Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 220012 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 812 PM EDT THU AUG 21 2014 .SYNOPSIS... SHOWERS CONTINUING ACROSS WESTERN NEW ENGLAND OVERNIGHT INTO FRIDAY...DISSOLVING SOUTHWEST AS HIGH PRESSURE BUILDS IN FROM THE NORTH. HIGH PRESSURE OUT OF THE MARITIMES WILL BRING DRIER AND COOLER CONDITIONS THIS WEEKEND. MILDER TEMPERATURES WILL RETURN EARLY NEXT WEEK. UNSETTLED CONDITIONS MAY RETURN LATE WEDNESDAY OR NEXT THURSDAY AS A FRONT MAY APPROACH OUT OF QUEBEC. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... 755 PM UPDATE... ORGANIZED AREA OF SHOWERS THAT MOVED NE ACROSS N MA/S NH HAS MOVED INTO CENTRAL NH/SW ME BY 23Z...BUT MORE SPOTTY SHOWERS HAVE DEVELOPED BEHIND THIS AREA WHICH CONTINUE OVER CENTRAL/N MA INTO S CENTRAL/SW NH. HEAVIER SHOWERS/SCT TSTMS CONTINUE ACROSS CENTRAL/E NY STATE/N PA INTO EXTREME N NJ. POCKET OF K INDICES INTO THE LOWER 30S HAS REACHED INTO THE AREA WHERE THE SPOTTY SHOWERS HAVE DEVELOPED...AS SEEN ON LATEST SPC MESOANALYSIS...BUT BEST INSTABILITY REMAINS FURTHER W. CURRENT TRENDS APPEAR TO KEEP THIS TO OUR W...FOR NOW. WITH MORE SPOTTY NATURE OF SHOWERS THIS EVENING...HAVE UPDATED FORECAST TO BACK OFF A BIT...BUT THINK THE LEFTOVER AREA OF CONVECTION WILL PUSH IN FROM THE W OVERNIGHT SO TRENDED TO THE PREVIOUS OVERNIGHT FORECAST WHICH LOOKED REASONABLE. DEWPTS INCREASING TO THE LOWER-MID 60S ALONG THE S COAST AND UP INTO THE MID AND LOWER CT VALLEY AT 23Z. KEPT PATCHY FOG IN AS TEMPS FALL BACK CLOSER TO THE INCREASING DEWPTS. REMAINDER OF FORECAST IN PRETTY GOOD SHAPE BUT UPDATED TO BRING CONDITIONS CURRENT. PREVIOUS DISCUSSION... TONIGHT... LOW TRANSITIONS AS AN OPEN WAVE LOW TOWARDS THE SE. ACCOMPANYING MAIN CRUX OF ENERGY YIELDS ASCENT OF AVAILABLE MOISTURE FUELED BY A SW-PLUME OF HIGHER THETA-E AIR WRAPPING AHEAD OF THE LOW /1.5 PWAT AIRMASS/ CONVERGING AGAINST HIGH PRESSURE AND DRY AIR BUILDING SW BELOW H8. THIS YIELDS NW-SE ORIENTED AREAS OF F-GEN FORCING WITHIN THE LOW-LEVELS THAT WILL LIKELY PARENT WITH MID- LEVEL FORCING. A CONSENSUS WEIGHTING OF MODEL GUIDANCE PUTS THE LIKELIHOOD OF SHOWERS TOWARDS THE W/SW FORECAST ZONE WHICH WOULD BE EXPECTED BUT CAN NOT RULE OUT OF CHANCE OF SHOWERS ELSEWHERE. ONLY THE IMMEDIATE E/SE MAY BE SPARED OF WET WEATHER...BUT AM NOT HOLDING MY BREATH. LOW CONFIDENCE OF THUNDER WITH THE STABLE ENVIRONMENT. WILL NEED TO MONITOR FOR FOG AND LOW CLOUDS. HIGHEST CONFIDENCE IS IN AREAS OF STRONG LOW-LEVEL CONVERGENCE AND SHOWERS... ESPECIALLY ACROSS THE HIGHER