Small Craft Advisory 309, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
140 PM AKDT THU MAR 31 2011

.ANALYSIS AND UPPER LEVELS...THERE ARE NUMEROUS LOW AMPLITUDE WAVES
EMBEDDED WITHIN THE LONG-WAVE TROUGH WHICH EXTENDS FROM EASTERN
ASIA TO WESTERN CANADA. THE SHORT-WAVE TROUGH WHICH BROUGHT SNOW
TO ANCHORAGE AND VICINITY THIS MORNING IS WEAKENING AS IT CONTINUES
EASTWARD ACROSS SOUTHCENTRAL ALASKA. MIDDLETON ISLAND RADAR ALSO
INDICATES THE PRESENCE OF A WEAK SURFACE LOW IN PRINCE WILLIAM SOUND
WHICH IS CONTINUING TO PRODUCE NUMEROUS SHOWERS. A SHORT-WAVE RIDGE
IS BUILDING IN BEHIND THE SOUTHCENTRAL TROUGH WHICH WILL CREATE
FAVORABLE CONDITIONS FOR FOG AS IT MOVES OVER SOUTHCENTRAL TONIGHT.

THE NEXT TROUGH OF INTEREST IS AN EAST-WEST ORIENTED TROUGH SOUTH
OF THE ALEUTIANS. AS A TROUGH BEGINS TO DIG FURTHER WEST THE EAST
SIDE OF THIS TROUGH IS BEGINNING TO LIFT NORTHWARD TOWARD ALASKA
AND COULD LEAD TO A LIGHT SNOW EVENT OVER SOUTHCENTRAL FRIDAY NIGHT.

LOOKING EVEN FURTHER SOUTH ALONG THE SUBTROPICAL JET IS A DEVELOPING
LOW WILL IS EXPECTED TO IMPACT THE ALASKA REGION THIS WEEKEND.

.MODEL DISCUSSION...MODELS ARE ALL IN DECENT AGREEMENT WITH HANDLING
OF SYNOPTIC SCALE FEATURES OVER THE NEXT FEW DAYS AND SHOW GOOD
RUN-TO-RUN CONSISTENCY. THIS HAS RESULTED IN INCREASING CONFIDENCE
IN LIGHT SNOW OVER PORTIONS OF SOUTHCENTRAL ALASKA FRIDAY NIGHT SO
WILL INCREASE POPS AND MENTION LIGHT ACCUMULATION. OTHERWISE...ONLY
MINOR ADJUSTMENTS WILL BE MADE TO EXISTING FORECASTS.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...SHOWERS WILL LINGER OVER THE COPPER RIVER
BASIN UNTIL THE UPPER TROUGH EXITS LATE TONIGHT. SHOWERS WILL
ALSO PERSIST IN THE PRINCE WILLIAM SOUND AREA AS THE WEAK LOW
WEAKENS OVER THE NORTHERN GULF. MEANWHILE...A SURFACE HIGH WILL
BUILD INTO INTERIOR ALASKA WHICH SHOULD MAINTAIN A TIGHT ENOUGH
GRAIDENT TO PREVENT WIDESPREAD FOG TONIGHT. STILL...WITH MELTING
SNOW AT THE SURFACE THIS AFTERNOON AND REMNANT LOW LEVEL
MOISTURE...EXPECT LOCALIZED AREAS OF FOG WILL DEVELOP. THE UPPER
LEVEL RIDGE WILL MOVE OVERHEAD FRIDAY AND SOUTHERLY FLOW ON THE
BACK SIDE OF IT WILL ADVECT MOISTURE FROM THE NORTHERN GULF AND
PRINCE WILLIAM SOUND NORTHWARD ACROSS SOUTHCENTRAL. THE UPPER
TROUGH MENTIONED IN THE ANALYSIS SECTION ABOVE WILL THEN MOVE
THROUGH FRIDAY NIGHT INTO SATURDAY MORNING LIKELY RESULTING IN
LIGHT SNOW MAINLY ON THE SOUTH AND WEST SIDE OF MOUNTAINS INCLUDING
ANCHORAGE AND THE MATANUSKA VALLEY. A MAJOR PACIFIC STORM WILL
FOLLOW...BUT THE ACTUAL LOW CENTER WILL REMAIN SOUTH OF THE ALASKA
PENINSULA. THE GULF AND SOUTHCENTRAL WILL BE IMPACTED BY A STRONG
OCCLUDED FRONT OVER THE WEEKEND. THIS FRONT WILL WEAKEN AS IT MOVES
TOWARD SOUTHCENTRAL SO THE BULK OF PRECIPITATION IS EXPECTED ALONG
THE GULF COAST.

