Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 132346 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 746 PM EDT SUN JUL 13 2014 .SYNOPSIS... A FRONTAL BOUNDARY WILL STALL ACROSS THE REGION THROUGH WEDNESDAY YIELDING PERIODS SHOWERS AND THUNDERSTORMS. A FEW STRONG TO SEVERE THUNDERSTORMS APPEAR LIKELY OVER THIS TIME ALONG WITH A HEAVY RAIN/LOCALIZED FLASH FLOOD THREAT. A TREND TOWARD DRIER AND SOMEWHAT LESS HUMID WEATHER FOLLOWS LATE IN THE WEEK. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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735 PM UPDATE... A FEW STRONG THUNDERSTORMS WILL MOVE ACROSS SW MA/N CENTRAL CT OVER THE NEXT FEW HOURS. SVR TSTM WATCH IS OUT UNTIL 11 PM OR SOONER IF THREAT DIMINISHES. WILL CONTINUE TO MONITOR. OTHERWISE...NOTING LOW CLOUDS ALONG THE S COAST AS NOTED ON 23Z OBSERVATIONS WITH THE S-SW FLOW. TEMPS FALLING BACK THROUGH THE 70S WITH DEWPTS IN THE 60S...SO WOULD NOT BE SURPRISED TO SEE SOME FOG DEVELOPING BY AROUND MIDNIGHT AS TEMPS FALL CLOSE TO THE DEWPTS. NEAR TERM GRIDS WERE IN GOOD SHAPE...BUT DID DO A QUICK UPDATE TO BRING CONDITIONS CURRENT. PREVIOUS DISCUSSION... A STRONG THUNDERSTORM OR TWO WITH LOCALLY GUSTY WINDS CAN NOT BE RULED OUT IN OUR FAR WESTERN ZONES THIS EVENING. IN ADDITION... BRIEF HEAVY RAINFALL CERTAINLY POSSIBLE WITH PWATS AROUND 2 INCHES. WHILE ACTIVITY WILL BE WEAKENING AS IT ENTERS OUR REGION...SOME MESOSCALE MODELS INDICATE AT LEAST SCATTERED SHOWERS MAY TRY TO MAKE IT ONTO THE COASTAL PLAIN BY LATE EVENING OR AFTER MIDNIGHT. AFTER THE MAIN SHORTWAVE OR WHAT/S LEFT OF IT EXITS THE COASTAL PLAIN...THERE STILL WILL BE THE RISK OF SCATTERED SHOWERS AND A FEW THUNDERSTORMS THROUGH DAYBREAK...THIS A RESULT OF SOME ELEVATED INSTABILITY AND A DEVELOPING LOW LEVEL JET. LOWS MAINLY IN THE UPPER 60S TO THE LOWER 70S AND IT WILL BE MUGGY. IN ADDITION...SOME PATCHY FOG POSSIBLE LATE WITH BEST CHANCE CAPE AND ISLANDS.
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/... ***A FEW STRONG TO SEVERE THUNDERSTORMS LIKELY MONDAY AFTERNOON AND/OR EVENING BUT LOW CONFIDENCE ON TIMING AND AREAL COVERAGE*** ***HEAVY RAIN/LOCALIZED FLASH FLOOD THREAT INCREASES MONDAY NIGHT*** AN INTERESTING SET UP IN PLACE FOR SOUTHERN NEW ENGLAND MONDAY INTO MONDAY NIGHT...BUT DETAILS/TIMING REMAIN UNCERTAIN. APPEARS THE MAIN TRIGGER FOR CONVECTION MONDAY AFTERNOON/EVENING WILL BE A SHORTWAVE THAT WILL LIFT NORTHEAST ACROSS SOUTHERN NEW ENGLAND. THE MODELS SEEM TO BE STRUGGLING WITH TIMING OF THE SHORTWAVE/S AND