Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 301400 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 1000 AM EDT THU JUL 30 2015 .SYNOPSIS... AN APPROACHING COLD FRONT WILL TRIGGER SHOWERS AND EMBEDDED THUNDERSTORMS THIS AFTERNOON AND EVENING WITH LOCALLY HEAVY RAINFALL...ESPECIALLY ACROSS WESTERN PORTIONS OF CT AND MA. NOT AS WARM AND LESS HUMID WEATHER ARRIVES FRIDAY AND CONTINUES INTO THE WEEKEND AND PROBABLY INTO MUCH OF NEXT WEEK. THERE IS A LOW RISK FOR A FEW SHOWERS AND AN ISOLATED THUNDERSTORM THIS WEEKEND INTO EARLY NEXT WEEK...HOWEVER MUCH OF THE TIME DRY WEATHER WILL PREVAIL. && .NEAR TERM /THROUGH TONIGHT/... 10 AM UPDATE... * STRONG TO POSSIBLY SEVERE STORMS 3 PM TO 9 PM * * LOCALIZED WIND DAMAGE/FLOODING AND PERHAPS AN ISOLATED TORNADO FORECAST IN GOOD SHAPE CONSIDERING RADAR TRENDS AND MESOANALYSIS DATA. ADJUSTED HOURLY POPS TO INCORPORATE HIGH-RES MODELS WHICH KEEP BULK OF ACTIVITY ACROSS WESTERN NEW ENGLAND BEFORE WEAKENING IT AS IT HEADS TOWARD COAST DUE TO SW FLOW. LINE OF SHOWERS/STORMS WAS MOVING THROUGH CENTRAL NY THIS MORNING AND WILL REACH WESTERN NEW ENGLAND EARLY THIS AFTERNOON. AHEAD OF LINE...WE MAY SEE AN ISOLATED SHOWER/STORM POP UP AS LEADING EDGE OF HIGHER THETA-E AIRMASS HEADS INTO SOUTHERN NEW ENGLAND. BUT WE EXPECT MOST OF ACTIVITY TO OCCUR BETWEEN 3 PM AND 9 PM AS LINE MOVES THROUGH. MESOSCALE ENVIRONMENT WILL FEATURE MODERATE SURFACE BASED CAPE AROUND 1000-2000 J/KG...MARGINAL 0-6KM SHEAR OF 25-30KT AND WEAK MID LEVEL LAPSE RATES. THEREFORE WE DO NOT EXPECT TO SEE WIDESPREAD SEVERE WEATHER OUTBREAK THIS AFTERNOON AND EVENING... BUT MORE OF LOCALIZED THREAT OF WIND DAMAGE FROM 40-60 MPH GUSTS MAINLY IN WESTERN NEW ENGLAND WHICH MATCHES LATEST SPC DAY 1 MARGINAL RISK OUTLOOK. 00Z CIPS ANALOGS ALSO AGREE. MAIN ISSUE MAY END UP BEING LOCALIZED URBAN FLOODING AS PRECIPITABLE WATER VALUES CLIMB TO AROUND 2 INCHES. DESPITE PROGRESSIVE NATURE OF STORMS...MAY SEE RAINFALL OF 2 TO 3 INCHES IN A SHORT TIME WHICH COULD RESULT IN SIGNIFICANT FLOODING OF POOR DRAINAGE AREAS. ALSO HAVE CONCERN FOR AN ISOLATED TORNADO PRIMARILY NEAR CT VALLEY. ALTHOUGH THIS IS NOT A CLASSIC SETUP FOR NEW ENGLAND TORNADOES...PRESENCE OF 30-35KT WINDS AT 925 MB AND LOW LCL FROM 70+ DEWPOINTS POINTS TOWARD THAT POTENTIAL. IF ONE DOES OCCUR... AND THAT IS A BIG IF...IT WOULD LIKELY BE TOWARD WEAKER SIDE GIVEN STRENGTH OF WIND FIELDS ALOFT. ACTIVITY DIMINISHES TONIGHT WITH LOSS OF DAYTIME HEATING AND PASSAGE OF COLD FRONT. && .SHORT TERM /FRIDAY/... FRIDAY... FRONT WILL BE OFFSHORE BY FRIDAY MORNING LEADING TO A DESCENT DAY. ALTHOUGH TEMPERATURES WILL BE WARM...HUMIDITY WILL BE LOWER THAN THE PREVIOUS DAYS. ABUNDANT SUNSHINE WILL LEAD TO MIXING SO WINDS COULD GET A TAD GUSTY IN THE AFTERNOON. