000 FXUS61 KBOX 250004 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 704 PM EST TUE NOV 24 2009 .SYNOPSIS... LOW PRESSURE DEPARTS THROUGH THE MARITIMES TONIGHT WHILE WEAK HIGH PRESSURE BUILDS FROM THE NORTH ACROSS NEW ENGLAND. LOW PRESSURE OVER THE GREAT LAKES REDEVELOPS ALONG THE MID ATLANTIC COAST THURSDAY AND MOVES UP THE COAST THURSDAY NIGHT...PASSING EAST OF CAPE COD FRIDAY. COOL NW FLOW PREVAILS OVER THE REGION DURING THE WEEKEND. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... LITTLE CHANGE TO THE PREVIOUS THINKING. A LOW LEVEL NE JET AROUND THE PERIPHERY OF LOW PRESSURE OFFSHORE WAS PROVIDING SOME LIGHT SPRINKLES AND DRIZZLE ACROSS PORTIONS OF EAST COASTAL MASSACHUSETTS. THIS IS EXPECTED TO DIMINISH WITH TIME AS THE LOW LEVEL JET WEAKENS AND THE SURFACE LOW DEPARTS. OTHERWISE LOW LEVEL MOISTURE WILL REMAIN TRAPPED UNDERNEATH AN INVERSION OVERNIGHT. LOW PRESSURE WELL EAST OF NEW ENGLAND WILL CONTINUE MOVING NORTHEAST TOWARD NOVA SCOTIA TONIGHT. NORTH TO NORTHEAST FLOW OFF MASSACHUSETTS BAY CONTINUES. SO THE FORECAST WILL KEEP SKIES CLOUDY OR MOSTLY CLOUDY THROUGH THE NIGHT WITH AREAS OF FOG. THE CLOUDS WILL KEEP TEMPERATURES MILDER THAN THE GFS MOS GUIDENCE...WE USED A BLEND THAT FAVORED THE WARMER NAM MOS. MAY STILL BE A FEW DEGREES TOO COLD IN THE NORTHWEST BUT A GENERAL RANGE OF UPPER 30S TO MID 40S LOOKS FINE. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... DEEP INVERSION UNDER THE RIDGE WITH A LINGERING NORTHEAST FLOW UNDERNEATH. GFS MOS IS RATHER OPTIMISTIC WITH A PERIOD OF MOSTLY SUNNY SKIES. BEST CHANCE FOR THIS WOULD BE IN THE CT VALLEY AND SOUTHERN NH. BUT WHILE SOME THINNING OF THE CLOUDS IS WITHIN THE REALM OF POSSIBILITY...LOWER SUN ANGLE AT THIS TIME OF YEAR AND THE MOIST FLOW FAVOR THE MORE PESSIMISTIC FORECAST. WE WILL GO WITH CLOUDY/MOSTLY CLOUDY SKIES WEDNESDAY. UPPER FLOW TURNS SOUTHWEST WEDNESDAY NIGHT BRINGING MORE CLOUDS. UPPER SHORTWAVE AND SUPPORTING JET PASS NORTHWEST OF US DURING THE NIGHT AND COMBINE WITH WEAK ISENTROPIC LIFT TO SUPPORT A FEW SHOWERS. BEST CHANCE WOULD BE ACROSS NEW YORK AND VT/NH. FOR NOW WE WILL USE 20-24 PERCENT POPS WEDNESDAY NIGHT...THE BEST CHANCE SHOULD BE IN NORTHWEST MASS AND SOUTHWEST NH. TEMPS ARE A BLEND OF THE NAM MOS AND GEM VALUES. THIS IS COOLER THAN GFS MOS DURING THE DAY AND NOT AS COLD AS GFS MOS AT NIGHT. && .LONG TERM /THURSDAY THROUGH TUESDAY/... THE MID TO LONG RANGE MODELS AND THE GLOBAL ENSEMBLES ARE IN DECENT AGREEMENT IN THE SYNOPTIC SCALE PATTERN THROUGH FRIDAY...THEN BEGIN TO DIVERGE BY EARLY NEXT WEEK REGARDING HOW MUCH NORTHERN PACIFIC JET STREAM ENERGY DROPS SOUTHEASTWARD INTO THE CONUS MEAN TROUGH AS WELL AS ITS POSITIONING. THURSDAY...NAM/GFS DIFFER REGARDING THE DETAILS WITH DEEPER LAYER MOISTURE ADVERTISED ON THE GFS VERSUS THE NAM. THIS IS PARTLY DUE TO A VARIATION IN THE STRENGTH AND ORIENTATION OF THE ESE LOW LEVEL JET WHICH IS SLIGHTLY MORE POTENT WITH THE GFS/ECMWF THAN THE NAM. ONSHORE FLOW AT