WHEN/WHERE TO TRIGGER CONVECTION. SOME OF OUR GUIDANCE HOLDS OFF MOST OF THE CONVECTION UNTIL VERY LATE MONDAY AFTERNOON OR EVENING...WHEN THE MAIN SHORTWAVE LIFTS NORTHEAST AND GETS THINGS GOING CLOSE TO 00Z IN OUR WESTERN ZONES. OTHER GUIDANCE SUCH AS THE NAM/GFS BREAKS OUT SCATTERED SHOWERS/THUNDERSTORMS SOMEWHAT EARLIER. WE ARE DEALING WITH A VERY MOIST/UNCAPPED ENVIRONMENT AND IT WON/T TAKE MUCH HEATING TO GET SOME CONVECTION GOING. WE SEE THE POTENTIAL FOR SCATTERED SHOWERS/THUNDERSTORMS DEVELOPING DURING THE AFTERNOON AND EARLIER THAN SOME OF THE OTHER GUIDANCE. OTHER THAN THE TIMING ISSUES...THE BIG UNCERTAINTY THAT NEEDS TO BE RESOLVED IS THE AMOUNT OF SOLAR INSULATION. GIVEN PATTERN...EXPECT TO SEE A LOT OF CLOUDS AROUND BUT A FEW PEEKS OF SUN WILL PROBABLY OCCUR. GIVEN THE FACT THAT WE WILL HAVE 70+ DEWPOINTS IN PLACE...WE CAN GET AWAY WITH A LOT OF CLOUDS AND STILL HAVE A SEVERE THREAT...BUT MORE SUN WILL CERTAINLY INCREASE POTENTIAL. LOOKS LIKE WE SHOULD SEE 1000 TO 1500 J/KG OF CAPE DEVELOP...0 TO 6 KM SHEAR OF 25 TO 35 KNOTS AND PERHAPS LOCALLY OVER 40 KNOTS WHEN THE MAIN SHORTWAVE KICKS OUT...AND 70+ DEWPOINTS. ALL IN ALL...DEEP LOW LEVEL MOISTURE/INSTABILITY AND ADEQUATE SHEAR SUPPORT THE THREAT FOR A FEW STRONG TO SEVERE THUNDERSTORMS DURING THE AFTERNOON AND/OR EVENING. PERHAPS THE HIGHEST POTENTIAL ENDS UP IN OUR SOUTHWEST ZONES...WHERE BETTER INSTABILITY/SHEAR OVERLAP...BUT CAN/T RULE OUT A FEW STRONG TO SEVERE STORMS ANYWHERE. THE MAIN THREAT WOULD BE LOCALLY STRONG TO DAMAGING WIND GUSTS WITH A SECONDARY CONCERN FOR HAIL WITH ANY DISCRETE CELLS. IN ADDITION...0 TO 1 KM HELICITY VALUES MAY EXCEED 100 ESPECIALLY DURING THE LATE AFTERNOON AND EVENING. THIS COMBINED WITH AN INCREASING LOW LEVEL JET/70+ DEWPOINTS AND LOW LCL/S...AN ISOLATED WEAK TORNADO IS CERTAINLY POSSIBLE. IT APPEARS THAT HEAVY RAIN/LOCALIZED FLASH FLOOD POTENTIAL WILL INCREASE MONDAY NIGHT AS LOW LEVEL JET INTENSIFIES. INDICATIONS ARE THAT THE SHOWERS/THUNDERSTORMS WILL BE COME MORE WIDESPREAD. PWATS ARE QUITE IMPRESSIVE AT 2+ INCHES ACROSS MUCH OF THE REGION. A FLASH FLOOD WATCH MAY BE NEEDED IN THE NEXT 12 TO 24 HOURS...BUT THOUGH THERE IS MORE TIME TO GET A BETTER FEEL ON THE LOCATION. