Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 300738 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 338 AM EDT THU JUL 30 2015 .SYNOPSIS...
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WARM AND HUMID CONDITIONS CONTINUE TODAY. 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.
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&& .NEAR TERM /UNTIL 6 AM THIS MORNING/... 2 AM UPDATE... FORECAST REMAINS ON TRACK THIS EARLY THIS MORNING. DRY WEATHER WILL PREVAIL AS UPPER LEVEL RIDGE AXIS MOVES OVER THE REGION. A STICKY NIGHT IS AHEAD AS DEWPOINTS ARE IN THE UPPER 60S TO LOW 70S. THIS COMBINED WITH LIGHT WINDS WILL HELP FOG BECOME ANOTHER ISSUE TONIGHT. RIGHT NOW LOW STRATUS IS SITTING JUST OFF THE COAST OF ACK AND COULD MOVE ONTO THE CAPE. MAY NEED TO WATCH THE CAPE AND ISLANDS FOR FOG. LOW TEMPS FOR MOST LOCATIONS WILL ONLY DROP TO BETWEEN 70 AND 75 WITH A FEW UPPER 60S POSSIBLE IN NORTHWEST MA. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM FRIDAY/... ***SHOWERS AND EMBEDDED THUNDERSTORMS WILL BRING HEAVY RAIN AND THE POTENTIAL FOR LOCALIZED STREET FLOODING THURSDAY AFTERNOON AND EVENING ESPECIALLY ACROSS INTERIOR SOUTHERN NEW ENGLAND*** ***A SECONDARY CONCERN WILL BE FOR A FEW STRONG TO MARGINALLY SEVERE THUNDERSTORMS LATE THURSDAY AFTERNOON/EARLY EVENING ACROSS WESTERN MA AND NORTHERN CT*** THURSDAY AND THURSDAY NIGHT... SOUTHWEST FLOW ALOFT AND AT THE SURFACE WILL TRANSPORT DEEP MOISTURE INTO SOUTHERN NEW ENGLAND. BOTH THE GFS/NAM SHOW PWATS EXCEEDING 2+ INCHES AND A SOUTHWEST LOW LEVEL JUST OF 25 TO 30 KNOTS. WE MAY SEE SOME PEEKS OF SUNSHINE IN THE MORNING...BUT SHOULD SEE CLOUDS BEGIN TO DOMINATE IN THE WARM AIR ADVECTION MOISTURE. GIVEN THE DEEP MOISTURE IN PLACE...SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS COULD BREAK OUT ANYWHERE ACROSS THE REGION BY THU AFTERNOON AND PERHAPS EVEN EARLIER. LOCALLY HEAVY RAINFALL WILL BE POSSIBLE WITH THIS ACTIVITY. THE MAIN SHOW WILL ARRIVE LATE THURSDAY AFTERNOON AND EVENING IN ASSOCIATION WITH A PRE-FRONTAL TROUGH AND ASSOCIATED COLD FRONT. POOR MID LEVEL LAPSE RATES AND CLOUD COVER WILL LIMIT INSTABILITY TO SOME DEGREE. NONETHELESS...WE SHOULD BE ABLE TO DEVELOP AROUND 1000 MLCAPES ACROSS THE INTERIOR GIVEN 70+ DEWPOINTS IN PLACE. 0 TO 6 KM SHEAR IS RATHER MARGINAL...BUT DOES INCREASE TO BETWEEN 30 AND 35 KNOTS ACROSS OUR NORTHWEST ZONES TOWARDS 00Z. A LOT OF THE MESOSCALE MODELS SHOW A LINE OF SHOWERS AND EMBEDDED THUNDERSTORMS WORKING INTO WESTERN MA/NORTHERN CT SOMETIME LATE THU AFTERNOON/EVENING. THAT ACTIVITY WEAKENS AS IT MOVES EAST INTO AN ENVIRONMENT WITH LESS INSTABILITY WHICH IS TYPICAL WITH SOUTHWEST FLOW ALOFT. BULK OF SHOWERS AND EMBEDDED STORMS SHOULD EXIT THE COASTAL PLAIN BY MIDNIGHT...BUT LINGERING ACTIVITY IS POSSIBLE ACROSS THE CAPE AND ISLANDS. SO TO SUM UP...HEAVY RAIN WITH THE POTENTIAL FOR LOCALIZED STREET FLOODING ACROSS THE INTERIOR WILL BE THE MAIN THREAT WITH THESE STORMS. HOWEVER...A FEW STRONG TO PERHAPS MARGINALLY SEVERE THUNDERSTORMS ARE POSSIBLE MAINLY ACROSS WESTERN MA AND NORTHERN CT. THE MAIN CONCERN WOULD BE LOCALIZED STRONG TO DAMAGING WIND GUSTS. THE HAIL THREAT IS RATHER LOW GIVEN 500 MB TEMPS OF AROUND -6C AND POOR MID LEVEL LAPSE RATES. ONE LITTLE NUANCE WE WANTED TO MENTION WAS THE LOW RISK FOR A BRIEF WEAK TORNADO ACROSS WESTERN MA AND NORTHERN CT. THERE IS ABOUT 25 TO 30 KNOTS OF WIND OFF THE DECK WITH RGEM/NAM SHOWING 0 TO 1 KM HELICITY VALUES NEAR OR OVER 100. GIVEN 70+ DEWPOINTS AND LOW LCL/S THERE IS A LOW RISK FOR THAT. HIGH TEMPS THU SHOULD MAINLY BE IN THE UPPER 80S TO NEAR 90...BUT A FEW PLACES ACROSS EASTERN NEW ENGLAND MAY END UP A FEW DEGREES WARMER IF THEY SEE A LONGER PERIOD OF SUNSHINE. EITHER WAY IT WILL BE VERY HUMID WITH 70+ DEWPOINTS. LOW TEMPS THU NIGHT WILL BE IN THE 60S TO NEAR 70 AND AREAS OF FOG WILL LIKELY DEVELOP IN THE TYPICALLY PRONE LOCATIONS LATE. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
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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.
