Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 210737 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 337 AM EDT MON JUL 21 2014 .SYNOPSIS...
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SHOWERS MOVE OFFSHORE THIS MORNING AS HIGH PRESSURE BUILDS OVER. THE HIGH WILL BRING MAINLY DRY CONDITIONS...BUT INCREASING HEAT AND HUMIDITY INTO MID WEEK. BY LATE WED INTO THU THERE IS THE RISK FOR SHOWERS AND THUNDERSTORMS AS A COLD FRONT ENTERS THE REGION. THEREAFTER THE TREND IS FOR DRIER...LESS HUMID AND NOT AS WARM CONDITIONS ARRIVING LATER THU INTO EARLY NEXT WEEKEND.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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LOW PRES CONTINUES TO DEEPEN WELL E OF ACK AND CAPE COD THIS MORNING. BUT AS IT DOES SO...WEAK DEFORMATION ON ITS NW QUAD IS WORKING ON MOISTURE TRAPPED IN THE LOWEST 300HPA TO BRING PERIODIC -SHRA AND DRIZZLE TO PORTIONS OF SRN RI AND SE MA. IT IS NOT UNTIL ATTENDANT SHORTWAVE ENERGY AND THE LOW PRES MOVES FURTHER E BY ABOUT MID MORNING THAT THESE WILL FULLY MOVE OFFSHORE AND WITHER. THEREFORE...HAVE GRADUALLY DIMINISHING POPS ACROSS THE REGION THROUGH ABOUT 15Z. QPF IS EXPECTED TO BE LIGHT FROM NOW ON...MAINLY BELOW A TENTH OF AN INCH. OTHERWISE...THROUGH THE MORNING...COOL TEMPS ARE EXPECTED ACROSS THE WRN VALLEYS THANKS TO RADIATIONAL COOLING PROCESSES UNDER MAINLY CLEAR SKIES AND LIGHT FLOW. AFTER THE THREAT FOR SHOWERS END...IT MAY TAKE A BIT LONGER FOR ALL OF THE CLOUDS IN VICINITY OF THE E COAST TO BREAK UP AS THE MOISTURE BECOMES TRAPPED BENEATH A BUILDING SUBSIDENCE INVERSION. THIS COMBINED WITH ANOTHER DAY OF MAINLY NE AND E FLOW IS LIKELY TO LEAD TO HIGH TEMPS BELOW NORMAL ESPECIALLY CLOSER TO THE E COAST. HOWEVER...BUILDING HIGH PRES CONNECTED TO THE BERMUDA HIGH WILL GRADUAL ALLOW FOR CLEARING THROUGH THE AFTERNOON AND EVENING...WHICH MAY ALLOW A LATE DAY SPIKE IN TEMPERATURES. CURRENT MOS TEMPS LOOKED GOOD. HUMIDITY SHOULD STILL STAY RELATIVELY LOW AS MIXING IS LIKELY TO KEEP DWPTS IN THE MID TO LOWER 50S.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/...