TERRAIN. YET WITH E-ONSHORE FLOW DRIVING IN HIGHER DEWPOINT AIR...ALONG WITH THE GREATER CAPACITY FOR AREAS TO RADIATE EFFICIENTLY THE LAST COUPLE OF NIGHTS...FOG AND LOW CLOUDS MAY BE POSSIBLE FOR E/SE PORTIONS OF NEW ENGLAND. INCREASING CLOUDS FROM THE W MAY COMPLICATE THE MATTER. WILL GO WITH LOWS AROUND THE UPPER-50S TO LOW-60S WITH THE COOL SPOTS TO THE N/W WHICH BARELY SAW ANY SUN...AND THE E/SE IMMEDIATE INTERIOR. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... FRIDAY... WITH THE LOW SWUNG SE OF THE REGION...CUTOFF ENERGY WRAPS REARWARD AND SE INTO THE REGION INVOKING A HANGING TROUGH. RISING HEIGHTS IN WAKE OF THE TROUGH ALLOW FOR ENHANCED RIDGING OF HIGH PRESSURE SW AHEAD OF WHICH F-GEN FORCING IS MAXIMIZED WITHIN THE LOW-LEVELS. PARENTING WITH MID-LEVEL ASCENT PER CUTOFF ENERGY...THERE IS THE LIKELIHOOD FOR CONTINUED SHOWERY WEATHER OVER SW PORTIONS OF NEW ENGLAND. WILL HOLD WITH LIKELY POPS ACROSS FAR W/SW PORTIONS OF THE FORECAST AREA BENEATH AN ABUNDANCE OF CLOUDS. AM NOT GOING TO GET SPECIFIC WITH THE FORECAST POPS BUT RATHER BROAD BRUSH AN AREA WHERE THERE IS HIGHEST CONFIDENCE. CHANCE TO SLIGHT CHANCE POPS E. COMBINATION OF CLOUDS AND RAIN COULD MAKE FOR A VERY CHILL DAY ESPECIALLY FOR MID- TO LATE-AUGUST. THE DREARY WEATHER COULD YIELD HIGHS AROUND THE LOW- TO MID-60S FOR THE S/W...WARMER E WHERE THE GREATER CHANCE OF SEEING SOME SUNSHINE YET ONLY INTO THE UPPER-60S WITH THE BRISK ONSHORE E-FLOW SURGING INTO INTERIOR NEW ENGLAND. FRIDAY NIGHT... ACTIVITY SHOULD DIMINISH WITH SUBSIDENCE AND DRY AIR BUILDING SW AS HEIGHTS RISE IN RESPONSE TO THE HANGING TROUGH SWINGING S/E. LOW- LEVEL F-GEN FORCING AND MID-LEVEL FORCING SHOULD CONTINUE TO PUSH SW INTO NY/PA AHEAD OF CONTINUED RIDGE ENHANCEMENT. WHILE CONSENSUS WEIGHTING OF MODEL GUIDANCE YIELDS A SLIGHT CHANCE OF SHOWERS FOR S/W PORTIONS OF THE FORECAST AREA...THE LONG E-FETCH OFF THE WATERS LIKELY RESULTING IN MOISTURE POOLING WITHIN THE LOW- LEVELS COULD RESULT IN LOW CLOUDS AND FOG...PERHAPS EVEN DRIZZLE AS THE FLOW UNDERGOES OROGRAPHIC LIFT ALONG THE E-SHORELINE. A TOUGH FORECAST AND A LIKELY COOL AND DREARY NIGHT WITH LOWS GETTING DOWN AROUND THE MID-50S. WITH DEWPOINTS AT SIMILAR VALUES... ANTICIPATING A PLETHORA OF PATCHY DENSE FOG WHERE THE E-FLOW IS LIGHT. && .LONG TERM /SATURDAY THROUGH THURSDAY/... HIGHLIGHTS... * QUIET WEATHER EXPECTED THROUGH MUCH OF THIS PERIOD * MILDER TEMPERATURES WILL RETURN MONDAY AND TUESDAY AS RIDGE TRIES TO BUILD EAST * TIMING OF APPROACHING FRONT BY LATE NEXT WEEK REMAINS