Small Craft Advisory 1022, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
945 PM AKST WED DEC 16 2009

EVENING UPDATE...

AN AREA OF LOW PRESSURE DEVELOPED ALONG THE LEADING EDGE OF THE
ARCTIC AIRMASS SPILLING IN TO THE WESTERN GULF. THIS LOW...COUPLED
WITH THE UPPER LEVEL DYNAMICS AND SUFFICIENT MOISTURE...IS SQUEEZING
OUT MORE SNOW ACROSS SOUTHCENTRAL ALASKA. WHAT WAS SUPPOSED TO BE
SCATTERED TO NUMEROUS SNOW SHOWERS OVERNIGHT HAS EVOLVED INTO ANOTHER
ROUND OF ACCUMULATING SNOWFALL.

ONE SNOW BAND HAS SET UP ACROSS THE NORTHERN KENAI PENINSULA INTO THE
SOUTHERN SUSITNA VALLEY WHILE A SECOND ONE IS CLOSER TO THE LEADING
EDGE OF THE COLD AIR BACK OVER SOUTHERN COOK INLET. THE INITIAL BAND
IS DROPPING SNOW IN ANCHORAGE AT A RATE OF ABOUT HALF AN INCH AN HOUR
OR LESS. THIS BAND WILL SLOWLY MOVE NORTH BEFORE THE SECOND BAND
INTENSIFIES AFTER MIDNIGHT...POSSIBLY BRINGING ANOTHER 2 TO 4 INCHES
OF SNOW TO ANCHORAGE AS THIS NEW LOW MOVES INLAND TO THE EAST OF
SEWARD.

WHEREAS THE PREVIOUS STORM BROUGHT THE MOST SIGNIFICANT SNOW TOTALS
TO EAGLE RIVER AND TAPERED OFF TOWARD WEST ANCHORAGE...THIS WILL BE A
MORE TYPICAL SETUP WITH THE GREATEST AMOUNTS IN SOUTH AND WEST
ANCHORAGE.

BLIZZARD CONDITIONS HAVE YET TO DEVELOP AROUND KACHEMAK BAY...AT
LEAST NOT AT THE HOMER AIRPORT. IT IS STILL POSSIBLE BLIZZARD
CONDITIONS ARE HAPPENING ALONG THE BLUFF WHERE HEAVIER SNOW AND GUSTY
WINDS COULD COMBINE TO BRING WHITE OUT CONDITIONS. SO FOR NOW...WILL
ALLOW THE BLIZZARD WARNING TO CONTINUE THROUGH THE NIGHT.

AB DEC 09

PREVIOUS FORECAST DISCUSSION.......

.MODEL DISCUSSION...MODELS ARE DOING WELL WITH THE BIG FEATURES. THE
NAM IS DOING WELL WITH THE DEVELOPMENT OF A MESO LOW IN COOK INLET
THAT IS COMPLETELY MISSED BY ALL OF THE OTHER MODELS. A LOCALLY RUN
MODEL IS SHOWING THAT LOW SLIPPING INTO THE LOWER INLET THIS EVENING
AND BRINGING BLIZZARD CONDITIONS TO THE KACHEMAK BAY REGION. THERE IS
A WARNING OUT FOR THIS BUT THERE IS STILL A LOT OF UNCERTAINTY ABOUT
THIS EVENT WORKING OUT.

.ANALYSIS AND UPPER LEVELS...THE COLD CORE UPPER LEVEL LOW IS
DROPPING DOWN OVER THE BRISTOL BAY AREA THIS AFTERNOON WHILE THE
SURFACE LOW IS IN PRINCE WILLIAM SOUND. THE COLD ADVECTION BETWEEN
THESE LOW IS INCREASING AND IS RESULTING IN STRONG WINDS OUT OF
CHANNELED TERRAIN IN WESTERN COOK INLET AND KODIAK. THIS COLD
ADVECTION IS ALSO WHAT IS DRIVING THE DEVELOPMENT OF THE MESO LOW IN
COOK INLET.

.SHORT TERM FORECAST...SNOW WILL BE LIFTING OUT OF THE ANCHORAGE BOWL
MID AFTERNOON AND MAT-SU VALLEY LATE IN THE AFTERNOON. SNOWFALL
SHOULD LIGHTEN UP IN THE PRINCE WILLIAM SOUND AREA AS THE LOW MOVES
THROUGH AND THOUGH TERRAIN EFFECTS IN THE SOUTHERLY FLOW WILL KEEP
SNOW SHOWERS AROUND.
THE BIGGEST UNCERTAINTY IN THE FORECAST REMAINS THE KACHEMAK BAY AREA
WHERE THE SUBTLE MOVEMENTS OF THE MESO LOW IN COOK INLET WILL
DETERMINE WHETHER THAT AREA WILL GET BLIZZARD CONDITIONS...OR VERY
LITTLE PRECIPITATION AT ALL.

WEST OF THE ALASKA RANGE THE COLD AIR WILL CONTINUE BUT WINDS SHOULD
BE LOWER RESULTING IN WINDS CHILLS THAT ARE NOT AS SEVERE AS THE LAST
FEW DAYS.

.LONG TERM FORECAST...THE COOLER AIR THAT IS COVERING MUCH OF THE
STATE WILL PERSIST INTO THE WEEKEND. TEMPERATURES WILL SLOWLY RISE AS
THE LOW RETROGRADES NORTHWESTWARD SATURDAY AND SOUTHERLY FLOW COVERS
MUCH OF THE STATE.  MEANWHILE...OUT WEST STRONG WINDS AND
PRECIPITATION WILL KEEP THINGS UNSETTLED DUE TO THE BERING LOW.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD 121.
MARINE...GALE 120 132 138 140 141 150 155 160 165 175 180
    STORM 130 176
    HEAVY FREEZING SPRAY 121 129 130 132 138 140 141 150 155 160 165
179 180 185
FIRE WEATHER...NONE.

DEC 09