Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 210200 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 1000 PM EDT SUN JUL 20 2014 .SYNOPSIS... SHOWERS OVER CAPE COD THIS EVENING TAPER OFF TONIGHT AS AN OFFSHORE LOW EXITS SEAWARD. HIGH PRESSURE THEN PROVIDES DRY AND PLEASANTLY WARM WEATHER MONDAY ALONG WITH LIGHT WINDS. THE HIGH THEN MOVES OFFSHORE TUE RESULTING IN WARMER AND MORE HUMID CONDITIONS TUE AND WED. 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. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... 7 PM UPDATE... MESO ANALYSES SHOW A MODEST DEFORMATION AXIS /MAINLY STRETCHING DEFORMATION/ ALONG THE NRN PERIPHERY OF WEAK OCEAN WAVE WHICH IS PROGGED TO CONTINUE TO DEEPEN AS IT SLIDES OFFSHORE EARLY IN THE MORNING. DUE TO BOTH THE SLOW MOVEMENT AND GRADUAL DEEPENING OF THE WAVE...WITH ENOUGH LOW LVL MOISTURE WILL LIKELY SEE A CONTINUATION OF THE RAINBANDS ACROSS SE MA THROUGH MUCH OF THE OVERNIGHT. HAVE TRANSITIONED POPS ACCORDINGLY...WITH CATEGORICAL POPS THROUGH AT LEAST 09Z. RAINFALL RATES WILL CONTINUE TO BE LIGHT HOWEVER...WITH SOME DRIZZLE IN BETWEEN THE MAIN RAINBANDS WITH THIS TRAPPED LOW LVL MOISTURE BENEATH A BUILDING SUBSIDENCE INVERSION. SOME PLACES COULD SEE ON THE ORDER OF A QUARTER INCH OF OVERALL RAINFALL THOUGH...BUT MAINLY DUE TO THE FACT THAT THESE RAIN BANDS ARE LIKELY TO LINGER WITH SLOW MOVEMENT. ELSEWHERE...AM ALREADY NOTING RAPID CLEARING IN THE W. COUPLE THIS WITH VERY LIGHT TO NEAR CALM FLOW AND EXPECT SOME DECENT RAD COOLING IN SPOTS. HAVE ADJUSTED MIN TEMPS TO COINCIDE WITH THIS THINKING. PREVIOUS DISCUSSION... TONIGHT... LOW PRESSURE NEAR 40N/70W LIFTS E TOWARDS THE N-ATLANTIC AS HIGH PRESSURE BUILDS BACK INTO THE REGION. SHOULD FIND OURSELVES WITHIN THE REAR OF THE INITIAL WAVE THROUGH THE BROAD TROUGHING REGIME ACROSS THE REGION WHERE NVA PREVAILS AN ENVIRONMENT OF SINKING AIR. SO WILL DROP RAIN CHANCES SW-NE ACROSS SE NEW ENGLAND AND ADJACENT WATERS. PLETHORA OF FORECAST GUIDANCE WANTS TO LINGER RAIN...BUT AM NOT BUYING IT. CLEARING SHOULD CONTINUE W TO E AS SEEN IN THE LATEST SATELLITE TRENDS. THOUGH MAY SEE SOME CLOUDS TO THE W DRIFT INTO THE REGION OVERNIGHT. SUCH CLOUDS ARE ASSOCIATED WITH A SECONDARY IMPULSE WITHIN THE E GREAT LAKES OPEN-WAVE TROUGH BEGINNING TO LIFT OUT OF THE REGION. THUS COULD TURN OUT TO BE A MILD NIGHT BENEATH A BLANKET OF CLOUDS. LOWS AROUND THE MID- TO UPPER-50S WITH THE WARMEST SPOTS IN URBAN AREAS AND ALONG THE COASTS. ISALLOBARIC COMPONENT OF THE WIND RELAXES ALLOWING NE-WINDS TO DIMINISH...BUT STILL EXPECT SOME 15 MPH GUSTS OVER THE E-SHORE OF MA INCLUDING THE CAPE AND ISLANDS. PATCHY FOG FOR INTERIOR SHELTERED VALLEY REGIMES SUCH AS WITHIN THE N-CT RIVER VALLEY...IN AND AROUND KEENE NH FOR EXAMPLE. MAY ALSO HAVE A FEW HAZY PATCHES HERE IN THERE IN CLIMATOLOGICALLY FAVORED AREAS SUCH AS NE-CT AND CENTRAL SE MA AROUND TAUNTON...THOUGH NOT AS HIGH OF CONFIDENCE SAY AS PLACES AROUND THE N-CT RIVER VALLEY. && .