Small Craft Advisory 80, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
430 PM AKST THU JAN 24 2013

.ANALYSIS AND UPPER LEVELS...THE UPPER LEVEL PATTERN OVER THE STATE
TODAY SHOWS A CUT OFF LOW SOUTH OF THE GULF OF ALASKA AND A TROUGH IN
THE INTERIOR OF THE STATE DIGGING SOUTHWARD. A PRONOUNCED RIDGE
EXTENDS OVER THE EASTERN ALEUTIANS NORTHWARD THROUGH THE BERING
STRAIT WITH ANOTHER UPPER LEVEL LOW SOUTHWEST OF ATTU. THE JET STREAM
REMAINS WELL SOUTH OF THE FORECAST AREA.

AT THE SURFACE THERE ARE THREE MAJOR FEATURES IMPACTING THE REGION.
THE FIRST IS A STRONG ARCTIC HIGH CENTERED WELL NORTH OF THE STATE
WITH A RIDGE PUSHING INTO THE NORTHERN AND INTERIOR OF THE STATE AS
WELL AS INTO A LARGE PART OF THE BERING SEA. THE OTHER TWO FEATURES
ARE LOW PRESSURE SYSTEMS. ONE IS IN THE SOUTHEASTERN GULF AND THE
OTHER SOUTH OF ATTU. BOTH OF THESE LOWS ARE MODERATE IN STRENGTH AND
SLOWLY WEAKENING.

.MODEL DISCUSSION...MODELS DO WELL FOR THE REMAINDER OF THE WEEK WITH
ONLY SOME MINOR CONCERNS SHOWING UP SATURDAY AFTERNOON. THEY RAPIDLY
GO DOWNHILL IN THE EARLY PART OF NEXT WEEK WITH THE GFS AND ECMWF
SHOWING VERY DIFFERENT PATTERNS SETTING UP. NEITHER MODEL HAS SHOWN
VERY GOOD CONSISTENCY RUN TO RUN EITHER. THIS IS MAKING THE FORECAST
FROM EARLY NEXT WEEK ON VERY UNCERTAIN.
AS FOR THE DIFFERENCES IN MODEL SOLUTIONS BEFORE SATURDAY: THE LOW IN
THE GULF INITIALIZED BETTER ON THE NAM AND THE ECMWF THAN THE GFS.
THIS ADDS CONFIDENCE TO THE NAM/ECMWF SOLUTION THAT KEEPS THE LOW IN
THE SOUTHEAST GULF AND THEN DISSIPATES IT FRIDAY NIGHT INSTEAD OF THE
GFS WHICH SENDS IS SOUTH OF THE AREA TOO QUICKLY. THE FRONT THAT WILL
MOVE FROM THE NORTH PACIFIC TO THE EAST/CENTRAL ALEUTIANS LATE
SATURDAY INTO SUNDAY CONTINUES TO CHALLENGE THE MODELS. THEY ALL HAVE
IT BUT TIMING AND LOCATION DIFFER FROM MODEL-TO-MODEL AND RUN-TO-RUN.
THE IMPACT ON THE FORECASTS FROM THE DIFFERENCES IN SOLUTIONS WILL BE
LIMITED TO THE SOUTHERN BERING SEA REGION AT FIRST BUT THE WAY THIS
SYSTEM DEVELOPS WILL SET THE STAGE FOR THE WEATHER PATTERN FOR THE
MAJORITY OF THE FORECAST AREA FOR NEXT WEEK.

