Area Forecast Discussion
Issued by NWS Boston, MA

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KBOX 211132 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 732 AM EDT MON JUL 21 2014 .SYNOPSIS... 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. A COLD FRONT ARRIVES LATE WED INTO THU. THEREAFTER THE TREND IS FOR DRIER...LESS HUMID AND NOT AS WARM CONDITIONS ARRIVING LATER THU INTO EARLY THIS WEEKEND. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 730 AM UPDATE... STRATUS AND FOG SLOWLY BREAKING UP ACROSS PORTIONS OF SOUTHEAST MA. LATEST HRRR...RAP AND 06Z GFS AND NAM...ALL INDICATE POTENTIAL FOR THIS STRATUS TO LINGER INTO THE LATE MORNING HOURS. DO THINK THE CLOUD BASES WILL LIFT SOME THIS MORNING BASED ON TRENDS IN OBSERVATIONS. OTHERWISE...THE PREVIOUS FORECAST IS LARGELY ON TRACK. MADE SOME MINOR TWEAKS TO NEAR-TERM CONDITIONS TO REFLECT THE OBSERVED TRENDS. PREVIOUS DISCUSSION... 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. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... 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. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... HIGHLIGHTS... * BECOMING 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. THE OTHER IS AN ACTIVE AND ROBUST NORTHERN STREAM JET ACROSS SOUTHERN CANADA AND THE NORTHERN TIER STATES INTO NEW ENGLAND. 21/00Z GUIDANCE CONTINUES TO BE IN RATHER GOOD AGREEMENT THROUGH MID WEEK. THEN THE GFS AND ITS ENSEMBLE MEAN DEVIATE SLIGHTLY FROM THE REST OF THE GUIDANCE SUITE THURSDAY NIGHT INTO FRIDAY. WHILE MOST OF THE GUIDANCE DEVELOPS A SURFACE WAVE ALONG AN OFFSHORE COLD FRONT...THE GFS-LED CAMP DOES SO MUCH CLOSER TO EAST COAST. IT IS INTERESTING TO NOTE SIMILAR FLOW PATTERNS ALOFT. AS SUCH...LEANING MORE TOWARD THE SLIGHTLY FASTER PASSAGE OF THIS COLD FRONT LATE THURSDAY INTO FRIDAY. DAILY DETAILS.... WEDNESDAY...FAIRLY STRONG NORTHERN STREAM SHORT WAVE /BY JULY STANDARDS/ ENTERS THE NORTHEAST. ITS ATTENDING COLD FRONT WILL PROVIDE SUFFICIENT LOW LEVEL CONVERGENCE FOR THUNDERSTORMS TO DEVELOP ALONG AND AHEAD OF THIS BOUNDARY. DEEP LAYER SHEAR IS LACKING OVER SOUTHERN NEW ENGLAND...WITH ONLY 25-30 KT ANTICIPATED. HOWEVER THERE MAY BE SUFFICIENT INSTABILITY/CAPE TO COMPENSATE FOR LACK OF SHEAR. BEFORE THE ANTICIPATED THUNDERSTORMS DEVELOP...A FEW LOCATIONS IN NORTHERN MA INTO SOUTHERN NH... ESPECIALLY THE MERRIMACK RIVER VALLEY...MAY MAKE A RUN AT 90F. THURSDAY AND FRIDAY...TRENDING DRIER AND LESS HUMID. NOT AS WARM AS A COLD FRONT EVENTUALLY MOVES OFFSHORE. TIMING OF THIS COLD FRONT MAY BE SLOWER TO DEPART THU PER GFS...SO A RISK OF SHOWERS/THUNDERSTORMS CONTINUES...ESPECIALLY ACROSS RI AND EASTERN MA. SHEAR/JET DYNAMICS STRONGER THU THAN WED...BUT INSTABILITY IS LESS. NEVERTHELESS...TRENDING DRIER LATE THU FROM WEST TO EAST. NEXT WEEKEND...ANOTHER ANOMALOUS LONGWAVE TROUGH SETS UP OVER THE GREAT LAKES...ALONG WITH WITH A CORRESPONDING SURFACE LOW PRESSURE. THIS WILL SHIFT THE LOW LEVEL FLOW TO THE SSW RESULTING IN A TREND OF WARMER AND MORE HUMID CONDITIONS. BY SUNDAY...THIS MID LEVEL TROUGH AND SURFACE LOW PRESSURE MOVES CLOSER TO NEW ENGLAND... YIELDING MORE CYCLONIC FLOW AND AN INCREASED CHANCE FOR SHOWERS/THUNDERSTORMS...ESPECIALLY ACROSS THE WESTERN HALF OF SOUTHERN NEW ENGLAND. && .AVIATION /12Z 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/... TODAY...HIGH CONFIDENCE IN TRENDS...MODERATE CONFIDENCE IN TIMING ACROSS SOUTHEAST MA. MAINLY VFR FOR TERMINALS NW OF A KUUU-KPYM LINE THROUGH TODAY. 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...WEDNESDAY THROUGH FRIDAY... WED...MODERATE CONFIDENCE. MAINLY VFR. 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...HIGH CONFIDENCE FOR VFR AND DRY CONDITIONS. && .MARINE... 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... TUESDAY NIGHT...HIGH CONFIDENCE. HIGH PRES OVER THE WATERS SHOULD LEAD TO MAINLY QUIET BOATING WEATHER...WITH MODEST SW WINDS AND SEAS. SOME FOG POSSIBLE WITH REDUCED VSBYS. WED AND THU...MODERATE CONFIDENCE. SW FLOW IS EXPECTED TO INCREASE WED AHEAD OF A COLD FRONT WHICH SHOULD CROSS THE WATERS THU INTO THU NIGHT. 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 THIS PERIOD. SOME SHOWERS AND THUNDERSTORMS ARE POSSIBLE OVER THE WATERS...PARTICULARLY LATE WED NIGHT AND THU. FRI...HIGH CONFIDENCE FOR LIGHT WINDS AND SEAS AS A WEAK HIGH PRES CRESTS OVER THE WATERS. SOME LINGERING SSW SWELL IS POSSIBLE. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...BELK/DOODY NEAR TERM...BELK/DOODY SHORT TERM...DOODY LONG TERM...BELK AVIATION...BELK/DOODY MARINE...BELK/DOODY

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.