Area Forecast Discussion
Issued by NWS Portland, ME

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467 FXUS61 KGYX 050031 AFDGYX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAY ME 731 PM EST THU FEB 4 2016 .SYNOPSIS... A COLD FRONT WILL EXIT THE COAST...STALLING TO OUR EAST TONIGHT. COLDER AIR WILL GRADUALLY FILTER INTO THE REGION BEHIND THIS FRONTAL SYSTEM LATER TONIGHT. LOW PRESSURE WILL TRACK NORTHEAST ALONG THIS FRONTAL BOUNDARY EARLY FRIDAY. THE WESTERN EDGE OF THE SNOW SHIELD WITH THIS SYSTEM WILL BRUSH SOUTHERN NEW HAMPSHIRE AND COASTAL SECTIONS WITH SNOW ACCUMULATION...WHERE AMOUNTS COULD TOP OUT AROUND 3 TO 6 INCHES. A RIDGE OF HIGH PRESSURE FOLLOWS FOR FRIDAY NIGHT INTO SATURDAY. A COLD FRONT WILL CROSS THE REGION SUNDAY. THERE IS A CHANCE THAT A COASTAL STORM AFFECTS THE REGION EARLY NEXT WEEK. && 00Z UPDATE... QUICK UPDATE TO MAINLY ADJUST TEMPS AND TDS. HIGH AND MID LEVEL CLOUDS CONTINUE TO THICKEN ACROSS THE REGION EARLY THIS EVENING AS THE 1ST OF SEVERAL WEAK WAVES MOVES ALONG A STALLED FRONTAL BOUNDARY OFFSHORE. RAIN HAS EDGED INTO SOUTHEAST NEW ENGLAND AND EXPECT THIS FIRST BATCH TO REMAIN SOUTH OF THE FORECAST AREA THROUGH MIDNIGHT. STILL LOOKING FOR SNOW OR A MIX RAIN AND SNOW AT THE ONSET TO SHIFT INTO SOUTHERN ZONES TOWARD DAYBREAK. NO OTHER CHANGES PLANNED ATTM. PREVIOUS DISCUSSION... .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... S/WV TROF MOVING THRU THE TENNESSEE RIVER VALLEY WILL APPROACH THE STALLED FRONTAL BOUNDARY OFF THE EAST COAST TONIGHT. A WAVE OF LOW PRESSURE WILL DEVELOP AND RIDE THE BAROCLINIC ZONE NWD TO A POSITION OFF NEW ENGLAND BY FRIDAY. AS THE WAVE OF LOW PRESSURE NEARS NEW ENGLAND...PRECIPITATION WILL BACK IN FROM THE OCEAN. 12Z MODEL GUIDANCE WAS A SIGNIFICANT SHIFT WEST IN PRECIPITATION AND TOTAL QPF AMOUNTS. GLOBAL MODEL GUIDANCE INDICATES THAT ADVECTIVE PROCESSES WILL RESULT IN STRONG FRONTOGENESIS VERY NEAR AND ROUGHLY ALIGNED ALONG THE NEW ENGLAND COAST. EXAMINATION OF THE H8 LAYER SHOWS THAT THERE IS SOME POTENTIAL FOR A MORE CONCENTRATED BAND OF PRECIPITATION...AND THAT COULD BE NEAR OR JUST OFFSHORE. I SAY PRECIPITATION...BECAUSE TONIGHT TEMPERATURES WILL SLOWLY FALL...BUT MAY BE MARGINAL FOR SNOWFALL AT ONSET. INITIALLY I WOULD NOT BE SURPRISED IF SOME RAINFALL MIXED IN...BUT EVENTUALLY HEAVIER PRECIPITATION RATES WILL WASH OUT WARMTH AND FROM EARLY FRIDAY MORNING ON ALL SNOWFALL IS EXPECTED. THE GREATEST UNCERTAINTY STILL RESIDES ON THE NWRN EDGE OF PRECIPITATION SHIELD. NCAR ENSEMBLES AT 00Z FROM LAST EVENING SHOWED QUITE THE RANGE OF POSSIBILITIES FOR THE LOCAL AREA. AS MUCH AS WARNING CRITERIA ON THE COAST...TO AS LITTLE AS NOTHING. 