Small Craft Advisory 798, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
400 PM AKST SAT DEC 22 2012

.SHORT TERM...THE LATEST SATELLITE IMAGERY SHOWS A WEAK LOW WEST
OF HAIDA GWAII THAT IS SPREADING CLOUD AND SOME
SCATTERED/ISOLATED SNOW SHOWERS OVER THE COASTAL AND NORTH
CENTRAL INNER CHANNELS. NO MUCH ACCUMULATIONS MANLY JUST SOME
FLURRIES. THERE IS ANOTHER BAND THAT IS LIFTING NORTH AT THIS
TIME THAT WILL KEEP A CHANCE OVER THOSE AREAS THROUGH THIS
EVENING. STRONG NORTH WIND ALONG WITH COLD TEMPS WILL PRODUCE
GALE FORCE WINDS WITH HIGH GUSTS AND HEAVY FREEZING SPRAY OVER
THE LYNN CANAL AND GLACIER BAY. MOST OTHER MARINE WATERS WILL SEE
SMALL CRAFT WINDS WITH STRONG GUSTS FROM INTERIOR PASSES FOR
AREAS ALONG THE COAST MOUNTAINS AND OVER THE NORTHEAST GULF
COAST. THESE CONDITIONS WILL PERSIST THROUGH THE SHORT TERM AS
THE HIGH IN THE YUKON WILL REMAIN IN PLACE. WITH THAT SAID
EXTENDED THE WINTER WEATHER ADVY FOR ZONE 18 AS THERE IS STILL
GUSTS TO 50 MPH WITH WIND CHILLS AS LOW AS 45 BELOW NEAR WHITE
PASS. THERE IS ALSO LOCALLY WINDY CONDITIONS ALONG LYNN CANAL,
NEAR YAKUTAT AND MISTY FJORDS THAT GUSTS TO 45 MPH WILL CONTINUE
THROUGH THE SHORT TERM PERIOD. THE JUNEAU AREA WILL SEE HIGH
GUSTS NEAR DOWN TOWN AND DOUGLAS BUT WITH THE CROSS BARRIER FLOW
WEAKENING THE THINKING IS THAT THE GUSTS WILL BE NEAR 35 MPH
THROUGH SUNDAY AFTERNOON.

THE BIGGEST FORECAST ISSUE TODAY WAS THE CLOUD COVER AND THAT
WILL DIRECTLY AFFECT THE LOW TEMPS TONIGHT. CLOUDS HAVE MOVED OVER
THE MOST OF THE FORECAST AREA AND THAT MAY LIMIT THE LOW TEMPS.
BUT THERE IS A BREAK OVER DIXON ENTRANCE THAT WILL MOVE OVER THE
AREA AND MAY EXPAND ALONG THE COAST MOUNTAINS TONIGHT. SO TEMPS
WILL RANGE FROM 10 ABOVE TO THE MID 20S OVER MOST OF THE AREA WITH
THE FAR NORTHERN AREAS AND WIND SHELTERED SEEING LOW TEMPS FROM 3
ABOVE TO 10 BELOW.

USED MAINLY THE NAM IN THE SHORT TERM PERIOD AND THERE IS ABOUT
AVERAGE FORECASTER CONFIDENCE THROUGH THE NEXT 24HRS. LOW
CONFIDENCE IN THE CLOUD COVER.

&&

.LONG TERM...MAIN POINT FOR THE EXTENDED FORECAST IS THAT THERE
WILL BE A GRADUAL WARMING TREND...MOST PLACES STAYING BELOW
FREEZING BUT NOT AS COLD AS IT HAS BEEN. THE EXTENDED FORECAST
STARTS OFF WITH A RELATIVELY WEAK UPPER LEVEL PATTERN. THERE WILL
BE SLIGHT ONSHORE FLOW AT THE UPPER LEVELS WITH A LOW OVER THE
BERING AND A RIDGE BUILDING OVER THE NE PACIFIC. AT THE MID LEVELS
FLOW WILL REMAIN OFFSHORE AND KEEP PRECIP CHANCES TO A MINIMUM.
THE SURFACE PRESSURE PATTERN TURNS MORE E-W ON MONDAY WITH LOWS IN
THE GULF AND HIGH PRESSURE OVER B.C. THIS WILL CAUSE WINDS THROUGH
N-S INSIDE WATERS TO EASE A BIT AND THE WINDS THROUGH THE E-W
CHANNELS TO INCREASE...INCLUDING E-W INTERIOR PASSES.