UNCERTAIN BLOCKING UPPER LEVEL PATTERN LOOKS TO REMAIN IN PLACE ACROSS NORTH AMERICA AS H5 CUTOFF LOW PRES REMAINS PERSISTENT S OF GREENLAND THROUGH MOST IF NOT ALL OF THE LONG TERM PERIOD. SOME QUESTIONS DO COME INTO PLAY AS THE NORTHERN STREAM UPPER FLOW TRIES TO RECONFIGURE EARLY NEXT WEEK. NW FLOW TRIES TO FLATTEN OUT LATER THIS WEEKEND...THEN UPPER LEVEL RIDGING APPEARS TO BUILD IN BRIEFLY AROUND MONDAY OR TUESDAY. OPERATIONAL MODEL RUN DIFFERENCES MAY BE RESOLVING...BUT STILL SOME TIMING ISSUES CONTINUE LATE NEXT WEEK. THIS LENDS TO LOWER FORECAST CONFIDENCE BEYOND TUESDAY. DETAILS... SATURDAY AND SUNDAY... EXPECT HIGH PRES RIDGING TO CONTINUE TO NOSE IN FROM THE MARITIMES. THE ORIENTATION OF THIS RIDGE WILL KEEP COOL ONSHORE WINDS. SEVERAL OPERATIONAL MODEL SOLUTIONS...MAINLY THE 12Z GFS/ECMWF...TRY TO WORK CLOUDS AND SOME LIGHT PRECIP OFF THE OCEAN DURING SAT WITH LONG FETCH OFF THE GULF OF MAINE. CAN NOT RULE OUT ISOLD SHOWERS THAT MAY MOVE ONSHORE SATURDAY MORNING THEN PUSH W. COULD EVEN SEE SOME LIGHT DRIZZLE AROUND SUNRISE ALONG THE IMMEDIATE COAST. HAVE MENTIONED ONLY SLIGHT CHANCE POPS AT THIS POINT...THOUGH...BECAUSE OF UNCERTAINTY OF HOW MUCH MOISTURE WILL BE REALIZED. ONE CERTAINTY THOUGH IS THAT COOLER THAN NORMAL TEMPS WILL REMAIN WITH THE ONSHORE WINDS THROUGH THE WEEKEND. MONDAY AND TUESDAY... LOOKS LIKE THE MARITIMES RIDGE AXIS TRIES TO PUSH OFFSHORE AS H5 RIDGE PUSHES SE OUT OF ONTARIO AND THE GREAT LAKES AND ACTUALLY BUILDS INTO QUEBEC...A SET UP THAT HAS BEEN RARE THIS SUMMER. WILL REMAIN DRY BUT LOOKS LIKE MILDER TEMPS ON THE HORIZON AS WINDS BACK AROUND TO W AND SW. TEMPS LOOK BE CLOSE TO SEASONAL NORMS FOR LATE AUGUST...THOUGH WILL REMAIN A BIT COOLER ALONG THE S COAST. HUMIDITY WILL ALSO START TO INCREASE DURING TUESDAY. WEDNESDAY AND THURSDAY... WHILE THE LAST SEVERAL ECMWF OP RUNS HAVE BEEN MUCH FASTER THAN THE COUNTERPART GFS...THE 12Z RUN LOOKS MUCH CLOSER WITH ITS SOLUTION IN KEEPING RIDGING ACROSS MOST OF THE EASTERN SEABOARD. ONE BIG FLY IN THE OINTMENT IS THE POSSIBILITY OF A SYSTEM THAT WILL TRY TO MAKE THE TURN AROUND THE SUBTROPICAL RIDGE OFFSHORE...BUT THAT IS HIGHLY UNCERTAIN. WEAK COLD FRONT MAY STILL TRY TO WORK OUT OF QUEBEC LAST WED OR THU...THEN COULD STALL SOMEWHERE ACROSS THE REGION. STILL A TOUGH CALL. ALSO...DEPENDING UPON AVAILABLE MOISTURE AND INSTABILITY...MIGHT SEE SOME SHOWERS AND/OR THUNDERSTORMS IN VICINITY OF THE FRONT. LEANED TOWARD A BLEND OF THE 12Z GFS RUN ALONG WITH GFS/EC ENSEMBLES FOR THIS PORTION OF THE FORECAST. