Issued by NWS Boston, MA
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-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --000 FXUS61 KBOX 222341 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 641 PM EST SUN NOV 22 2009 .SYNOPSIS... HIGH PRESSURE ACROSS THE SAINT LAWRENCE VALLEY WILL MOVE EAST OF NOVA SCOTIA MONDAY. A LOW PRESSURE WILL APPROACH OUR REGION MONDAY INTO TUESDAY. WEAK HIGH PRESSURE WILL BRIEFLY VISIT THE AREA TUESDAY NIGHT INTO WEDNESDAY NIGHT...BEFORE ANOTHER LOW PRESSURE SYSTEM TRACKS UP THE COAST LATER THURSDAY AND FRIDAY BRINGING THE CHANCE FOR RAIN. COLD AND BLUSTERY WEATHER IS FORECAST BEHIND THE LOW ON SATURDAY...WITH DRIER WEATHER FINISHING OFF NEXT WEEKEND. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... HIGH PRESSURE ACROSS THE SAINT LAWRENCE VALLEY THIS AFTERNOON WILL MOVE TO NOVA SCOTIA OVERNIGHT. THIS WILL ALLOW NORTHEAST WINDS TO BECOME MORE FROM THE EAST BY DAYBREAK. CURRENTLY WATCHING AN EXPANSIVE AREA OF MARINE STRATUS ACROSS THE GULF OF MAINE AND GEORGES BANK. LATEST VISIBLE IMAGERY SHOWING SOME OF THESE CLOUDS ARE DIURNAL IN NATURE...AND SHOULD BRIEFLY DISSIPATE AROUND SUNSET...MAINLY ACROSS THE INTERIOR. HOWEVER...THE ONSHORE FLOW AND LOWERING TEMPERATURES WILL INCREASE RELATIVE HUMIDITY AS THE EVENING WEARS ON. EXPECTING THESE LOWER CLOUDS TO COME BACK LATE THIS EVENING AND LINGER THROUGH THE NIGHT. SOME DRIZZLE IS POSSIBLE LATE TONIGHT...ESPECIALLY ALONG THE IMMEDIATE COAST...BUT NOT OVERLY IMPRESSED WITH THE POTENTIAL. A BLEND OF THE MAV/MET GUIDANCE LOOKS REASONABLE FOR TEMPERATURES. && .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... STILL SOME UNCERTAINTY WITH THE TRACK AND INTENSITY OF A LOW PRESSURE MOVING NORTHEAST FROM THE MID ATLANTIC COAST MONDAY NIGHT. FOR NOW...USED A BLEND OF THE GFS AND NAM TO MINIMIZE FORECAST ERROR. 22/15Z SREF MEAN IS EVEN SLOWER AND WEAKER AND SLOWER THAN THAT SOLUTION. MOST 22/12Z MODELS BRING SOME RAINFALL TO SOUTHERN NEW ENGLAND DURING THE DAY MONDAY...ESPECIALLY DURING THE AFTERNOON. GIVEN THE UNCERTAINTY IN THE MODEL TIMING...DID TREND THE ARRIVAL OF THIS PRECIPITATION FASTER THAN PREVIOUS FORECAST. THINKING THE BEST CHANCE FOR THE ARRIVAL OF THIS RAIN WILL BE MONDAY NIGHT. USED A BLEND OF THE MAV/MET GUIDANCE ONCE MORE FOR TEMPERATURES DURING THIS PORTION OF THE FORECAST. && .LONG TERM /TUESDAY THROUGH SUNDAY/... TUESDAY...LOW PRESSURE CENTER PROBABLY NEAR/SOUTH OF NANTUCKET 12Z TUE THEN TRACKS GRADUALLY NORTHEASTWARD TOWARDS NOVA SCOTIA. NAM IS A BIT WEAKER AND FURTHER INLAND THAN THE OTHER MODELS...TAKING LOW OVER THE CAPE. FOR THIS PACKAGE GENERALLY LEANED TOWARDS THE GFS/ECMWF/GGEM. STARTED OFF WITH CHANCE POPS OVER THE INTERIOR...BUT STILL OPTED TO GO WITH LIKELY NEAR THE COAST. LOW LEVEL MOISTURE SHOULD KEEP CLOUDS AROUND THROUGH THE DAY. TUESDAY NIGHT/WEDNESDAY...LOW PRESSURE CONTINUES TO MOVE FURTHER NORTH/EAST OF THE AREA...BEING REPLACED BY WEAK HIGH PRESSURE. NAM INDICATES A LAYER OF LOW LEVEL MOISTURE JUST DEEP ENOUGH TO KEEP CLOUDS AROUND FOR THESE 2 PERIODS...GFS MUCH DRIER. THINK THAT AT LEAST SOME LOW LEVEL MOISTURE WILL LINGER...AND MID/HIGH CLOUDS POSSIBLE WITH A SHORT WAVE. SO KEPT PARTLY TO MOSTLY CLOUDY SKIES IN FORECAST. BUT LOW LEVEL MOISTURE LAYER LIKELY TOO THIN FOR MEASURABLE PRECIP. TEMPERATURES ARE A BLEND OF