12Z TRENDS HAVE PUSHED THAT WWD IN MY MIND...SO THAT THE COAST IS LOOKING AT LIKELY ACCUMULATION AND AROUND MORNING COMMUTE. FOR THAT REASON I HAVE ISSUED A WINTER WEATHER ADVISORY FOR PARTS OF SOUTHERN NH THRU COASTAL WESTERN ME. THERE STILL REMAINS A SMALL CHANCE THAT PARTS OF SERN NH SEE GREATER THAN 6 INCHES OF SNOWFALL...BUT CONFIDENCE IS TOO LOW FOR A WARNING AT THIS TIME. AROUND COMMUTE TIME A FEW AREAS OF LOCALLY HEAVY SNOWFALL ARE POSSIBLE...WITH LOW VISIBILITIES AND RATES AROUND 1 INCH PER HOUR. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... LOW PRESSURE QUICKLY DEPARTS EWD BY FRIDAY AFTERNOON FOR MUCH OF THE FORECAST AREA. S/WV TROF IS QUITE PROGRESSIVE...AND ONLY SNOWFALL THAT I EXPECT TO BE CONTINUING THRU THE AFTERNOON WILL BE OVER THE MIDCOAST ZONES. S/WV RIDGING AND HIGH PRESSURE BUILDS IN FOR FRIDAY NIGHT. && .LONG TERM /SATURDAY THROUGH THURSDAY/... HIGH PRESSURE MOVES EAST SATURDAY WITH A GRADUAL INCREASE IN TEMPERATURES AND DEWPOINTS. UPPER TROUGH ALOFT WILL CAUSE SURFACE LOW PRESSURE TO TRACK EASTWARD THROUGH CENTRAL QUEBEC. BEHIND IT A COLD FRONT WILL DROP SOUTHWARD WITH COLDER AIR DRIVING IN BEHIND IT. AS THIS UPPER TROUGH MOVES THROUGH THE AREA AND THE COLD FRONT ARRIVES THERE COULD BE SOME SNOW SHOWERS PRIMARILY IN THE MOUNTAINS. ONLY LIGHT ACCUMULATIONS ARE EXPECTED AT THIS POINT. COLD FRONT MOVES THROUGH ON SUNDAY. BY MONDAY TEMPERATURES WILL BE IN THE 20S FOR HIGHS. NOW THAT THE UPPER LEVEL TRIGGERING ENERGY HAS MOVED ONSHORE ON THE WEST COAST AND HAS BEEN SAMPLED BY THE UPPER AIR NETWORK... MODELS ARE BEGINNING TO COME INTO BETTER AGREEMENT ON THE EVOLUTION OF A LARGE UPPER TROUGH OVER THE CENTRAL AND EASTERN UNITED STATES AND THE RESULTING SURFACE LOWS WHICH WILL TRACK OFFSHORE IN THE WESTERN ATLANTIC... THOUGH DIFFERENCES IN TIMING AND QPF AMOUNTS REMAIN. SOUTHERN STREAM WAVE WHICH TRIGGERS THE FIRST SURFACE LOW NOW LOOKS LIKE IT WILL TRACK OUT INTO THE ATLANTIC. ECMWF IS STILL A LITTLE SLOWER WITH THIS SYSTEM AND PULLS IT FURTHER NORTH THAN EAST... WITH A SLIGHT GRAZING OF COASTAL NEW ENGLAND WITH LIGHT SNOW MONDAY. HOWEVER... THE BETTER CHANCE OF SNOW WILL BE ON TUESDAY. MONDAY NIGHT THE UPPER TROUGH WILL BE NEARING