Gale Warning 154, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
209 PM AKST SUN FEB 19 2012

.SHORT TERM...LAST NIGHT'S SYSTEM IS ALL READY WELL INTO CANADA
TODAY. SNOW AMOUNTS ONLY RANGED FROM TRACE AMOUNTS TO 3 TO
4 INCHES AROUND HAINES AND SKAGWAY. WE ARE CURRENTLY UNDER SOME
WEAK RIDGING THAT IS BRINGING THE BREAKS IN THE CLOUD COVER OVER
MOST OF THE AREA EXCEPT FOR THE EXTREME SE PART. SOME SNOW AND
RAIN SHOWERS ARE STILL PRESENT PARTICULARLY OVER THE SE PART OF
THE PANHANDLE. WINDS ARE ALSO LESS THEN 20 KT IN MOST PLACES.

 FOCUS NOW SHIFTS TO THE NEXT SYSTEM MOVING ACROSS THE SOUTHERN
GULF AT THE MOMENT. THE SYSTEM SEEMS TO BE TEARING ITSELF APART
AS VISIBLE SATELLITE TODAY REVEALS THAT THE SURFACE LOW IS ABOUT
200 MILES BEHIND THE MID LEVEL CIRCULATION. THIS DOES NOT BODE
WELL FOR THE CONTINUED STRENGTH OF THIS SYSTEM AS CUT OFF FROM
ITS UPPER LEVEL SUPPORT IT WILL WEAKEN AWAY JUST WEST OF HAIDA
GWAII TONIGHT. STILL THE PRESSURE GRADIENT BETWEEN IT AND THE
RETREATING RIDGE IN CANADA WILL CAUSE SOME HIGHER SE WINDS IN THE
SOUTHERN PANHANDLE WITH SMALL CRAFT WINDS FOR CLARENCE STRAIT AND
THE SOUTHERN OUTER COASTAL MARINE ZONES TONIGHT. THE SOUTHERN
PANHANDLE WILL ALSO SEE CONTINUED PRECIP FROM THIS WEAKENING
SYSTEM TONIGHT THROUGH PRECIP AMOUNTS WILL BE LIGHT.

 TOMORROW, THE PRECIP AND WIND WILL CONTINUE ACROSS THE SOUTH AND
WILL SPREAD NORTH THROUGH THE DAY AS THE NEXT RAPIDLY MOVING
FRONT STALKS ACROSS THE GULF. THIS SYSTEM IS MUCH BETTER
ORGANIZED WITH THE SUPPORT OF A 130 KT JET STREAK AT 500 MB AND A
GOOD MID LATITUDE MOISTURE CONNECTION. THIS SYSTEM IS SHAPING UP
TO BRING UP TO A HALF AN INCH OF QPF TO THE MOST OF THE AREA
STARTING LATE MON AFTERNOON. THICKNESS VALUES TEND TO SHOW THAT
THERE REALLY ISN'T THAT MUCH COLD AIR TO WORK WITH IN THE
PANHANDLE RIGHT NOW AND WHAT IS THERE WILL BE QUICKLY ERODED BY
THE SOUTHERLY FLOW AHEAD OF THE FRONT. THEREFOR MOST PLACES UP TO
AND INCLUDING THE ICE STRAIT CORRIDOR WILL START OUT WITH A
RAIN/SNOW MIX OR ALL RAIN AND RAPIDLY CHANGE OVER TO ALL RAIN.
FARTHER NORTH HAINES, SKAGWAY, AND YAKUTAT HAVE ENOUGH COLD AIR
TO BE SNOW BUT BY LATE AFTERNOON SE FLOW SHOULD BE WORKING INTO
YAKUTAT AND CHANGE THEIR PRECIP OVER TO RAIN. BREEZY CONDITIONS
WILL ALSO BE PRESENT OVER THE PANHANDLE BY LATE AFTERNOON. I HAVE
HELD OFF ON ANY STRONG WIND HEADLINES DUE TO THE DISTANCE OF THE
FRONT FROM THE PARENT LOW AND THAT THE SYSTEM WILL BE WEAKENING
AS IT APPROACHES THE AREA.

 MODELS HAD SOME MARKED DIFFERENCES IN SOME CASES IN THE SHORT
RANGE TODAY. 0Z EC AND NAM WERE WAY TO SLOW WITH THE LOW
CURRENTLY MOVING ACROSS THE SOUTHERN GULF. UK, GFS, AND THE 12Z
EC SEEMED TO HAVE THE RIGHT IDEA WITH IT. NAM SEEMED TO REMAIN A
BIT OF AN OUTLIER EVEN WITH THE NEXT SYSTEM IN LINE. SO DECIDED
TO USE A BLEND OF THE UK WITH SOME GFS AND 12Z EC FOR FORECAST
UPDATES TODAY. FORECAST CONFIDENCE IS A LITTLE ABOVE AVERAGE.

