Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 150221
AFDGYX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAY ME
920 PM EST SUN DEC 14 2014

.SYNOPSIS...
HIGH PRESSURE WILL MOVE OVER THE REGION TONIGHT AND MONDAY THEN
SHIFT INTO THE CANADIAN MARITIMES ON TUESDAY. WEAK LOW PRESSURE
MOVES OFFSHORE TUE NIGHT INTO WEDNESDAY...AND WILL BRING A ROUND
OF LIGHT PRECIPITATION. HIGH PRESSURE WILL BUILD INTO THE REGION
TOWARD THE END OF THE WEEK.

&&

.NEAR TERM /TONIGHT/...
920 PM UPDATE...CLOUDS CONTINUE TO HANG TOUGH ACROSS WESTERN AND
NORTHERN NH AND ARE EXPECTED TO DO SO FOR MUCH OF THE NIGHT. THE
ONLY FORECAST CHANGE WAS TO ADD A LITTLE PATCHY FREEZING DRIZZLE
ACROSS NORTHERN NH WHERE FORECAST SOUNDINGS SUPPORT AT LEAST A
LOW PROB. OTHERWISE...MOSTLY CLEAR FOR THE REST OF THE AREA.

6 PM UPDATE...HAVE UPDATED THE FORECAST MAINLY FOR MINOR CHANGES IN
SKY COVER. HAVE KEPT WESTERN AND NORTHERN NH CLOUDY ALL NIGHT AS
STRENGTHENING SUBSIDENCE INVERSION KEEPS LOWER-LEVEL MOISTURE
TRAPPED. OTHERWISE...CLOUDS ACROSS EASTERNMOST ZONES SHOULD
GRADUALLY DISSIPATE OVERNIGHT. THE REST OF THE REGION SHOULD REMAIN
MOSTLY CLEAR WITH SOME LATE-NITE FOG.

PREVIOUSLY...

AS HIGH PRESSURE NUDGES CLOSER TO THE AREA... A NORTHWEST FLOW HAS
PERSISTED THROUGH THE DAY TODAY. THIS FLOW HAS CAUSED CLOUDS TO
LINGER IN THE MOUNTAINS WHILE LEADING TO SIGNIFICANT CLEARING
DOWNWIND OF THE MOUNTAINS. EXPECT CLOUDS TO BE SLOW TO DISSIPATE
IN THE MOUNTAINS... POTENTIALLY LASTING ALL NIGHT AS HIGH PRESSURE
SLOWLY MOVES INTO THE AREA. MEANWHILE... THE CLEAR CONDITIONS WILL
CONTINUE FOR AREAS DOWNWIND OF THE MOUNTAINS. CLEAR SKY WILL LEAD
TO BETTER RADIATIONAL COOLING CONDITIONS ON THE COASTAL PLAIN...
BUT WINDS WILL STAY UP A BIT AND PREVENT THE INVERSION FROM
BECOMING TOO STRONG. IN ADDITION... DEWPOINTS IN THE UPPER 20S AND
LOW 30S WILL LIKELY PREVENT TEMPERATURES FROM FALLING TOO FAR.
VALLEY LOCATIONS MAY BE ABLE TO CRATER BELOW THEIR DEWPOINTS WITH
LOCALLY BETTER COOLING CONDITIONS.

RECENT TRENDS IN THE MODELS HAVE BEEN TO DROP TEMPERATURES TOO
MUCH AT NIGHT. FOR EXAMPLE...PORTLAND HAS NOT BEEN BELOW FREEZING
SINCE DECEMBER 9 IN SPITE OF SEVERAL DAYS OF FORECAST LOWS IN THE
20S. HOWEVER... TONIGHT SHOULD BE DIFFERENT AS THE CLOUDS AND
PRECIPITATION HAVE FINALLY EXITED. THIS WILL ALLOW BETTER COOLING
CONDITIONS BUT STILL NOT QUITE AS COLD AS NORMAL FOR NIGHTTIME
LOWS.

&&

.SHORT TERM /MONDAY AND MONDAY NIGHT/...
HIGH PRESSURE MOVES OVERHEAD ON MONDAY WITH WINDS SHIFTING FROM
NORTHWEST TO NORTH AND THEN BECOMING NEARLY CALM. TEMPERATURES
ALOFT WILL BE WARMING WITH 850 MB TEMPERATURES RISING AS MUCH AS
5C FROM TODAY. AS A RESULT... IT CAN BE EXPECTED THAT TEMPERATURES
TOMORROW AFTERNOON SHOULD BE SIMILAR OR WARMER THAN TODAY OVER
MUCH OF THE COASTAL PLAIN. HOWEVER... MODELS ARE NOT PICKING UP ON
THE WARMER TEMPERATURES TOMORROW. ONE FACTOR LEADING TO COOLER
TEMPERATURES IS A COOLER START TO MORNING TEMPERATURES THAN WAS
THE CASE THIS MORNING. ALSO... WINDS WILL NOT BE AS STRONG AND NOT
AS DOMINANTLY DOWNSLOPING... LEADING TO LESS FORCED MIXING. IT IS
ALSO GETTING PRETTY CLOSE TO THE SOLSTICE... SO TOTAL HEATING
POTENTIAL FROM THE SUN IS NEAR ITS YEARLY MINIMUM. HOWEVER...
CONSIDERING TEMPERATURES WERE SO WARM TODAY... PLENTY OF SUN WILL
BE AVAILABLE TOMORROW... AND TEMPERATURES ALOFT ARE WARMING... IT
IS LIKELY THAT TOMORROW WILL SEE TEMPERATURES SIMILAR TO TODAY
OVER THE COASTAL PLAIN WITH LOW 40S EXPECTED. IN THE MOUNTAINS
TEMPERATURES WILL BE WARMER WITH CLOUDS FINALLY DISSIPATING AND
LEADING TO MORE SUN.