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... HIGHLIGHTS... * PATTERN CHANGE TO MORE SEASONABLE TEMPS AND LOWER HUMIDITY * LOW RISK OF A FEW SHOWERS SHOWERS/ISOLATED THUNDER EACH DAY BUT MUCH OF THE TIME REMAINING DRY SYNOPTIC OVERVIEW AND MODEL PREFERENCES... ANOMALOUS CANADIAN VORTEX OVER HUDSON AND JAMES BAYS THIS PERIOD RESULTS IN A MEAN MID LEVEL TROUGH DEVELOPING ACROSS THE GREAT LAKES INTO THE NORTHEAST AND WILL BE ACCOMPANIED BY BELOW NORMAL HEIGHTS. NUMEROUS SHORT WAVES WILL ROTATE THRU THIS BROAD TROUGH INTO NEW ENGLAND THIS TIME PERIOD AND WILL RESULT IN A REINFORCING SURGE OF DRIER AIR WITH EACH PASSING JET IMPULSE. THESE SHORT WAVE TROUGHS MAY YIELD A FEW SHOWERS/ISOLATED T-STORM WITH EACH FRONTAL PASSAGE. HOWEVER GIVEN THE LACK OF MOISTURE AND INSTABILITY MUCH OF THE PERIOD WILL FEATURE DRY WEATHER. DETERMINISTIC GUIDANCE IS DISPLAYING LARGE TIMING DIFFERENCES WITH THESE SHORT WAVES GIVEN THE FAST/BROAD FLOW ALOFT. THUS LOW FORECAST CONFIDENCE ON TIMING OF CONVECTIVE THREAT. GIVEN TIMING AND AMPLITUDE DIFFERENCES A MODEL BLEND PROVIDES THE MOST SKILL AND WILL USE THIS AS A BASIS FOR THIS FORECAST. DAILY SENSIBLE WEATHER DETAILS... FRI NIGHT...DRY WEATHER AND COMFORTABLE HUMIDITY /DEW PTS IN THE U50S TO L60S/ WITH POST FRONTAL AIRMASS OVER THE REGION. SATURDAY...LOW AMPLITUDE SHORT WAVE TROUGH MOVES ACROSS NY STATE INTO NORTHERN NEW ENGLAND. MOISTURE AND INSTABILITY IS LACKING AND THIS SHOULD LIMIT AREAL COVERAGE OF SHOWERS/T-STORMS TO WIDELY SCATTERED. THUS MOST LOCATIONS REMAIN DRY. SEASONABLY WARM WITH HIGHS IN THE 80S AND LOWS IN THE 60S. SUNDAY...SHOULD BE A MAINLY DRY DAY ALONG WITH SEASONABLE TEMPS /H85 +15/ WITH HIGHS IN THE 80S AND LOWS IN THE 60S. MONDAY...ANOTHER POTENTIAL SHORT WAVE TROUGH APPROACHES THE REGION FROM THE WEST. THUS LOW RISK OF SCATTERED SHOWERS/T-STORMS THIS PERIOD. SEASONABLY WARM WITH H5 TEMPS AROUND +15C. TUESDAY...CANADIAN VORTEX DIGS SOUTHWARD INTO QUEBEC WITH LOWERING HEIGHTS AND COOLER TEMPS ALOFT INTO NEW ENGLAND. THIS SHOULD YIELD A GREATER CHANCE FOR CONVECTION. WARMER AND MORE HUMID CONDITIONS LIKELY AHEAD OF MID LEVEL TROUGH AND ATTENDING COLD FRONT. WEDNESDAY...ITS DAY 7 BUT GOOD AGREEMENT AMONG DETERMINISTIC AND ENSEMBLE GUIDANCE THAT CLOSED LOW WILL BE OVER EASTERN QUEBEC WITH MEAN TROUGH AXIS ACROSS NEW ENGLAND. 