Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 181202 AAA AFDGYX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE GRAY ME 702 AM EST THU DEC 18 2014 .SYNOPSIS... LOW PRESSURE SYSTEM HAS PUSHED OFF INTO THE CANADIAN MARITIMES...HOWEVER TROUGH REMAINS OVERHEAD AND SOME SNOW SHOWERS CAN STILL BE EXPECTED FROM THIS ON THURSDAY. WEAK HIGH PRESSURE WILL START TO BUILD IN THIS EVENING. SOME OCEAN EFFECT SNOW MAY BE POSSIBLE SUNDAY INTO MONDAY DUE TO WEAK ONSHORE FLOW. A WEAK COASTAL LOW WILL LIKELY STRENGTHEN AND PASS BY TO OUR WEST TUESDAY AND MAY SPREAD LIGHT PRECIP INTO NEW ENGLAND. AN INTENSE LOW PRESSURE SYSTEM WILL MOST LIKELY DEVELOP OFF TO OUR WEST ON WEDNESDAY AND POSSIBLY BRING HEAVY RAIN AND STRONG WINDS WEDNESDAY AND INTO CHRISTMAS MORNING. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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.UPDATE... ADJUSTED POPS AS WELL AS TEMPERATURES AND DEW POINTS FOR THIS UPDATE BASED ON HOURLY OBSERVATIONS. LIGHT SNOW AND RAIN SHOWERS STILL MOVING ACROSS THE AREA. SOME SLIGHTLY HEAVIER SNOWFALL IS OCCURRING FROM TIME TO TIME OVER THE MID COAST REGION AND HAVE INCREASED POPS THERE. OTHERWISE NO MAJOR CHANGES.
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&& .PREVIOUS DISCUSSION...
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A SURFACE LOW PRESSURE NOW MOVING INTO NOVA SCOTIA WITH UPPER LEVEL LOW PRESSURE SPINNING OVER THE NORTHEAST. THE MOST VIGOROUS SHORT WAVE ENERGY IS TO OUR SOUTH AND OFFSHORE... AS WELL AS TO OUR NE. THIS WILL KEEP ANY SIGNIFICANT BANDING JUST OUT OF THE FORECAST AREA AND THUS SNOWFALL AMOUNTS SHOULD STAY WITHIN WINTER WEATHER ADVISORY CRITERIA. THE ADVISORIES CONTINUE THROUGH 1 PM FOR 3-6" OF SNOW. NORTHERN SECTIONS AND ESPECIALLY PORTIONS OF SOMERSET WILL HAVE THE HIGHEST ACCUMULATIONS. SHOWERS WILL TAPER OFF AROUND MIDDAY WITH THE PASSAGE OF A SURFACE TROUGH. UPSLOPE SHOWERS ARE EXPECTED TO LINGER ALONG THE WHITES AND THE WESTERN MAINE MOUNTAINS BUT SNOWFALL ACCUMULATIONS WILL BE VERY LIGHT AS DRY AIR FILTERS IN ALOFT. MODERATE COLD AIR ADVECTION AS WELL AS A TIGHT PRESSURE GRADIENT WILL ALLOW NW WINDS BEHIND THE SURFACE TROUGH TO GUST TO NEAR 30PH AT TIMES. TEMPERATURES RANGE FROM THE LOWER TO MID 30S NORTH TO LOWER 40S SOUTH.