THE COAST AND SURFACE LOW PRESSURE WILL DEVELOP OFF THE MID ATLANTIC COAST AND TRACK NORTHEAST. BY TUESDAY AFTERNOON THIS LOW SHOULD BE NEAR CAPE COD. GFS AND ECMWF STILL HAVE SOME TIMING DIFFERENCES AND THE GFS WOULD LIKE TO PRODUCE MUCH MORE QPF... BUT AT LEAST THE MODELS ARE IN AGREEMENT ON THE OVERALL TRACK OF THIS LOW UP THE COAST. IT SEEMS LIKELY AT THIS POINT THAT SNOW WILL FALL ACROSS MUCH OF NEW HAMPSHIRE AND MAINE... WITH THE GREATEST SNOW CHANCES AND HIGHEST ACCUMULATIONS CLOSER TO THE COAST. THERE COULD BE SOME RAIN MIXING IN ALONG THE IMMEDIATE COASTLINE DEPENDING ON HOW SURFACE TEMPERATURES EVOLVE. LOW PRESSURE MOVES OFF TO THE NORTHEAST WEDNESDAY WITH A COLD OFFSHORE FLOW EXPECTED OVER NEW ENGLAND. && .AVIATION /01Z FRIDAY THROUGH TUESDAY/... SHORT TERM...SHORT TERM...VFR CONDITIONS EXPECTED THRU THE FIRST PART OF TONIGHT. LOW PRESSURE IS FORECAST TO DEVELOP NEAR NEW ENGLAND LATE TONIGHT...AND SNOWFALL WILL BACK TOWARDS THE COAST AFTER 09Z. EXPECT IFR CONDITIONS TO MOVE INTO SOUTHERN NH FIRST...AND EVENTUALLY AFFECT ALL TERMINALS OUTSIDE OF LEB AND HIE. THE RISK FOR 1/4SM +SN IS HIGHEST FROM PSM TO PWM TO RKD. IFR CONDITIONS QUICKLY MOVE EWD FRIDAY AFTERNOON...AS LOW PRESSURE PULLS AWAY. VFR CONDITIONS EXPECTED FROM THERE THRU FRIDAY NIGHT. LONG TERM...COULD SEE SOME SNOW SHOWERS AND MVFR/IFR CONDITIONS IN THE MOUNTAINS SATURDAY NIGHT THROUGH SUNDAY. OTHERWISE IT SHOULD BE VFR ACROSS THE REGION. LOW PRESSURE TRACKING UP THE COAST WILL LIKELY BRING LOWER CEILINGS AND SNOWFALL MONDAY NIGHT INTO TUESDAY. && .MARINE... SHORT TERM...SHORT TERM...SEAS REMAIN HIGH THIS EVENING...WITH WINDS EXPECTED TO INCREASE AGAIN AS LOW PRESSURE DEVELOPS. WILL EXTEND SCA THRU FRIDAY. LONG TERM...A COLD FRONT DROPPING DOWN FROM THE NORTHWEST ON SUNDAY WILL BRING STRONG OFFSHORE WINDS WITH GUSTS 25 TO 30 KT. HIGH PRESSURE THEN CROSSES THE AREA MONDAY. LOW PRESSURE TRACKS UP THE EAST COAST AND TOWARD CAPE COD TUESDAY WITH EASTERLY GALES POSSIBLE ACROSS THE GULF OF MAINE ON TUESDAY. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...WINTER WEATHER ADVISORY FROM 5 AM TO 7 PM EST FRIDAY FOR MEZ022-026>028. WINTER WEATHER ADVISORY FROM 3 AM TO 1 PM EST FRIDAY FOR MEZ023>025. NH...WINTER WEATHER ADVISORY FROM 3 AM TO 1 PM EST FRIDAY FOR NHZ010-012>014. MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EST FRIDAY FOR ANZ150>154. && $$

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