925 MB AND 850 MB TEMPS ARE ABOUT -1 STD DEVIATION COOLER THAN CLIMO. THUS COULD HAVE A PERIOD OF SLIGHTLY COOLER THAN NORMAL WEATHER THIS PERIOD. && .AVIATION /14Z THURSDAY THROUGH MONDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH THURSDAY NIGHT/... 14Z UPDATE... HIGH CONFIDENCE. LEFTOVER IFR/MVFR CIGS IMPROVE TO VFR BY MIDDAY. LINE OF SHOWERS/TSTMS ARRIVE IN W NEW ENGLAND AROUND 18Z AND SHOULD WEAKEN BEFORE REACHING COAST 21Z-00Z. HEAVY RAIN MAIN THREAT BUT POTENTIAL FOR 40-50KT GUSTS IN STRONGER STORMS. ANTICIPATE ANY LINGERING SHOWERS TO BE OUT OF THE REGION BY 06Z. PATCHY FOG COULD DEVELOP ACROSS THE NORMAL PRONE REGIONS OVERNIGHT WITH LOCAL MVFR/IFR. LINGERING FOG AND STRATUS WILL DISSIPATE FRI MORNING GIVING WAY TO VFR WITH DIURNAL CU AND GUSTY WINDS AROUND 15-20 KTS. KBOS TERMINAL...HIGH CONFIDENCE IN TAF. MAIN WINDOW FOR TSTMS 22Z-01Z. KBDL TERMINAL...HIGH CONFIDENCE IN TAF. MAIN WINDOW FOR TSTMS 19Z-22Z. 40KT GUSTS POSSIBLE IN STRONGER STORMS. OUTLOOK /FRIDAY NIGHT THROUGH MONDAY/... VFR MUCH OF THE TIME WITH A LOW RISK FOR SCATTERED SHOWERS SAT AND AGAIN MONDAY. GREATER RISK FOR THUNDER MON. MODERATE FORECAST CONFIDENCE. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THIS AFTERNOON THROUGH THURSDAY NIGHT/... HIGH CONFIDENCE. KEEPING SCA POSTED FOR 20-30KT GUSTS THIS AFTERNOON NEAR SHORE AS GRADIENT TIGHTENS AHEAD OF COLD FRONT. IN ADDITION...LONG SOUTHWEST FETCH WILL ALLOW FOR SEAS TO BUILD TO BETWEEN 3 TO 5 FEET ACROSS MOST OPEN WATERS. WINDS DIMINISH THIS EVENING...BUT WILL NEED TO KEEP HEADLINES UP THROUGH TONIGHT FOR THE OUTER- WATERS FROM THE LEFT OVER SWELL. HIGH PRESSURE WILL BUILD ON FRIDAY SO SCA MAY BE ALLOWED TO DROP. OUTLOOK /FRIDAY NIGHT THROUGH MONDAY/... FAIRLY TRANQUIL BOATING WEATHER THIS PERIOD WITH MODEST SW WINDS...GOOD VSBY AND MAINLY DRY WEATHER. LOW RISK OF SCATTERED SHOWERS AND T-STORMS MONDAY. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 7 PM EDT THIS EVENING FOR ANZ230>234-236-251. SMALL CRAFT ADVISORY UNTIL 11 PM EDT THIS EVENING FOR ANZ235- 237. SMALL CRAFT ADVISORY UNTIL 8 AM EDT FRIDAY FOR ANZ250-254>256. && $$ SYNOPSIS...NOCERA/DUNTEN NEAR TERM...JWD SHORT TERM...DUNTEN LONG TERM...NOCERA AVIATION...NOCERA/DUNTEN/JWD MARINE...NOCERA/DUNTEN/JWD

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