Small Craft Advisory 152, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
400 PM AKST SAT FEB 16 2013

.ANALYSIS AND UPPER LEVELS...THE UPPER LEVELS ARE IN A PROGRESSIVE
PATTERN OVER THE STATE THIS WEEKEND. THE MAIN UPPER LEVEL TROUGH OVER
THE REGION EXTENDS OUT OF THE ARCTIC AND ACROSS THE BERING STRAIT
THEN SOUTHWARD OVER THE ALASKA PENINSULA. THIS TROUGH WILL MOVE OVER
SOUTH CENTRAL ALASKA SUNDAY MORNING AND THEN SLOW DOWN AS IT
CONTINUES EASTWARD. TWO UPPER LEVEL RIDGES ARE OVER THE AREA. THE
AXIS OF THE EASTERN ONE IS OVER SOUTH CENTRAL ALASKA AND WILL MOVE
QUICKLY EASTWARD OVERNIGHT. THE SECOND ONE IS OVER THE WESTERN
ALEUTIANS AND BERING SEA. IT TOO IS MOVING EASTWARD BUT WILL AMPLIFY
AS IT DOES SO. THIS WILL CAUSE THE JET STREAM TO MOVE FARTHER NORTH.
BY MONDAY THE JET WILL ENTER THE CENTRAL BERING SEA FROM THE SOUTH
AND THEN CURVE CLOCKWISE AROUND THE RIDGE BRINGING STRONG NORTHWEST
FLOW OVER SOUTHWEST AND SOUTH CENTRAL ALASKA.
AT THE SURFACE THERE IS A LOW NEAR COLD BAY WHICH IS BEGINNING TO
ELONGATE ALONG THE FRONT AS IT MOVES NORTHEAST. IT WILL DEVELOP A
TRIPLE POINT LOW IN THE GULF OVERNIGHT WHICH WILL BECOME THE MAIN LOW
BY SUNDAY AFTERNOON. THIS ELONGATED FRONT WILL SERVE A A FOCUS OF
PRECIPITATION THROUGH THE REMAINDER OF THE WEEKEND.

.MODEL DISCUSSION...MODELS REMAIN LOCKED IN TO THE SYNOPTIC PATTERN
AND HAVE CONVERGED ON A VERY SIMILAR SOLUTION AS TO THE LOCATION AND
STRENGTH OF THE LOW THAT WILL BE IN THE BERING SEA SUNDAY NIGHT. THE
LOCATION THE GFS HAD THE LOW FROM YESTERDAY'S MODEL RUNS IS THE
LOCATION WHERE THE NAM AND ECMWF ARE NOW SHOWING AS WELL.

.SHORT TERM FORECAST...
SNOW ASSOCIATED WITH THE FRONT ALONG THE ALASKA PENINSULA IS
SPREADING NORTH AND NORTHEAST. THE STRUCTURE OF THIS FRONT WILL CAUSE
WINDS TO INCREASE IN SOUTHWEST ALASKA AND WILL BRING SNOW INTO THE
BRISTOL BAY AND KUSKOKWIM VALLEY REGIONS. THE SNOWFALL AND WINDY
CONDITIONS WILL CAUSE SOME VISIBILITY RESTRICTIONS DUE TO BLOWING
SNOW TONIGHT FOR THE BRISTOL BAY REGION. THEREFORE THERE IS A WINTER
WEATHER ADVISORY FOR SNOW AND BLOWING SNOW IN EFFECT INTO SUNDAY
MORNING FOR ZONE 161.
THE SNOW WILL STAY EAST OF THE KUSKOKWIM DELTA BUT THE BELOW ZERO
TEMPERATURES AND NORTHERLY WINDS WILL COMBINE FOR LOW WINDS CHILLS.
THE WIND CHILL ADVISORY FOR ZONE 155 IS ACTIVE INTO SUNDAY AFTERNOON.
AFTER THAT THE PRESSURE GRADIENT SHOULD HAVE RELAXED ENOUGH TO LET
THE WINDS DIMINISH.

THE SNOW WILL SPREAD INTO SOUTH CENTRAL ALASKA THIS EVENING BUT THEN
CUT OFF IN THE NORMAL DOWN SLOPE AREAS. THE GULF COAST WILL SEE
SNOWFALL PERSIST INTO TOMORROW. THERE IS A CHANCE THAT SOME RAIN WILL
MIX IN WITH THE SNOW SUNDAY AFTERNOON ALONG THE GULF COAST. HOWEVER
IT LOOKS TO REMAIN MOSTLY SNOW..EXCEPT FOR KODIAK ISLANDS WHICH WILL
WARM ENOUGH TO SWITCH PRECIPITATION TO RAIN OVERNIGHT.

BY SUNDAY AFTERNOON THE SURFACE LOW IN THE GULF WILL HAVE MOVED FAR
ENOUGH EAST TO BRING IN A STRONGER PUSH OF COLD AIR INTO SOUTH
CENTRAL ALASKA AS WELL AS CUT OFF THE DOWN SLOPE. THIS WILL CAUSE
WIDESPREAD SNOW TO DEVELOP BY SUNDAY AFTERNOON ACROSS SOUTH CENTRAL
ALASKA WHICH WILL PERSIST INTO MONDAY. SNOW SHOULD END ACROSS THE
KENAI PENINSULA EARLY MONDAY MORNING BUT IT WILL PERSIST INTO MONDAY
EVENING IN THE COPPER RIVER BASIN.

.LONG TERM FORECAST...THE PATTERN WILL REMAIN ACTIVE ACROSS SOUTHERN
ALASKA THROUGH THE WEEK NEXT WEEK WITH MULTIPLE SYSTEMS BRINGING SOME
PRECIPITATION. TEMPERATURES WILL GENERALLY BE CLOSE TO NORMAL FOR
THIS TIME OF YEAR.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...WIND CHILL ADVISORY 155. WINTER WEATHER ADVISORY 161.
         BLIZZARD WATCH 195.
MARINE...GALE 120 130 132 136 137 140 150 165 170 172 175 179 185.
         STORM 176.
         HEAVY FREEZING SPRAY 130 138 140 150 165.
FIRE WEATHER...NONE.

FEB 13