Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 211407 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 1007 AM EDT THU AUG 21 2014 .SYNOPSIS... SHOWERS ACROSS THE WESTERN HALF OF NEW ENGLAND THROUGH EARLY FRIDAY. DRIER AND COOLER WEATHER FOLLOWS THIS WEEKEND. A WARM-UP IS POSSIBLE NEXT WEEK PRIOR TO AN UNSETTLED PATTERN AHEAD OF A FRONTAL BOUNDARY SWEEPING SOUTH OUT OF CANADA. && .NEAR TERM /THROUGH TONIGHT/... 10 AM UPDATE... ONE GIANT MESS. CLOSED LOW OUT OF THE GREAT LAKES TRANSITIONING AS AN OPEN WAVE AS IT WEAKENS. NOTED WELL BY THE PRIOR FORECASTER... LINGERING ENERGY PROVIDING MODEST LIFT THROUGH WEAK DIFFERENTIAL VORTICITY ADVECTION UPON AVAILABLE MOISTURE IS LENDING TO SHOWER ACTIVITY ACROSS THE AREA WITHIN A WEAK FLOW REGIME. THIS DESPITE THE WARM-FRONT HELD UP TO THE W BY DRIER AIR ASSOCIATED WITH A CUT-OFF HIGH PRESSURE CENTER SUSTAINED BY THE NEIGHBORING LOW SE AND WELL OFFSHORE. AIR HAS TO SINK SOMEWHERE. THE WEAK ISENTROPIC FLOW FROM THE SW IS ALLOWING FOR MOISTURE LOADING WITHIN THE MID- LEVELS UP AGAINST THE DRIER AIR CLEARLY EVIDENT WITHIN MESORAP H925-85 FIELDS AND 12Z CHATHAM/PORTLAND SOUNDINGS. PRESENT ACTIVITY APPEARS FOCUSED ALONG THE CONVERGENT NOSE OF A H85 PLUME PER MESORAP AND COLLOCATED WITH STRETCHED MID-LEVEL ENERGY. FEEL THIS AREA OF ACTIVITY WILL LINGER INTO THE EVENING HOURS TOWARDS THE NE ERODING INTO THE DRIER AIR AND GRADUALLY DISSIPATING AS THE OPEN- WAVE LOW AND MAIN CRUX OF ENERGY SHIFTS SE ALLOWING HIGH PRESSURE RIDGING TO BUILD SW. AS TO THE WEAKENING LOW...DURING THE AFTERNOON INTO EVENING ANTICIPATING ATTENDANT ENERGY THAT DEVELOPS OVER PA/NY THIS AFTERNOON TO SHIFT SE TOWARDS BETTER THERMAL/INSTABILITY AXES. HRRR- AND WRF-MODEL SOLUTIONS MAY HAVE THE RIGHT IDEA WITH REGARDS TO TRENDS...BUT THE 21.06Z NAM DOES NOT LOOK TOO BAD WITH THE ENERGY SHIFT TO THE SE. ECMWF/CANADIAN/GFS SHOW A SIMILAR TREND AS TO THE NAM...KEEPING ACTIVITY NE LIGHT BENEATH BUILDING INFLUENCE OF THE HIGH PRESSURE RIDGE. WILL KEEP THE FOCUS OF PRECIPITATION ALONG A NE-SW LINE W OF THE WORCESTER HILLS WITH HIGHEST CHANCES OVER THE CT-VALLEY TO THE W. CONDITIONALLY UNSTABLE ENVIRONMENT WITH MOIST-ADIABATIC PROFILES AND DEEP-LAYER / OROGRAPHIC FORCING. HAVE INSERTED ISOLATED THUNDER. FEEL ONGOING ACTIVITY WILL LIFT NE AND LESSEN INTO THE REALM OF DRIER AIR. HAVE DONE THE BEST TO TIME OUT POPS ACCORDINGLY ALONG WITH AVERAGE PRECIPITATION AMOUNTS AROUND 0.3 INCHES. LOTS OF CLOUD COVER AND WET WEATHER. WILL HOLD TEMPERATURES AROUND THE LOW-70S...QUITE UNSEASONABLE FOR THIS TIME OF YEAR. && .SHORT TERM /TONIGHT INTO FRIDAY/... TONIGHT... SLIGHTLY INCREASED THREAT FOR OVERNIGHT SHOWERS...BUT STILL MAINLY ACROSS THE W THANKS TO SOME LEFTOVER SUBSIDENCE CLOSER TO THE GRADUALLY REBOUNDING INVERTED RIDGE. THE REMNANT VORT MAX FROM AN UPPER LVL DISTURBANCE WILL BE MOVING ACROSS THE AREA THROUGH THE OVERNIGHT HOURS. JET ENERGY THROUGHOUT THE