Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 210540 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 140 AM EDT THU AUG 21 2014 .SYNOPSIS... WET WEATHER LIKELY IMPACTING WESTERN AND CENTRAL PORTIONS OF NEW ENGLAND BEGINNING TONIGHT AND CONTINUING THROUGH FRIDAY. DRIER AND COOLER WEATHER FOLLOWS INTO THE WEEKEND. A WARM-UP IS POSSIBLE INTO NEXT WEEK PRIOR TO AN UNSETTLED PATTERN AHEAD OF A FRONTAL BOUNDARY SWEEPING SOUTH OUT OF CANADA. && .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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130 AM UPDATE... MOST FORECAST PARAMETERS ON TRACK. ALTHOUGH SOME RAIN IS JUST BEGINNING TO BREAK THE WRN MOST BORDER OF BOX CWA. INCREASED POPS IN THIS REGION BY JUST A BIT. PREVIOUS DISCUSSION... PREVIOUS DISCUSSION... HEIGHTS FALL AS THE GREAT LAKES LOW SHIFTS INTO THE NE CONUS... TROUGHING TOWARDS THE W-E AXIS OF LOW PRESSURE AND INSTABILITY OFF THE MID-ATLANTIC. LABRADOR RIDGE OF HIGH PRESSURE ALONG WITH DRY AIR AND SUBSIDENCE WILL PERSIST INTO NEW ENGLAND...AHEAD OF WHICH THE COLLISION TOWARDS LOW PRESSURE AND HIGHER THETA-E AIR WILL RESULT IN A DEFINED AREA OF CONVERGENCE ACROSS PA/NY...AND POSSIBLY SE MA. TO THE W...INCREASING THETA-E MOISTURE LOADING THE MID- TO UPPER- LEVELS WILL LIKELY RESULT IN INCREASING AND THICKENING CLOUDS W TO E. BUT STILL A LOT OF DRY AIR TO OVERCOME BELOW H6-7 ESPECIALLY OVER E NEW ENGLAND WITH THE INVERTED RIDGE. NOTING THE WARM FRONT WELL W ACROSS PA/NY ALONG WITH PARENT DYNAMICS AND LOW-LEVEL CONVERGENCE... BEST CHANCES FOR SHOWERS WITHIN AREAS OF DEEP-LAYER ASCENT SHOULD BE NO FURTHER E OF THE CT-RIVER VALLEY. EXPECTING SPRINKLES. ITS LIKELY BETTER ACTIVITY WILL BE WELL N/W PARENT WITH BETTER MOISTURE CONVERGENT ALONG THE NOSE OF THE H925-85 JET INTO THE ADIRONDACKS ON UP INTO ONTARIO/QUEBEC AS DESTABILIZATION CONCLUDES. PREFER CHANCE POPS ONLY INTO THE CT-VALLEY. TO THE SE...TROUGHING SE BACKS LOW PRESSURE AND HIGHER THETA-E AIR OFF THE E-W STALLED FRONT OFF THE MID-ATLANTIC. THE CONVERGENCE OF AIR MASSES ALONG AN INVERTED-TROUGH TO THE AFOREMENTIONED LOW WILL BE THE FOCUS FOR POTENTIAL HEAVY RAIN...EVEN THUNDERSTORMS. MAINLY A WARM-RAIN PROCESS WITH PWATS UP TO 1.75 INCHES. WHILE A CONSISTENT SIGNAL AMONG FORECAST SOLUTIONS...OUTCOMES VARY SLIGHTLY LIKELY DUE TO THE STRENGTH OF INVERTED-RIDGE. WILL GO WITH LIKELY POPS FOR NANTUCKET WITH CHANCE POPS INTO THE CAPE AND SE MA. THE SETUP IS ALREADY COMING TOGETHER SEEN PER IR/VISIBLE SATELLITE...BUT A LOT OF UNCERTAINTY BETWEEN THE STRENGTH OF THE RIDGE AND THE ZONE SETUP OF CONVERGENCE. WRF/NAM THE MOST ROBUST WITH OUTCOMES. 17Z HRRR/18Z RAP HAS ACTIVITY MISSING NANTUCKET. NOT ENOUGH CONFIDENCE TO GO HIGH CATEGORICAL POPS. THICKER CLOUDS ACROSS THE REGION WILL LIMIT RADIATIONAL COOLING. ANTICIPATING A MORE MILD NIGHT OVER MUCH OF THE REGION WITH LOWS AROUND THE UPPER-50S. COOLEST CONDITIONS EXPECTED ACROSS E/SE MA UNDER LIGHT AND VARIABLE WINDS AND THE BETTER CHANCE OF RADIATING OUT...LOWS AROUND THE MID-50S. FOR SUCH AREAS THERE IS ALSO THE POSSIBILITY OF PATCHY GROUND FOG.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM FRIDAY/... THURSDAY INTO THURSDAY NIGHT... CLOSED LOW OUT OF THE GREAT LAKES GRADUALLY WOBBLES INTO NEW ENGLAND THROUGH THE FORECAST PERIOD. THE SYSTEM WEAKENS AS IT TRANSITIONS SW RE-EMERGING ALONG THE W-E FRONTAL BOUNDARY OFF THE MID-ATLANTIC TOWARDS THE BETTER THERMAL-INSTABILITY AXIS. SUBSEQUENT RISING HEIGHTS ALLOWS RIDGING TO BUILD SW THURSDAY NIGHT. WHILE HIGHER THETA-E AIR STREAMS ACROSS THE REGION WITHIN THE MID-LEVELS...E-FLOW WITHIN LOW-LEVELS FROM THE LABRADOR HIGH