Small Craft Advisory 995, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
400 PM AKST WED DEC 11 2013

.ANALYSIS AND UPPER LEVELS...AN UPPER LEVEL TROUGH OVER THE NORTHERN
YUKON AND INTO THE INTERIOR OF THE STATE IS STRENGTHENING AS IT DIGS
TO THE SOUTHWEST. THIS WILL INCREASE THE SOUTHWEST UPPER LEVEL FLOW
OVER SOUTH CENTRAL ALASKA WHILE KEEPING THE SOUTHWEST ALASKA COAST
AND BERING SEA UNDER NORTHERLY FLOW. THIS WILL BE ENHANCED AS THE
UPPER LEVEL RIDGE IN THE WESTERN BERING SEA BUILDS OVER THE NEXT FEW
DAYS.
AT THE SURFACE A 1046 MB HIGH SITS IN THE ARCTIC OCEAN JUST NORTH OF
THE STATE WITH A LOW IN THE GULF OF ALASKA. THIS IS SETTING UP A
STRONG PRESSURE GRADIENT ACROSS THE MAINLAND PART OF THE STATE.

.MODEL DISCUSSION...MODELS ARE STILL DOING WELL AND ARE IN GOOD
AGREEMENT WITH THE LOW CURRENTLY IN THE GULF OF ALASKA. THE MODELS
ARE IMPROVING WITH THE SECOND LOW THAT WILL MOVE INTO THE GULF ON
FRIDAY...HOWEVER THERE ARE SOME DIFFERENCES THAT WILL IMPACT THE
FORECAST. TO START WITH THE NAM NOW HAS THE WARM FRONT ORIENTED THE
SAME WAY AS THE OTHER MODELS BUT IS STRUGGLING WITH THE TIMING...TO
THE POINT IT STILL CANNOT BE USED FOR THIS SYSTEM. HOWEVER SINCE IT
IS STILL MOVING IN THE RIGHT DIRECTION EACH RUN IT MAY BE USEFUL WITH
LATER RUNS. THE GFS AND ECMWF ARE QUITE SIMILAR INTO SATURDAY. THE
BIG DIFFERENCE BETWEEN THESE MODELS IS THE WAY THE LOW MOVES ON SHORE
NEAR WESTERN PRINCE WILLIAM SOUND SATURDAY AND THE WAY IT PROGRESSES
INTO SUNDAY. THE GFS KEEPS THE LOW STRONGER AND IN THE SOUND INTO
SUNDAY WHILE THE ECMWF IS WEAKER AND FARTHER WEST. THESE DETAILS WILL
HAVE A BIG IMPACT AS TO HOW MUCH SNOW FALLS AND WHERE THIS WEEKEND.

.SHORT TERM FORECAST...THE HIGH PRESSURE IN THE ARCTIC AND TIGHT
PRESSURE GRADIENT OVER THE MAINLAND PART OF THE STATE WILL KEEP GUSTY
WINDS THROUGH CHANNELED TERRAIN FOR THE OVERNIGHT HOURS. THIS
GRADIENT WILL EASE UP SOME IN SOUTH CENTRAL ALASKA TOMORROW AS THE
GULF LOW WEAKENS. AS THIS WEAKENING LOW MOVES INT WESTERN PRINCE
WILLIAM SOUND IT MAY BRING SOME LIGHT SNOWFALL TO THE NORTH GULF
COAST.  MOISTURE FROM THIS SYSTEM MAY ALSO BRING SOME LIGHT SNOW TO
INLAND AREAS OF SOUTH CENTRAL THURSDAY NIGHT. THE MORE SIGNIFICANT
SYSTEM WILL MOVE TO THE NORTH GULF COAST FRIDAY MORNING AND THEN PUSH
SNOW FARTHER INLAND FRIDAY AFTERNOON. AT THIS TIME SNOW AMOUNTS FOR
INLAND AREAS LOOK MODEST...HOWEVER THERE IS A CHANCE THAT THERE COULD
BE SOME HEAVIER SNOWFALL AMOUNTS FRIDAY NIGHT SHOULD THE ECMWF MODEL
VERIFY BETTER THAN THE GFS.
SOUTHWEST ALASKA WILL CONTINUE TO SEE GUSTY WINDS AS THE PRESSURE
GRADIENT PERSISTS OVER THAT REGION. THIS WILL ALSO KEEP PRECIPITATION
OUT OF SOUTHWEST ALASKA FOR THE REMAINDER OF THE WEEK...WITH THE ONLY
EXCEPTION NEAR THE ALASKA AND ALEUTIAN RANGE AS THE LOW IN THE GULF
PUSHES WESTWARD ON FRIDAY.

.LONG TERM FORECAST...THE LOW THAT WILL BRING SNOW TO SOUTH CENTRAL
ALASKA THIS WEEKEND WILL PUSH EASTWARD EARLY NEXT WEEK AS THE BERING
SEA RIDGE BUILDS OVER THE WESTERN PART OF THE STATE. THIS WILL BRING
ANOTHER PERIOD OF CLEARING TO MOST OF SOUTHWEST AND SOUTH CENTRAL
ALASKA BEFORE THE NEXT SYSTEM MOVES INTO THE AREA IN THE MIDDLE OF
NEXT WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...WIND CHILL ADVISORY 141. BLOWING SNOW ADVISORY 131.
MARINE...GALE 127 128 130 173 179 180 181.
         HEAVY FREEZING SPRAY 121-130 140 141 160 180 181 185.
FIRE WEATHER...NONE.

DEC 13