THE SURFACE SHOULD BE MODEST. DRY AIR WILL BE PRESENT ABOVE THE H85 LEVEL. HOWEVER GIVEN THE TIME OF YEAR...LOW LEVEL MOISTURE IN TERMS OF CLOUD COVER WILL LIKELY PREVAIL. IN ADDITION WITH SHALLOW/WEAK ISENTROPIC LIFT AVAILABLE BETWEEN H925-H85... SHOULD SEE SOME SPOTTY DRIZZLE AS WELL AS A FEW SCATTERED SHOWERS ACROSS THE AREA...BUT OVERALL THE PRECIPITATION IS EXPECTED TO BE LIGHT. TEMPERATURES ARE EXPECTED TO BE SEASONABLY COOL. THURSDAY NIGHT AND FRIDAY...MODELS IN DECENT AGREEMENT WITH THE OHIO VALLEY UPPER LEVEL LOW CLOSING OFF ACROSS THE NORTHEAST BUT WITH SOME VARIATION IN THE ORIENTATION OF THE 250MB JET STREAK. NAM IS WEAKER AND MORE PROGRESSIVE WHILE THE GFS/ECMWF DEEPEN THE LOW FASTER. THE NAM APPEARS TO BE A BIT OF AN OUTLIER AND ALSO GIVEN THE HIGH AMPLITUDE OF THE TROUGH WILL LEAN TOWARDS THE SLOWER 12Z GFS/00Z ECMWF SOLUTIONS AT THIS TIME WHICH FOLLOWS THE CONSENSUS OF THE GFS ENSEMBLE CLUSTERING. CYCLOGENESIS WILL OCCUR IN RESPONSE TO THE APPROACHING H5 JET STREAK JUST OFFSHORE WHICH WILL BRING SUBTROPICAL MOISTURE NORTHEAST FROM THE GULF OF MEXICO. LOW LEVEL CONVERGENCE WILL INCREASE AS WELL FROM THE ATLANTIC OCEAN. MID LEVEL FRONTOGENESIS IS EXPECTED AS AN INVERTED TROUGH DEVELOPS. THE FOCUS AREA OF HEAVIEST PRECIPITATION REMAINS A BIT UNCERTAIN AT THIS TIME...DEPENDING ON THE EXACT TRACK AND INTENSITY OF THE SURFACE LOW...BUT OVERALL WILL HAVE SHOWERS LIKELY IN THE FORECAST. IT APPEARS THE TIMING WOULD BE MOST LIKELY LATE THURSDAY NIGHT THROUGH FRIDAY EVENING. FRIDAY NIGHT THROUGH SATURDAY...H7 TROUGH CLEARS THE AREA FRIDAY NIGHT...WITH A PERIOD OF WINDY CONDITIONS AND INCREASING SUBSIDENCE BEHIND THE DEPARTING AND INTENSIFYING CANADIAN MARITIMES LOW. RAIN SHOWERS COULD MIX WITH A PERIOD OF WET SNOW BEFORE ENDING FRIDAY NIGHT AS COLDER AIR USHERS INTO THE REGION. ECMWF/GFS INDICATE WNW BLYR WINDS 35-40KT IN THE BOUNDARY LAYER...POSSIBLY STRONGER IF THE LOW DEEPENS FASTER AS THE 12Z ECMWF INFERS...SO MAY REACH MARGINAL WIND ADVISORY CRITERIA FOR A TIME. OTHERWISE...DRIER CONDITIONS DEVELOPING FRIDAY NIGHT AND SATURDAY WITH TEMPERATURES SLIGHTLY BELOW SEASONAL NORMS. SUNDAY...RIDGING DEVELOPS ALOFT WITH DRY WESTERLY FLOW AT THE SURFACE. WINDS WILL SUBSIDE. EXPECT HIGHS AROUND OR SLIGHTLY ABOVE SEASONAL NORMS. MONDAY AND TUESDAY...LONG RANGE MODELS AND GLOBAL ENSEMBLES ARE IN SPLIT CAMPS REGARDING THE POSITIONING OF THE CONUS MEAN TROUGH AS PREVIOUSLY MENTIONED. THE 12Z OPERATIONAL GFS IS MORE PROGRESSIVE WHILE THE ECMWF EVOLUTION IS SLOWER...KEEPING SURFACE HIGH PRESSURE AND DRY CONDITIONS OVER THE AREA. TEND TO PREFER THE SLOWER ECMWF AT THIS POINT GIVEN TELECONNECTION TRENDS...BUT FOR NOW WILL GO WITH A COMPROMISE AND BRING CHANCE POPS IN MONDAY NIGHT AND TUESDAY...AND WILL UNDERCUT MEX POPS A BIT. