Gale Warning 52, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
341 PM AKST SAT JAN 26 2013

.SHORT TERM...ARCTIC OUTBREAK HAS BEGUN TO OCCUR IN THE NORTHERN
PANHANDLE. TIMING OF THE ARCTIC OUTBREAK HAS BEEN SLOWED DOWN BY
3 TO 6 HOURS FOR REACHING CENTRAL SOUTHEAST ALASKA. THE ONLY
LARGER CHANGE BEING A DELAY IN THE ONSET OF FREEZING SPRAY BY
9 TO 12 HOURS. SNOW AMOUNTS IN THE VICINITY OF YAKUTAT HAVE BEEN
RAISED AS THE ARCTIC OUTFLOW IN THE VICINITY OF PRINCE WILLIAM
SOUND HAS RESULTED IN STRONG IF SHALLOW INSTABILITY OVER THE
WARMER WATER. THE WEAK CYCLONIC CIRCULATION IN THE NE GULF WILL
THEN SEND THE MARITIME MODIFIED AIRMASS ONSHORE NEAR YAKUTAT WITH
THE RAISED SNOW AMOUNTS.

 CONFIDENCE IS AVERAGE.

 THE ARCTIC FRONTAL BOUNDARY IS STRONG AND ABRUPT WIND SHIFTS AND
STRONG PRESSURE FALLS WILL OCCUR UNTIL THE OUTBREAK IS SOUTH OF
FREDERICK SOUND SUNDAY. A STRONG ARCTIC FRONTAL PASSAGE BY
SKAGWAY SHOWS UP WITH THE 2153Z OBSERVATION. THE WIND SHIFTED
FROM SSW GUSTING 39 KT TO NE GUSTING TO 39 KT. TEMPERATURE FELL
15F FROM 21Z TO 23Z. IN THE CENTRAL GULF A MARITIME FRONTAL
BOUNDARY IS MOVING ZONALLY TOWARD THE EAST GULF COAST AND WILL
BEGIN AN OVERRUNNING EVENT SUNDAY.

 NAM USEFUL DUE TO ARCTIC OUTBREAK, BOTH THE OUTFLOW WINDS WITH
OROGRAPHY AND THE MOISTURE CONVERGENCE OVER THE NORTH GULF. ECMWF
AND GFS WERE ALSO USED FOR THE ZONALLY TRACKING SYSTEM.

 THE ARCTIC OUTFLOW WILL REACH ZONES 23 AND 26 SUNDAY BUT WILL BE
MUCH SHALLOWER AND WEAKER THAN THE ZONES TO THE NORTH IN THE
INNER  CHANNELS.

 PRECIP INCLUDES THE SHALLOW CONVECTION ON THE GULF COAST FOR
TODAY, AND THE MAIN PRECIP WILL BE ON WEST-FACING SLOPES, WITH
THE HEAVIEST BEING THIS EVENING ON THE AK SIDE OF THE COAST
MOUNTAIN RANGE S OF JUNEAU.

 &&

 .LONG TERM...REMNANTS OF LOW PRESSURE SYSTEM IN THE AK GULF WILL
TRACK TO THE SOUTHEAST CROSSING THE SOUTHERN PANHANDLE AND MOVING
INTO BRITISH COLUMBIA BY MONDAY EVENING. FRONT ASSOCIATED WITH
THIS LOW WILL PUSH TO THE SOUTH WITH ARCTIC AIR DROPPING SOUTH.
ARCTIC HIGH OVER THE YUKON WILL BEGIN TO SLOWLY DRIFT TO THE EAST
AS A 975 MB LOW MOVES FROM THE NORTH PACIFIC TOWARDS THE
ALEUTIANS. THIS LOW CONTINUES ITS NORTHEASTWARD TRACK INTO THE
BERING SEA BY TUESDAY. THE WARM FRONT ASSOCIATED WITH LOW WILL
TRACK ACROSS THE GULF AND REACH THE PANHANDLE COAST BY MONDAY
EVENING. HIGH PRESSURE RIDGE IN THE EASTERN PACIFIC WILL JUST
EXTEND INTO THE SOUTHERN AK GULF MONDAY INTO TUESDAY BELOW THE
FRONT. BY MID WEEK THE BERING SEA LOW WILL CONTINUE TO WEAKEN
WITH ASSOCIATED COLD FRONT IN THE WESTERN GULF. SOME MODELS HAVE
THE TRIPLE POINT ALONG THIS FRONT DEVELOPING A WEAK CIRCULATION
AS THE FRONT MOVES ACROSS THE EASTERN GULF AND REACHING THE
PANHANDLE. BY THE END OF THE WEEK ANOTHER 978 MB LOW TRACKS
ACROSS THE NORTH PACIFIC, UNDER THE ALEUTIANS AND INTO THE
WESTERN GULF.