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... COLDER AIR DAMS ALONG THE HIGH TERRAIN TONIGHT WITH TEENS NORTH AND LOWER TO MID 20S SOUTH. THE BOUNDARY LAYER DECOUPLES AND ALLOWS WINDS TO DECREASE QUITE A BIT OVERNIGHT. THE DOWNSLOPING WINDS WILL BEGIN TO SCOUR CLOUDS OUT OVER THE COASTAL PLAIN OVERNIGHT. DRIER AND COLDER AIR CONTINUES TO FILTER IN FRIDAY WITH THE DEPARTURE OF THE UPPER LOW. LOOKING AT A DRY...COOL AND SOMEWHAT GUSTY FRIDAY WITH CLOUDS CLEARING OUT OVER THE COASTAL PLAIN AND THEN EVENTUALLY OVER THE MOUNTAINS. THERE MAY BE ENOUGH MOISTURE LEFT TO SQUEEZE OUT A FEW STRAY SNOWFLAKES OVER THE HIGHEST PEAKS... BUT LITTLE ELSE. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... START OFF WITH HIGH PRESSURE OVER THE REGION WHICH SHOULD BRING FAIR WEATHER INTO THE BEGINNING OF NEXT WEEK. THE PATTERN WILL THEN SIGNIFICANTLY CHANGE FROM ZONAL FLOW TO HIGHLY AMPLIFIED AS A DEEP LONG WAVE TROUGH DIGS OVER THE CENTRAL U.S. THE WEAK COASTAL LOW THAT THE GFS WAS SHOWING LAST NIGHT FOR SUNDAY INTO MONDAY IS NOW COMPLETELY REMOVED FROM THE 00Z RUN. THE CANADIAN STILL DEVELOPS THIS WEAK SYSTEM OUT OF THE SOUTHERN STREAM...BUT IT IS NOW WAY TOO FAR EAST TO POSE MUCH OF A THREAT TO OUR AREA. IF WE SEE ANY LIGHT SNOW BY THE END OF THE WEEKEND IT WILL BE DUE TO ONSHORE FLOW AND SOME OCEAN EFFECT SNOW SHOWERS. MODELS ARE NOW IN DECENT AGREEMENT THAT ANOTHER SOUTHERN STREAM SYSTEM WILL MOVE SOUTH OF NEW ENGLAND ON TUESDAY. STILL CONFIDENCE IS LOW AT THIS TIME. THE OPERATIONAL EURO/GEM/GFS ARE SHOWING THIS SYSTEM PASSING TO OUR SOUTH AND EAST...HOWEVER TIMING ISSUES ON WHEN THE LOW PASSES AND HOW FAR NORTH ANY LIGHT PRECIP MAKES IT INTO NEW ENGLAND IS STILL UP IN THE AIR. 00Z EURO IS ALSO THE FURTHEST EAST WITH THIS SYSTEM...BRINGING VERY LITTLE IF ANY MOISTURE INTO NEW ENGLAND. AFTER THIS SYSTEM PASSES OUR FOCUS THEN SHIFTS TO THE LONG WAVE TROUGH STARTING TO MATERIALIZE TUESDAY IN THE CENTRAL U.S. MODELS ARE IN GOOD AGREEMENT WITH 500 MB CLOSED LOW FORMING IN THE UPPER MIDWEST. TROUGH TILTS NEGATIVE BY WEDNESDAY MORNING AND VIGOROUS SHORTWAVE ROTATES AROUND IT...DEVELOPING A DEEP LOW PRESSURE AT THE SURFACE. AS IT STANDS RIGHT NOW...WE END UP IN THE WARM SECTOR WITH A DEEP MOISTURE FETCH FROM THE GULF OF MEXICO AND ATLANTIC. EURO ENSEMBLES/GEFS/AND GEM ENSEMBLES ALL ARE IN GOOD AGREEMENT WITH THIS SCENARIO. HOWEVER...THERE IS SOME CONCERN ON HOW NEGATIVELY AMPLIFIED THE 500MB TROUGH BECOMES...WITH THE 00Z EURO NOW SHOWING THE TROUGH TILTING FURTHER EAST...FORMING THE SURFACE LOW CLOSER TO DELMARVA AND TRACKING RIGHT UP THE HUDSON VALLEY AND THEN INTO NORTHERN NEW ENGLAND. ALTHOUGH THIS IS STILL A WARM TRACK FOR US...IF IT WERE TO CONTINUE THIS TREND AND FORM THE LOW FURTHER SOUTH AND EAST OFF THE COAST...THEN OF COURSE THE FORECAST WILL