Issued by NWS Portland, ME
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-- Discussion containing changed information from previous version are highlighted. --000 FXUS61 KGYX 230048 AAA AFDGYX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE GRAY ME 748 PM EST SUN NOV 22 2009 .SYNOPSIS...-- Changed Discussion --EASTERLY FLOW WILL DEVELOP OVERNIGHT AS HIGH PRESSURE SHIFTS INTO THE CANADIAN MARITIMES. LOW PRESSURE WILL PASS SOUTHEAST OF THE GULF OF MAINE MONDAY NIGHT AND TUESDAY...BRINGING A CHANCE OF SHOWERS DURING THAT PERIOD. HIGH PRESSURE WILL BUILD SOUTH FROM EASTERN QUEBEC TUESDAY NIGHT AND WEDNESDAY. A WARM FRONT EXTENDING FROM LOW PRESSURE OVER THE GREAT LAKES WILL APPROACH THURSDAY. ANOTHER LOW PRESSURE SYSTEM IS EXPECTED TO DEVELOP OFF THE MID ATLANTIC COAST AND AFFECT NORTHERN NEW ENGLAND THURSDAY NIGHT INTO EARLY NEXT WEEKEND.-- End Changed Discussion --&& .NEAR TERM /UNTIL 7 AM MONDAY MORNING/...-- Changed Discussion --.UPDATE... SURFACE HIGH PRESSURE WILL ACTUALLY STRENGTHEN OVER THE NEXT FEW HOURS BEFORE WEAKENING AND BEING NUDGED ENE BY THE COASTAL LOW NOW ORGANIZING OVER SOUTH GEORGIA. STRATUS LOCATED ON THE EDGE OF THE SURFACE HIGH WAS OFF THE NEW ENGLAND COAST AND THREATENING TO MOVE NORTHWARD. THIS MOISTURE WILL EVENTUALLY APPROACH THE SEACOAST OF NEW HAMPSHIRE AND COASTAL MAINE OVERNIGHT...KEEPING LOWS A BIT HIGHER THAN THEY WOULD BE OTHERWISE. OTHER AREAS HAVE ALREADY DROPPED INTO THE UPPER 20S TO LOWER 30S UNDER CLEAR SKIES AND LIGHT WINDS. RADIATION FOG WILL FORM SHORTLY ALONG THE CONNECTICUT RIVER VALLEY AND REMAIN THERE THROUGH SUNRISE. ADJUSTED OVERNIGHT LOWS SLIGHTLY TO REFLECT THE STRATUS AND FOG. OTHERWISE FORECAST IS IN GOOD SHAPE.-- End Changed Discussion --&& .SHORT TERM /7 AM MONDAY MORNING THROUGH 6 PM MONDAY/...-- Changed Discussion --ON MONDAY...LOW CLOUDS SPREAD FURTHER INLAND IN INCREASING ONSHORE FLOW WITH SLIGHT CHC POPS BY AFTERNOON CONFINED TO AREAS FAR SOUTHERN NEW HAMPSHIRE AND YORK COUNTY MAINE. SHOULD BE SEVERAL DEGREES COOLER THAN TODAY GIVEN THE ONSHORE BREEZE AND INCREASING CLOUD COVER...BUT STILL SEVERAL DEGREES ABOVE AVERAGE FOR LATE NOVEMBER.-- End Changed Discussion --&& .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...-- Changed Discussion --TWO SYSTEMS WILL AFFECT THE REGION DURING THIS PERIOD. THERE IS A BIT MORE CONFIDENCE WITH THE FIRST SYSTEM...AND LESS CONFIDENCE ON HOW THE SECOND WILL UNFOLD LATE THIS WEEK. FAIRLY GOOD MODEL AGREEMENT WITH RESPECT TO MASS FIELDS MONDAY NIGHT AND TUESDAY. SHOULD SEE A SURFACE WAVE DEVELOP ON THE LOW LEVEL BAROCLINIC ZONE LOCATED OFF THE MID ATLANTIC COAST MONDAY AFTERNOON AS THE SHORT WAVE OVER THE GULF OF MEXICO APPROACHES. AT THIS POINT...IT APPEARS AS THOUGH THE DEVELOPMENT OF THE SYSTEM WILL BE FAIRLY LIMITED...AND TRACK SHOULD BE NEAR THE BENCHMARK. THE 1200 UTC NAM BRINGS A FAIR AMOUNT OF QPF NORTH ALONG A SURFACE TROUGH AHEAD OF THE SURFACE WAVE...WHILE MODEL CONSENSUS IS TO KEEP THE HEAVIEST QPF OFFSHORE (CLOSE TO THE BAROCLINIC ZONE). BASED ON THE ABOVE...LEANED TOWARD A MODEL CONSENSUS FOR PLACEMENT OF QPF. THIS