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TONIGHT... HIGH PRES CONTINUES TO BUILD ACROSS NEW ENGLAND OVERNIGHT TONIGHT...BUT BEGINS TO SLIDE E. SAVE FOR SOME LEFTOVER CLOUDS FROM CONVECTION TO THE W...EXPECT PARTLY CLOUDY CONDITIONS. THE WEAK PRES GRADIENT...AND BREAKS IN CLOUDS WILL ONCE AGAIN ALLOW FOR SOME RADIATIONAL COOLING. THE SHIFT E IN THE HIGH PRES MAY LEAD TO GRADUALLY INCREASING DWPTS OVERNIGHT SO SUSPECT MINS TO BE A BIT WARMER THAN SUN NIGHT...MAINLY IN THE LOW-MID 60S. THIS INCREASE IN DWPTS MAY ALSO ALLOW FOR MORE LOCAL FOG DEVELOPMENT...PARTICULARLY IN TYPICALLY PRONE VALLEYS. TUE... HIGH PRES CONTINUES TO SHIFT SE OF THE REGION...BUT REMAINS IN CONTROL...ALLOWING FOR A PARTLY CLOUDY START TO THE DAY. HOWEVER...WITH RETURN FLOW IN PLACE EXPECT INCREASING DWPTS AND DIURNAL CU THROUGH THE DAY. THEN ATTENTION FOCUSES ON THE AFTERNOON THREAT FOR CONVECTION. SOUNDING PROFILES SUPPORT 1000-1300J/KG OF SKINNY SB CAPE ALONG AN AXIS FROM CENTRAL NY INTO NW MA AND SRN NH. HOWEVER...WE ARE MISSING A DECENT TRIGGER /JET ENERGY AND PRE FRONTAL TROF REMAIN TO THE W/. WE ARE ALSO MISSING SHEAR...WHICH IS GENERALLY 15 KT OR LESS BETWEEN BOTH 0-3 AND 0-6KM LAYERS. THEREFORE...SHOULD ANYTHING EVEN DEVELOP...IT WOULD LIKELY HAVE DIFFICULTY HOLDING TOGETHER WITHOUT THE ABILITY TO ORGANIZE. THEREFORE...WILL CARRY SOME SLIGHT CHANCE POPS BY PEAK HEATING FOR SHOWERS AND THUNDERSTORMS...BUT ITS LIKELY THE BULK OF THE ACTIVITY REMAINS TO THE W. OTHERWISE...WITH INCREASING MID LVL TEMPS /H85 TEMPS APPROACH +18C/ EXPECT INCREASING SFC TEMPS...WITH SOME LOCALES SEEING HIGHS IN THE UPPER 80S. DWPTS INCREASING INTO THE MID 60S SUGGESTS THE HUMIDITY WILL BE MUCH MORE NOTICEABLE.
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&& .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... HIGHLIGHTS... * BECOMING WARMER AND MORE HUMID TUESDAY AND HOT BY WEDNESDAY * CHANCE OF T-STORMS LATE WED INTO THU * TRENDING DRIER...LESS HUMID AND NOT AS WARM THU NGT/FRI/SAT SYNOPTIC OVERVIEW AND MODEL DIAGNOSTICS... THE TWO MAIN WEATHER FEATURES NEXT WEEK AND INTO NEXT WEEKEND ACROSS THE CONUS WILL BE A PERSISTENT POSITIVE HEIGHT ANOMALY /SUBTROPICAL RIDGE/ OVER THE FOUR CORNERS REGION ALONG WITH AN ACTIVE AND ROBUST NORTHERN STREAM JET ACROSS SOUTHERN CANADA AND THE NORTHER TIER STATES INTO NEW ENGLAND. BOTH THE GEFS AND ECENS ENSEMBLES SUGGEST A LEAD SHORT WAVE TROUGH CROSSES THE NORTHEAST STATES LATER WED INTO THU...FOLLOWED BY LOW AMPLITUDE SHORT WAVE RIDGING OVER NEW ENGLAND FRI AND SAT BEFORE THE NORTHERN STREAM RELOADS WITH A HIGHER AMPLITUDE TROUGH SETTING UP OVER THE GREAT LAKES/MS AND OH VLYS SUNDAY. AS FOR MODEL DETAILS...MAIN DILEMMA FOR THIS FORECAST PERIOD BECOMES THE TIMING OF THE FRONTAL PASSAGE WED NIGHT INTO THU. THE 00Z GEFS ENSEMBLES WERE ON THE SLOW EDGE OF THE GUIDANCE