MOS. CONTINUED WITH PREVIOUS THINKING THAT WED WILL BE COOL AND RAW DURING THE AFTERNOON WITH ONSHORE FLOW. WEDNESDAY NIGHT THROUGH THANKSGIVING...MOSTLY CLOUDY SKIES/CHANCE POPS DUE TO COMBINATION OF LOW LEVEL MOISTURE FROM EASTERLY FLOW AS HIGH PRESSURE DEPARTS...AND AS LOW PRESSURE DEVELOPS OFF THE CAROLINA COAST. THURSDAY NIGHT THROUGH FRIDAY NIGHT...WENT WITH HPC GUIDANCE FOR THIS PERIOD WITH A VIGOROUS LOW PRESSURE SYSTEM POTENTIALLY AFFECTING OUR AREA. MODEL DISCREPANCIES EXIST...AS ECMWF AND GFS SHOW SURFACE LOW TRACKING OVER SOUTHERN NEW ENGLAND BUT GGEM KEEPS CENTER WELL TO THE SOUTH AND EAST. BUT AT THIS TIME HIGH CHANCE TO LIKELY POPS SEEM PRUDENT FOR THU NIGHT THRU FRI. POSSIBILITY THAT PRECIP COULD END AS A LIGHT RAIN/SNOW MIX FRI NIGHT IN INTERIOR AS COLDER AIR SPILLS INTO THE AREA. SATURDAY...POTENTIAL FOR BLUSTERY AND CHILLY WEATHER AS TIGHT GRADIENT LINGERS WHILE SURFACE LOW PULLS TO THE NORTHEAST. BOTH ECMWF AND GFS INDICATE A COLD POOL ALOFT AND LINGERING MOISTURE WHICH COULD POTENTIALLY LEND ITSELF TO SOME SHOWERS. 1000-500 MB THICKNESS ARE QUITE LOW...IF THIS SCENARIO PANS OUT CAN/T RULE OUT A SOME SNOW SHOWERS IN THE FAR INTERIOR...BUT IT WOULD BE TOO WARM AT THE SURFACE FOR ANY ACCUMULATION. SUNDAY...HIGH PRESSURE WITH BELOW NORMAL TEMPS. && .AVIATION /00Z MONDAY THROUGH FRIDAY/...-- Changed Discussion --TONIGHT...MVFR CIGS INITIALLY OVER BOS TO PVD AND SE WILL SPREAD NORTHWEST OVERNIGHT. MONDAY...EXPECT VFR CIGS NW MA/FAR SW NH...WHILE CONDITIONS LOWER TO MVFR-IFR CIGS TO THE S AND E. LOCAL IFR CIGS ALONG THE S COAST...CAPE COD AND THE ISLANDS DURING THE AFTERNOON. PATCHY RAIN WILL APPROACH N CT/RI/SE MA DURING THE AFTERNOON WITH LOCAL MVFR VSBYS. MONDAY NIGHT...MVFR CIGS...LOWERING TO IFR EASTERN SECTIONS. AREAS OF MVFR/IFR VSBYS IN RAIN AND FOG...ALSO MAINLY EASTERN SECTIONS. OUTLOOK /TUESDAY THROUGH FRIDAY/... TUESDAY...MVFR WITH AREAS OF IFR IN LOW CLOUDS AND SCATTERED SHOWERS. TUE NIGHT THROUGH THU...MVFR-IFR CONDITIONS MAY LINGER IN LOW CLOUDS THROUGH THIS PERIOD. MAY HAVE AREAS OF DRIZZLE AND FOG DEVELOPING LATER WED/WED NIGHT. THU NIGHT AND FRI...LOW TO MEDIUM CONFIDENCE OF IFR CEILINGS AND VSBYS IN SHOWERS.-- End Changed Discussion --&& .MARINE... NORTHEAST WINDS SHOULD SHIFT EAST OVERNIGHT. THE PERSISTENT ONSHORE FLOW WILL CONTINUE TO BUILD SEAS OVERNIGHT ACROSS THE COASTAL WATERS OF MA AND RI. A LOW PRESSURE MOVING NORTHEAST FROM THE MID ATLANTIC COAST MONDAY AND MONDAY NIGHT WILL LIKELY INCREASE WINDS DURING THIS TIME AS WELL. SMALL CRAFT ADVISORIES CONTINUE FOR MOST WATERS. OUTLOOK /TUESDAY THROUGH FRIDAY/... TUESDAY AND TUE NIGHT...SCA WINDS/SEAS LINGER TUE AS LOW PRESSURE TRACKS TOWARDS NOVA SCOTIA. WINDS DIMINISH TUE NIGHT AND WED BUT SEAS WILL BE SLOWER TO SUBSIDE. WEDNESDAY THROUGH FRIDAY...PERSISTENT EASTERLY WINDS WILL LIKELY CAUSE SEAS TO REMAIN ABOVE SCA THRESHOLDS ACROSS THE OUTER WATERS. WINDS AND SEAS SHOULD INCREASE THANKSGIVING NIGHT AND FRIDAY IN ADVANCE OF THE NEXT SYSTEM APPROACHING FROM THE SOUTH. POSSIBILITY OF GALES FRI. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY FROM 5 AM TO 5 PM EST MONDAY FOR ANZ232>235-237. SMALL CRAFT ADVISORY UNTIL 5 PM EST MONDAY FOR ANZ250-254>256. && $$ SYNOPSIS...BELK/NMB NEAR TERM...BELK SHORT TERM...BELK LONG TERM...NMB AVIATION...BELK/NMB MARINE...BELK/NMB