COLUMN IS WEAK AND WHAT IS LEFT OF A SFC WARM FRONT WILL LIKELY HAVE WASHED OUT FOR MOST PART. THEREFORE...IT IS ONLY THE VORT MAX WHICH WILL BE PROVIDING LIFT TO WORK ON THE 1.5 OR LESS PWAT AIRMASS IN PLACE ACROSS THE REGION. DRIER AIR STILL REMAINS MAINLY ACROSS THE E...SO WILL ONCE AGAIN FOCUS MAINLY FROM THE WORCESTER HILLS AND POINTS W FOR THE SHOWERS. NO THUNDER WITH THIS UPDATE...AS THE AIRMASS REMAINS QUITE STABLE THROUGHOUT. GUIDANCE HAS BACKED OFF ON THE QPF BULLSEYES THAT IT WAS SHOWING IN PREVIOUS RUNS FOR THE MOST PART...BUT THESE ARE LIKELY JUST A CONVECTIVE FEEDBACK ISSUE. OTHERWISE...MILD OVERNIGHT MINS WITH A FAIR AMOUNT OF CLOUD COVER. MAY NEED TO ALSO MONITOR ESPECIALLY THE E AND SE COASTLINES FOR FOG AND STRATUS THANKS TO CONTINUED E FLOW AND SLIGHTLY HIGHER DWPTS WITHIN THE MOISTENED COLUMN IN COMPARISON TO PREVIOUS DAYS. FRIDAY... UPPER LVL VORT MAX SLIDES TO THE SE DURING THE MORNING...COMBINING WITH LEFTOVER CUTOFF ENERGY ACROSS ATLANTIC CANADA. WHILE THIS WILL FORM A HANGING TROF WITH AXIS FROM THE MID ATLANTIC THROUGH THE 40/70 BENCHMARK...MID LVL RIDGING WILL THEN BE ABLE TO REGAIN CONTROL INTO WRN NEW ENGLAND. THIS WILL ALSO ALLOW THE INVERTED RIDGE TO BUILD BACK IN ACROSS THE REGION. THIS SHOULD ALLOW SHOWERS ACROSS THE AREA TO GRADUALLY DISSIPATE THROUGH THE DAY AS THE COLUMN DRIES FROM INCREASING SUBSIDENCE. HAVE POPS DIMINISHING THROUGH THE DAY ACROSS THE AREA. IT WILL LIKELY TAKE A BIT MORE TIME FOR THE CLOUDS TO DISSIPATE GIVEN MOISTURE IS LIKELY TO BE TRAPPED BENEATH THE SUBSIDENCE INVERSION AND E FLOW CONTINUES. IN FACT...LOOKS LIKE AN UPPER LVL BACKDOOR COLD FRONT WILL LEAD TO DECREASING H85 TEMPS. HAVE HELD HIGHS BACK...MAINLY IN THE 60S TO AROUND 70. E COASTAL REGIONS ARE LIKELY TO TAKE THE LONGEST TO SEE ANY CLEARING. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... HIGHLIGHTS... * QUIET WEATHER EXPECTED THROUGH MUCH OF THIS PERIOD * UNCERTAINTY INCREASES MIDDLE OF NEXT WEEK WITH AN APPROACHING FRONT 21/00Z MODELS ARE IN GOOD AGREEMENT THROUGH ABOUT TUESDAY. THEN SIGNIFICANT DIFFERENCES ARISE FOR THE LATTER HALF OF NEXT WEEK... MAKING FOR A LOWER CONFIDENCE FORECAST FROM THE MIDDLE OF NEXT WEEK ONWARD. A PERSISTENT UPPER LEVEL TROUGH OVER THE NORTHEAST WILL SLOWLY MAKE ITS WAY EAST...MOVING JUST OFFSHORE THIS WEEKEND AS AN UPPER LEVEL RIDGE TRIES TO PUSH NORTHEASTWARD FROM THE SOUTHERN USA. THIS UPPER TROUGH IS RATHER PERSISTENT THOUGH...WITH EACH SUCCESSIVE MODEL RUN LINGERING THIS TROUGH OVER THE NORTH ATLANTIC LONGER AND LONGER. COOLER...LESS SEASONABLE WEATHER IS EXPECTED WHILE HIGH PRESSURE IN QUEBEC WILL KEEP THINGS RELATIVELY DRY. STILL AGREE WITH THE PREVIOUS FORECASTER...THINKING 21/00Z GUIDANCE CONTINUES TO STRUGGLE WITH CONVECTIVE FEEDBACK INTO EARLY NEXT WEEK. AS SUCH...KEPT A DRY FORECAST ACROSS MOST OF SOUTHERN NEW ENGLAND. A HIGH PRESSURE WILL SINK SOUTH INTO EARLY NEXT WEEK...EVENTUALLY MOVING