.LONG TERM...MODELS IN GOOD AGREEMENT ON EVOLUTION OF THE LARGE
SCALE PATTERN OVER THE NEXT WEEK. THE PATTERN THAT HAS BEEN FAIRLY
PERSISTENT OVER THE PAST 3 WEEKS...A RIDGE OVER THE FAR ERN PAC
AND TROF OVER THE CENTRAL PAC AND BERING SEA...WILL MOST LIKELY
CHANGE DURING LATE WEEK. RIDGE SHOULD BUILD OVER THE BERING
SEA/WRN AK WHILE TROF DEVELOPS OVER THE FAR ERN PAC BY LATE WEEK.
THERE ARE SOME DIFFERENCES IN AMPLITUDE OF THE RIDGE/TROF COUPLET
THOUGH...WITH THE ECMWF THE MOST AMPLIFIED OF THE MODELS. MODEL
TREND SEEMS TO BE IN THAT DIRECTION BUT THE ECMWF MAY STILL BE TOO
AMPLIFIED AT THIS POINT. STILL...A RETURN TO COLDER WEATHER IS
LOOKING LIKELY BEGINNING LATE THIS WEEK. USED 12Z UKMET/GFS BLEND
OUT TO 12Z WED...THEN USED GFS UNTIL HPC WAS USED BEGINNING 12Z
THU.

WILL HAVE AN OCCLUDED FRONT MOVING ACROSS THE AREA MON
EVENING...AND IT SHOULD BE E OF THE AREA BY LATE MON NIGHT. PRECIP
WILL TEND TO DIMINISH FROM THE W MON NIGHT AFTER FROPA...EXCEPT
THE FAR N WILL CONTINUE TO PRECIP STEADILY AS THERE WILL BE SOME
OVERRUNNING OCCURRING THERE UNTIL LOW LEVEL FLOW BECOMES STRONGLY
S ALL THE WAY N TO PAGY. TEMPS UP N WILL HANG NEAR FREEZING BEFORE
THAT TIME SO PRECIP SHOULD BE MOSTLY SNOW. WILL KEEP WW ADVY GOING
FOR PAHN ZONE AND PAGY ZONE ABOVE 500 FEET UNTIL 5 AM TUE.
ELSEWHERE PRECIP SHOULD BE RAIN...ALTHOUGH HYDER COULD ALSO SEE
SOME WET SNOW UNTIL THE LOWER LEVEL FLOW TURNS SWLY LATE MON EVENING.
ONSHORE FLOW WILL KEEP SPOTTY PRECIP GOING THRU TUE MORNING ALONG
THE INNER CHANNELS AND NRN GULF AREA.

A LOW WILL TRACK ENE TO THE SE GULF BY TUE EVENING. THIS WILL
SPREAD MORE PRECIP TO THE SRN AND CENTRAL AREA BEGINNING LATE TUE
MORNING ALONG THE SW COAST AND REACHING THE N-CENTRAL AND HYDER
AREAS BY LATE AFTERNOON. SINCE AIRMASS PRECEDING THIS SYSTEM WILL
BE ON MILD SIDE PRECIP SHOULD BE MOSTLY...IF NOT ALL...RAIN. HYDER
COULD BE THE EXCEPTION AS LOW LEVEL FLOW BECOMES LIGHT WHILE PRECIP
INCREASES...WHICH COULD LEAD TO SNOWMELT COOLING EFFECT AND ALLOW
WET SNOW TO REACH SFC. THE LOW SHOULD MOVE INLAND ACROSS CENTRAL
SE AK TUE NIGHT...AND BE WELL E OF THE AREA BY WED MORNING. PRECIP
SHOULD DIMINISH AGAIN ONCE LOW MOVES INLAND...BUT ONSHORE FLOW
WILL KEEP SPOTTY PRECIP GOING WED ESPECIALLY ALONG THE COAST MTNS
AND NRN GULF COAST.

COOLER AIR WILL FILTER IN FROM THE WEST WED AND WED NIGHT...AND
THIS WILL LIKELY CAUSE PRECIP TO CHANGE TO SNOW BY WED NIGHT MOST
PLACES. WILL HAVE TO WATCH FOR A SHORTWAVE TO MOVE ACROSS THE
AREA WED NIGHT WHICH MAY BRING A HIGHER THREAT FOR SNOW...BUT
MODELS DIFFER TOO MUCH ON THIS TO GO MUCH HIGHER THAN LIKELY POPS
FOR WED NIGHT AT THIS POINT.

COOLER AIR WILL CONTINUE TO SLOWLY FILTER IN FROM THE W THU INTO
FRI...THEN A SOMEWHAT COLDER AIRMASS SHOULD MOVE IN FROM THE N FRI
NIGHT INTO THE WEEKEND. HAVE LOWERED TEMPS SOMEWHAT FOR THU INTO
THE WEEKEND...AND THEY MAY NEED FURTHER LOWERING ESPECIALLY HIGH
TEMPS SAT ONWARD. INTERESTING SCENARIO ON THE 12Z EC AND NEW 18Z
GFS FOR NEXT MON...POTENTIALLY A SNOWSTORM. STAY TUNED...

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER WEATHER ADVISORY FROM NOON MONDAY TO 5 AM AKST TUESDAY
     FOR AKZ018-019.
MARINE...GALE WARNING FOR PKZ022-043-051-052.
         SMALL CRAFT ADVISORY FOR PKZ021-033-035-036-041-042-053.

&&

EAL/RWT