Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 201204 AFDGYX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAY ME 704 AM EST SAT DEC 20 2014 .SYNOPSIS... WEAK HIGH PRESSURE MOVES ACROSS THE REGION THROUGH SATURDAY. THE HIGH BUILDS OVER NORTHERN MAINE SUNDAY...ALLOWING THE FLOW TO TURN ONSHORE. A WEAK WEATHER DISTURBANCE MAY TRIGGER SOME FLURRIES OR LIGHT SNOW OVER SOUTHERN REGIONS LATER SUNDAY INTO MONDAY. A WEAK AREA OF LOW PRESSURE WILL MOVE UP THE COAST TUESDAY...WITH A MORE SIGNIFICANT SYSTEM GRADUALLY ORGANIZING WEDNESDAY...BEFORE MOVING OVER THE GREAT LAKES. THIS COULD BRING WINDY CONDITIONS AND THE POTENTIAL FOR HEAVY RAIN AROUND CHRISTMAS EVE INTO EARLY CHRISTMAS MORNING. && .NEAR TERM /THROUGH TONIGHT/...
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7 AM UPDATE...SOME IMPRESSIVE RADIATIONAL COOLING ACROSS THE NORTH THIS MORNING...WITH LOWS NOW DROPPING BELOW ZERO. UPDATED THE LOW TEMPERATURE FORECAST BASED ON THE CURRENT OBS AND TRENDS...AS GUIDANCE WAS OVER 10 DEGREES OFF IN MANY AREAS ACROSS THE NORTH. STILL JUST A FEW CLOUDS HOLDING ON IN THE CT RIVER VALLEY...OTHERWISE MOSTLY CLEAR SKIES ELSEWHERE. FORECAST IS STILL ON TRACK FOR CLOUDS TO INCREASE THROUGH OUT THE DAY WITH LOW STRATUS PUSHING IN FROM THE OCEAN AND FROM THE NORTH. PREVIOUS DISCUSSION... A WEAK SHORT WAVE IS CLEARLY VISIBLE ON WATER VAPOR IMAGERY MOVING EAST ACROSS NY AS OF 3AM. OTHER THAN THE CT RIVER VALLEY THE BULK OF THE CWA IS MOSTLY CLEAR. AS THE SHORT WAVE APPROACHES WE SHOULD SEE NORTHEAST FLOW SWITCH AT 925MB TO MORE ON SHORE EAST TO SOUTHEASTERLY FLOW. THIS WILL START TO ADVECT LOW CLOUDS IN OFF THE OCEAN. LOW CLOUDS MOVING AROUND THE SURFACE HIGH TO THE NORTH WILL ALSO START TO PUSH IN FROM THE NORTHEAST. SO MOST OF THE AREA WILL GO FROM CLEAR TO MOSTLY CLOUDY/OVERCAST SKIES BY THIS EVENING.
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&& .SHORT TERM /SUNDAY/... LOW LEVEL ONSHORE FLOW BELOW THE RIDGE ALOFT WILL PUSH MOISTURE INLAND. THE WEAK SHORT WAVE TROF WILL BE THE FOCUS AS IT CONTINUES TO DRIFT EASTWARD ACROSS THE REGION LATE TONIGHT AND EARLY SUNDAY. AN INVERTED TROUGH SETS UP AT THE SURFACE ACROSS THE FAR SOUTHERN CWA. THIS COMBINED WITH THE SHORT WAVE SHOULD ALLOW ENOUGH FORCING FOR ASCENT TO SATURATE UP TO 700MB. AS MENTIONED IN YESTERDAY`S AFTERNOON FORECAST PACKAGE...THIS SETS UP A NICE SEEDER-FEEDER PROCESS TO INCREASE THE SNOW SHOWER ACTIVITY ACROSS SOUTHERN ZONES IN SOUTHEASTERN NEW HAMPSHIRE AND POSSIBLY COASTAL YORK COUNTY. THERE IS GOOD MODEL AGREEMENT BETWEEN MESOSCALE AND SYNOPTIC MODELS HINTING AT LIGHT QPF IN THESE AREAS...AND ACCUMULATING SNOWFALL MAY BE POSSIBLE. USED A BLEND OF NAM/GFS/ARW/NMM FOR POP AND QPF FORECAST. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
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MEDIUM RANGE MODELS CONTINUE TO TRANSITION FROM A HIGHER WAVE NUMBER TO A LOWER ONE NEXT WEEK WITH STRONG BLOCKING UPSTREAM AND DOWNSTREAM AND MEAN TROUGH DEVELOPING ACROSS NRN TWO THIRDS OF NOAM. THE TRANSITION PERIOD WILL MAKE FOR AN ACTIVE WX WEEK. HOWEVER...WE LOOK TO STAY ON THE WARM SIDE OF THE TROUGH THROUGH FRIDAY...WITH HIGHS RUNNING ABV NORMAL AND MAINLY RAIN. BEST CHC FOR ANY ACCUMULATING SNOW IN THE EXTENDED WILL BE ALONG THE COAST SUNDAY NIGHT INTO EARLY MONDAY AS MODELS INDICATING DEVELOPMENT OF INVERTED TROUGH. NAM12/GFS IN FAIR AGREEMENT AS TO TIMING AND LOCATION...DEVELOPING ALONG THE MID-COAST SUN NIGHT...AND SHIFT WEST TOWARD THE NH AND SW ME COASTS DURING THE DAY ON MONDAY. EURO TENDS TO HOLD THE QPF