Small Craft Advisory 384, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
140 PM AKDT FRI MAY 3 2013

.ANALYSIS AND UPPER LEVELS...
A COLD UPPER LEVEL TROUGH CONTINUES TO STRETCH FROM THE INTERIOR
THROUGH THE EASTERN BERING SEA...WITH A LONGWAVE RIDGE REMAINING IN
PLACE OVER WESTERN NORTH AMERICA. AN UNSEASONABLY STRONG 130+ KT JET
STREAM EXISTS BETWEEN THESE FEATURES AND IS BRINGING DEEP-LAYER MOIST
SOUTHWEST FLOW TO THE SOUTHERN MAINLAND. SATELLITE IMAGERY SHOWS THE
PLUME OF ATMOSPHERIC MOISTURE STRETCHING ALL THE WAY TO THE HAWAIIAN
ISLANDS. A SERIES OF SHORTWAVE TROUGHS ARE MOVING THROUGH THIS JET
STREAM BRINGING WIDESPREAD HEAVY PRECIP TO PRINCE WILLIAM SOUND AND
THE NORTH GULF COAST...WITH GENERALLY LIGHTER PRECIP ALSO STRETCHING
BACK INTO COOK INLET AND THE SUSITNA VALLEY. PRECIPITATION IS FALLING
MOSTLY AS RAIN AT SEA LEVEL LOCATIONS...WITH THE EXCEPTION OF VALDEZ
WHERE HEAVY WET SNOW CONTINUES TO FALL THROUGH COLD AIR TRAPPED AT
THE LOWER LEVELS OF THE ATMOSPHERE. IN GENERAL...SNOW LEVELS ARE
AROUND 2000 FT ACROSS THE REGION TODAY.

.MODEL DISCUSSION...
SIGNIFICANT DIFFERENCES EMERGE IMMEDIATELY AMONG THE MAJOR MODEL
GUIDANCE TODAY. THE PRIMARY CONCERN REVOLVES AROUND HOW QUICKLY THE
UPPER LEVEL TROUGH CURRENTLY OVER THE SOUTHWEST MAINLAND MOVES TO THE
EAST. THE NAM WEAKENS AND MOVES THE LONGWAVE TROUGH EASTWARD FASTER
THAN THE OTHER MODELS. IF THIS HAPPENED...IT WOULD KEEP THE DEEP
MOISTURE AND STEADY RAIN FROM CROSSING BACK INTO THE KENAI ANCHORAGE
AND MAT-SU AREAS LATE TONIGHT INTO SATURDAY. HOWEVER...THE NAM DID
NOT INITIALIZE WELL WITH THE CURRENT POSITION OF THE LONGWAVE TROUGH.
COMBINED WITH GFS/ECMWF CONSENSUS FOR THE MORE WESTWARD
SOLUTION...THE NAM WAS LARGELY TOSSED OUT IN THE DEVELOPMENT OF THE
AFTERNOON FORECAST.

.SHORT TERM FORECAST...
SOUTHCENTRAL...HEAVY PRECIP EVENT ONGOING ACROSS THE REGION THROUGH
SATURDAY EVENING. THE PRIMARY FORECAST CHALLENGES ARE TWO-FOLD...HOW
FAR WEST THE PRECIP SPREADS LATE TONIGHT AND PRECIPITATION-TYPE
ACROSS THE REGION. LOCATIONS AROUND PRINCE WILLIAM SOUND AND POINTS
EAST ARE LIKELY TO SEE AN ADDITIONAL 2+ INCHES OF PRECIPITATION
BEFORE SKIES CLEAR FROM THE WEST ON SUNDAY. MOST OF THIS WILL FALL AS
RAIN ALONG THE COAST. HOWEVER...THOMPSON PASS AS WELL AS NORTHERN
SECTIONS OF THE SUSITNA VALLEY AND COPPER RIVER BASIN WILL CONTINUE
TO SEE ACCUMULATING SNOW. THE LARGEST QUESTION IS WHETHER THE COLD
AIR WILL ARRIVE FROM THE WEST IN TIME TOMORROW TO CHANGE RAIN BACK TO
SNOW ACROSS THE ANCHORAGE BOWL. AT THIS POINT IT LOOKS LIKELY THAT
SOME SNOWFLAKES WILL BE MIXING IN DURING THE DAY...BUT ANY
ACCUMULATIONS SHOULD BE MINOR AND LIMITED LARGELY TO THE ANCHORAGE
HILLSIDE.

SOUTHWEST MAINLAND AND BERING SEA REGION...RELATIVELY DRY NORTHERLY
FLOW WILL CONTINUE THROUGH THE WEEKEND FOR MOST OF THE AREA. WITH
HIGH PRESSURE IN COMMAND OVER THE CENTRAL BERING WIDESPREAD MARINE
STRATUS IS APPARENT ON SATELLITE IMAGERY AND SURFACE OBSERVATIONS. SO
FAR INVERSION HEIGHTS HAVE REMAINED HIGH ENOUGH THAT FOG HAS NOT BEEN
MUCH OF AN ISSUE...AND THIS SHOULD CONTINUE TO BE THE CASE FOR MOST
OF THE AREA. A WEAK LOW PRESSURE CENTER WILL LINGER AROUND THE
WESTERN BERING THROUGH SUNDAY...BUT WILL PRODUCE LITTLE MORE THAN
GUSTY WINDS AND SOME LIGHT RAIN.

.LONG TERM FORECAST...
THE LONG RANGE MODELS CONTINUE TO SUGGEST A CHANGE BY THE MIDDLE OF
NEXT WEEK TO MORE TYPICAL SPRING WEATHER ACROSS MUCH OF THE REGION.
THE GFS AND ECMWF BOTH AGREE THAT AN UPPER LOW WILL CUTOFF ACROSS THE
NORTH PACIFIC...WELL SOUTH OF OUR AREA...ALLOWING HIGH PRESSURE AND
WARMER TEMPERATURES TO CREEP INTO MAINLAND ALASKA FROM THE EAST.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...NONE
FIRE WEATHER...NONE

AMD MAY 13

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1206 PM AKDT FRI MAY 03 2013

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0855 AM     SNOW             6 WSW TALKEETNA         62.31N 150.26W
05/03/2013  M3.8 INCH                           AK   TRAINED SPOTTER

&&

KUTZ