UNDERCUTS MOISTURE LOADING ALOFT KEEPING CONDITIONS FAIRLY STABLE AND DRY...LIKELY TO ERODE ACTIVITY S AND W. AS THE LOW TRANSITIONS AND WEAKENS...PRECIPITATION ACROSS THE CAPE AND ISLANDS CONCLUDES WITH THE STRENGTHENING INFLUENCE OF THE RIDGE. ENERGY AND MOISTURE PARENT TO THE LOW IS ANTICIPATED TO SWEEP MAINLY ACROSS SW NEW ENGLAND...PERHAPS SW OF A LINE FROM BOSTON TO KEENE NH. WILL KEEP THESE AREAS UNDER CHANCE POPS ACCORDINGLY WITH ASCENT AND LIKELY CONVERGENCE AGAINST THE SW BUILDING RIDGE. WITH THE UNDERCUTTING DRY AND STABLE AIRMASS OFF THE OCEAN WITH THE STRENGTHENING RIDGE LATE...AND CLOUDS THROUGH THE PERIOD LIMITING DESTABILIZATION...NOT EXPECTING ANY THUNDER. HIGHS AROUND THE MID- TO UPPER-70S DURING THE DAY WITH LOWS AROUND THE UPPER-50S. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... HIGHLIGHTS... * QUIET WEATHER EXPECTED THROUGH MUCH OF THE LONG TERM * UNCERTAINTY INCREASES MIDDLE OF NEXT WEEK WITH AN APPROACHING FRONT. MODELS ARE IN GOOD AGREEMENT THROUGH MUCH OF THE LONG TERM. 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 U.S. THE UPPER TROUGH IS RATHER PERSISTENT THOUGH AND EACH MODEL RUN KEEPS THE TROUGH JUST OFFSHORE LONGER AND LONGER. COOLER...LESS SEASONABLE WEATHER IS EXPECTED WHILE HIGH PRESSURE IN QUEBEC WILL KEEP THINGS RELATIVELY DRY. MODELS ARE INDICATING SOME POTENTIAL FOR QPF EACH DAY THROUGH THE WEEKEND BUT GIVEN THE LACK OF ANY FORCING MECHANISM AND VERY LITTLE MOISTURE TO SPEAK OF... THINKING THIS COULD BE CONVECTIVE FEEDBACK RATHER THAN A DEPICTION OF ANYTHING LIKELY TO OCCUR. THE HIGH WILL SINK SOUTH THROUGH THE WEEKEND INTO EARLY NEXT WEEK...EVENTUALLY DROPPING SOUTH AND EAST OF SOUTHERN NEW ENGLAND AND RETURNING US TO A MORE WESTERLY FLOW. LOW PRESSURE IN ONTARIO MAY EVENTUALLY MOVE EASTWARD INTO QUEBEC BRINGING A COLD FRONT THROUGH SOUTHERN NEW ENGLAND WEDNESDAY OR THURSDAY. THIS IS WHERE MODELS START TO DIVERGE A BIT WITH THE ECMWF A BIT QUICKER THAN THE GFS WITH THE APPROACH OF THE FRONT. DEPENDING ON AVAILABLE MOISTURE THIS MAY INITIATE A FEW SHOWERS AND THUNDERSTORMS AHEAD OF THE FRONT. && .AVIATION /06Z THURSDAY THROUGH MONDAY/...
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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 FRIDAY...MODERATE CONFIDENCE. THROUGH 12Z... MAINLY VFR EXCEPT SOME IFR/MVFR POSSIBLE AT SOME SITES ACROSS E MA IN FOG. SOME MVFR CIGS POSSIBLE MAINLY ACROSS ACK AND THE OUTER ARM OF CAPE COD. TODAY AND TONIGHT... MAINLY VFR. EXCEPT FOR ACK...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... MODERATE CONFIDENCE. MAINLY VFR. LOW PROBABILITY OF PATCHY MVFR/IFR FOG EACH NIGHT.
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&& .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT-TERM...THROUGH THURSDAY NIGHT...MODERATE CONFIDENCE. CLOSELY MONITORING THE SE WATERS. MAY SEE A SURGANCE OF RAIN ALONG WITH VISIBILITY IMPACTS DURING THE OVERNIGHT HOURS INTO THURSDAY ALONG WITH AN INCREASE IN E-NE FLOW AS AN AREA OF LOW PRESSURE DEVELOPS WELL OUT TO SEA. QUITE POSSIBLE WIND GUST UP TO 25 KTS...BUT WILL HOLD AROUND 20 KTS FOR NOW. WILL KEEP SEAS AROUND 3 TO 4 FEET. CONDITIONS RELAX INTO FRIDAY MORNING. OUTLOOK...FRIDAY THROUGH MONDAY... MODERATE TO HIGH CONFIDENCE. QUIET BOATING WEATHER IS EXPECTED THROUGH MUCH OF THE PERIOD WITH HIGH PRESSURE ACROSS THE REGION. LOW PROBABILITY OF PATCHY OVERNIGHT FOG LIMITING VISIBILITIES. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...RLG/SIPPRELL NEAR TERM...DOODY/SIPPRELL SHORT TERM...SIPPRELL LONG TERM...RLG AVIATION...KJC/DOODY/RLG MARINE...RLG/SIPPRELL

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