A TROUGH ROTATES AROUND THE MAIN LOW FROM THE PACIFIC INTO THE
EASTERN GULF THROUGH TUESDAY. THIS WILL LIKELY BRING IN SOME
WARMER/MOIST AIR TO THE SOUTHERN PANHANDLE. A SURFACE CLOSED LOW
ASSOC WITH THE UPPER LEVEL TROUGH WILL MOVE INTO THE SE GULF ON
TUESDAY HOWEVER WEAKENING AS IT DOES. THIS WILL KEEP SOME GRADIENT
THROUGH THE N-S CHANNELS ENOUGH TO KEEP THE NORTH DIRECTION.

THE PARENT UPPER LEVEL LOW IN THE BERING WILL DIMINISH AND
RETROGRADED TO THE WEST WHILE A RIDGE OF HIGH PRESSURE BUILDS INTO
THE WESTERN GULF ON TUESDAY. THIS RIDGE PUSHES THE TROUGH TO THE
EAST AND CAUSES A MORE NWLY FLOW OVER THE REGION ON WEDNESDAY. THE
UPPER LEVEL RIDGE WILL BE OVER THE PANHANDLE THURSDAY CAUSING MID
AND UPPER LEVEL FLOW TO TURN SWLY AND ONSHORE WITH WAA ALONG THE
COAST AHEAD OF THE NEXT SYSTEM.

THURSDAY A LOW IN THE WESTERN GULF INCREASES THE E-W GRADIENT AGAIN.
THE ASSOC FRONTAL TROUGH REACHES THE PANHANDLE BY THURSDAY EVENING
WITH STRONG SE WINDS AHEAD OF IT. THIS FRONT LOOKS TO BE THE NEXT
BEST CHANCE OF GETTING ACCUMULATING SNOW AS IT PASSES THURS NIGHT
THROUGH FRIDAY. 1-3 INCHES OF SNOW IS EXPECTED ON THURSDAY AND
ANOTHER 1-3 IN ON FRIDAY.

A RIDGE BUILDS OVER THE PANHANDLE BEHIND THE FRONT ALLOWING THE
WINDS THROUGH THE INSIDE WATERS TO TURN SOUTHERLY AND KEEP FLOW
ONSHORE THROUGH THE WEEKEND. THE PATTERN BECOMES MORE PROGRESSIVE
THEREAFTER WITH MULTIPLE LOWS/FRONTS PASSING WITH GREATER CHANCES OF
PRECIP.

THE ECMWF HAD THE BEST REPRESENTATION OF THE PRESSURE GRADIENT OVER
THE NORTHERN INNER CHANNELS BUT THE GEM IS THE ONLY MODEL THAT HAD
PRESSURE LOW ENOUGH IN THE GULF. OVERALL THOUGH...THE MODEL PRESSURE
FIELDS THROUGH THE EXTENDED WERE VERY SIMILAR TO EACH OTHER. USED A
BLEND OF AVAILABLE MODELS WITH SOME EMPHASIS ON THE GEM. FORECAST
CONFIDENCE IS AVERAGE.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND THROUGH LATE TONIGHT FOR AKZ025.
         STRONG WIND THROUGH SUNDAY AFTERNOON FOR AKZ017-019-029.
         WINTER WEATHER ADVISORY UNTIL 4 PM AKST SUNDAY FOR AKZ018.
MARINE...HEAVY FREEZING SPRAY WARNING FOR PKZ011-012.
         HEAVY FREEZING SPRAY WARNING FOR PKZ013.
         GALE WARNING FOR PKZ011>013-022.
         SMALL CRAFT ADVISORY FOR PKZ021-031>036-041>043-051-052.

&&

ABJ/HANNON