SOUTHWEST ALASKA...CONDITIONS WILL REMAIN BENIGN OVER SOUTHWEST
ALASKA UNTIL EARLY SATURDAY WHEN A POWERFUL PACIFIC LOW APPROACHES
THE ALASKA PENINSULA. STRONG EASTERLY FLOW ALONG THE OCCLUDED FRONT
WILL RESULT IN SIGNIFICANT DOWNSLOPE DRYING SO WOULD EXPECT THE
BULK OF PRECIPITATION TO FALL IN UPSLOPE AREAS FROM DILLINGHAM
NORTH AND WEST. AS THE FRONT MOVES INTO BRISTOL BAY DURING THE
SATURDAY PRECIPITATION WILL MIX WITH OR CHANGE TO SNOW. ANY
PRECIPITATION THAT MAKES IT UP TO THE KUSKOKWIM DELTA AND KUSKOKWIM
VALLEY ZONES WILL STAY ALL SNOW. THERE COULD BE SOME BLOWING SNOW
ISSUES IN THE KUSKOKWIM DELTA BUT IT IS TOO EARLY TO NAIL DOWN
WHETHER ENOUGH SNOW WILL ACTUALLY FALL TO CAUSE PROBLEMS.

BERING SEA/ALEUTIANS...CURRENT FORECASTS LOOK ON TRACK FOR EXPECTED
WEATHER WITH THE MAJOR PACIFIC LOW THIS WEEKEND AS IT MOVES TO
SOUTH OF THE SOUTHERN ALASKA PENINSULA. THERE IS SOME POTENTIAL
FOR BLIZZARD CONDITIONS FROM THE PRIBILOF ISLANDS TO THE EASTERN
ALEUTIANS SATURDAY NIGHT INTO SUNDAY ON THE BACK SIDE OF THE LOW.
MODELS ARE INDICATING A SHORT-WAVE TROUGH MOVING IN FROM THE WEST
PROVIDING ADDITIONAL VERTICAL MOTION AND FEEDING ARCTIC AIR INTO
THE SYSTEM HELPING TO STRENGTHEN THE OCCLUDED FRONT. IT IS TOO SOON
TO ISSUE ANYTHING BUT WILL RE-EVALUATE THIS POTENTIAL OVER THE NEXT
COUPLE DAYS.

.LONG TERM FORECAST...THE STRONG LOW SOUTH OF THE ALASKA PENINSULA
SATURDAY WILL TRACK EASTWARD ACROSS THE GULF SUNDAY AND MONDAY
WHICH WILL DRY OUT THE EASTERN BERING TO SOUTHERN MAINLAND REGION.
THE NEXT MAJOR SYSTEM WILL TRACK INTO THE WESTERN BERING SUNDAY
INTO MONDAY AS A TROUGH OVER THE FAR NORTHWEST PACIFIC AMPLIFIES
AND BENDS THE SUBTROPICAL JET NORTHWARD. THE MEDIUM RANGE MODELS
HAVE QUITE A BIT OF SPREAD IN THE ULTIMATE DESTINATION OF THIS
LOW...HOWEVER AS PER THE HPC ALASKA EXTENDED FORECAST DISCUSSION
MOST OF THE LATEST GUIDANCE FAVORS THE ECMWF SOLUTION OF BRINGING
THIS LOW TO WESTERN ALASKA. LOOKS LIKE AN ACTIVE PATTERN SETS UP
FOR THE REST OF NEXT WEEK AS MEAN TROUGH SETS UP OVER BERING SEA
WITH A STORM TRACK FROM THE PACIFIC NORTHEASTWARD TOWARD THE
EASTERN BERING AND MAINLAND ALASKA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING...150 155 165 170 171 172.
FIRE WEATHER...NONE.

SEB MAR 11

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1045 AM AKDT THU MAR 31 2011

AKZ101-111-311915-

...STEADY SNOW HAS ENDED IN ANCHORAGE AND THE MATANUSKA VALLEY...

STEADY SNOW HAS ENDED IN ANCHORAGE AND THE MATANUSKA VALLEY. MOSTLY
CLOUDY SKIES AND ISOLATED SHOWERS WILL PERSIST THROUGH THE AFTERNOON
HOURS. TEMPERATURES WILL WARM INTO THE MID TO UPPER 30S WHICH WILL
HELP MELT SNOW ALONG MANY OF THE LOCAL ROADWAYS. SKIES WILL THEN
GRADUALLY CLEAR LATE THIS AFTERNOON AND EVENING.