.SHORT TERM FORECAST...WHILE THE STRONGEST SURFACE FEATURE ON THE MAP
IN THE GULF OF ALASKA AND SOUTH CENTRAL ALASKA IS THE LOW IN THE GULF
IT WILL REMAIN IN THE GULF AND NOT IMPACT THE WEATHER MUCH. THE
FEATURE THAT IS SIGNIFICANT IS THE UPPER LEVEL TROUGH THAT IS
DROPPING OUT OF THE INTERIOR IN SOUTH CENTRAL ALASKA. A SMALL BUT
SIGNIFICANT LOW IS THE ONE THAT IS CURRENTLY DEVELOPING IN THE COOK
INLET REGION. THIS COMBINATION WILL GENERATE SNOWFALL OVERNIGHT. SNOW
IS ALREADY FALLING IN THE ALASKA RANGE AND THE SUSITNA VALLEY FROM
THE PARKS HIGHWAY EAST IS UNDER A WINTER WEATHER ADVISORY FOR SNOW
DUE TO THIS SYSTEM. SNOWFALL WILL LESSEN AS ONE HEAD SOUTH BUT THERE
SHOULD BE ACCUMULATION INTO THE NORTHERN PART OF THE KENAI PENINSULA.
THIS SYSTEM WILL CONTINUE TO LOSE SOME PUNCH AS IT HEADS EASTWARD BUT
IT SHOULD STILL BE ENOUGH TO CAUSE SNOW IN THE COPPER RIVER BASIN AND
ALONG THE GULF COAST. WHILE IT IS RATHER WARM NOW IN COASTAL AREAS
THERE IS A LOT OF COLD AIR ASSOCIATED WITH THIS TROUGH AND THE
TEMPERATURES WILL DROP AS IT MOVES INTO THE AREA.
AS THE PRESSURE GRADIENT INCREASES FRIDAY NIGHT INTO SATURDAY WINDS
WILL LIKELY INCREASE ENOUGH IN THOMPSON PASS TO PRODUCE BLOWING SNOW.
THERE IS A POSSIBILITY FOR BLIZZARD CONDITIONS DUE TO NEARLY 16
INCHES OF TRANSPORTABLE SNOW IN THE PASS. THE UNCERTAINTY IS MERELY
DUE TO THE LACK OF ANY UPPER LEVEL SUPPORT. HOWEVER THE PRESSURE
GRADIENT AND TEMPERATURE GRADIENT ACROSS THOMPSON PASS WILL LIKELY BE
ENOUGH TO KICK UP THE WINDS SIGNIFICANTLY THEREFORE A BLIZZARD WATCH
WAS ISSUED.

THE SOUTHWEST MAINLAND SHOULD CONTINUE TO CLEAR OUT AS SEE GUSTY
WINDS AND DROPPING TEMPERATURES AS THE UPPER LEVEL TROUGH MOVES
THROUGH THE AREA TONIGHT. WIND CHILL VALUES IN THE KUSKOKWIM DELTA
ARE EXPECTED TO FALL TO 30 BELOW TO 45 BELOW ZERO TONIGHT PROMPTING A
WIND CHILL ADVISORY FOR THAT AREA. WINDS ACROSS SOUTHWEST ALASKA
SHOULD SLOWLY DIMINISH THROUGH THE DAY FRIDAY SO IT IS NOT EXPECTED
TO PERSIST WITH WIND CHILLS THAT LOW BEYOND FRIDAY MORNING.
THE CENTRAL AND WESTERN ALEUTIANS WILL SEE STRONG WINDS AND A MIX OF
PRECIPITATION TYPES WITH THE LOW THAT IS APPROACHING IT.

.LONG TERM FORECAST...THE LONG TERM FORECAST CONFIDENCE IS CURRENTLY
QUITE LOW...ESPECIALLY EARLY NEXT WEEK WHEN THE MODELS STRUGGLE WITH
THE INTERACTION BETWEEN AN ALEUTIAN LOW AND RIDGE HOLDING OVER
INTERIOR ALASKA. THE ECMWF IS CURRENTLY THE STRONGEST WITH THE
INTERIOR RIDGE...AND AS A RESULT IS ALSO THE FURTHEST WEST WITH THE
LOW. THE CURRENT FORECAST SOLUTION IS WEAKER WITH THE INTERIOR
RIDGE...ALLOWING THE LOW TO PROGRESS FURTHER EAST INTO THE ALASKA
PENINSULA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...SNOW ADVISORY 145. WIND CHILL ADVISORY 155.
         BLIZZARD WATCH 131.
MARINE...GALE 130 175 176. HEAVY FREEZING SPRAY 130 185.
FIRE WEATHER...NONE.

JAN 13