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... HIGHLIGHTS... * NUMEROUS SHOWERS & THUNDERSTORMS TUESDAY INTO WEDNESDAY WITH HEAVY RAIN AND FLASH FLOOD POTENTIAL * SOME THUNDERSTORMS MAY PRODUCE LOCALLY STRONG TO DAMAGING WINDS ON TUESDAY * WARM AND VERY HUMID TUESDAY * IMPROVING WEATHER WITH DRIER AND LESS HUMID CONDITIONS LATE THIS WEEK HIGH AMPLITUDE MID AND UPPER LEVEL PATTERN CONTINUES TO TAKE SHAPE FROM THE WESTERN ATLANTIC TO THE EASTERN PACIFIC...WITH AN ANOMALOUS TROUGH/CUTOFF COLD POOL MOVING INTO THE GREAT LAKES EARLY THIS WEEK. AS THIS TROUGH EVOLVES INTO THE LONG RANGE TIMEFRAME AND SHIFTS SLOWLY SE...SURFACE WAVES AND TROUGHS WILL SLOWLY MOVE IN THE DEVELOPING SW FLOW AT THE SURFACE AND ALOFT. THE SW FLOW WILL CONTINUE TO PUSH TROPICAL AIR ACROSS THE REGION ALONG WITH PWATS REMAINING IN THE 2.1 TO 2.2 INCH RANGE TUESDAY INTO WEDNESDAY. ALL THIS...ALONG WITH THE SW FLOW IN PLACE...CONTINUES TO SIGNAL THE POTENTIAL FOR FLASH FLOODING AS CELLS TRAIN ACROSS THE REGION. HAVE QPF OF 1 TO 2 INCHES BETWEEN 12Z TUE AND 00Z THU IN THE FORECAST... BUT THAT IS AERIAL COVERAGE. MAY SEE HIGHER AMOUNTS IN LOCALLY HEAVIER SHOWERS/TSTMS. 12Z MODEL CYCLE SHOWING GOOD AGREEMENT IN VERY SLOW PROGRESSION OF THE FRONT TUE NIGHT INTO WED MORNING AS LOW PRES WAVE MOVES ALONG THE FRONT LYING ACROSS THE REGION. NOTING RR QUADRANT OF 120 KT H3 JET PASSING ACROSS THE REGION LATE TUE INTO WED...ALONG WITH GOOD INSTABILITY IN PLACE ESPECIALLY TUESDAY AFTERNOON/EVENING WITH SBCAPES AROUND 1000-1500 J/KG...AND EVEN 0-1 KM HELICITIES UP TO AROUND 100 /M2. WILL SEE CONTINUED CHANCE FOR STRONG TO SEVERE THUNDERSTORMS DURING TUESDAY INTO TUESDAY EVENING. MAY ALSO SEE HAIL AND...AGAIN...CAN NOT RULE OUT A POSSIBLE SPINUP. HOWEVER...THE ONLY LIMITING FACTOR WILL BE SOLAR INSULATION...AS THERE WILL BE A LOT OF CLOUDS AROUND. SPC HAS PLACED PORTIONS OF THE REGION INTO A SLIGHT RISK OF SEVERE STORMS. MODELS NOW IN GOOD AGREEMENT IN SLOWLY PUSHING THE FRONT E DURING WEDNESDAY AS THE H5 TROUGH DEAMPLIFIES. SOME INSTABILITY WILL LINGER ACROSS EASTERN AREAS SO HAVE KEPT MENTION OF TSTMS IN THE FORECAST THERE THROUGH MOST OF WEDNESDAY...AND THERE WILL STILL BE SOME HEAVY RAINERS AS DEWPTS REMAIN IN THE MID-UPPER 60S. SHOULD SEE IMPROVING CONDITIONS WED NIGHT. MODELS AND ENSEMBLES CONTINUE TO SIGNAL DRIER CONDITIONS WITH LOWER HUMIDITIES ON THURSDAY AND FRIDAY AS HIGH PRES RIDGE BUILDS ACROSS THE REGION. EXPECT DAYTIME HIGHS TO RUN CLOSE TO OR JUST SLIGHTLY BELOW SEASONAL NORMALS. AS FOR NEXT WEEKEND...SOME TIMING ISSUES WITH A POSSIBLE TRAILING H5 SHORT WAVE TRYING TO APPROACH LATE SAT OR SUN. HAVE KEPT ONLY SLIGHT CHANCE POPS GOING FOR THIS POSSIBLE FEATURE...THOUGH LOOKS LIKE THE HIGH SHOULD KEEP DRY CONDITIONS IN PLACE...FOR NOW. && .AVIATION /00Z MONDAY THROUGH FRIDAY/...
