Area Forecast Discussion
Issued by NWS Portland, ME

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000
FXUS61 KGYX 201447
AFDGYX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAY ME
947 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/...
UPDATE...
HAVE UPDATED THE GRIDS BASED ON CURRENT CONDITIONS AND LATEST
SUITE OF MESOSCALE MODELS. HAVE INCREASED CLOUD GRIDS FOR THE
IMMEDIATE COASTLINE AND THE COASTAL WATERS FOR TODAY AND TONIGHT.
STRONGEST WESTWARD PUSH OF THE LOW SC OVER THE GULF OF MAINE
CONTUINUES TO BE OVER THE NH SEACOAST. HAVE INCREASED POPS FOR
THIS REGION FOR LATER TODAY AND TONIGHT...BRINGING A LIGHT COATING
OF SNOWFALL TO THAT REGION.

MAD MINOR ADJUSTMENTS TO TODAYS WIND FORECAST...OTHERWISE
FORECAST ON TRACK.

PREV DISC...
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.

&&

.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/...
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.

&&

.AVIATION /15Z 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.

&&

$$


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