Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 312122 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 522 PM EDT FRI JUL 31 2015 .SYNOPSIS... SEASONABLY WARM THIS WEEKEND WITH A RISK OF SCATTERED SHOWERS AND WIDELY SCATTERED THUNDERSTORMS MID TO LATE SATURDAY AFTERNOON. WARM CONDITIONS WILL CONTINUE INTO EARLY NEXT WEEK. THERE WILL BE THE THREAT OF SHOWERS AND THUNDERSTORMS LATE MON INTO TUE. ANOTHER WEAK COLD FRONT MOVES THROUGH ON WEDNESDAY. LOW PRESSURE MOVING ALONG THE FRONT STALLED NEAR THE S COAST WILL BRING SOME SHOWERS AND ISOLATED THUNDERSTORMS WEDNESDAY NIGHT AND THURSDAY MAINLY ACROSS SOUTH COASTAL AREAS. HIGH PRESSURE OUT OF CENTRAL CANADA LOOKS TO BRING DRIER AND COOLER CONDITIONS LATE NEXT WEEK. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... ALTHOUGH EVIDENCE OF A WEAK SHORT WAVE...THINK ACTIVITY NOW OVER WESTERN NY WILL NOT BE ABLE TO OVERCOME DRY AIR OVER OUR REGION ALONG WITH ANY FORCING OF CONSEQUENCE STAYING NORTH. THUS...HAVE GONE WITH A DRY FORECAST THROUGH TONIGHT. HAVE STAYED WITH A MODEL CONSENSUS FOR TEMPERATURES TONIGHT. DEWPOINTS GIVE SOME SPACE FOR RADIATIONAL COOLING BUT STARTING THE DESCENT AT RATHER HIGH VALUES...UPPER 80S MOST AREAS...AND SO EXPECT LOWS NEAR TO A LITTLE ABOVE AVERAGE FOR TONIGHT. WINDS HAVE BEEN A BIT GUSTY OVER LAND TO 25 TO 30 MPH BUT SHOULD SETTLE DOWN FAIRLY QUICKLY WITH SUNSET. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... MAIN ISSUE FOR THIS TIME PERIOD IS WHETHER OR NOT WE WILL SEE ANY CONVECTION SATURDAY AFTERNOON/EARLY EVENING. A SHORT WAVE TROF AND RELATIVELY WEAK SURFACE COLD FRONT WILL HAVE A MARGINALLY UNSTABLE AIR MASS TO WORK WITH AND FAIRLY NOTABLE VERTICAL WIND SHEAR OF 40 TO 50 KT. THINK THE NAM IS A LITTLE TOO ROBUST WITH ITS INSTABILITY AS IS A COMMON BIAS BUT NONETHELESS OTHER MODELS...INCLUDING THE HIGHER RESOLUTION ARW AND NMM...PROVIDE AT LEAST SOME SUPPORT FOR WIDELY SCATTERED THUNDERSTORMS. THINK WE MAY LACK SUFFICIENT MOISTURE BUT MOST MODELS DO TRY TO PRODUCE AT LEAST A LITTLE QPF. RELATIVELY COOL 500 MB TEMPERATURES ARE A CONCERN. EXPERIENCE HAS SHOWN THAT WE HAVE A TENDENCY TO OVERPRODUCE AT THIS TIME OF YEAR WITH COLD TEMPERATURES ALOFT. THE VERTICAL WIND SHEAR OF 40 TO 50 KT SUGGESTS THAT ITS NOT OUT OF THE QUESTION THAT ONE OR TWO STORMS...IF THEY ARE ABLE TO GET GOING...COULD PRODUCE LOCALLY STRONG WIND GUSTS AND HAIL. ALTHOUGH SOME VARIATION FROM MODEL TO MODEL...INCLINED TO THINK BEST INSTABILITY AND CHANCE FOR CONVECTION WILL BE ACROSS SE MA...S CENTRAL MA ALONG AND S OF THE MASS PIKE...NORTHERN RI AND NE CT. HAVE GONE WIDELY SCATTERED TO SCATTERED. THIS IS A RELATIVELY LOW CONFIDENCE SITUATION AND FOR THE MOST PART SATURDAY SHOULD BE A DRY SUMMER DAY WITH TEMPERATURES