Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 202009 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 409 PM EDT WED AUG 20 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 THURSDAY MORNING/... INTO THIS EVENING... DIURNAL CUMULUS WILL DISSIPATE WITH THE CONCLUSION OF DAYTIME MIXING. HIGH CLOUDS WILL LIKELY BEGIN TO FILTER INTO THE REGION FROM THE CONVECTION ONGOING OVER NY/PA. ALSO MONITORING THE AREA SE OF NANTUCKET WHERE LOW-LEVEL CONVERGENCE OF HIGHER THETA-E AIR IS LIKELY ONGOING LENDING TO SOME LOW CLOUDS. EXPECT THIS ACTIVITY TO FILTER ACROSS THE ISLAND TOWARDS THE CAPE AS WE GO INTO THE EVENING HOURS. WILL SEE WINDS BECOME LIGHT AND VARIABLE. TONIGHT... 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. SLIGHT CHANCE OF THUNDER WITH AT LEAST A LITTLE INSTABILITY PRESENT. 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. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/... 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 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 /20Z WEDNESDAY THROUGH MONDAY/... 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. VFR. SEA-BREEZES CONTINUE...BECOMING LIGHT/VRB OVERNIGHT BEFORE PREVAILING E/SE THURSDAY INTO THURSDAY NIGHT. LOW-END VFR CIGS SLOWLY BUILDING E ALONG WITH -RA CHANCES TOWARDS IJD-ORH-AFN. WILL ALSO NEED TO WATCH SE MA FOR POTENTIAL +RA AND MVFR-IFR IMPACTS BEGINNING AFTER MIDNIGHT THURSDAY. CONDITIONS BEGIN TO IMPROVE CLOSER TO FRIDAY MORNING. KBOS TERMINAL...HIGH CONFIDENCE IN TAF. E/SE FLOW PREVAILS. EXPECT CONDITIONS NO LOWER THAN LOW-END VFR CIGS. -RA CHANCES MINIMAL. KBDL TERMINAL...HIGH CONFIDENCE IN TAF. -RA CHANCES BEGIN TOWARDS THURSDAY MORNING ALONG WITH LOW-END VFR CIGS. MVFR CIGS POSSIBLE THOUGH LOW-CONFIDENCE AT THIS TIME. OUTLOOK...FRIDAY THROUGH MONDAY... MODERATE CONFIDENCE. MAINLY 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 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...SIPPRELL SHORT TERM...SIPPRELL LONG TERM...RLG AVIATION...RLG/SIPPRELL MARINE...RLG/SIPPRELL

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