SIGNIFICANTLY CHANGE. ALSO...JUST CAUGHT THE 00Z EURO ENSEMBLE AND A SMALL HANDFUL OF THE 50 MEMBERS ARE ALSO SHOWING THIS SCENARIO. FOR NOW THOUGH IT APPEARS WE WILL NOT BE LOOKING AT SNOW...BUT EVEN SO THIS SYSTEM HAS POTENTIAL FOR MAJOR IMPACTS IN OUR AREA. WITH THE WESTERLY TRACK...PWATS ARE LOOKING TO BE IN THE 1.1 TO 1.2 RANGE...WHICH IS MORE THAN 2 STANDARD DEVIATIONS ABOVE NORMAL FOR THIS TIME OF YEAR. WILL HAVE TO MONITOR THE POTENTIAL FOR VERY HEAVY RAINFALL AND POSSIBLE FLOODING AS WE START TO GET CLOSER...BUT A LOT CAN STILL CHANGE OVER THE NEXT 6 DAYS. THE POTENTIAL FOR HIGH WINDS WILL ALSO EXIST WITH TIGHT SOUTHEASTERLY GRADIENT...THIS WILL BE ESPECIALLY TRUE ALONG THE COAST AND HIGHER TERRAIN. CONFIDENCE REMAINS LOW AT THIS TIME AS FAR AS TIMING AND TRACK OF THIS SYSTEM...BUT CONFIDENCE IS GROWING THAT WE WILL SEE PRECIP IN THE FORM OF RAIN AND NOT SNOW AS MODELS HAVE NOW BEEN FAIRLY CONSISTENT IN SHOWING A WESTERN TRACK OVER THE PAST SEVERAL RUNS...WILL CONTINUE TO HAVE TO KEEP A CLOSE EYE ON THIS OVER THE DAYS AHEAD DUE TO THE POSSIBLE STRENGTH OF THIS SYSTEM. && .AVIATION /12Z THURSDAY THROUGH MONDAY/... SHORT TERM...SCATTERED SNOW SHOWERS THIS MORNING WILL CONTINUE THROUGH EARLY AFTERNOON CAUSING MAINLY MVFR CEILINGS WITH SOME LOWER VISIBILITIES. WE SHOULD SEE IMPROVEMENT TO VFR BY THIS AFTERNOON WITH NW GUSTING INTO THE LOWER 20S AT TIMES. WINDS DECREASE AFTER THE BOUNDARY LAYER DECOUPLES AFTER DARK. LONG TERM...VFR CONDITIONS CAN BE EXPECTED THROUGH THE WEEKEND. THERE IS A CHANCE FOR MVFR CONDITIONS ALONG THE COAST DUE TO OCEAN EFFECT SNOW EARLY SUNDAY NIGHT THROUGH MONDAY MORNING && .MARINE... SHORT TERM...WINDS ARE ON THE LOW SIDE AT THE MOMENT BUT SHOULD PICK BACK UP WITH THE PASSAGE OF A SURFACE TROUGH AND RENEWED COLD AIR ADVECTION. MIXING WILL BRING WIND GUSTS INTO THE 20-30 KT RANGE BY MID MORNING. SEAS ARE CURRENTLY MARGINAL BUT SHOULD DROP BELOW 5 FT TODAY. LONG TERM...NO FLAGS EXPECTED AT LEAST THROUGH TUESDAY. THEN A WEAK COASTAL LOW MAY BRING BORDERLINE SCA CONDITIONS ON TUESDAY AFTERNOON. A SIGNIFICANT STORM WILL DEVELOP MIDWEEK AND DEPENDING ON THE TRACK OF THIS SYSTEM...STORM FORCE WINDS MAY BE POSSIBLE. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...WINTER WEATHER ADVISORY UNTIL 1 PM EST THIS AFTERNOON FOR MEZ007>009-012>014. NH...WINTER WEATHER ADVISORY UNTIL 1 PM EST THIS AFTERNOON FOR NHZ001-002. MARINE...SMALL CRAFT ADVISORY UNTIL 4 AM EST FRIDAY FOR ANZ150>154. && $$ HANES/KISTNER

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