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&& .AVIATION /08Z THURSDAY THROUGH MONDAY/...
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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 NIGHT/... TONIGHT...HIGH CONFIDENCE. MAINLY VFR CONDITIONS EXCEPT ACROSS THE CAPE...ISLANDS AND SOUTH COAST WHERE FOG HAS DEVELOPED. CONDITIONS COULD DROP DOWN TO IFR. ALSO NEED TO WATCH THE CT VALLEY. BEFORE 18Z...HIGH CONFIDENCE. VFR TO START WITH LINGERING FOG ALONG SOUTHERN TERMINALS. SCT SHOWERS AND ISO THUNDER OUT AHEAD OF APPROACHING COLD FRONT COULD DROP CONDITIONS TO MVFR. WINDS ACROSS THE SOUTH COAST COULD GUST OUT OF THE SW AROUND 25-30 KTS. AFTER 18Z AND TONIGHT...MODERATE CONFIDENCE. WINDS AHEAD OF AN APPROACHING COLD FRONT WILL GUST BETWEEN 20-30 KTS...ESP ACROSS THE SOUTH COAST. COLD FRONT WILL MOVE ACROSS THE REGION FROM WEST TO EAST BEGINNING AROUND 18-21Z. THIS CONVECTIVE LINE COULD BRING STRONG TO SEVERE STORMS ACROSS WESTERN MASS BEFORE FIZZLING OUT ACROSS THE EASTERN HALF OF THE REGION. ANTICIPATE ANY LINGERING SHOWERS TO BE OUT OF THE REGION BY 06Z. PATCHY FOG COULD DEVELOP ACROSS THE NORMAL PRONE REGIONS OVERNIGHT. FRIDAY...HIGH CONFIDENCE. LINGERING FOG AND STRATUS WILL DISSIPATE. EXPECT VFR WITH DIURNAL CU AND GUSTY WINDS AROUND 15-20 KTS. KBOS TERMINAL...HIGH CONFIDENCE. KBDL TERMINAL...HIGH CONFIDENCE IN TAF. THERE IS A PROBABILITY THAT A STRONG STORM COULD IMPACT THE TERMINAL THIS AFTERNOON. 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.
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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 /TONIGHT THROUGH THURSDAY NIGHT/... TONIGHT...HIGH CONFIDENCE. WEAK PRESSURE GRADIENT SHOULD KEEP WINDS AND SEAS BELOW SMALL CRAFT ADVISORY THRESHOLDS. MAY SEE SOME AREAS OF FOG DEVELOP LATE ACROSS THE SOUTHERN WATERS. THURSDAY AND THURSDAY NIGHT...MODERATE TO HIGH CONFIDENCE. DEVELOPING LOW LEVEL JET WILL RESULT IN NEAR SHORE SOUTHWEST WIND GUSTS OF 25 TO 30 KNOTS DEVELOPING THU AFTERNOON. IN ADDITION...LONG SOUTHWEST FETCH WILL ALLOW FOR SEAS TO BUILD TO BETWEEN 3 TO 5 FEET ACROSS MOST OPEN WATERS. SCA HEADLINES GO INTO EFFECT FOR ALL WATERS THU AFTERNOON. WINDS DIMINISH THU EVENING...BUT WILL NEED TO KEEP HEADLINES UP THROUGH THU NIGHT FOR THE OUTER-WATERS THROUGH THU NIGHT FROM THE LEFT OVER SWELL. 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.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY FROM NOON TODAY TO 7 PM EDT THIS EVENING FOR ANZ230>234-236-251. SMALL CRAFT ADVISORY FROM NOON TODAY TO 11 PM EDT THIS EVENING FOR ANZ235-237. SMALL CRAFT ADVISORY FROM NOON TODAY TO 8 AM EDT FRIDAY FOR ANZ250-254>256. && $$ SYNOPSIS...NOCERA/DUNTEN NEAR TERM...DUNTEN SHORT TERM...FRANK LONG TERM...NOCERA AVIATION...NOCERA/DUNTEN MARINE...FRANK/NOCERA

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