Small Craft Advisory 239, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1140 AM AKDT SAT MAR 16 2013

.ANALYSIS AND UPPER LEVELS...A COLD CORE ANCHOR LOW IS CENTERED
OVER THE SEA OF OKHOTSK WITH A TROUGH EXTENDING EASTWARD ACROSS
THE BERING SEA. A STRONG BLOCKING HIGH IS CENTERED OVER THE BEAUFORT
SEE WITH RIDGING EXTENDING SOUTHWARD INTO MAINLAND ALASKA. SYSTEMS
CROSSING THE BERING SEA HAVE BEEN SHEARING APART AS THEY REACH AN
AREA OF DIVERGENT FLOW OVER SOUTHWEST ALASKA...AS SOME OF THE ENERGY
LIFTS NORTHWARD ALONG THE WEST SIDE OF THE RIDGE AND SOME ENERGY
MOVES EASTWARD ACROSS THE GULF OF ALASKA. THIS IS OCCURRING TODAY
OVER SOUTHWEST ALASKA WITH AN OLD FRONTAL BOUNDARY AND UPPER LEVEL
SHORT-WAVE...WITH SNOW DIMINISHING AS IT MOVES INLAND. MEANWHILE...
A COMPACT LOW IS NEARLY STATIONARY SOUTH OF CORDOVA. ASIDE FROM SOME
LOCALIZED WINDS NEAR THE LOW CENTER THE ONLY IMPACT IS A SMALL AREA
OF PRECIP SPREADING WESTWARD ACROSS PRINCE WILLIAM SOUND.  THE REST
OF SOUTHCENTRAL ALASKA IS CLEAR AND CALM UNDER THE INFLUENCE OF THE
UPPER RIDGE.

LOOKING OUT WEST...A MODERATE STRENGTH LOW OVER THE WESTERN BERING
IS TRACKING QUICKLY EASTWARD. SATELLITE IMAGERY INDICATES A STRONG
JET ON THE SOUTH SIDE OF THE LOW CENTER HELPING TO FEED COLD AIR
INTO THE CENTER. THIS COLD AIR ALOFT HAS CREATED UNSTABLE CONDITIONS
WHICH ARE LEADING TO STRONG GUSTY WINDS AT THE SURFACE AND SOME
LIKELY SOME FAIRLY INTENSE CONVECTION.

.MODEL DISCUSSION...MODELS ARE IN VERY GOOD AGREEMENT THROUGH
THE NEXT FEW DAYS WITH JUST SOME MINOR (LOW IMPACT) POSITIONAL
DIFFERENCES. FORECAST CONFIDENCE IS HIGH.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE UPPER LEVEL RIDGE TO THE NORTH WILL
MAINTAIN COOL AND DRY CONDITIONS THE NEXT COUPLE DAYS OVER
SOUTHCENTRAL ALASKA. A FEW WEAK FEATURES WILL TRANSIT TO THE
SOUTH ACROSS THE GULF OF ALASKA. THE UPPER LEVEL PATTERN WILL
CHANGE EARLY NEXT WEEK AS THE BEAUFORT SEA RIDGE RETREATS TO
THE POLE AND A NEW RIDGE BUILDS OVER THE BERING SEA. THIS WILL
ALLOW ARCTIC AIR TO SPILL SOUTHWARD ACROSS MAINLAND ALASKA INTO
THE GULF...PRODUCING COLDER CONDITIONS WHILE MAINTAINING THE DRY
THEME AS WE HEAD THROUGH NEXT WEEK. THIS WILL ALSO RESULT IN
STRONG GAP WINDS ALONG THE NORTH GULF COAST BEGINNING IN THE
TUESDAY/WEDNESDAY TIME FRAME.

SOUTHWEST ALASKA...ONE MORE SYSTEM WILL CROSS THE BERING SEA AND
AFFECT SOUTHWEST ALASKA ON SUNDAY. BY THE TIME THE LOW REACHES THE
SOUTHWEST COAST IT WILL BE MUCH WEAKER THAN IT IS NOW. HOWEVER...IT
WILL BRING A MUCH MORE UNSTABLE AIR MASS THAN IS CURRENTLY IN
PLACE...SO EXPECT SOME LOCALIZED GUSTY WINDS...ESPECIALLY ALONG THE
KUSKOKWIM DELTA COAST. DON'T EXPECT THESE WINDS TO BE WIDESPREAD
OR LONG-LIVED ENOUGH TO PRODUCE ANY MAJOR BLOWING SNOW PROBLEMS.
COLD AND DRY CONDITIONS WILL THEN BEGIN TO SETTLE IN MONDAY AS A
STRONG UPPER RIDGE BUILDS OVER THE CENTRAL BERING SEA.

BERING SEA/ALEUTIANS...THE LOW OVER THE WESTERN BERING WILL TAKE A
EAST-NORTHEAST TRACK ACROSS THE BERING SEA TONIGHT AND SUNDAY WITH
MOST OF THE PRECIP AND WINDS REMAINING NORTH OF THE ALEUTIANS. DO
EXPECT SOME STRONG GUSTY WINDS AND MODERATE TO HEAVY SNOW SHOWERS
TO MOVE THROUGH THE PRIBILOF ISLANDS OVERNIGHT. MEANWHILE A TROUGH
DIGGING OUT OF ASIA TODAY WILL INITIATE CYCLOGENESIS SOUTH OF THE
ALEUTIANS SUNDAY. A RIDGE WILL BUILD OVER THE BERING AND KEEP THIS
SYSTEM CENTERED OVER THE PACIFIC. HOWEVER...A STRONG FRONTAL BOUNDARY
WILL MAKE ITS WAY NORTHWARD AND AFFECT THE ALEUTIANS SUNDAY AND
MONDAY.

.LONG TERM FORECAST...THE GFS 500MB 5-WAVE SHOWS A MEAN RIDGE OVER
THE BERING AND A MEAN TROUGH OVER MAINLAND ALASKA. THE OPERATIONAL
RUNS HAVE BEEN FLUCTUATING WITH EXACT POSITION OF BERING RIDGE AND
AS WELL AS POSITION OF COLD UPPER LOW OVER MAINLAND ALASKA. SOME
RUNS OCCASIONALLY TRY AND MOVE ENERGY THROUGH THE BERING RIDGE. FOR
NOW...THE MOST LIKELY SCENARIO IS FOR AN EXTENDED PERIOD OF COLD AND
DRY WEATHER FROM THE EASTERN BERING TO MAINLAND ALASKA THROUGH MOST
OF NEXT WEEK WITH THE STORM TRACK SUPPRESSED SOUTH AND WEST OF THE
ALASKA REGION. COLD AIR SPILLING FROM THE MAINLAND INTO THE GULF
WILL MAINTAIN ONE OR MORE LOW CENTERS...BUT ANY PRECIP WITH THESE
WILL LIKELY REMAIN OFFSHORE.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING...172 175 176.
         HEAVY FREEZING SPRAY WARNING...127.
FIRE WEATHER...NONE.

SEB MAR 13