Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 011801 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 201 PM EDT MON SEP 1 2014 .SYNOPSIS... A WARM HUMID FLOW WILL CONTINUE ACROSS NEW ENGLAND THROUGH TUESDAY WITH SCATTERED SHOWERS AND THUNDERSTORMS EACH DAY. A COLD FRONT WILL PUSH ACROSS THE REGION TUESDAY NIGHT. WARM BUT LESS HUMID WEATHER WILL FOLLOW FOR WEDNESDAY THROUGH FRIDAY. ANOTHER COLD FRONT MAY BRING A CHANCE OF SHOWERS AND THUNDERSTORMS SATURDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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2 PM UPDATE...DIURNAL CUMULUS CLOUDS HAVE DEVELOPED ACROSS THE REGION AND SEA BREEZES HAVE DEVELOPED ALONG BOTH COASTS. STARTING TO SEE A FEW SHOWERS POP UP IN SOUTHERN CONNECTICUT THIS AFTERNOON. WILL START TO SEE MORE SHOWERS AND THUNDERSTORMS AS THE AFTERNOON WEARS ON...MAINLY SOUTH OF THE CT/MA BORDER AND EASTWARD INTO SOUTHEASTERN MASSACHUSETTS. THIS IS WHERE THE BEST INSTABILITY IS LOCATED. PREVIOUS DISCUSSION... WARM HUMID AIR WITH DEWPOINTS IN THE UPPER 60S AND 70S. A FRONT IS STALLED ALONG THE CANADIAN BORDER. MEANWHILE A LEE TROUGH WILL BE POSITIONED NEAR THE MID ATLANTIC COAST. BOTH OF THESE WILL SERVE AS FOCI FOR THUNDERSTORM DEVELOPMENT. SOMEWHAT DRIER AIR MOVES INTO NORTHERN NEW ENGLAND WITH PRECIP WATER VALUES NEAR 1 INCH. MEANWHILE...2 INCH VALUES LINGER ALONG THE SOUTH COAST. THIS MOISTURE WILL BE THE POTENTIAL FUEL FOR ANY DAYTIME CONVECTION. STABILITY PARAMETERS LOOK FAVORABLE FOR TSTMS BUT LIKELY NOT AT SEVERE LEVELS. TOTALS START LOW AND CLIMB TO 46-47 IN THE AFTERNOON WITH HIGHEST VALUES ACROSS CT-RI-SE MASS. THE GFS SHOWS SHOWS SBCAPE REACHING 1000-1500 J/KG ESPECIALLY IN CT. LOW LEVEL HELICITY IS MUCH LOWER THAN SUNDAY...20-30 M2/S2. POPS WILL FAVOR AFTERNOON/EVENING TSTMS WITH HIGHEST VALUES AT THE SOUTH COAST. WITH PRECIP WATER VALUES AT 1.5-2.0 INCHES SOUTH OF THE MASS PIKE...ANY STORMS IN THIS AREA WILL HAVE POTENTIAL FOR HEAVY DOWNPOURS AND POSSIBLE URBAN/POOR DRAINAGE FLOODING. MAX SFC TEMPS WILL AGAIN BE IN THE MID 80S.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... TONIGHT... LINGERING CONVECTION IN THE EVENING BUT DIMINISHING. HIGH HUMIDITY AND LIGHT WIND WILL AGAIN FAVOR DEVELOPMENT OF FOG OVERNIGHT. MIN SFC TEMPS WILL BE NEAR THE DEW POINTS...MAINLY UPPER 60S AND LOWER 70S. TUESDAY... UPPER SHORTWAVE DIGS OVER THE GREAT LAKES WHILE HIGH PRESSURE REMAINS TO OUR EAST. THIS WILL MAINTAIN THE WARM MOIST SOUTHWEST FLOW ACROSS NEW ENGLAND. A COLD FRONT ASSOCIATED