IN THE 80S. HAVE GONE WITH MODEL CONSENSUS FOR SATURDAY TEMPERATURES. && .LONG TERM /SUNDAY THROUGH FRIDAY/... HIGHLIGHTS... * LOW RISK FOR A FEW STRONG STORMS MONDAY AFTERNOON/EVENING * LOW PRESSURE MAY MOVE ALONG STALLED FRONT OFF S COAST AROUND LATE WED OR THU * PATTERN CHANGE BY LATE WEEK TO BRING BELOW NORMAL TEMPS OVERVIEW AND MODEL PREFERENCES... MEDIUM RANGE MODEL GUIDANCE IN PRETTY GOOD AGREEMENT THROUGH AROUND MID WEEK...THEN SOLUTION SPREAD WORKS IN WITH TIMING OF NEXT COLD FRONT AND ITS HANDLING OF POSSIBLE SHORT WAVE LATE THU- NEXT FRI OR IF HIGH PRES BUILDS OUT OF CENTRAL CANADA BRINGING COOLER CONDITIONS. WITH FAST H5 FLOW CONTINUING AS VORTEX SPINS ACROSS EASTERN ONTARIO/QUEBEC...SHORT WAVES WILL ROTATE AROUND THE BASE OF THIS VORTEX BRINGING CHANCE FOR PRECIP EVERY OTHER DAY OR SO. ONE STRONGER SHORT WAVE LOOKS TO MOVE ACROSS LATE MON/MON NIGHT. ANOTHER FRONT MOVES ACROSS DURING WED/WED NIGHT...THEN MAY STALL S OF NEW ENGLAND AS THE TROUGH AXIS MOVES INTO NEW ENGLAND AROUND THAT TIME. SOME QUESTION TOWARD THE END OF NEXT WEEK AS TO WHETHER LOW PRES OUT OF THE OHIO VALLEY MOVES ALONG THE FRONT AND HOW FAR N THE PRECIP FROM THIS LOW WILL PUSH INTO THE REGION. BY THE END OF NEXT WEEK... LOOKS LIKE NW FLOW REINFORCES AS RIDGING BUILDS ACROSS THE PLAINS STATES INTO CENTRAL CANADA. THIS MAY MEAN A COOLING TREND AS WE HEAD INTO NEXT WEEKEND. DETAILS... SUNDAY...MODERATE TO HIGH CONFIDENCE. WEAK RIDGE BUILDS ACROSS THE REGION WITH W-SW FLOW REMAINING IN PLACE. AT THIS POINT...LOOKS LIKE THERE IS JUST ENOUGH SUBSIDENCE ALONG WITH LOWER DEWPTS /IN THE UPPER 50S TO LOWER 60S AWAY FROM THE S COAST/ TO PRECLUDE ANY DIURNAL CONVECTION. WILL CONTINUE TO SEE LIGHT W-SW WIND FLOW. WILL REMAIN WARM THOUGH WITH A MAINLY OFFSHORE FLOW AS TEMPS TOP OFF IN THE MID TO UPPER 80S. LOWS WILL BE MAINLY IN THE 60S...THOUGH WILL HOVER AROUND 70 ALONG THE IMMEDIATE COAST. MONDAY AND TUESDAY...MODERATE CONFIDENCE. RATHER STRONG H5 SHORT WAVE APPROACHES IN THE TRANSITIONING W-SW UPPER FLOW AS LONG WAVE TROUGH REORIENTS ACROSS THE GREAT LAKES. NOTING DECENT DIFFLUENCE ALOFT AHEAD OF THE SHORT WAVE...BUT TIMING IS IN QUESTION IN THE FAST FLOW. FOR NOW...LOOKS LIKE BEST INSTABILITY MOVES INTO WESTERN AREAS AROUND 18Z OR SO...THEN SHIFTS E MONDAY EVENING. NOTING TOTAL TOTALS IN THE LOWER 50S...K INDICES IN THE LOWER-MID 30S AND CAPES INCREASING TO 1000-1500 J/KG THOUGH THIS IS OUT AHEAD OF MAIN CONVECTION. ALSO SEE TQ VALUES AROUND 20 WHICH MAY KEEP ELEVATED CONVECTION GOING INTO MON NIGHT. WINDS AT H925 ARE SW AT 25-35 KT LATE MON/MON EVENING AS FRONT APPROACHES AND AROUND 35 KT AT H85... WHICH IS PRETTY GOOD SUPPORT FOR SOME STRONG STORMS. IF ANY DO OCCUR FEEL BEST SHOT WILL BE ACROSS CENTRAL