Small Craft Advisory 445, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
400 PM AKDT WED MAY 29 2013

.ANALYSIS AND UPPER LEVELS...THE UPPER LEVEL RIDGE REMAINS IN PLACE
OVER THE INTERIOR AND SOUTHERN PORTIONS OF THE STATE TODAY. THERE IS
ALSO A BROAD UPPER LEVEL TROUGH THAT EXTENDS FROM JUST SOUTH OF THE
ALASKA PENINSULA TO NEAR VANCOUVER ISLAND. THERE ARE TWO DISTINCT LOW
CENTERS AT THE WESTERN AND EASTERN SIDES OF THIS TROUGH. THIS PATTERN
IS BRINGING MOSTLY CLEAR SKIES IN THE EASTERLY FLOW OVER THE SOUTHERN
PART OF THE MAINLAND. THIS EASTERLY FLOW INCREASES IN STRENGTH OVER
THE GULF OF ALASKA AND ALASKA PENINSULA. EVEN THE EASTERN BERING SEA
IS CLEARING OUT DUE TO THE DRY AIRMASS COMING OFF THE MAINLAND PART
OF THE STATE.
THERE IS A THERMAL TROUGH EXTENDING OUT OF THE INTERIOR INTO THE
BRISTOL BAY REGION. HOWEVER THE UPPER RIDGE IS SUPPRESSING MOST OF
THE CONVECTIVE POTENTIAL.

IN ADDITION TO THESE FEATURES THERE IS AN UPPER LEVEL TROUGH IN THE
WESTERN BERING SEA THAT IS DIGGING SOUTHWARD OUT OF A LARGE UPPER
LEVEL LOW CENTERED NEAR THE NORTH POLE. THIS LOW WILL CUT OFF
OVERNIGHT AND MOVE SOUTHEASTWARD...CROSSING THE CENTRAL ALEUTIANS
THURSDAY AFTERNOON. THE ENERGY WILL THEN COALESCE AROUND THIS LOW AS
IT BECOMES A SIGNIFICANT WEATHER FEATURE FOR NEXT WEEK.

.MODEL DISCUSSION...MODELS ARE SITTING FAT AND HAPPY AGAIN TODAY WITH
VERY GOOD AGREEMENT THROUGH SATURDAY. ONE HAS TO DIG INTO THE DETAILS
OF THE SMALL UPPER LEVEL EASTERLY WAVES OVER THE GULF TO FIND
ANYTHING THAT WILL MAKE A BIG DIFFERENCE TO THE FORECAST. IN THIS
CASE THERE IS A WAVE THAT WILL MOVE OVER KODIAK THURSDAY THAT THE GFS
AND ECMWF HAVE BETTER DEFINED THAN THE NAM AND THAT WILL INCREASES
POPS OVER KODIAK AS A RESULT. THE OTHER INTERESTING ITEM IS THAT THE
HIGHER RESOLUTION NAM MODEL IS HINTING AT THE MARINE LAYER PUSHING UP
COOK INLET ALL THE WAY TO ANCHORAGE ON FRIDAY. THERE WILL BE A WEAK
SOUTHERLY PUSH UP THE INLET AT THAT TIME BUT IT IS QUITE DICEY TO
FORECAST THE MARINE PUSH DAYS IN ADVANCE, BUT THE NAM IS TRYING.

.SHORT TERM FORECAST...THE WEAK TROUGH THAT WAS IN THE NORTHERN GULF
WHICH CANCELED OUT THE SEA BREEZE IN THAT AREA AND REPLACED IT WITH
WARM OFFSHORE FLOW HAS NOW MOVED TO THE WEST. THIS WILL ALLOW THE
NORMAL DEVELOPMENT OF THE SEA BREEZE THE NEXT FEW DAYS.
THERE IS SLIGHTLY MORE MOIST AIR MOVING INTO THE COPPER RIVER BASIN
FROM THE EAST WHICH WILL KEEP RH VALUES A LITTLE HIGHER THAN THEY
WERE YESTERDAY. THIS WILL ALSO INCREASE THE CLOUDS OVER ALL OF SOUTH
CENTRAL ALASKA THURSDAY.
THE EXPECTED DEVELOPMENT OF A RIDGE ALONG THE NORTH GULF COAST HAS
BEEN DELAYED A LITTLE AND WILL NOT DEVELOP IN EARNEST UNTIL THURSDAY.
THIS WILL INCREASE WINDS THROUGH TURNAGAIN ARM AND THE KNIK RIVER
VALLEY AT THAT TIME.
SOUTHWEST ALASKA IS MOSTLY CLEAR UNDER THE HIGH PRESSURE. HOWEVER
THERE IS SOME CONVECTION TRYING TO DEVELOP IN THE KUSKOKWIM VALLEY
AND SHOULD THIS DEVELOP STRONGER AS THE AFTERNOON AND EVENING
PROGRESSES IT COULD BRING A COUPLE OF SHOWERS TO THAT AREA.

.LONG TERM FORECAST...THE UPPER LEVEL RIDGE WILL WEAKEN THIS WEEKEND
AS AN UPPER LEVEL LOW APPROACHES THE SOUTHWEST GULF. THIS WILL BRING
IN MORE CLOUDS AND COOLER TEMPERATURES AS WELL AS A GREATER CHANCE
FOR AFTERNOON SHOWERS OVER SOUTHWEST AND SOUTH CENTRAL ALASKA. THIS
PATTERN WILL ALSO ENHANCE THE PRESSURE GRADIENT OVER THE NORTH GULF
COAST WHICH WILL INCREASE WINDS IN THE NORMAL SOUTH AND SOUTHEAST
CHANNELED AREAS...SUCH AS TURNAGAIN ARM AND ALONG THE COPPER RIVER.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...FLOOD ADVISORY 111 141 145.
         FLOOD WATCH 145 155.
MARINE...GALE 176.
FIRE WEATHER...RED FLAG WARNING 145.

MAY 13