Small Craft Advisory 332, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
100 PM ADT SUN APR 13 2008

.ANALYSIS AND UPPER LEVELS...A FAIRLY FLAT RIDGE CENTERED OVER THE
NORTH PACIFIC EXTENDS UP INTO THE SOUTHERN BERING WHILE AN ANCHOR
LOW SITS TO THE NORTH OVER THE CHUKCHI SEA. THERE IS A TROUGH ON
EITHER SIDE OF THE RIDGE OVER THE FAR WESTERN BERING AND OVER THE
FAR EASTERN GULF. ANOTHER TROUGH EXTENDS SOUTHEAST FROM THE ANCHOR
LOW OVER MAINLAND ALASKA...NOT QUITE IN PHASE WITH THE EASTERN GULF
TROUGH. THE UPPER JET IS RIDING RIGHT OVER TOP OF THE RIDGE...DRIVING
WARM AIR AND MOISTURE ACROSS THE BERING SEA INTO SOUTHWEST ALASKA. AT
THE SURFACE THERE IS A LOW OVER NORTON SOUND TRACKING EAST-NORTHEAST
WITH WARM FRONT EXTENDING SOUTHEASTWARD OVER INTERIOR SOUTHWEST
ALASKA. WARM AIR HAS CHANGED PRECIPITATION TO MAINLY RAIN ALONG THE
COAST WHILE INLAND TEMPERATURES REMAIN PLENTY COLD FOR ALL SNOW.
MID TO HIGH CLOUDS HAVE BEEN TRYING TO MOVE INTO SOUTHCENTRAL THIS
MORNING...BUT ANTICYCLONIC FLOW ALOFT HAS RESULTED IN SOME
DISSIPATION. STILL THE TREND IS TOWARD INCREASING AND LOWERING
CLOUDS. THE TROUGH EXITING TO THE EAST COMBINED WITH A NORTHEAST
GULF SURFACE LOW HAVE BEEN PRODUCING AREAS OF SNOW FROM EASTERN
PRINCE WILLIAM SOUND TO THE COPPER RIVER BASIN. OBSERVATIONS SHOW
SLOW IMPROVEMENT IN THESE AREAS.

.MODEL DISCUSSION...NAM INITIALIZED BEST WITH DUAL SURFACE LOWS
OVER THE NORTH TO EAST GULF. OTHERWISE...MODELS CONTINUE TO SHOW
EXCELLENT AGREEMENT AND EXPECT ONLY MINOR ADJUSTMENTS AND FINE-TUNING
OF CURRENT FORECAST.

.SHORT TERM FORECAST...THE MAINLAND ALASKA TROUGH WILL LIFT
NORTHEASTWARD TONIGHT WHILE SURFACE LOW TRACKS TO INTERIOR ALASKA.
PROGRESSIVE PATTERN TO THE SOUTH WILL MOVE RIDGE EASTWARD WITH
STRONG WESTERLIES ON TOP OF THE RIDGE PUSHING MOST OF WARM AIR
EASTWARD INTO THE GULF. THERE ARE A COUPLE WAVES EMBEDDED IN THE
WESTERLY FLOW THAT MAY PRODUCE SOME AREAS OF LIGHT PRECIPITATION
OVER SOUTHCENTRAL TONIGHT AND MONDAY...MAINLY AT HIGHER ELEVATIONS.
LOW LEVELS ARE QUITE DRY AND THERE IS NOT ENOUGH MOISTURE TO SATURATE
THE AIR. MEANWHILE...ARCTIC AIR BEHIND THE WESTERN BERING UPPER
TROUGH AND CHUKCHI SEA UPPER LOW WILL BEGIN TO USHER DOWN INTO THE
NORTHERN TO WESTERN BERING CHANGING PRECIPITATION BACK TO SNOW. WITH
A PROGRESSIVE PATTERN THIS TROUGH WILL QUICKLY MOVE EASTWARD ACROSS
THE BERING MONDAY AND MAINLAND ALASKA TUESDAY AND WEDNESDAY. IT WILL
AMPLIFY AS IT MOVES EASTWARD IN RESPONSE TO BUILDING RIDGE UPSTREAM
AND RESULTANT STRENGTHENING NORTHERLY JET. THERE WILL BE GOOD MID
TO UPPER LEVEL LIFT AHEAD OF THIS TROUGH...BUT IN THE LOW LEVELS
COLD AND DRY AIR WILL QUICKLY USHER IN. THEREFORE...FOR SOUTHWEST
AND SOUTHCENTRAL ALASKA EXPECT ONLY MINOR SNOW MONDAY NIGHT AND
TUESDAY WITH THE TROUGH...MAINLY IN UPSLOPE AREAS. THE BERING
SEA/ALEUTIANS/ALASKA PENINSULA WILL SEE MORE PRECIPITATION AS WELL
AS COLD ADVECTION SNOW SHOWERS BEHIND THE TROUGH. A SURFACE LOW
WILL FORM OVER THE NORTHERN GULF/PRINCE WILLIAM SOUND REGION MONDAY
NIGHT...NOT SOON ENOUGH TO PUSH ANY MOISTURE BACK WESTWARD. IT WILL
HOWEVER LIKELY RESULT IN ENHANCED SNOW OVER PORTIONS OF EASTERN
PRINCE WILLIAM SOUND AND THE EASTERN COPPER RIVER BASIN. AN UPPER
LOW WILL FORM OVER THE GULF WEDNESDAY AS THE UPPER TROUGH BECOMES
NEUTRALLY TILTED...WHICH WILL SLOW THE EASTWARD PROGRESSION OF THE
TROUGH. STILL...EXPECT IMPROVING CONDITIONS FROM WEST TO EAST ON
WEDNESDAY. ANOTHER SHORTWAVE WILL DROP INTO WESTERN ALASKA WEDNESDAY
BRINGING ANOTHER SHOT OF SNOW TO SOUTHWEST ALASKA AND REINFORCEMENT
OF COLD AIR. THE UPCOMING COLD ADVECTION EVENT WILL RESULT IN
WIDESPREAD GUSTY WINDS...WITH STRONG WINDS THROUGH CHANNELED AREAS
OF THE MOUNTAIN RANGES OVER THE SOUTHERN MAINLAND AND ALASKA
PENINSULA. WILL START TO BETTER REFLECT SOME OF THESE GAP WINDS
WITH THE NEW FORECAST. FINALLY...THE BERING SEA WILL DRY OUT TUESDAY
AS HIGH PRESSURE BUILDS OVER THE REGION. ANOTHER SYSTEM WILL APPROACH
THE WESTERN ALEUTIANS WEDNESDAY.

.LONG TERM FORECAST...MEDIUM RANGE MODELS ARE IN VERY GOOD AGREEMENT
WITH EVOLUTION OF UPPER LEVEL PATTERN WHILE DETAILS ARE AS USUAL IN
QUESTION. PATTERN WILL BECOME MORE AMPLIFIED WITH A RIDGE BUILDING
OVER MAINLAND ALASKA/GULF AND TROUGH SETTING UP OVER THE BERING SEA.
THEREFORE...EXPECT AN ACTIVE STORM TRACK FROM THE PACIFIC NORTH INTO
THE BERING SEA WHILE MOST OF MAINLAND ALASKA...ESPECIALLY THE EASTERN
HALF...WILL REMAIN DRY UNDERNEATH THE BLOCKING RIDGE.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING 132 138 150 155 170 172 175 176.
FIRE WEATHER...NONE.

SEB APR 08