AROUND AND E OF PENOBSCOT BAY UNTIL LATE MONDAY AND THEN SHIFTS IT EAST MONDAY NIGHT. THE AGREEMENT BETWEEN THE NAM AND GFS THIS FAR OUT IS INTERESTING...SINCE MODELS TEND TO NOT HANDLE THESE INVERTED TROUGHS WELL UNTIL THEY IN THE 12-24 HOUR RANGE....BUT HAVE GENERALLY FOLLOWED A NAM/GFS BLEND SUN NIGHT THRU MON NIGHT. QPF WILL BE LIGHT AND SUN NIGHT IS THE BEST CHC FOR ANY ACCUMS AS PRECIP WILL LKLY MIX WITH OR CHANGE TO RAIN DURING THE DAY MONDAY...AND EVEN IF IT DOES STAY AS SNOW...WILL HAVE TOUGH TIME ACCUMULATING. THE ONE THING TO WATCH FRO WITH INVERTED TROUGHS IS IF IT LOCKS INTO ONE AREA...AND SETS UP CONVERGENT ONSHORE FLOW SIMILAR TO COASTAL FRONT...WHICH WOULD GIVE A SPECIFIC AREA SEVERAL INCHES WITH VERY LITTLE ELSEWHERE. FOR NOW...HOLDING ONTO THE IDEA OF A MOVING TROUGH WITH ACCUMS OF A COATING IN MOST SPOTS. INLAND JUST LOOKS FOR MAINLY CLOUDY SKIES IN THIS TIME FRAMEWITH A FEW FLURRIES. MAY SEE A LITTLE BIT OF A BREAK ON TUE AS WEAK OFFSHORE SFC LOW EXITS AND ALLOWS SOME RIDGING TO BUILD BACK IN FROM THE NE...THEN WE START GETTING INTO THE EFFECTS OF THE IMPRESSIVE STORM SYSTEM THAT RAPIDLY INTENSIFIES TO OUR WEST. PRECIP MOVES IN TUE NIGHT...WHICH WILL BEGIN AS RAIN ALONG THE COAST...WITH EARLY LOWS IN THE MID TO UPPER 30S. INLAND...PRECIP WILL START AS SNOW...AND TRANSITIONS TO FREEZING RAIN OR RAIN LATE TUE NIGHT...AND EVENTUALLY TRANSITION TO RAIN WED MORNING. THE HEAVY PRECIP WILL MAINLY FALL AS RAIN WED AFTERNOON AND WED NIGHT. GFS QPF SEEMS HIGH...AS IT MAY BE DEALING WITH CONVECTIVE SCALING ISSUES...AND THE 1.5-2.5" OF THE EURO SEEMS MORE REASONABLE ATTM...STRONG SE FLOW DEVELOPS EAST OF THE OCCLUSION POINT WHICH CROSSES WRN NEW ENGLAND WED NIGHT. WILL SEE STRONG LOW LEVEL SE JET DEVELOP ABOVE THE INVERSION AROUND THIS TIME AS WELL...AND ALTHOUGH THE INVERSION SHOULD PREVENT FULL MIXING...ESPECIALLY OVER LAND...COULD SEE WIND GUSTS APPROACHING ADV LEVELS. HIGHS WED WILL LKLY OCCUR LATE IN THE DAY WED OR WED EVE...AND WILL MAKE A RUN AT 50 IN SRN NH AND ALONG THE COAST. SHARP BACK EDGE TO THE RAIN WILL CROSS THE REGION EARLY WED AND RAIN SHOULD END FROM SW TO NE DURING THE MORNING AND EARLY AFTERNOON...WITH SOME PARTIAL CLEARING POSSIBLE IN THE AFTERNOON. GUSTY W-SW WINDS WILL DEVELOP BEHIND THE SYSTEM....BUT HIGHS WILL STILL BE ABV NORMAL...IN THE 40S.
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&& .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/... SHORT TERM...MVFR CONDITIONS WILL CONTINUE UNTIL ABOUT DAYBREAK IN THE CT RIVER VALLEY AS LOW LEVEL MOISTURE HAS BECOME TRAPPED. SHOULD SEE ALL AREAS RETURN TO VFR DURING THE DAY AND THEN MORE MOISTURE WILL WORK ITS WAY INTO THE REGION AS LOW LEVEL WIND FLOW TURNS ON SHORE. THIS WILL BRING SOME MVFR CEILING AND POSSIBLE SOME LIGHT SNOW SHOWERS FROM SATURDAY EVENING THROUGH MONDAY. LONG TERM...POSSIBLE PERIODS OF MVFR TO IFR AT COASTAL TERMINALS SUN NIGHT INTO MONDAY AS INVERTED TROUGH DEVELOPS ACROSS THE GULF OF ME. MVFR LIKELY TO HOLD TUE INTO TUE NIGHT...WITH LOWERING TO IFR LATE TUE NIGHT AND WED IN RAIN...WITH INCREASING E-SE WINDS LATE IN THE DAY WED. && .MARINE... SHORT TERM...WINDS AND SEAS WILL REMAIN BELOW SCA CONDITIONS THRU SUNDAY. LONG TERM...WATER REMAIN BLO SCA LVLS SUN NIGHT THROUGH TUE NIGHT. STRONG LOW PRES TO THE WEST WILL SEE WINDS INCREASE TO GALES WED AFTERNOON WITH BORDERLINE STORM FORCE WINDS POSSIBLE WED NIGHT. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...NONE. NH...NONE. MARINE...NONE. && $$ KISTNER/CEMPA

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