AND WESTERN AREAS...THOUGH STILL RATHER LOW CONFIDENCE AT THIS POINT. SPC DID MENTION SOMETHING IN THEIR DAY 4-8 DISCUSSION...BUT LOOKS LIKE THINGS MAY COME TOGETHER A BIT FARTHER W EARLIER ON MON. SHOWERS WILL LINGER THROUGH MON NIGHT THOUGH LOOKS LIKE CONVECTION SHOULD WEAKEN AFTER MIDNIGHT AS COLD FRONT CROSSES. TUESDAY LOOKS TO BE A SOMEWHAT BETTER DAY...THOUGH UPPER LEVEL ENERGY AND MARGINAL INSTABILITY MAY KEEP SLIGHT CHANCE FOR SHOWERS/TSTMS DUE TO DIURNAL HEATING AS TOTAL TOTALS HANG AT AROUND 50S. EXPECT ANOTHER WARM DAY WITH HIGHS IN THE LOWER-MID 80S. WEDNESDAY AND THURSDAY... HIGH CONFIDENCE IN TEMPS...LOW CONFIDENCE IN PRECIP/TRACK. CUTOFF LOW OVER QUEBEC SHIFTS SLOWLY E DURING THIS TIMEFRAME... PUSHING ITS ASSOCIATED LONG WAVE TROUGH ALONG WITH IT. ANOTHER SHORT WAVE WORKS AROUND BASE OF THIS TROUGH LATE WED INTO THU. STILL SOME QUESTION AS TO TIMING AND PLACEMENT OF THIS SHORT WAVE AND ITS ASSOCIATED SURFACE FEATURE. GFS LOOKS MOST ROBUST IN BRINGING STRONG VORT MAX TOWARD THE S COAST...WHILE GGEM/ECMWF KEEP MOST ENERGY A BIT FURTHER N. FOR NOW...ONLY MENTIONED SLIGHT CHANCE FOR DIURNAL PRECIP FROM ABOUT THE MASS PIKE NORTHWARD ON WED AS COLD FRONT MOVES THROUGH THEN STALLS CLOSE TO OR JUST S OF THE SOUTH COAST TO THE OHIO VALLEY. MODEL SUITE ALL SIGNALING DEVELOPMENT OF LOW PRES ALONG STALLED FRONT ACROSS THE OHIO VALLEY/MID ATLC STATES WED NIGHT...THEN TRIES TO PUSH N INTO SOUTHERN PORTION OF THE REGION TOWARD DAYBREAK THU. MODELS HAVING TROUBLE DENOTING HOW FAR N THIS PRECIP WILL PUSH. FOR NOW...HAVE KEPT BEST CHANCE ACROSS N CT/RI/SE MA DURING THU. ALSO NOTING SOME INSTABILITY...SO DID MENTION SLIGHT CHANCE FOR THUNDER. BY THU...LOWER H5 HEIGHTS WILL BRING COOLER TEMPS. EXPECT HIGHS ONLY IN THE UPPER 70S TO AROUND 80. FRIDAY...LOW CONFIDENCE. A LOT OF QUESTION WITH SURFACE AND UPPER LEVEL FEATURES AND HOW THE WILL INTERACT AS THEY APPROACH THE REGION. 12Z GFS VS. ECMWF YIELDED VERY DIFFERENT SOLUTIONS...SO LEANED TOWARD THE GEFC/ECENS SOLUTIONS. CURRENT FORECAST HAS LEFTOVER PRECIP MOVING OFFSHORE AS HIGH PRES BUILDS SE OUT OF CENTRAL CANADA. THIS WILL BRING COOLER TEMPS. HOWEVER...NOT A LOT OF CONFIDENCE WITH THIS CHANGING PATTERN. && .AVIATION /21Z FRIDAY THROUGH WEDNESDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH SATURDAY/...HIGH CONFIDENCE EXCEPT ONLY LOW TO MODERATE CONFIDENCE IN DEVELOPMENT OF ANY CONVECTION SATURDAY AFTERNOON. REST OF THIS AFTERNOON...VFR FOR ALL TERMINALS. TONIGHT...VFR WITH PERHAPS JUST A LITTLE PATCHY FOG IN A FEW INTERIOR LOW SPOTS. SATURDAY...VFR BUT RISK OF WIDELY SCATTERED THUNDERSTORMS IN THE AFTERNOON...WITH HIGHEST CHANCE ACROSS INTERIOR SE MA...S CENTRAL MA ALONG AND S OF MASS PIKE...NORTHERN RI AND NE CT. KBOS TERMINAL...HIGH