 AS ARCTIC AIR CONTINUES TO POUR IN OVERNIGHT TEMPERATURES ACROSS
THE PANHANDLE FOR SUNDAY NIGHT WILL HAVE DROPPED INTO THE SINGLE
DIGITS FOR THE NORTHERN PANHANDLE AND RANGE TO THE LOW 30S FOR
THE SOUTHERN PANHANDLE. DAY TIME HIGHS FOR MONDAY WILL BE IN THE
LOW TEENS TO THE NORTH AND RANGE TO THE UPPER 30S TO THE SOUTH.
AS THE YUKON ARCTIC HIGH MOVES TO THE EAST AND WARM FRONT MOVES
IN FROM THE AK GULF THE COLD AIR WILL BEGIN TO EXIT THE REGION
WITH HIGHS PICKING BACK UP TO THE LOW 30S FOR THE NORTH AND LOW
40S FOR THE SOUTH.

 PRECIPITATION IS THE TRICKY PART OF THE FORECAST. FOR SUNDAY
NIGHT INTO MONDAY PRECIP WILL MAINLY BE OVER THE SOUTHERN
PANHANDLE FROM THE REMNANTS OF THE FIRST AK GULF LOW MOVING
ACROSS THE AREA. PRECIP TYPE WILL BE ALL SNOW FROM AREAS
FREDERICK SOUND NORTH AND TRANSITION FROM A RAIN SNOW MIX TO ALL
SNOW FOR POINTS SOUTH. SNOW AMOUNTS KEPT IN THE 1 TO 3 INCH RANGE
FOR NOW WITH A FEW FACTORS THAT WILL EFFECT THESE AMOUNTS. IF THE
AIR MASS REMAINS CONVECTIVE WHICH MAY INCREASE AMOUNTS BUT FOR
THE FAR SOUTH IF TEMPS REMAIN NEAR FREEZING WITH A DELAY IN THE
ARCTIC AIR MOVING IN AND THEN DAY TIME TEMPERATURES INCREASING
THE RAIN SNOW MIX WILL KEEP SNOW AMOUNTS LOWER. FOR THE MONDAY
INTO TUESDAY FRONT THE DEEP MOIST WARM AIR ALOFT MOVING IN WITH
THE COLD SURFACE AIR IN PLACE IS SETTING UP FOR AN OVER RUNNING
SNOW EVENT. 12 HOUR SNOW AMOUNTS IN THE 4 TO 8 INCH RANGE MAY BE
POSSIBLE BEFORE WARMER SURFACE AIR MOVES IN. BY MID WEEK PRECIP
BEGINS TO SHIFT BACK TO RAIN AS TEMPS CONTINUE TO RISE.

 WITH THE TIGHT PRESSURE AND TEMPERATURE GRADIENT OVER THE
CENTRAL AND NORTHERN PANHANDLE WINDS WILL CONTINUE TO INCREASE.
EXPECTING STORM FORCE WINDS FOR NORTHERN LYNN CANAL AND WINDS
GUSTS OF 45 TO 55 MPH NEAR SKAGWAY AND HAINES, JUST BELOW WARNING
LEVEL. STRONG OUTFLOW WINDS FORT HE CENTRAL PANHANDLE FOR THE
START OF THE WEEK WITH THE HIGH IN THE YUKON AND BRITISH COLUMBIA
AND THE LOW TO THE WEST. THESE STRONG WINDS ALONG THE THE ARCTIC
ARI WILL PRODUCE COLD WIND CHILL VALUES WHICH MAY NEAR 30 BELOW
AT HIGHER ELEVATIONS. INNER CHANNELS AND LOCATIONS NEAR OUTFLOW
BOUNDARIES WILL SEE FREEZE SPRAY WITH HEAVY FREEZING SPRAY FOR
THE NORTHERN INNER CHANNELS. LATER IN THE WEEK WINDS WILL SHIFT
FROM THE NORTH TO SOUTH AND WEAKEN AS THE ARCTIC HIGH TRACKS TO
THE EAST.

 SOME MODEL SPREAD AT THE START OF THE LONG TERM DEALING THE
REMNANTS OF THE LOW PRESSURE SYSTEM. THE ECMWF AND GFS FALL BACK
IN LINE BUT AS OF NOW THE ECMWF SEEMS A BIT MORE CONSISTENT. IN
ADDITION THE ECMWF IS A BIT CLOSER TO ENSEMBLES. THE NAM BECAME
AND OUTLIER EARLY ON AS IT TRIED TO MOVE THE NEXT FRONT IN MUCH
FASTER. USED A BLEND OF ECMWF WITH SOME GFS THROUGH DAY 4 THEN
TRANSITIONED TO NEW HPC, WHICH KEPT WITH AN ECMWF AND ENSEMBLE
BLEND. FORECAST CONFIDENCE IS AVERAGE. THE SYNOPTIC PATTERN HAS
BEEN FAIRLY CONSISTENT BUT DETAILS REGARDING PRECIP TYPE AND
AMOUNTS CAUSING THE MOST UNCERTAINTY.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND FROM 9 PM AKST THIS EVENING THROUGH SUNDAY AFTERNOON
     FOR AKZ019.
         STRONG WIND THROUGH SUNDAY AFTERNOON FOR AKZ018.
MARINE...GALE WARNING FOR PKZ012-022.
         SMALL CRAFT ADVISORY FOR PKZ011-013-041>043.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ051-052.

&&

JBT/PRB