WITH THE UPPER SHORTWAVE WILL MOVE EAST THROUGH THE EASTERN GREAT LAKES TO EASTERN NEW YORK BY EVENING. A PRE-FRONTAL TROUGH WILL REMAIN OVER THE HUDSON AND DELAWARE VALLEYS. FAVORABLE JET DYNAMICS REMAIN WELL TO OUR WEST MUCH OF THE DAY...BUT APPROACH WESTERN MASS/SOUTHERN NH LATE. TOTALS ON THE GFS ARE 50-51 WHILE THE ECMWF AND GGEM ARE 47-48. MID LEVEL LAPSE RATES ARE AROUND 6C/KM. SBCAPES ARE 500-1000 J/KG BY THE GFS HINTS AT 1000-1500 J/KG. OVERALL WE WILL FAVOR CHANCE POPS FOR SHOWERS/TSTMS IN THE AFTERNOON WITH THE BEST CHANCE IN WESTERN MASS/SOUTHERN NH AND DIMINISHING VALUES FARTHER EAST. PRECIPITABLE WATER VALUES START AROUND 1.5 INCHES AND CLIMB TO NEAR 2 INCHES...SO LOCALLY HEAVY DOWNPOURS WILL AGAIN BE A CONCERN. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... OVERVIEW AND MODEL PREFERENCES... MEDIUM RANGE MODELS CONTINUE TO SHOW GOOD CONTINUITY EARLY IN THE FORECAST CYCLE...AS H5 TROUGH LIFTS INTO SOUTHERN QUEBEC AND ONTARIO AS IT FLATTENS OUT. THE UPPER PATTERN THEN BECOMES MORE TYPICAL OF MID SUMMER RATHER THAN EARLY FALL...WITH BROAD RIDGING DOMINATING FOR THE MIDDLE AND LATTER PORTIONS OF THE WEEK. BEYOND THIS...MODELS START TO DIVERGE IN BREAKING DOWN THIS RIDGE...WITH THE 12Z/00Z ECMWF OP RUNS AS WELL AS ECENS AND GFS MEANS SHOWING A SLOWER BREAKDOWN OF THE UPPER PATTERN WHILE THE GFS OP RUNS TENDING TO SIGNAL A QUICKER BREAKDOWN. ALSO NOTING UPPER LEVEL ENERGY CROSSING CENTRAL AND NORTHERN CANADA AROUND THE MIDDLE AND LATTER PORTIONS OF THIS FORECAST...THOUGH LOOKS LIKE THIS WILL REMAIN WELL N OF THE U.S./CANADIAN BORDER...FOR NOW. HAVE LEANED THIS FORECAST TOWARD A BLEND OF AVAILABLE GUIDANCE THROUGH LATE THIS WEEK...AS THIS BLEND HAS SHOWN VERY GOOD CONSISTENCY OVER THE LAST SEVERAL DAYS...THEN PUSHED CLOSER TO THE EC/ECENS MEANS FOR NEXT WEEKEND WHICH TEND TO BE SLOWER THAN MOST OF THE OTHER GUIDANCE. EXPERIENCE SHOWS THAT...WITH A STRONG DOMINANT PATTERN IN PLACE SUCH AS WHAT WILL BE DEVELOPING...THIS TENDS TO TAKE MORE TIME TO BREAK DOWN UNLESS SOME MAJOR SYSTEM SHOWS UP IN THE OVERALL FLOW. DAILY DETAILS... TUESDAY NIGHT...COLD FRONT CONTINUES TO MOVE OFFSHORE OVERNIGHT. LEFTOVER ENERGY WILL LIFT NE INTO NORTHERN NEW ENGLAND AND THE MARITIMES OVERNIGHT AS H5 SHORT WAVE LIFTS INTO SOUTHERN QUEBEC. EXPECT DRIER AIR TO START FILTERING IN...MAINLY ACROSS S NH/N CENTRAL AND W MA. WILL TAKE SOME TIME FOR SW WINDS TO SHIFT ACROSS SOUTHERN AND EASTERN AREAS OVERNIGHT...SO MORE HUMID CONDITIONS WILL HOLD IN. OVERNIGHT LOWS WILL RANGE FROM