BUT NOW THE 12Z GEFS HAVE SPED UP WITH FROPA EARLY THU. THE 00Z ECENS ENSEMBLES WERE ON THE FAST EDGE OF THE GUIDANCE AND NOW THE 12Z OPERATIONAL RUN OF THE ECMWF HAS SLOWED DOWN WITH FROPA EARLY THU. THE 12Z GFS IS THE SLOWEST OF THE GUID AS IT FORMS A FRONTAL WAVE WITH FROPA LATE THU. GIVEN TIME SCALE IS STILL 96+ HRS AWAY A MODEL BLEND IS LIKELY THE BEST APPROACH. DAILY DETAILS.... TUESDAY...BECOMING WARMER AS MID LEVEL TROUGHINESS MOVES OFFSHORE AND IS REPLACED BY SHORT WAVE RIDGING. DESPITE LIGHT MODEL QPF THIS RIDGING SHOULD PROVIDE A SUFFICIENT CAP TO PRECLUDE ANY SHOWER/T- STORM DEVELOPMENT. CROSS SECTIONS REVEAL LOTS OF LOW LEVEL MOISTURE TUE MORNING SO MODEL QPF COULD BE MORE MORNING DRIZZLE THAN DIURNAL CONVECTION. AS FOR TEMPS...LOW PROBABILITY OF A FEW LOCATIONS IN NORTHERN MA INTO SOUTHERN NH MAY MAKE A RUN AT 90F...ESPECIALLY THE MERRIMACK VALLEY. COOLEST SOUTH COAST GIVEN SSW SURFACE WINDS OFF THE RELATIVELY COOL OCEAN WATERS. ALTHOUGH LATEST BUOYS AND TIDE GAGES REPORTS INDICATE SOUTH COASTAL WATER TEMPS NOW INTO THE U60S TO AROUND 70! WEDNESDAY...FAIRLY STRONG NORTHERN STREAM SHORT WAVE /BY JULY STANDARDS/ ENTERS THE NORTHEAST. ITS ATTENDING COLD FRONT WILL PROVIDE SUFFICIENT LOW LEVEL CONVERGENCE FOR T-STORMS TO FIRE ALONG AND AHEAD OF THIS BOUNDARY. DESPITE THE GFS AND GEFS NOT OFFERING MUCH OF A PREFRONTAL TROUGH WED ITS GENERATING 60-70% PROBS OF 1200 J/KG OF CAPE INTO WESTERN NEW ENGLAND. THIS COMBINED WITH PREFRONTAL TROUGH APPROACHING THE AREA FROM THE WEST SUGGEST AT LEAST A LOW RISK FOR STORMS IN EASTERN NY AND WESTERN NEW ENGLAND...LOWERING EASTWARD TOWARD THE COAST. DEEP LAYER SHEAR IS LACKING OVER WESTERN NEW ENGLAND WITH ONLY 25-30 KT...MUCH LESS EASTWARD. HOWEVER MAY BE SUFFICIENT INSTABILITY/CAPE TO COMPENSATE FOR LACK OF SHEAR. BEFORE THE STORMS DEVELOP A FEW LOCATIONS IN NORTHERN MA INTO SOUTHERN NH ESPECIALLY THE MERRIMACK RIVER VALLEY MAY ONCE AGAIN MAKE A RUN AT 90F. HOWEVER THE PGRAD WILL TIGHTEN DURING THE AFTN AS PREFRONTAL TROUGH APPROACHES FROM THE WEST. THUS THERE SHOULD BE A STIFF SSW WIND WHICH WILL TAKE SOME OF THE EDGE OFF THE HEAT. IN FACT GFS BUKFIT SOUNDINGS SUGGEST SSW WIND GUST POTENTIAL UP TO 25-30 MPH OVER RI AND EASTERN MA! THURSDAY AND FRIDAY...TRENDING DRIER AND LESS HUMID. NOT AS WARM AS COLD FRONT MOVES OFFSHORE. COLD FRONT MAY BE SLOW TO DEPART THU PER GFS SO A RISK OF SHOWERS/T-STORMS ESPECIALLY RI AND EASTERN MA. SHEAR/JET DYNAMICS STRONGER THU THAN WED BUT INSTABILITY IS LACKING. NEVERTHELESS TRENDING DRIER LATER THU FROM WEST TO EAST. NEXT WEEKEND...LONG WAVE TROUGH SETS UP OVER THE GREAT LAKES ALONG WITH WITH SURFACE LOW PRES. THIS WILL SHIFT THE LOW LEVEL FLOW TO THE SSW RESULTING IN A WARMER MORE HUMID TREND. BY SUNDAY THE MID LEVEL TROUGH AND SURFACE LOW PRES FROM THE GREAT LAKES ADVECTS CLOSER TO NEW ENGLAND...YIELDING