WOULD BRING A CHANCE OF RAIN AS FAR NORTH AS THE FOOTHILLS MONDAY NIGHT. NORTH OF THIS...THE AIRMASS MAY BE DRY ENOUGH TO LEAVE THE MENTION OF PRECIPITATION OUT FOR NOW. THE COLUMN IS WARM ENOUGH FOR RAIN IN JUST ABOUT ALL AREAS. IN FACT...TEMPERATURES SHOULD BECOME STEADY AFTER MIDNIGHT...SO A BLEND OF MOS NUMBERS WAS USED FOR LOWS. SAME SITUATION FOR TUESDAY...USING THE SAME RATIONALE. THIS PLACES THE HIGHEST CHANCE OF RAIN SOUTH OF THE FOOTHILLS. THE GRADIENT NEAR THE COAST MAY BE STRONG ENOUGH FOR WINDS GUSTS CLOSE TO 25 MPH...ESPECIALLY ALONG THE MID COAST. AT THIS POINT...THE MOS BLEND APPEARS TO BE A BIT TOO WARM FOR ALL AREAS...AND THESE NUMBERS WERE NUDGED DOWN. MOST OF THE RAIN SHOULD EXIT TUESDAY EVENING. AFTER THIS...THERE IS SOME MODEL SPREAD IN JUST HOW FAST THE LOW LEVEL MOISTURE LEAVES. IT APPEARS NOW THAT THE PUSH OF DRIER AIR MAY WAIT UNTIL LATE AT NIGHT...SO LEANED TOWARD THE SLOWER NAM TIMING FOR CLEARING. THE TIMING DIFFERENCE IS IMPORTANT FOR LOWS...AS THERE IS AS MUCH AS A 15 DEGREE DIFFERENCE IN LOWS BETWEEN MOS VALUES. RIGHT NOW...IT APPEARS AS THOUGH THE MUCH COLDER GFS MOS IS TOO COLD AND LOWS WERE BASED MORE CLOSELY ON THE WARMER NAM MOS. HIGH PRESSURE BUILDING SOUTH FROM EASTERN QUEBEC SHOULD BRING CLEARING WEDNESDAY MORNING (AT THE LATEST). SHORT WAVE RIDGING DEVELOPS IN THE WAKE OF THE SHORT WAVE EXITING AND THE CLOSED LOW OVER THE GREAT LAKES. THIS SHOULD RESULT IN DRY CONDITIONS WEDNESDAY AND WEDNESDAY NIGHT. THE SECOND SYSTEM WILL BEGIN AFFECTING THE AREA SOMETIME THURSDAY. THE 1200 UTC GFS IS SHOWING MOISTURE MOVING NORTHEAST IN THE MID LEVEL FLOW THURSDAY AFTERNOON. NOT SURE WHAT TO MAKE OF THIS YET...BUT MAY HAVE TO CARRY A CHANCE OF SHOWERS FOR THANKSGIVING DAY TO ACCOUNT. AFTER THIS...MID RANGE MODELS AGREE ON A SYSTEM DEVELOPING OFF THE MID ATLANTIC COAST ON THE OLD BAROCLINIC ZONE. THE 1200 UTC ECMWF IS NOW CLOSER TO THE 1200 UTC GFS IN THE DETAILS FOR THURSDAY NIGHT INTO FRIDAY NIGHT. BOTH ARE NOW KEYING DEVELOPMENT ON THE OLD BAROCLINIC ZONE THURSDAY NIGHT. THE 1200 UTC GFS SHIFTS THE FIRST (AND PERHAPS BOGUS?) SHORT WAVE OUT AND BOTH MODELS DEEPEN THE SURFACE LOW RAPIDLY AHEAD OF THE COLD CLOSED MID LEVEL SYSTEM. THE PLACEMENT OF THE CLOSED MID LEVEL SYSTEM SHOULD ALLOW ENOUGH WARM AIR ADVECTION TO MOISTEN AND WARM THE COLUMN TO KEEP MOST OF THE PRECIPITATION IN THE FORM OF RAIN. THE OVERALL AMOUNT OF PRECIPITATION DIFFERS BETWEEN MODELS...WITH THE 1200 UTC GFS MUCH HEAVIER WITH REGARD TO QPF...WITH THE ECMWF ABOUT HALF OF THE 3+ INCHES SHOWN BY THE GFS ACROSS WESTERN ZONES. THIS SEEMS TO BE DUE TO WARM AIR ADVECTION FOCUSING ON A ZONE OF SURFACE CONVERGENCE WHICH MAY OR MAY NOT ACTUALLY OCCUR. THE SURFACE GRADIENT AHEAD OF THE LOW MAY PRODUCE GUSTY WINDS NEAR THE COAST...BUT RIGHT NOW NOT ENOUGH INFORMATION ON THE DEPTH OF THE MIXED LAYER FOR MORE THAN THAT. ON THE BACK SIDE OF THE SYSTEM...COLD AIR IS AVAILABLE...AND THE PRECIPITATION COULD CHANGE TO SNOW IN THE MOUNTAINS BEFORE IT ENDS. WOULD EXPECT UPSLOPE SHOWERS IN THE MOUNTAINS SATURDAY...BUT ELSEWHERE THERE MAY BE ENOUGH DOWNSLOPE TO KEEP SHOWERS SCATTERED.