SOUTH AND EAST OF SOUTHERN NEW ENGLAND AND RETURNING US TO A MORE WESTERLY FLOW. A LOW PRESSURE IN ONTARIO MAY EVENTUALLY MOVE EAST INTO QUEBEC...SWINGING A COLD FRONT THROUGH SOUTHERN NEW ENGLAND WEDNESDAY OR THURSDAY. THIS IS WHERE MODELS START TO DIVERGE MORE SIGNIFICANTLY. THE ECMWF LOOKS A BIT QUICKER THAN THE GFS WITH THE APPROACH OF THIS FRONT...BUT NEITHER IS AS PROGRESSIVE AS THE CANADIAN. WILL TAKE A BLENDED APPROACH WITH THE TIMING FOR NOW. GIVEN THE STRENGTH OF THE SURFACE RIDGE EXPECTED TO BE NEAR THE COAST...WOULD NOT BE OVERLY SURPRISED IF THE ULTIMATE TIMING TURNS OUT TO BE SLOWER THAN THE GFS. DEPENDING ON AVAILABLE MOISTURE...WE COULD SEE SOME SHOWERS AND THUNDERSTORMS AHEAD OF THIS FRONT. && .AVIATION /13Z THURSDAY THROUGH MONDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM...THROUGH FRIDAY...MODERATE CONFIDENCE. TODAY AND TONIGHT... MAINLY VFR. EXCEPT POSSIBLY FOR KACK...MOST OF THE RAIN REMAINS TO THE W THROUGH THE DAY. THEN...BETTER CHANCE FOR SHOWERS ACROSS WRN MA/CT/NH OVERNIGHT ESPECIALLY...WITH OCCASIONAL MVFR CONDITIONS POSSIBLE. SOME LOW MVFR/IFR POSSIBLE MAINLY ACROSS THE E COAST. FRI... CONDITIONS IMPROVE THROUGH THE DAY. SOME MVFR/IFR POSSIBLE IN THE MORNING GIVES WAY TO VFR THROUGH THE DAY...BUT MAY TAKE MOST OF THE DAY ALONG THE E COAST. KBOS TERMINAL...MODERATE CONFIDENCE. MAIN CONCERN IS WHETHER A BRIEF PERIOD OF IFR CONDITIONS MOVE IN EARLY THIS MORNING BRIEFLY...AND THEN RETURNS LATE THU NIGHT. OTHERWISE VFR WITH E FLOW ASSISTED BY SEABREEZES EXPECTED. KBDL TERMINAL...HIGH CONFIDENCE IN TAF. -RA CHANCES BEGIN TOWARDS THURSDAY MORNING ALONG WITH LOW-END VFR CIGS. MVFR CIGS POSSIBLE THOUGH MAINLY TONIGHT...BUT REMAINS LOW-CONFIDENCE AT THIS TIME. OUTLOOK...FRIDAY THROUGH MONDAY... HIGH CONFIDENCE VFR. LOW PROBABILITY OF PATCHY MVFR/IFR FOG 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. LOW PRES WILL GRADUALLY STRENGTHEN OFFSHORE THROUGH THE DAY...BUT THEN MOVE E INTO FRI. A FEW SHOWERS ARE LIKELY TO IMPACT MAINLY THE WATERS S OF THE VINEYARD AND ACK INTO MID DAY UNTIL THE LOW MOVES FURTHER E. THE WEAK LOW PRES WILL ALSO GENERATE A MODEST SWELL...BUT IT SHOULD GENERALLY REMAIN BELOW 4 FT INTO THE DAY ON FRI. WINDS TOO MAY GUST TO ABOUT 15-20 KT AT TIMES OUT OF THE E...BUT SHOULD REMAIN BELOW SMALL CRAFT ADVISORY LEVELS THROUGH THE PERIOD. OUTLOOK...FRIDAY NIGHT THROUGH MONDAY... HIGH CONFIDENCE. QUIET BOATING WEATHER IS EXPECTED FOR MUCH OF THIS PERIOD WITH HIGH PRESSURE ACROSS THE REGION. SEAS COULD APPROACH 5 FT ACROSS THE OUTERMOST SOUTHERN COASTAL WATERS THIS WEEKEND. NOT ENOUGH CONFIDENCE TO ISSUE A SMALL CRAFT ADVISORY THOUGH. LOW PROBABILITY OF PATCHY OVERNIGHT FOG LIMITING VISIBILITIES. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...BELK/DOODY NEAR TERM...SIPPRELL SHORT TERM...DOODY LONG TERM...BELK AVIATION...BELK/DOODY MARINE...BELK/DOODY

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