MORE CYCLONIC FLOW AND AN INCREASE CHANCE OF SHOWERS/T-STORMS. && .AVIATION /07Z MONDAY THROUGH FRIDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH TUESDAY/... THROUGH 12Z...MODERATE CONFIDENCE. MAINLY VFR FOR TERMINALS NW OF A UUU-PYM LINE THROUGH THE REST OF THE NIGHT SAVE FOR ISOLATED PATCHES OF FOG AT TYPICALLY PRONE AIRPORTS. SE OF THIS LINE...PERIODS OF MVFR AND EVEN IFR ARE POSSIBLE IN A MIX OF SHRA/FOG/DZ THROUGH MID MORNING. NE FLOW...MAINLY LIGHT. TUE...HIGH CONFIDENCE. VFR MOST OF THE DAY. CONDITIONS IMPROVE THROUGH THE MORNING AT ANY TERMINAL MVFR/IFR. SHOWERS GRADUALLY END AS WELL ACROSS SE MA. NE FLOW THROUGH MUCH OF THE DAY...DUE E NEAR SHORE THANKS TO SEA BREEZES. TUE NIGHT...HIGH CONFIDENCE. MAINLY VFR. HOWEVER MAY SEE SOME LATE NIGHT FOG POSSIBLE...WITH BEST CHANCE OVER THE CAPE/ISLANDS. KBOS TAF...HIGH CONFIDENCE IN TAF. KBDL TAF...HIGH CONFIDENCE IN TAF. OUTLOOK...TUESDAY NIGHT THROUGH FRIDAY... TUE/WED...MAINLY VFR. HOWEVER EACH NIGHT THE THREAT FOR FOG WITH IFR/MVFR CONDITIONS IS POSSIBLE...PARTICULARLY ALONG THE S COAST. ISOLATED SHOWER/T-STORM POSSIBLE WED AFTERNOON MAINLY IN THE W. WED NIGHT INTO THU...MODERATE CONFIDENCE. A COLD FRONT CROSSES THE REGION...WITH A CHANCE FOR SHOWERS OR THUNDERSTORMS AND MVFR/IFR CONDITIONS MAINLY EASTERN MA AND RI. FRIDAY...MODERATE TO HIGH CONFIDENCE FOR VFR AND DRY CONDITIONS. && .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 TUESDAY/...MODERATE CONFIDENCE. A PERIOD OF MAINLY QUIET BOATING WEATHER IS EXPECTED AS HIGH PRES BUILDS ACROSS THE WATERS. MAY SEE AN A NARROW THREAT FOR 5 FT SEAS UNDER A SLOWLY BUILDING SWELL ACROSS THE EXTREME SE WATERS DURING THE DAY TODAY...BUT THIS IS LIKELY A LOW PROBABILITY. OTHERWISE...WILL HAVE TO MONITOR FOR SOME FOG AND LOW VISIBILITY ACROSS THE WATERS TONIGHT. BUT ONLY HAVE LOW CONFIDENCE IN WHERE OR IF...IT WILL FORM. OUTLOOK...TUESDAY NIGHT THROUGH FRIDAY... TUE...HIGH CONFIDENCE. HIGH PRES OVER THE WATERS SHOULD LEAD TO MAINLY QUIET BOATING WEATHER...WITH MODEST SW WINDS AND SEAS. SOME FOG POSSIBLE TUE WITH REDUCED VSBYS. WED AND THU...MODERATE CONFIDENCE. SW FLOW IS EXPECTED TO INCREASE WED AHEAD OF A COLD FRONT WHICH WILL CROSS THE WATERS EARLY THU. WINDS NEAR THE SE COAST OF MA MAY GUST TO AROUND 25 KT AT TIMES...POTENTIALLY REQUIRING A SMALL CRAFT ADVISORY. SEAS SHOULD REMAIN BELOW 5 FT THROUGH THE PERIOD. SOME SHOWERS AND THUNDERSTORMS ARE POSSIBLE OVER THE WATERS PARTICULARLY LATE WED NIGHT AND THU. FRI...MODERATE TO HIGH CONFIDENCE FOR LIGHT WINDS AND SEAS AS WEAK HIGH PRES CREST OVER THE WATERS. SOME LINGERING SSW SWELL IS POSSIBLE.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...BELK/DOODY NEAR TERM...DOODY SHORT TERM...DOODY LONG TERM...NOCERA AVIATION...NOCERA/DOODY MARINE...NOCERA/DOODY

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