HIGH PRESSURE BEGINS TO SHIFT EAST MONDAY NIGHT. SHOULD SEE GOOD
RADIATIONAL COOLING CONDITIONS ESPECIALLY OVER MUCH OF MAINE.
HOWEVER... DEWPOINTS ARE NOT ALL THAT LOW SO TEMPERATURES WILL NOT
GET TO EXTREME COLD LEVELS. IN FACT... IT MAY BE PRETTY CLOSE TO
NORMAL LOWS FOR THIS TIME OF THE YEAR... IN THE LOW 20S NEAR THE
COAST AND IN THE LOW TEENS IN THE MOUNTAIN VALLEYS OF NEW
HAMPSHIRE.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
THE 500MB HIGH WAVE NUMBER PATTERN STARTS TRENDING BACK TO BROADER
TROUGHS AND RIDGES DURING THE EXTENDED AS WE SEE A MORE ZONAL
PATTERN...ALTHOUGH THE COLDEST AIR STILL REMAINS LOCKED UP IN THE
POLAR REGIONS AND SIBERIA. SO...LOOK FOR THE TREND OF NORMAL TO
ABV NORMAL TEMPS TO CONTINUE INTO NEXT WEEK....WITH A MORE NORMAL
PATTERN OF PRECIP EVENTS EVERY 3-4 DAYS.

THE MID-UPPR LVL RIDGING WILL BE GOING STRONG ON TUESDAY...BUT
WILL BEGIN TO SHIFT OFFSHORE LATE IN THE DAY. WILL SEE CLOUDS
INCREASE DURING THE DAY AS WAA IN THE S FLOW STARTS TO BRING IN
WAA...WITH HIGHS MID 30S TO LOW 40S.

NEXT SYSTEM WILL BE SET OFF BY OPEN 500 MB WAVE APPROACHING FROM
THE W...THAT CLOSES OFF TOO LATE TO BRING MUCH PRECIP TO THE
REGION TUE NIGHT INTO WED. LOOKS LIKE WE WILL SEE A SHOT OF WAA
PRECIP WITH SOME UNCERTAINTY AS TO P-TYPE...ESPECIALLY AT THE
START...ALTHOUGH COASTAL AREAS AND SRN NH COASTAL PLAIN WILL LKLY
BE MAINLY RA...WITH INLAND AREAS STARTING AS A PERIOD FZRA /GIVEN
WARM 850MB TEMPS ACCUMULATING SN LOOKS LIMITED/ BEFORE EVERYWHERE
CHANGES TO RAIN DURING THE DAY WED. QPF LOOK TO BE ON THE ORDER
OF TWO TO THREE TENTHS OF AN INCH...SO NOT A MAJOR EVENT BY ANY
EVENT...BUT WILL LKLY CAUSE SOME TRAVEL ISSUES IN SPOTS...MOST
LKLY FOR WED MORNING COMMUTE.

THE COLD FRONT BEHIND THE SYSTEM PASSES LATE WED OR D NIGHT...AND
ANY RA/SHRA WILL CHANGE TO SN...WITH SOME LIGHT ACCUMS POSSIBLE IN
THE MTNS. THE SFC LOW SLOWS AS IT MOVES TOWARD THE MARITIMES...SO
SOME N-NE FLOW COULD KEEP CLOUDS AND SOME SHSN AROUND ON
THU...WITH HIGHS JUST A LITTLE COOLER...AND CLOSE TO
NORMAL...UPPER 20S TO MID 30S. SFC HIGH BUILDS IN FRI INTO
SAT...AND THEN WATCHING NEXT SYSTEM WHICH COULD ARRIVE SAT NIGHT
OR SUNDAY. IT HAS POTENTIAL TO BE MORE SIGNIFICANT THAN MID-WEEK
EVENT...BUT NOT A HUGE STORM EITHER...WITH...AGAIN...GREAT
UNCERTAINTY AS TO P-TYPE.

 &&

.AVIATION /20Z SUNDAY THROUGH FRIDAY/...
SHORT TERM...EXPECT VFR CONDITIONS DOWNWIND OF THE MOUNTAINS.
HOWEVER... MVFR CEILINGS HANG ON TO THE NORTH AND WEST OF THE
MOUNTAINS THROUGH TONIGHT. SHOULD SEE SOME IMPROVEMENT EVEN IN THE
MOUNTAINS BY MORNING.

LONG TERM...VFR TUE...THEN POTENTIAL FOR IFR IN LOW GIGS AND
MIXED PRECIP TUE NIGHT INTO WED WITH A RETURN TO VFR FOR THU/FRI.

&&

.MARINE...
SHORT TERM...HIGH PRESSURE MOVING INTO THE AREA WILL KEEP
CONDITIONS ON THE WATERS FAIRLY QUIET WITH WINDS STAYING WELL
BELOW ADVISORY LEVELS.

LONG TERM...GENERALLY THE WATERS WILL CONTINUE REMAIN FAIRLY QUIET
FOR MID-DECEMBER...WITH SUB SCA CONDS EXPECTED TUE THRU FRI.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...NONE.
NH...NONE.
MARINE...NONE.

&&

$$
NEAR TERM UPDATE...EKSTER
LONG TERM... CEMPA



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