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... MVFR CIGS WILL PERSIST INTO THIS EVENING KBOS-KBDL-KMHT BUT WILL LOWER BACK TO IFR TONIGHT DUE TO PERSISTENT N FLOW WITH PLENTY OF LOW LEVEL MOISTURE. IFR/LIFR EXPECTED KPVD TO KFMH/KHYA/KACK WITH SLOWLY DIMINISHING WINDS. CIGS EXPECTED TO REMAIN MVFR THROUGH MUCH OF WED...THOUGH KBDL/KBAF COULD LIFT TO VFR BY MIDDAY. IFR CIGS ACROSS RI AND SE MA SHOULD IMPROVE TO MVFR WED AFTERNOON. KBOS...CIGS EXPECTED TO REMAIN MVFR BUT BELOW 1500 FT THROUGH THIS EVENING. SMALL CHANCE CIGS COULD BRIEFLY LIFT TO 2000 FT BEFORE 23Z BUT THIS SEEMS UNLIKELY BASED UPON SATELLITE TRENDS. CIGS 005-010 WILL REMAIN IN PLACE S OF KBOS. OUTLOOK /THURSDAY THROUGH SUNDAY/... THU...VFR WITH AREAS MVFR CIGS GENERALLY 2000-3000 FT. THU NIGHT AND FRI...WIDESPREAD MVFR CIGS AND VSBYS WITH AREAS OF IFR CONDITIONS FRI IN SHOWERS AND FOG PATCHES. FRI NIGHT AND SAT...IMPROVEMENT TO VFR. STRONG SURFACE WINDS WITH W WIND GUSTS TO 35 KT AND ASSOCIATED MECHANICAL TURBULENCE. SUN...VFR WITH DIMINISHING WINDS. && .MARINE... WINDS GUSTING NEAR GALE AT NANTUCKET AIRPORT BUT BUOYS AND OTHER MARINE SOURCES ARE MAINLY AROUND 30-32 KNOTS. WITH THE GALE CENTER NOW PULLING AWAY FROM NEW ENGLAND AND WITH WINDS AT 2000-4000 FEET EXPECTED TO DIMINISH THIS EVENING...SURFACE WINDS SHOULD ALSO START TRENDING TO LOWER VALUES. WINDS SHOULD DIMINISH BELOW 25 KNOTS DURING THE NIGHT. SEAS WILL REMAIN ROUGH THIS EVENING...BUT DIMINISH BELOW 5 FEET ON THE SOUNDS DURING THE NIGHT. SEAS 5 FEET OR HIGHER SHOULD CONTINUE ON THE OUTER WATERS THROUGH WEDNESDAY AND WEDNESDAY NIGHT. THE INNER BAYS AND SOUNDS WILL LOSE THE 25 KNOT WINDS BUT MAINTAIN ROUGH SEAS UNTIL SUNRISE...SO CONTINUE HEADLINES THERE UNTIL MORNING. ROUGH SEAS WILL LINGER ON THE OUTER WATERS THROUGH WEDNESDAY NIGHT...SMALL CRAFT HEADLINES ARE EXTENDED TO COVER THROUGH THAT TIME. OUTLOOK /THURSDAY THROUGH SUNDAY/... THU...LIGHT ONSHORE FLOW. WINDS EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY CRITERIA BUT PERSISTENT E SWELL WILL BRING 4 TO 6 FOOT SEAS ACROSS THE OUTER WATERS. THU NIGHT AND FRI...NE WINDS INCREASE THEN SHIFT TO W LATE FRIDAY. WINDS MAY GUST TO 25 KT AHEAD OF THE LOW THU NIGHT AND BEHIND THE LOW FRIDAY. COULD BE STRONGER IF THE LOW INTENSIFIES MORE QUICKLY. SEAS 4 TO 7 FT ACROSS THE OUTER WATERS. FRI NIGHT AND SAT...W WINDS STRENGTHEN TO GALE FORCE BEHIND THE DEPARTING LOW WHICH WILL INTENSIFY ACROSS THE CANADIAN MARITIMES. W WINDS COULD GUST TO 40 KT OR MORE. SEAS BUILD TO 7 TO 10 FT. SUN...DIMINISHING W WINDS WITH LINGERING GUSTS TO 25 KT. SEAS 4 TO 6 FT ACROSS THE OPEN WATERS. PERSISTENT ONSHORE FLOW AND 6 TO 8 FOOT EAST SWELLS COULD LEAD TO MINOR BEACH EROSION ACROSS THE EASTERN MASSACHUSETTS COAST. WE COULD SEE A SURGE OF 1.0 TO 1.5 FT DURING THE TIMES OF HIGH TIDE THURSDAY NIGHT THROUGH FRIDAY BUT ASTRONOMICAL TIDES ARE QUITE LOW. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 9 AM EST WEDNESDAY FOR ANZ231>235- 237. SMALL CRAFT ADVISORY UNTIL 6 AM EST THURSDAY FOR ANZ250-251- 254>256. && $$ SYNOPSIS...WTB NEAR TERM...WTB/STRAUSS SHORT TERM...WTB LONG TERM...STRAUSS AVIATION...WTB/STRAUSS MARINE...WTB/STRAUSS