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... MONDAY... TROUGHING AND LOWER HEIGHTS TO THE W RESULTS IN AN ACCOMPANYING SURFACE REFLECTION OF BROADSCALE LOW PRESSURE. ANTICIPATE CONVECTIVE ACTIVITY TO STRETCH ACROSS UPSTATE NY INTO PA WHILE HIGH PRESSURE AND DRIER AIR KEEPS CONDITIONS QUIET OVER NEW ENGLAND. PLAUSIBLE THAT THE W/SW COMPONENT OF LOW- TO MID-LEVEL FLOW THROUGH THE MID- ATLANTIC N/NE INTO NEW ENGLAND IMPINGING ON THE W-SLOPES OF HIGHER TERRAIN COULD YIELD A CHANCE OF SHOWERS FOR W NEW ENGLAND. WILL NOTE THIS IN THE FORECAST WITH SLIGHT CHANCE POPS. RENEWED ISALLOBARIC RESPONSE TO THE WINDS RESULTING IN AN ONSHORE E- FLOW. BENEATH A WARMING AIRMASS ALOFT AIDED BY THE AFOREMENTIONED W/SW FLOW...HIGHS WARM INTO THE UPPER-70S TO LOW-80S...THE WARMEST OF CONDITIONS OF WHICH OCCUR ACROSS THE INTERIOR...COOLEST ALONG THE IMMEDIATE E-SHORES WITH ONSHORE FLOW OFF COOLER WATERS. MONDAY NIGHT... WITH DAYTIME HEATING CONCLUDING...CONVECTIVE ACTIVITY TO THE W SHOULD END. HIGH PRESSURE REMAINS IN CONTROL RESULTING IN LIGHT WINDS AND A QUIET NIGHT. SOME QUESTION AS TO WHETHER CONVECTIVE REMNANTS ADVECTING E WILL RESULT IN MID- TO HIGH-LEVEL CLOUDS. THIS PERHAPS WILL YIELD A BLANKET OF INSOLATION RESULTING IN WARMER OVERNIGHT LOWS. BETTER CHANCES FOR W NEW ENGLAND...THUS MAY KEEP THOSE AREAS MILDER AROUND THE MID-60S WITH LOWS AROUND THE LOW-60S ELSEWHERE. DEWPOINTS ON THE INCREASE TOWARDS MORNING AS WINDS BEGIN TO TURN MORE SOUTHERLY. FOG PERHAPS OF SOME CONCERN ALONG THE S-COAST AND ADJACENT WATERS...AS WELL AS OVER THE N-CT RIVER VALLEY...OTHERWISE STICKY HUMID CONDITIONS ARE MAKING A COMEBACK. && .LONG TERM /TUESDAY 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 /02Z MONDAY THROUGH FRIDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. 7 PM UPDATE... NO MAJOR CHANGES FROM 18Z TAFS. EARLIER DISCUSSION BELOW. ================================================================ SHORT TERM /THROUGH MONDAY NIGHT/...MODERATE CONFIDENCE. WILL HOLD VFR THIS EVENING FOR A MAJORITY OF TERMINALS...EVEN WITH SHRA OVER SE MA. ONLY CONCERN IS THE LIKELY REPEAT OF PATCHY DENSE FOG OVER THE N-CT VALLEY /I.E. EEN AND AFN IN S NH/. WINDS TURNING LIGHT OUT OF THE N. SOME MID- TO HIGH-LEVEL CLOUDS MAY STREAM IN FROM THE W LATE TOWARDS MORNING. VFR TRENDS CONTINUE INTO MONDAY AS WINDS VEER S/SE. MID- TO HIGH- LEVEL CLOUDS WILL STREAM OVER THE TERMINALS. SUCH TRENDS CONTINUE OVERNIGHT ALONG WITH THERE IS THE POSSIBILITY OF LOW STRATUS/FOG ALONG THE S-COAST. CONFIDENCE IS LOW TO MODERATE AT THIS TIME. SO HAVE GONE CONSERVATIVE WITH VSBYS OF AROUND 3 SM. KBOS TAF...HIGH CONFIDENCE IN TAF. KBDL TAF...HIGH CONFIDENCE IN TAF. OUTLOOK...TUESDAY 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... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH MONDAY/...MODERATE CONFIDENCE. SMALL-CRAFT ADVISORIES CONTINUE THROUGH THIS EVENING WITH THE POTENTIAL OF GUSTS UP TO 25 KTS OUT OF THE NE WITH SEAS BUILDING TO 5 FEET AS A RESULT OF THE STRESS. BUOY 44017 S OF RI/BI SOUND CONTINUES TO OBSERVE WAVES UP TO 4.6 FEET. HIGH PRESSURE BUILDS BACK INTO THE WATERS OVERNIGHT AND TOWARDS MORNING ALLOWING WINDS TO LIGHTEN AND SEAS TO DIMINISH. WHILE MONDAY WILL CONSIST OF TRANQUIL BOATING WEATHER...WILL HAVE TO WATCH FOR POTENTIAL DETERIORATING CONDITIONS MONDAY NIGHT TOWARDS TUESDAY MORNING. THERE IS THE POSSIBILITY OF DENSE FOG DEVELOPING OVER THE WATERS. PRESENTLY HAVE LOW TO MODERATE CONFIDENCE. OUTLOOK...TUESDAY 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. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...NOCERA/SIPPRELL NEAR TERM...DOODY/SIPPRELL SHORT TERM...SIPPRELL LONG TERM...NOCERA AVIATION...NOCERA/SIPPRELL MARINE...NOCERA/SIPPRELL

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