Small Craft Advisory 220, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
400 PM AKDT SUN MAR 10 2013

.ANALYSIS AND UPPER LEVELS...WE ARE IN THE MIDDLE OF A PATTERN SHIFT
OVER THE STATE. THE PERSISTENT UPPER LEVEL LOW IN THE EASTERN BERING
SEA IS BEING DISPLACED BY AN UPPER LEVEL RIDGE AS THE LOW PUSHES
RAPIDLY EASTWARD WITH COLDER AIR MOVING INTO SOUTHERN ALASKA. THIS
RIDGE WILL BECOME ENTRENCHED IN THE EASTERN BERING SEA AND CHUKCHI
SEA THROUGH THE MIDDLE OF THE WEEK WHICH WILL BRING IN CLEARING SKIES
OVER MOST OF THE FORECAST AREA.
AT THE SURFACE THE RIDGE IS BUILDING INTO THE EASTERN BERING SEA AND
NORTHERN PART OF THE STATE. THE SURFACE LOW IS REDEVELOPING IN THE
NORTHWEST GULF TODAY AND WILL MOVE SOUTHEASTWARD OVER THE NEXT FEW
DAYS.
IN THE CENTRAL AND WESTERN ALEUTIANS/BERING SEA THE FRONT ASSOCIATED
WITH THE NEXT LOW IS ATTEMPTING TO PUSH INTO THE RIDGE WITH NO AVAIL.
THIS FRONT WILL REMAIN NEARLY STATIONARY AND THEN WEAKEN ON TUESDAY.

.MODEL DISCUSSION...MODELS ARE IN MOSTLY GOOD AGREEMENT THROUGH THE
MIDDLE OF THE WEEK AND ARE DOING MUCH BETTER WITH THE LATTER PART OF
THE WEEK AS WELL. YESTERDAY THERE WAS A HUGE DIFFERENCE BETWEEN GFS
AND ECMWF SOLUTION WITH THE ECMWF BEING PREFERRED DUE TO IT KEEPING
THE RIDGE ENTRENCHED OVER THE NORTHERN PART OF THE STATE THROUGH THE
EASTERN BERING SEA. THE GFS HAS NOW SHIFTED SIGNIFICANTLY TOWARD THIS
SOLUTION WHICH IS BRINGING GREATER CONFIDENCE IN THE LONG TERM
FORECASTS.

.SHORT TERM FORECAST...THE STRONG SHORT WAVE MOVING THROUGH SOUTH
CENTRAL ALASKA IS DIVING SOUTHEASTWARD AND INTO THE GULF OF ALASKA.
THE SNOWFALL ASSOCIATED WITH THIS SYSTEM WILL END QUICKLY AFTER THE
DISTURBANCE MOVES THROUGH THE AREA THIS EVENING. THE SNOW WAS
ENHANCED FROM THE CENTRAL KENAI PENINSULA NORTHWARD INTO THE SUSITNA
VALLEY AS DIVERGENCE ALOFT INCREASED THE LIFT. FURTHER ENHANCING THE
LIFT OVER ANCHORAGE WAS THE LIGHT EASTERLY FLOW THROUGH TURNAGAIN
ARM. THIS HAS NOT BEEN STRONG ENOUGH EASTERLY FLOW TO CAUSE DOWN
SLOPING. INSTEAD IT ENHANCED THE SNOW AS IT PRODUCED A CONVERGENCE
ZONE OVER ANCHORAGE WHEN THE LIGHT SOUTHEAST WINDS OUT OF TURNAGAIN
ARM MET THE SOUTH WINDS MOVING UP COOK INLET.
AFTER THIS SYSTEM MOVES INTO THE GULF THE TIGHT PRESSURE GRADIENT
FROM THE RIDGE IN THE INTERIOR AND THE LOW IN THE GULF WILL INCREASE
NORTHERLY WINDS OVER SOUTH CENTRAL ALASKA AND THE NORTH GULF COAST.
THOMPSON PASS WILL LIKELY SEE THE STRONGEST WINDS AND THEREFORE THERE
IS A HIGH WIND WATCH IN EFFECT FOR THOMPSON PASS FOR MONDAY EVENING
THROUGH TUESDAY NIGHT FOR THIS.
SOUTHWEST ALASKA IS SOLIDLY IN THE COLD AIR AND NORTHWESTERLY WINDS
AS THE SHORT WAVE HAD COMPLETELY MOVED THROUGH THAT AREA. WHILE
REGIONS NEAR BRISTOL BAY NORTHWARD INTO THE KUSKOKWIM VALLEY HAVE
CLEARED OUT THE KUSKOKWIM DELTA CONTINUES TO SEE WIDESPREAD STRATUS.
THIS STRATUS WILL LIKELY DIMINISH OVERNIGHT.
THE FRONT IN THE WESTERN ALEUTIANS IS BRINGING IS STRONG SOUTHERLY
WINDS AND WARM AIR SO MOST OF THE PRECIPITATION WILL BE RAIN. THE
WIND AND RAIN WILL DIMINISH AS THE FRONT WEAKENS TUESDAY.

.LONG TERM FORECAST...THE AMPLIFIED PATTERN THAT IS SETTING UP WITH
THE BUILDING HIGH PRESSURE OVER THE BERING WILL BEGIN TO BREAK DOWN
LATE IN THE WEEK AS AN UPPER LEVEL LOW OVER NORTHWEST CANADA DIGS
SOUTHWESTWARD OVER THE GULF OF ALASKA. THIS WILL RESULT IN ZONAL FLOW
OVER THE ALEUTIANS AND A BLOCKING RIDGE OVER THE ARCTIC BY NEXT
WEEKEND. THIS WILL KEEP TEMPERATURES NEAR OR JUST BELOW NORMAL FOR
LATE IN THE WEEK WITH A FEW SNOW SHOWERS...BUT WITH SOME SUNNY BREAKS
AS WELL.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WATCH 131.
MARINE...GALE 130 138 175 176 185.
         HEAVY FREEZING SPRAY 160.
FIRE WEATHER...NONE.

MAR 13