Gale Warning 477, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
130 PM AKST TUE DEC 30 2008

.SYNOPSIS...
COLD UPPER LOW COMPLEX OVR THE GULF THIS MORNING AS PART OF A
COMPLEX UPR AIR PATTERN FOR THE NORTHERN HEMISPHERE & -42C AT 500
HPA WITH MANY TCU AND PSBL CBS. ANCHOR UPPER LOW OVER NORTH
CENTRAL RUSSIA AND A REX TYPE BLOCK OVER THE WESTERN BERING SEA.
VERY STRONG SUBTROPICAL JET FROM SOUTHERN ASIA AIMED AT MIDWAY
ISL AND POLAR JET 250 HPA WESTERLY OVER THE QUEEN CHARLOTTES
ABOUT 125 KT. 999 MB SFC LOW IN GULF WITH ARCTIC FRONT THROUGH
DIXON ENTRANCE THEN OVER PRINCE OF WALES ISLAND AT 17Z.
1040 MB HIGH OVR NW CANADA CONNECTED TO 1037 HIGH CELL OVR WRN
BERING SEA AT 12Z. DEVELOPING SFC LOW OFF PACIFIC NW 48N 135W AT
18Z AROUND 997 MB WELL SUPPORTED ALF.

.SHORT TERM...THE 999MB VERTICALLY STACKED LOW IN THE CENTRAL
GULF CONTINUES TO SLOWLY FILL AND LUMBER OFF TOWARD THE WEST THEN
SOUTHWEST AND THEN SOUTHEAST AS A RAPIDLY DEVELOPING LOW MOVES
NORTHEAST OUT OF THE NORTHERN PACIFIC TOWARD THE QUEEN CHARLOTTE
ISLANDS. THIS LOW IS FORECAST TO DEEPEN TO 982MB AND MOVE INTO BC
JUST SOUTH OF QUEEN CHARLOTTE ISLAND TUESDAY NIGHT.

A VORT LOBE CONTINUES TO ROTATE AROUND THE PARENT LOW IN THE EAST
CENTRAL GULF OF ALASKA BRINGING SNOW SHOWERS TO THE SOUTHERN
ZONES AND IN PARTICULAR ZONE 28 WHERE A WINTER WEATHER ADVISORY
HAS BEEN POSTED THROUGH 3 AM WEDNESDAY. ARCTIC AIRMASS IS
SITUATED OVER INTERIOR ALASKA AND THE YUKON. VERY COLD AIR
CONTINUES TO POUR INTO THE PANHANDLE THROUGH INTERIOR PASSES
PROVIDING REINFORCEMENT FOR THE ALREADY COLD AIR MASS IN PLACE
OVER THE PANHANDLE. THE STRONG PRESSURE GRADIENT BETWEEN THE
ARCTIC HIGH IN THE YUKON AND THE LOW IN THE GULF OF ALASKA IS
CONTRIBUTING TO WIND ADVISORIES FOR ZONES 17 18 19 20 AND 25 FOR
GAP WINDS OUT OF INTERIOR BAYS AND PASSES. BRUTAL WIND CHILL
VALUES CONTINUE IN ZONE 18 ESPECIALLY NEAR WHITE PASS WHERE WIND
CHILL VALUES TO MINUS 35 ARE OCCURRING. THE COMBINATION OF GALE
FORCE WIND AND LOW AIR AND WATER TEMPERATURES HAVE CONTRIBUTED TO
HEAVY FREEZING SPRAY IN THE NORTHERN INTERIOR CHANNELS.

12Z GFS INITIALIZED WELL AND HAD A BETTER HANDLE ON THE ARCTIC
HIGH PRESSURE IN THE YUKON AND INTERIOR ALASKA WHICH PROVIDED THE
BEST PRESSURE GRADIENT FOR ONGOING GAP WIND. THE TONIGHT AND
TOMORROW PERIOD GRIDS WERE DERIVED FROM INHERITED GRIDS AND 12Z
GFS.

.LONG TERM...
CHALLENGE IS TO FORECAST PATTERN CHANGE. ALTHOUGH UPR LOW COMPLEX
KICKS OUT E IN SHORT TERM...A NUMBER OF SHORT WAVES MOVE INTO THE
EASTERN GULF FROM THE NORTH ON THE DOWNWIND SIDE OF THE REX
BLOCK. THIS IS REASONABLE TO ACCEPT AS PER ALL 12Z OPS MODEL RUNS
WHICH WILL RE-ESTABLISH A SFC LOW OFF YAKUTAT BY THU NITE WHILE
THE MAIN STORM TRACK IS INTO THE PACIFIC NORTHWEST. HIGH
CONFIDENCE THAT THE ARCTIC FRONT WILL MOVE VERY LITTLE THROUGH
SAT BY USING A BLEND OF ALL OPS MODELS AND ENSEMBLES. ERGO NO
PATTERN CHANGE YET. WILL ACCEPT THE HPC SFC PROG FOR 12Z SAT AND
THEIR MODEL OF KEEPING LOWS TO THE SOUTH OF THE PANHANDLE QUITE
REASONABLE AND WILL ACCEPT HPC GUIDANCE FOR DAYS 5 THROUGH 8 WITH
MODERATE CONFIDENCE ADJUSTING THEIR ARCTIC FRONT SLIGHTLY SOUTH.
&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WIND ADVISORY AKZ017-018-019-020-025-026.
         WINTER WEATHER ADVISORY AKZ028.
         WIND CHILL ADVISORY AKZ018.
MARINE...HEAVY FREEZING SPRAY WARNING PKZ011-012-013.
         GALE WARNING PKZ011>013-021-022-031-032-034-043-051.
         SMALL CRAFT ADVISORY PKZ033-035-036-041-042-052.

CCC/JCC