CONFIDENCE IN TAF. SFC WIND SHOULD DIMINISH TOWARD SUNSET. FOR SATURDAY AFTERNOON...WIDELY SCATTERED TSTMS MAY DEVELOP ACROSS BOS AREA LATE SATURDAY AFTERNOON BUT NOT ENOUGH CONFIDENCE TO REFLECT IN TAF AT THIS TIME. KBDL TERMINAL...HIGH CONFIDENCE IN TAF. ISOLATED THUNDERSTORM NOT OUT OF THE QUESTION SATURDAY AFTERNOON. OUTLOOK /SUNDAY THROUGH WEDNESDAY/... SUNDAY...MODERATE TO HIGH CONFIDENCE. VFR. MAY SEE BRIEF MVFR- IFR CONDITIONS IN LATE NIGHT PATCHY FOG IN SOME OF THE TYPICALLY PRONE INLAND AREAS. MONDAY-TUESDAY...MODERATE CONFIDENCE. MAINLY VFR. ANY LEFTOVER PATCHY FOG DISSIPATES BY MID MORNING MON. SCT SHOWERS/TSTMS MOVE INTO CT VALLEY MON AFTERNOON...THEN SHIFT E BY MON EVENING. BEST CHANCE FOR ANY GUSTY WINDS WILL BE FROM ABOUT KFIT-KORH-KIJD WESTWARD AFTER 18Z TO AROUND 02Z-03Z. PATCHY LATE NIGHT FOG WITH LOCAL MVFR CONDITIONS POSSIBLE. WIDELY SCT SHOWERS/ISOLD TSTM POSSIBLE DURING TUE. WEDNESDAY...MODERATE CONFIDENCE. MAINLY VFR. ISOLD SHOWERS POSSIBLE LATE MORNING/AFTERNOON FROM ABOUT THE MASS PIKE NORTHWARD. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT-TERM /THROUGH SATURDAY NIGHT/...MODERATE CONFIDENCE. TONIGHT...TRANQUIL CONDITIONS WITH GENERALLY GOOD VSBY AND LIGHT SW WIND. SATURDAY AND SATURDAY NIGHT...ENOUGH OF A SW FETCH AHEAD OF A COLD FRONT THAT SEAS ARE PROJECTED TO BUILD TO NEAR 5 FEET ACROSS THE OUTER S COASTAL WATERS. THINK THAT THE WAVE GUIDANCE IS OVERDONE BUT NONETHELESS PROBABLY STILL ENOUGH FETCH AHEAD OF A WEAK COLD FRONT TO GET THOSE 5 FOOT SEAS AND HENCE HAVE RAISED A SMALL CRAFT ADVISORY FROM LATE SATURDAY MORNING TO SATURDAY NIGHT. ALSO...ISOLATED THUNDERSTORMS ARE POSSIBLE SATURDAY EVENING AHEAD OF THE COLD FRONT. OTHER ISSUE FOR SATURDAY AFTERNOON IS THAT THERE LOOKS TO BE ENOUGH IN WAY OF INCOMING SEAS TO PRODUCE POCKETS OF MODERATE RIP CURRENT ACTIVITY ACROSS THE EXPOSED SOUTHERN RI SHORELINE...ESPECIALLY BLOCK ISLAND. OUTLOOK /SUNDAY THROUGH WEDNESDAY/...MODERATE CONFIDENCE. EXPECT GENERALLY W-SW WINDS IN PLACE. MAY SEE GUSTS UP TO 20 KT MAINLY ACROSS THE OPEN WATERS FROM CAPE COD SOUTHWARD FROM SUNDAY NIGHT ONWARD. SEAS ALSO BUILD UP TO 5-6 FT...HIGHEST ON THE SOUTHERN OUTER WATERS. WILL SEE MAINLY GOOD VSBY AND DRY CONDITIONS. MAY SEE LOCAL PATCHY FOG MON/MON NIGHT ALONG WITH LOW RISK FOR SHOWERS/ISOLD T-STORMS. LOCALLY REDUCED VSBYS POSSIBLE. WINDS SHIFT TO W AND DIMINISH WED. SEAS UP TO 5 FT LINGER WED... THEN SHOULD SUBSIDE WED NIGHT. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 11 AM SATURDAY TO 2 AM EDT SUNDAY FOR ANZ255-256. && $$ SYNOPSIS...EVT/THOMPSON NEAR TERM...THOMPSON SHORT TERM...THOMPSON LONG TERM...EVT AVIATION...EVT/THOMPSON MARINE...EVT/THOMPSON

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