY SEE LOCAL MVFR-IFR CONDITIONS EARLY FRI MORNING ALONG S COAST IN PATCHY FOG...THEN WILL LOWER AGAIN LATE FRI NIGHT/SAT MORNING TO MVFR-IFR. SATURDAY...PATCHY FOG EARLY SAT MORNING WITH MVFR-IFR CONDITIONS WILL IMPROVE. SCT SHRA/TSRA SAT THROUGH SAT NIGHT WITH LOCAL MVFR- IFR CONDITIONS. SW WINDS GUSTING TO 20-25 KT MAINLY ALONG THE COAST SAT AFTERNOON/EVENING. SUNDAY...SCT SHOWERS TSTMS LINGER THROUGH SUNDAY...BUT SHOULD END SUN NIGHT. MAY SEE BRIEF MVFR CONDITIONS.
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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 THURSDAY/...HIGH CONFIDENCE. NEW SET OF SMALL CRAFT ADVISORIES ARE UP TODAY AND INTO TONIGHT. EXPECT NEAR SHORE WATERS TO SEE GUSTS NEAR 25 KTS...JUST LIKE YESTERDAY. OTHERWISE SOUTHERLY SWELL WILL CONTINUE TO BUILD INCREASING OUTER WATER SEAS TO 5FT. IN ADDITION...AREAS OF DENSE FOG ARE LIKELY TO DEVELOP ON THE WATERS LATER TODAY AND TONIGHT...SUBSTANTIALLY REDUCING VISIBILITIES. OUTLOOK...THURSDAY THROUGH SUNDAY...MODERATE CONFIDENCE. THURSDAY...EXPECT SW WINDS GUSTING TO AROUND 20 KT. SEAS BUILD TO AROUND 5 FT ACROSS THE SOUTHERN WATERS TO THE OUTER WATERS E OF CAPE COD...BUT SHOULD SUBSIDE BELOW 5 FT THU NIGHT. VSBYS REDUCED IN AREAS OF FOG...LOCALLY DENSE OFFSHORE BOTH THU AND FRI NIGHTS. FRIDAY...LIGHT N-NE WINDS BECOME E DURING THE DAY...THEN SHIFT TO S-SW FRI NIGHT. EXPECT WINDS AND SEAS BELOW SMALL CRAFT CRITERIA. SATURDAY-SUNDAY...SW WINDS MAY BRIEFLY GUST TO 25 KT DURING SAT ON THE EASTERN WATERS...OTHERWISE EXPECT GUSTS UP TO 20 KT SEAS BUILD AGAIN TO AROUND 5 FT ACROSS THE OUTER WATERS...WHICH WILL SLOWLY SUBSIDE LATE SUN OR SUN NIGHT.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...NONE. MA...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY FROM 10 AM THIS MORNING TO 10 PM EDT THIS EVENING FOR ANZ231>234. SMALL CRAFT ADVISORY FROM NOON TODAY TO 8 PM EDT THIS EVENING FOR ANZ230-236. SMALL CRAFT ADVISORY FROM 10 AM THIS MORNING TO 8 PM EDT THIS EVENING FOR ANZ235-237-251. SMALL CRAFT ADVISORY FROM 11 AM THIS MORNING TO 8 AM EDT THURSDAY FOR ANZ250-254>256.
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&& $$ SYNOPSIS...DUNTEN/EVT NEAR TERM...DUNTEN SHORT TERM...DUNTEN LONG TERM...EVT AVIATION...DUNTEN/EVT MARINE...DUNTEN/EVT

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