THE LOWER-MID 60S OF THE HIGHER INLAND TERRAIN OF SW NH/W MA TO AROUND 70 ALONG THE IMMEDIATE COAST. WEDNESDAY...SURFACE HIGH PRES WILL BUILD E OUT OF THE GREAT LAKES...ALLOWING DRIER AIR TO SPILL IN ACROSS THE REGION DURING THE DAY AS WINDS SHIFT TO NW. HOWEVER...WITH THE GENERAL OFFSHORE FLOW IN PLACE AND H5 HEIGHTS RISING WITH BROAD RIDGE BUILDING ALOFT... LOOKS LIKE TEMPS WILL REMAIN ON THE WARM SIDE. TEMPS WILL TOP OFF IN THE LOWER-MID 80S...EXCEPT FROM 75 TO 80 ALONG THE IMMEDIATE COAST. MAY SEE SOME PATCHY FOG DEVELOP IN NORMALLY PRONE VALLEY AREAS WED NIGHT AS TEMPS FINALLY FALL BACK TO THE 50S...THOUGH HOLDING IN THE LOWER-MID 60S ALONG THE IMMEDIATE COAST. WINDS BECOME LIGHT/VRBL OR CALM...WHICH MAY HELP TO PROMOTE THE FOG DEVELOPMENT. THURSDAY AND FRIDAY...HIGH PRESSURE WILL DOMINATE...SO EXPECT DRY AND WARM CONDITIONS TO CONTINUE ACROSS THE REGION. DEWPTS WILL BE COMFORTABLE...MAINLY IN THE MID 50S TO AROUND 60 ON THURSDAY...BUT LOOK TO START CREEPING BACK UP AGAIN ON FRIDAY AS THE HIGH WILL SLIP OFF THE COAST AND SW WINDS TAKE OVER. HIGHS THURSDAY WILL BE IN THE LOWER-MID 80S AGAIN...THOUGH SOME READINGS MAY REACH THE UPPER 80S WELL INLAND ON FRIDAY. SATURDAY AND SUNDAY...MODEL RUNS TENDING TO DIVERGE ON THE BREAKDOWN OF THE UPPER LEVEL PATTERN ACROSS THE EASTERN U.S. DURING THIS TIMEFRAME AND THE APPROACH OF A COLD FRONT...SO LOWER FORECAST CONFIDENCE. AT THIS POINT...A COLD FRONT WILL APPROACH THE REGION DURING SAT...PUSHING OFFSHORE SAT NIGHT OR EARLY SUNDAY WITH HIGH PRES RETURNING. && .AVIATION /18Z MONDAY THROUGH SATURDAY/...
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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 MONDAY NIGHT/...HIGH CONFIDENCE IN TRENDS...LOWER CONFIDENCE IN TIMING. THROUGH 00Z...IFR CIGS LINGER ALONG THE SOUTH COAST WITH VFR CONDITIONS ELSEWHERE. ISOLD TO SCT SHRA/TSRA ACROSS CT/RI/SE MASS THIS AFTERNOON/EVENING WITH LOCALLY HEAVY DOWNPOURS POSSIBLE. BRIEF MVFR/IFR IN ANY TSTMS. SEA BREEZE ALONG BOTH COASTS RESULTING IN SOUTHEASTERLY WINDS AT LOGAN. TONIGHT...EVENING SHRA/TSRA ESPECIALLY OVER THE CAPE AND ISLANDS. BRIEF MVFR/IFR IN ANY STORMS. QUIET WEATHER THE REMAINDER OF THE NIGHT WITH AREAS OF IFR IN STRATUS AND FOG. BEST CHANCE WILL AGAIN BE ALONG THE SOUTH COAST AND ISLANDS AS WELL AS THE CT RIVER VALLEY. TUESDAY...MORNING FOG AND IFR CONDITIONS BURN OFF. VFR THROUGH MUCH OF THE DAY. INCREASING CLOUDS FROM THE WEST DURING THE AFTERNOON/EVENING WITH POTENTIAL FOR BRIEF MVFR IN SCATTERED THUNDERSTORMS. TUESDAY