-- End Changed Discussion --&& .AVIATION /00Z MONDAY THROUGH FRIDAY/...-- Changed Discussion --SHORT TERM /THROUGH 23Z MONDAY/...VFR CONDITIONS BECOMING MVFR AROUND 0600 UTC FOR ALL SITES EXCEPT KAUG WHICH WILL REMAIN VFR. DECREASING TO IFR AROUND 09-10Z AT KPWM/KPSM/KCON WITH LIFR EXPECTED AT KLEB IN FOG AND STRATUS. LONG TERM...WOULD EXPECT MOISTURE TO BECOME TRAPPED UNDER THE LOWERING INVERSION. MVFR CONDITIONS SHOULD BECOME IFR FOR CEILINGS AFTER ABOUT 0600 UTC TUESDAY (SOONER NEAR THE COAST...A BIT LATER AT KCON AND KLEB). VISIBILITY IS A LITTLE LESS CERTAIN...AS IT DEPENDS ON HOW FAR NORTH THE RAIN SHIELD WITH AN OFFSHORE WAVE GETS...WITH THE BEST CHANCE AT KPSM AND KPWM. ALL TERMINALS SHOULD BE IFR IN CEILINGS AND POSSIBLY VISIBILITY AS THE SURFACE WAVE PASSES SOUTHEAST OF THE AREA. SOME MODEL DIFFERENCES ON HOW FAST THE LOW LEVEL MOISTURE EXITS TUESDAY NIGHT...BUT ALL TERMINALS SHOULD BE VFR BY 1200 WEDNESDAY. AFTER THIS...WOULD EXPECT LOWERING CONDITIONS LATER THURSDAY AND THURSDAY NIGHT...WITH WIDESPREAD IFR/LIFR CONDITIONS INTO FRIDAY AND BEYOND.-- End Changed Discussion --&& .MARINE... SHORT TERM /THROUGH MONDAY/...SEAS GRADUALLY BUILD IN NORTHEAST FLOW AND WILL APPROACH SMALL CRAFT BY LATE IN THE PERIOD. LONG TERM...THE GRADIENT STARTS TO INCREASE MONDAY NIGHT AS HIGH PRESSURE EXITS AND A WEAK SURFACE WAVE DEVELOPS ON A FRONTAL BOUNDARY OFF THE MID ATLANTIC COAST. AS THE WAVE PASSES NEAR THE BENCHMARK LATE MONDAY NIGHT...THE GRADIENT INCREASES ENOUGH (ESPECIALLY ACROSS THE SOUTHERN WATERS) TO SUPPORT GALE FORCE WINDS. IN FACT...BY 1200 UTC TUESDAY...WINDS MAY GE GUSTING NEAR 35 KNOTS AT IOSN3. MODELS TEND NOT TO PICK UP ON THIS LOCAL ACCELERATION. WOULD EXPECT TO SEAS TO REACT TO THE INCREASINGLY FAVORABLE FETCH MONDAY NIGHT. SEAS SHOULD BE NEAR 5 FEET ACROSS ANZ154 BY MORNING... AND APPROACHING THAT IN THE OTHER OCEAN WATERS. THE WAVE MAKES IT CLOSEST APPROACH TUESDAY MORNING...AND THE GRADIENT SUPPORTS SMALL CRAFT WINDS IN ALL WATERS. MODEL SOUNDINGS SUGGEST THE MIXED LAYER WILL BE CLOSE TO 400 FEET TUESDAY MORNING... AND THIS WOULD BE CLOSE ENOUGH FOR GALE FORCE GUSTS ON THE OCEAN. WILL NOT INDICATE THIS YET...BUT KEEP WINDS JUST BELOW GALE FORCE. WITH THE PASSAGE OF THE WAVE TUESDAY NIGHT...WINDS WILL SLOWLY DROP BELOW SMALL CRAFT LEVELS...OVER THE BAYS FIRST AND ACROSS THE OCEAN WATERS LATE AT NIGHT. SEAS OVER THE OCEAN MAY TAKE ALL NIGHT AND INTO WEDNESDAY MORNING AS THE EAST TO NORTHEAST FETCH SORTS ITSELF OUT. WINDS AND SEAS SHOULD DROP BELOW SMALL CRAFT LEVELS WEDNESDAY AFTERNOON AND REMAIN THERE THROUGH THURSDAY EVENING. AFTER THAT...THE MID RANGE MODELS ARE IN BETTER AGREEMENT ABOUT THE DETAILS OF SYSTEM FOR THE END OF THE WEEK. THE GRADIENT CERTAINLY APPEARS TO SUPPORT THE POTENTIAL FOR GALES IN THE SOUTHEAST FLOW. WHETHER WINDS GETS ANY HIGHER WILL ULTIMATELY DEPEND ON THE FINAL TRACK...AND HOW THIS INFLUENCES THE DEPTH OF THE MIXED LAYER. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...NONE. NH...NONE. MARINE...NONE. && $$ LONG TERM...HAYES SHORT TERM...SCHWIBS UPDATE...HANES