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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/... TONIGHT...MODERATE CONFIDENCE. CLUSTER OF WEAKENING SHOWERS AND A FEW THUNDERSTORMS WILL WORK ACROSS THE REGION THROUGH 06Z. WHILE SOME SHOWERS MAY AFFECT THE COASTAL PLAIN...BEST SHOT FOR THUNDER WILL BE ACROSS OUR WESTERN ZONES. CAN NOT EVEN RULE OUT LOCALLY GUSTY WINDS IN OUR FAR WESTERN ZONES. OTHERWISE...SCT SHOWERS AND A FEW THUNDERSTORMS WILL REMAIN POSSIBLE BETWEEN 06Z AND 12Z. MAIN UNCERTAINTY TONIGHT IS HOW MUCH LOW CLOUDS AND PATCHY FOG WILL DEVELOP. WILL KEEP THINGS MORE OPTIMISTIC FOR NOW AND SHOW JUST MVFR CONDITIONS DEVELOPING OVERNIGHT IN OUR WESTERN AND SOUTHERN ZONES...EXCEPT IFR CONDITIONS ARE POSSIBLE ACROSS THE CAPE/ISLANDS. TUESDAY AND TUESDAY NIGHT....MODERATE CONFIDENCE. LOW CONFIDENCE ON TIMING...BUT SCATTERED SHOWERS/THUNDERSTORMS EXPECTED PARTICULARLY TUE AFTERNOON AND NIGHT. A FEW OF THE STORMS WILL LIKELY BE STRONG TO SEVERE...POSSIBLE ANYWHERE BUT BEST SHOT MAY BE IN OUR WESTERN AND SOUTHERN ZONES. BIGGEST THREATS TORRENTIAL RAINFALL AND LOCALLY STRONG TO DAMAGING WINDS. AS FOR SKY/VSBYS OUTSIDE OF PRECIPITATION VFR CONDITIONS DOMINATE DURING THE DAY TUE EXCEPT LOWER CONDITIONS MAINLY NEAR SOUTH COAST. CIGS/VSBYS WILL DETERIORATE FROM SOUTH TO NORTH TUE NIGHT WITH MAINLY MVFR TO IFR DEVELOPING FROM SOUTH TO NORTH. KBOS TAF...MODERATE CONFIDENCE IN TAF. KBDL TAF...MODERATE CONFIDENCE IN TAF. MODERATE PROB OF AN ISOLATED THUNDERSTORM THROUGH 05Z. OUTLOOK...TUESDAY THROUGH FRIDAY... TUESDAY...MODERATE TO HIGH CONFIDENCE. EXPECT SHOWERS WITH SCT TO NUMEROUS TSTMS. HEAVY DOWNPOURS LIKELY. WILL SEE AREAS OF MVFR-IFR CONDITIONS IN HEAVIER PRECIP. SOME GUSTY WINDS IN TSTMS LIKELY TUE AFTERNOON/EVENING. PATCHY FOG DEVELOPING TUE NIGHT WITH MVFR-IFR CONDITIONS MAINLY ACROSS CENTRAL-E MA/RI. IMPROVING CONDITIONS ACROSS CT VALLEY TUE EVENING. WEDNESDAY...MODERATE CONFIDENCE MAINLY FOR TIMING. MVFR-IFR CONDITIONS EARLY WED. SHOULD SEE CONDITIONS IMPROVE TO VFR BY MIDDAY ACROSS CT VALLEY AND SLOWLY PUSHING E DURING THE AFTERNOON. MVFR MAY LINGER INTO WED EVENING ACROSS E MA/RI. PATCHY FOG MAY DEVELOP IN NORMALLY PRONE AREAS WITH MVFR-IFR CIGS/VSBYS. THURSDAY...MODERATE CONFIDENCE. ANY LEFTOVER MVFR-IFR CIGS/VSBYS ACROSS E MA SHOULD IMPROVE BY MIDDAY. OTHERWISE...VFR. FRIDAY...MODERATE TO HIGH CONFIDENCE. VFR.
