Area Forecast Discussion
Issued by NWS Portland, ME

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000
FXUS61 KGYX 301428
AFDGYX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAY ME
1028 AM EDT SAT APR 30 2016

.SYNOPSIS...
HIGH PRESSURE MOVES EAST INTO THE ATLANTIC AND THE CANADIAN
MARITIME PROVINCES TODAY. LOW PRESSURE WILL TRACK THROUGH THE
EASTERN GREAT LAKES AND THEN OFFSHORE TO THE SOUTH OF NEW ENGLAND
SUNDAY INTO MONDAY WITH A PERIOD OF RAIN EXPECTED. A LARGE TROUGH
OF LOW PRESSURE WILL MOVE INTO NEW ENGLAND ON WEDNESDAY AND REMAIN
NEAR THE AREA THROUGH THE WEEKEND...KEEPING COOL TEMPERATURES AND
WET WEATHER IN THE FORECAST.

&&

14Z UPDATE...
QUIET WEATHER CONTINUES ACROSS NORTHERN NEW ENGLAND LATE THIS
MORNING. PATCH OF MID LEVEL CLOUDS ACROSS SOUTHWEST NEW HAMPSHIRE
QUICKLY MIXING OUT AND EXPECT THE ENTIRE FORECAST AREA TO BE
MOSTLY CLEAR BY EARLY AFTERNOON. LIGHT GRADIENT AND FULL SUN WILL
PRODUCE A RATHER SHARP SEA BREEZE WHICH SHOULD COME ROARING IN
DURING THE EARLY AFTERNOON CAPPING TEMPS IN COASTAL AND SOUTHERN
INTERIOR SECTIONS IN THE LOWER TO MID 50S. AWAY FROM THE COAST
HIGH TEMPS WILL TOP OUT IN THE MID 50S TO LOWER 60S. HAVE ADJUSTED
TEMPS/TD`S/SKY GRIDS BASED ON CURRENT OBS AND NO OTHER CHANGES
PLANNED ATTM.


PREVIOUS DISCUSSION...
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
710 AM...THE FORECAST ISSUE THIS MORNING IS THE DECK OF OF MID-
LVL CLOUDS IN SW NH. MODELS ARE NOT REALLY HANDLING IT WELL...BUT
NAM12 SEEMS TO BE THE BEST OF THE BUNCH AND SHOWS THE CLOUDS
BRIEFLY SPREAD EWD ALONG THE NH/MA BORDER FOR THE NEXT HOUR OR TWO
AND THE SLOWLY DISSIPATING MID-LATE MORNING...AND WENT WITH THE
NAM12 FOR SKY...AT LEAST IN THAT AREA.

PREVIOUSLY...500 MB WAVE CROSSING NEW ENGLAND OVERNIGHT IS
PRODUCING MAINLY A DECK OF CIRRUS...BUT HIS SHOULD SHIFT EAST OF
THE CWA AROUND OR SHORTLY AFTER SUNRISE MAKING FOR A MOSTLY SUNNY
DAY WITH JUST SOME PATCHY CIRRUS AND A FEW SCT STRATOCU THAT WILL
FORM ALONG SEA BREEZE FRONT AS IT WORKS INLAND. THE LACK OF ANY
PRE GRADIENT WILL ALLOW THE SEA BREEZE TO WORK FAIRLY FAIR INLAND
AND THIS WILL KEEP TEMPS DOWN IN THE LOW TO MID 50S NEAR THE
COAST...BUT REACH UP TO AROUND 60 INLAND AREAS.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
TONIGHT WILL SEE THE SFC RIDGE BEGIN TO SHIFT SLOWLY OFFSHORE...A
PROCESS THAT WILL TAKE INTO SUNDAY TO FINISH...AS 500 MB RIDGING
BUILDS JUST TO OUR EAST. LOOK FOR CLOUDS TO INCREASE FROM THE
WEST...BUT ANY RAIN SHOULD HOLD OFF UNTIL...AT LEAST...AFTER
SUNRISE ON SUNDAY. MINS WILL LKLY OCCUR CLOSER TO MIDNIGHT WITH
TEMPS STEADY OR RISING AFTER THAT...AND WILL BE IN THE MID TO
UPPER 30S.