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM...THROUGH FRIDAY NIGHT...MODERATE CONFIDENCE. THROUGH THE OVERNIGHT... EXPECT MAINLY VFR ACROSS E MA INTO RI EARLY. LIGHT ONSHORE FLOW WILL BRING PATCHY FOG...WHILE AREA OF SHOWERS OVER NY STATE WILL MOVE E. WILL SEE CONDITIONS LOWER TO AREAS OF MVFR-IFR. MAY SEE BRIEF PATCHES OF DENSE FOG FROM 06Z-12Z ACROSS THE NORMALLY PRONE VALLEY LOCATIONS. INTO THE FRIDAY INTO FRIDAY NIGHT PERIOD...ANTICIPATING LOW-END VFR CLOUDS MIXED IN WITH MVFR AND SHOWERS TO THE S/W ESPECIALLY ACROSS THE HIGH TERRAIN. E-WINDS CONTINUING WITH A LONG FETCH OFF THE WATERS. TRANSITIONING INTO EVENING...WHILE SHOWERS CONCLUDE... A MAJORITY OF THE TERMINALS MAY BECOME SOCKED IN WITH LOW-CLOUDS AND/OR DENSE FOG. LIKELY TO SEE -DZ ALONG THE E-SHORE TERMINALS TOWARDS SATURDAY MORNING. KBOS TERMINAL...MODERATE CONFIDENCE. WILL HOLD LOW-END VFR FOR A MAJORITY OF THE FORECAST. COULD SEE CONDITIONS GRADUALLY LOWER FRIDAY INTO FRIDAY NIGHT. E-FLOW PERSISTING THROUGHOUT AND INCREASING TOWARDS THE END OF THE PERIOD...THUS LENDING TO CONFIDENCE MORE SO OF MVFR-IFR LOW-CLOUDS OVER DENSE FOG WITH -DZ. KBDL TERMINAL...MODERATE CONFIDENCE. CONDITIONS ANTICIPATED TO LOWER INTO EVENING WITH INCREASING -SHRA CHANCES...MAINLY AFTER MIDNIGHT. MAY REMAIN SOCKED IN AROUND MVFR TO AT LEAST MID MORNING SATURDAY. OUTLOOK...SATURDAY THROUGH TUESDAY... HIGH CONFIDENCE FOR VFR. LOW PROBABILITY OF PATCHY FOG WITH BRIEF LOCAL MVFR-IFR CONDITIONS EACH NIGHT. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT-TERM...THROUGH FRIDAY...MODERATE CONFIDENCE. NE-WINDS INCREASING IN RESPONSE TO INTERIOR LOW PRESSURE SHIFTING SE ACROSS THE WATERS WITH SOME MILD STRENGTHENING AS HIGH PRESSURE BUILDS IN FROM THE N. SUBSEQUENT PRESSURE-GRADIENT MAY YIELD SOME DECENT FETCH WITH GUSTS UP TO 20 KTS TO CAUSE SEAS TO RISE...BUT WILL HOLD AT 4 FEET. FEEL BRISK WINDS WILL DIMINISH FOG POTENTIAL YET LOW CLOUDS AND SHOWERS MAY BE AN ISSUE FOR AREAS TOWARDS THE SW. OUTLOOK...SATURDAY THROUGH TUESDAY... HIGH CONFIDENCE. EXPECT WINDS AND SEAS BELOW SMALL CRAFT CRITERIA THROUGH THE PERIOD. THERE IS A CHANCE THAT E SWELLS COULD BUILD CLOSE TO 5 FT ON THE OUTER WATERS THIS WEEKEND WITH LONG E FETCH...EVEN WITH WIND SPEEDS LESS THAN 15 KT. MAY SEE PATCHY OVERNIGHT FOG REDUCING VISIBILITIES EACH NIGHT. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...SIPPRELL/EVT NEAR TERM...SIPPRELL/EVT SHORT TERM...SIPPRELL LONG TERM...EVT AVIATION...SIPPRELL/EVT MARINE...SIPPRELL/EVT

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