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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. TONIGHT... SOUTHWEST WIND GUSTS OF 25 KNOTS WILL CONTINUE ACROSS MANY OF THE NEAR SHORE WATERS INTO THE FIRST PART OF THE NIGHT. IN ADDITION...LONG SOUTHWEST FETCH MAY BUILD SEAS TO AROUND 5 FEET ACROSS THE OUTER-WATERS. THEREFORE...SCA HEADLINES REMAIN IN PLACE. MAY HAVE SOME FOG DEVELOP LATE TONIGHT. MONDAY AND MONDAY NIGHT... SOUTHWEST WIND GUSTS NOT QUITE AS STRONG ON MONDAY...BUT STILL EXPECT THEM TO GUST TO AROUND 20 KNOTS. THEREFORE...DO NOT THINK WILL NEED NEAR SHORE SCA HEADLINES. ACROSS THE OUTER-WATERS...SEAS MAY BRIEFLY DIMINISH BELOW 5 FEET BUT SHOULD INCREASE AGAIN MONDAY NIGHT. THEREFORE...OPTED TO JUST EXTEND THOSE SCA HEADLINES THROUGH THE NIGHT. MAY HAVE A FEW STRONG TO SEVERE THUNDERSTORMS MONDAY AFTERNOON AND NIGHT. IN ADDITION...MORE FOG MAY DEVELOP MONDAY NIGHT. OUTLOOK...TUESDAY THROUGH FRIDAY... TUESDAY...MODERATE TO HIGH CONFIDENCE. EXPECT S-SW WINDS TO CONTINUE THROUGH TUE NIGHT...WITH SOME GUSTS TO 25 KT. SEAS ON THE OPEN WATERS UP TO 5-6 FT. SHOWERS/SCT TSTMS WITH VERY HEAVY DOWNPOURS AND REDUCED VSBYS. LOW CHANCE OF STRONG WIND GUSTS IN ANY TSTMS. VSBYS ALSO REDUCED IN PATCHY FOG TUE NIGHT. WEDNESDAY...MODERATE CONFIDENCE MAINLY FOR TIMING. COLD FRONT SLOWLY CROSSES THE WATERS. S-SW WINDS CONTINUE TO GUST TO 20 KT. SEAS REMAIN AOA 5 FT ON THE OPEN WATERS. STILL EXPECT HEAVY SHOWERS/SCT TSTMS AND PATCHY FOG REDUCING VSBYS. WILL SEE IMPROVEMENT FROM W-E WED NIGHT...BUT SHOWERS AND PATCHY FOG LINGERS ON THE EASTERN WATERS THROUGH LATE WED NIGHT. THURSDAY AND FRIDAY...MODERATE TO HIGH CONFIDENCE. EXPECT IMPROVING CONDITIONS ON THE EASTERN WATERS EARLY THU...OTHERWISE GOOD VSBYS. W TO NW WINDS DIMINISHING...BUT SEAS MAY LINGER AT AROUND 5 FT ON THE OUTER WATERS THU...WHICH SHOULD SUBSIDE THU NIGHT. WILL SEE LIGHT S TO SW WINDS FRIDAY.
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&& .TIDES/COASTAL FLOODING... VERY HIGH ASTRONOMICAL HIGH TIDES WITH BOSTON AT 12.2 FEET AROUND MIDNIGHT TONIGHT. HOWEVER...SOUTH TO SOUTHWEST WINDS WILL PREVENT ANY PROBLEMS ALONG THE EASTERN MA COAST. ALONG THE SOUTH COAST...WINDS WILL NOT BE STRONG ENOUGH TO CAUSE ANY ISSUES. NO COASTAL PRODUCTS ARE ANTICIPATED. WORST CASE SCENARIO IS VERY MINOR SPLASH OVER WITH NO REAL IMPACTS. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 4 AM EDT MONDAY FOR ANZ231>234-251. SMALL CRAFT ADVISORY UNTIL 11 PM EDT THIS EVENING FOR ANZ230- 236. SMALL CRAFT ADVISORY UNTIL 8 AM EDT MONDAY FOR ANZ235-237. SMALL CRAFT ADVISORY UNTIL 8 AM EDT TUESDAY FOR ANZ250. SMALL CRAFT ADVISORY FROM 11 PM THIS EVENING TO 8 AM EDT TUESDAY FOR ANZ254>256. && $$ SYNOPSIS...FRANK/EVT NEAR TERM...FRANK/EVT SHORT TERM...FRANK LONG TERM...EVT AVIATION...FRANK/EVT MARINE...FRANK/EVT TIDES/COASTAL FLOODING...STAFF

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