THE BIG QUESTION FOR SUNDAY IS HOW QUICKLY THE RAIN MOVES IN...AND
HOW FAR EAST IT GETS. ANY PRECIP IS DRIVEN BY SOME MID LVL ISENTROPIC
LIFT...MAINLY IN THE 600-800MB RANGE. THE NAM BRINGS A ROUND OF
RAIN INTO NH SUNDAY AFTERNOON...WHILE THE EURO HOLDS IT BACK A
LITTLE LONGER. THERE IS PROBABLY ENOUGH TO LIFT TO GENERATE A FEW
SHOWERS OR SOME VERY LIGHT RAIN IN NH SOMETIME TUE AFTERNOON...BUT
DYNAMIC FORCING IS FORCED BY 500MB WAVE CRASHING INTO RIDGE SO
HOLDING OFF LKLY POPS UNTIL MID-LATE AFTERNOON IN NH AND JUST
KEEPING CHC IN ME. MAX T WILL BE AFFECTED BY CLOUDS AND RAIN...AND
WARMEST TEMPS WILL BE IN THE INLAND KENNEBEC AND PENOBSCOT VALLEY
WHERE HIGHS COULD GET CLOSE TO 60. ELSEWHERE LOOK FOR LOW TO MID
50S AT BEST.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
POTENT SHORTWAVE TROUGH ALOFT TRACKS EAST THROUGH THE GREAT LAKES
AND NEW ENGLAND SUNDAY NIGHT AND MONDAY. THIS WILL DRIVE SURFACE
LOW PRESSURE THROUGH THE EASTERN GREAT LAKES... WITH A NEW AREA OF
LOW PRESSURE FORMING NEAR THE SOUTHERN NEW ENGLAND COASTLINE. THE
NEW LOW BECOMES DOMINANT BY MONDAY NIGHT AS IT CONTINUES EASTWARD
INTO THE ATLANTIC TOWARD NOVA SCOTIA. SHOULD SEE AN INITIAL AREA
OF RAIN SUNDAY EVENING WITH A LEADING SHORTWAVE TROUGH BEFORE
ANOTHER ROUND OF RAIN BEGINS MONDAY MORNING LASTING INTO MONDAY
EVENING AS THE OFFSHORE LOW BEGINS TO TAKE OVER. WITH THE COASTAL
LOW FORMING IT WILL PULL IN COLDER AIR ON THE BACK SIDE OF IT JUST
AS PRECIPITATION IS ENDING. THIS COULD ALLOW FOR A BRIEF CHANGE TO
SNOW MAINLY IN THE HIGHER TERRAIN BUT POSSIBLY EXTENDING INTO THE
VALLEYS OF NORTHWEST MAINE AND NORTHERN NEW HAMPSHIRE MONDAY
EVENING. THE ECMWF IS MORE AGGRESSIVE WITH THE HAND OFF BETWEEN
THE FIRST SURFACE LOW AND THE DEVELOPING COASTAL LOW... AND AS A
RESULT THE ECMWF SCENARIO WOULD GIVE THE BEST CHANCE OF A CHANGE
OVER TO SNOW AS PRECIPITATION ENDS.

SHOULD SEE A BREAK ON TUESDAY AS WEAK HIGH PRESSURE BUILDS INTO
THE AREA. TEMPERATURES REMAIN COOL WITH HIGHS REACHING THE UPPER
50S TO LOW 60S.