NIGHT...MVFR/IFR CONDITIONS IN STRATUS AND FOG LIKELY AGAIN...PARTICULARLY ALONG THE SOUTH COAST...CAPE...AND ISLANDS. COLD FRONT MOVES THROUGH AFTER MIDNIGHT ALLOWING SHRA/TSRA TO END AND CONDITIONS TO IMPROVE. KBOS TERMINAL...HIGH CONFIDENCE IN TRENDS. LOWER CONFIDENCE ON TIMING. SEABREEZE CONTINUES THROUGH SUNSET. KBDL TERMINAL...HIGH CONFIDENCE IN TRENDS. LOWER CONFIDENCE ON TIMING. OUTLOOK...WEDNESDAY THROUGH FRIDAY... WEDNESDAY THROUGH FRIDAY...MODERATE CONFIDENCE. EXPECTING MAINLY VFR CONDITIONS. LOCAL MVFR-IFR VSBYS AND CIGS IN LATE NIGHT PATCHY FOG AND LOW CLOUDS. MAIN AREAS OF CONCERN WILL BE THE TYPICALLY PRONE LOCATIONS ACROSS THE FAR INTERIOR /SW NH AND NORTH CENTRAL AND WESTERN MA/. ON THU NIGHT...WITH SW WINDS IN PLACE...MAY SEE PATCHY FOG ALONG THE S COAST WITH LOCAL MVFR-IFR CONDITIONS AS WELL.
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&& .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. MODERATE CONFIDENCE THROUGH TUESDAY. TODAY... HIGH PRESSURE OFFSHORE AND LOW PRESSURE OVER THE GREAT LAKES WILL MAINTAIN A SOUTHWEST WIND FLOW ACROSS THE WATERS THROUGH TUESDAY. WINDS WILL REMAIN AT OR BELOW 20 KNOTS. SEAS WILL START AROUND 5 FEET ON THE OUTER WATERS BUT WILL DIMINISH THROUGH THE DAY. WE HAVE MAINTAINED SMALL CRAFT ADVISORY ON THE SOUTHERN OUTER WATERS THROUGH THE DAY DUE TO THE LINGERING ROUGH SEAS. A FEW THUNDERSTORMS WILL MOVE ACROSS SOUTHERN NEW ENGLAND WITH THE BEST CHANCE ON THE WATERS OCCURRING SOUTH OF BOSTON. TONIGHT... EVENING THUNDERSTORMS DIMINISH EARLY AT NIGHT. LIGHT SOUTHWEST FLOW WILL ALLOW AREAS OF FOG OVERNIGHT WITH POOR VISIBILITY. TUESDAY... AREAS OF FOG WILL START THE MORNING...WITH VISIBILITY IMPROVING DURING THE MORNING. SHOWERS AND THUNDERSTORMS WILL MOVE INTO WESTERN NEW ENGLAND DURING THE AFTERNOON AND MAY THREATEN THE COASTAL WATERS TOWARD EVENING. TSTMS COULD CAUSE STRONG WIND GUSTS...OTHERWISE EXPECT WINDS AND SEAS TO REMAIN BELOW SMALL CRAFT LEVELS. OUTLOOK...TUESDAY NIGHT THROUGH FRIDAY... MODERATE CONFIDENCE THROUGH THE PERIOD. EXPECT WINDS AND SEAS TO REMAIN BELOW SMALL CRAFT CRITERIA. MAY SEE SW WIND GUSTS UP TO 20 KT TUE NIGHT ON THE SOUTHERN WATERS BEFORE SHIFTING TO W AND DIMINISHING BY WED MORNING. WINDS BACK AROUND TO SW AGAIN LATE THU NIGHT/FRI. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT THIS EVENING FOR ANZ254>256. && $$ SYNOPSIS...WTB/EVT NEAR TERM...WTB/RLG SHORT TERM...WTB LONG TERM...EVT AVIATION...RLG/EVT MARINE...WTB/EVT

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