ON WEDNESDAY A LARGE TROUGH BEGINS TO DIG INTO THE GREAT LAKES AND
CUTS ITSELF OFF OVER THE CENTRAL APPALACHIANS. CUT OFF LOWS AND
THE ASSOCIATED MINOR WAVES ROTATING AROUND THEM ARE NOTORIOUSLY
DIFFICULT FOR MODELS TO FORECAST... SO THE SPECIFIC DETAILS OF THE
FORECAST FROM WEDNESDAY ONWARD ARE VERY MURKY. BUT WITH THE LOW
JUST TO OUR WEST EXPECT OUR AREA TO SEE AT LEAST A FEW ROUNDS OF
WET WEATHER WITH TEMPERATURES NEAR OR JUST BELOW SEASONAL
NORMALS...VULNERABLE TO AN ONSHORE FLOW. WITH A LONG FETCH OF
SOUTHERLY FLOW OVER THE WESTERN ATLANTIC ON THE EAST SIDE OF THE
CUT OFF LOW... THIS WOULD PUT US IN A FAVORABLE POSITION FOR
SEEING A HEAVY PRECIPITATION EVENT IF AND WHEN A MORE SUBSTANTIAL
SURFACE LOW CAN FORM AND TRACK NORTHWARD TOWARD THE AREA. THE
LATEST ECMWF DEVELOPS JUST SUCH A SYSTEM ON THURSDAY... THOUGH
GIVEN THE DIFFICULTY IN TIMING THE MINOR WAVES WITHIN A CUT OFF
LOW... THIS SYSTEM COULD AFFECT OUR AREA ANYTIME FROM THURSDAY
THROUGH SATURDAY SO WE CANNOT BE TOO CONFIDENT ON TIMING OF THE
BEST RAIN CHANCES AT THIS POINT IN TIME.

&&

.AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
SHORT TERM...VFR THRU SUN MORNING. SHOULD SEE CONDS DROP TO MVFR
IN THE AFTERNOON...ESPECIALLY ACROSS NH. COULD SEE SOME LATE IFR
MOVE IN AT THE COASTAL TERMINALS LATE SUNDAY AS WELL.

LONG TERM...SHOULD SEE A GOOD PERIOD OF IFR CONDITIONS AS EARLY AS
SUNDAY NIGHT BUT FOCUSED MAINLY ON THE MONDAY TIME FRAME.
CONDITIONS IMPROVE TO VFR TUESDAY AS LOW PRESSURE DEPARTS TO THE
EAST.

&&

.MARINE...
SHORT TERM...WIND WILL BE VERY LIGHT OVERALL...BUT WILL TURN
ONSHORE NEAR THE COAST AND INCREASE TO ABOUT 10 KTS THIS
AFTERNOON IN SEA BREEZE CIRCULATIONS.

LONG TERM...LOW PRESSURE DEVELOPING JUST SOUTH OF NEW ENGLAND ON
MONDAY WILL TRACK EASTWARD NEAR THE GULF OF MAINE. DEPENDING ON
THE STRENGTH AND TRACK OF THE LOW... THIS COULD PROVIDE A PERIOD
OF STRONGER EASTERLY WINDS. THIS EASTERLY FLOW WILL PRODUCE A
FAVORABLE FETCH FOR LARGER WAVES IN THE GULF OF MAINE MONDAY INTO
EARLY TUESDAY.

&&

.FIRE WEATHER...
ONSHORE FLOW WILL KEEP RH MODERATE TODAY OVER THE COASTAL PLAIN.
ACROSS THE FOOTHILLS AND MOUNTAINS A MUCH DRIER AIR MASS WILL
BRING RELATIVE HUMIDITY VALUES DOWN TO 25 TO 30 PERCENT THIS AFTERNOON.
WINDS WILL BE VERY LIGHT...BUT FUELS REMAIN DRY SO FIRE DANGER
MAY STAY ELEVATED. MUCH OF THE AREA WILL SEE RAINFALL SUNDAY INTO
MONDAY...WITH WETTING RAINS POSSIBLE FOR MANY OF THOSE LOCATIONS.

&&

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

&&

$$


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