Small Craft Advisory 622, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
124 PM AKDT SAT AUG 16 2014

.ANALYSIS AND UPPER LEVELS...
UPPER LEVEL TROUGH MOVING INTO SOUTHWEST INTERIOR TODAY MOVES INTO
THE INTERIOR TONIGHT AND SUNDAY. VERY WET AND MILD SOUTH AND
SOUTHWEST FLOW BECOMES A COOLER WESTERLY FLOW SUNDAY THROUGH
TUESDAY. A WEAK UPPER RIDGE IS SHIFTING EASTWARD TOWARD THE
CENTRAL ALEUTIANS THIS AFTERNOON. AT THE SURFACE...LOW PRESSURE IS
MOVING ONTO THE NORTH COAST OF BRISTOL BAY AND WILL MOVE TO THE
KUSKOKWIM DELTA TONIGHT AND MONDAY. HIGH PRESSURE MOVING TOWARD
THE CENTRAL ALEUTIANS WILL STRENGTHEN AND MOVE TO THE EASTERN
ALEUTIANS, SOUTHEAST BERING SEA AND BRISTOL BAY MONDAY.

&&

.MODEL DISCUSSION...

MODELS ARE IN BASIC AGREEMENT. THERE IS SOME DISAGREEMENT EARLY
WITH THE TRIPLE POINT LOW THAT MOVES INTO THE GULF LATE TONIGHT AT
UP TO THE COAST SUNDAY AFTERNOON. THE MAJOR PATTERN CHANGE THAT
BEGAN A FEW DAYS AGO IS NEARING COMPLETION. THE UPPER LEVEL LOW
OVER THE BERING AND AKPEN IS MOVING OVER WESTERN AK AND THEN WILL BE
ABSORBED INTO A POLAR LOW WELL NORTH OF THE STATE BY MON. WHILE AN
UPPER LEVEL TROUGH WILL REMAIN...IT WILL BE MUCH BROADER AND
WEAKER AND CHARACTERIZED BY A FEW FAIRLY WEAK WAVES MOVING THROUGH
CYCLONIC FLOW EARLY NEXT WEEK.

THE GFS AND NAM WERE USED EARLY IN THE FORECAST FOR DETAIL...AND
THEN THE EC...IN PARTICULAR FOR THE LOCATION AND MOVEMENT OF THE
LOW IN THE GULF ON SUN BEING SLIGHTLY FASTER THAN OTHER SOLUTIONS.
THE INTERMEDIATE MODELS WERE IN BETTER AGREEMENT WITH THE EC...WHICH
INCREASED FORECAST CONFIDENCE IN THAT SOLUTION.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...

AS THE FRONT MOVES ONSHORE TONIGHT EXPECT RAIN AND SHOWERS ACROSS
THE AREA...STRONG WINDS WILL CONTINUE THROUGH THE CHANNELED TERRAIN
OF TURNAGAIN ARM...PORTAGE VALLEY...AND THE KNIK RIVER VALLEY. A
WEAK RESIDUAL LOW PRESSURE OVER THE AREA WILL KEEP SHOWERS IN THE
FORECAST THROUGH TUE.

SOUTHWEST ALASKA...

THE LOW MOVING INTO WESTERN AK WILL BRING RAIN AND THEN SHOWERS
THROUGH TUE. SIGNIFICANT WINDS ARE ALSO EXPECTED TODAY THROUGH
CHANNELED TERRAIN OF THE ALASKA AND ALEUTIAN RANGES AS THE WESTERN
PORTION OF THE FRONT MOVES INLAND...AND A FEW THUNDERSTORMS ARE
AGAIN POSSIBLE THIS AFTERNOON AND EVENING BEFORE THE WEAKENING OF
THE SYSTEM COMMENCES SUN.

BERING SEA/ALEUTIANS...

NORTHWEST FLOW ACROSS THE BERING WILL BRING SHOWERS TO THE EASTERN
HALF OF THE ALEUTIANS INTO MON. HIGH PRESSURE WILL THEN MOVE
ACROSS THE BERING THROUGH TUE WITH PLENTY OF LOW CLOUDS AND FOG. A
WEAK LOW WILL ENTER THE WESTERN BERING LATER TODAY AND MAKE VERY
SLOW HEADWAY EAST WITH SOME RAIN SPREADING ACROSS THE WESTERN
ALEUTIANS THROUGH TUE.

&&

.LONG TERM FORECAST...
AN UPPER-LVL LOW OVER THE WESTERN ALEUTIAN CHAIN NEXT WED/THU LOOKS
TO BEGIN DIGGING SOUTH TO SOUTHEASTWARD. THE PROGRESSIVE FLOW
OVER THE SOUTHERN MAINLAND MID WEEK WILL START TO AMPLIFY AS THIS
OCCURS. FORECAST CONFIDENCE IS LOW WITH REGARDS TO JUST HOW
AMPLIFIED THE FLOW BECOMES. THE GENERAL SUBSTANCE IS THAT AS THE
LOW OUT WEST DIGS THE RIDGING DOWNSTREAM ACROSS THE GULF AND
SOUTHERN MAINLAND WILL BUILD ENOUGH TO YIELD A PERIOD OF DRIER
WEATHER IN THE MID WEEK TIME FRAME. MEANWHILE THE LOW OVER THE
CHAIN WILL CONTINUE TO DIG SOUTHEAST AND BEGIN INTERACTING WITH
ENERGY ROTATING OFF THE ASIAN MAINLAND. THIS WILL BROADEN LOW'S
SCOPE OF INFLUENCE AND ESTABLISH IT AS A MORE DOMINANT FEATURE IN
THE AOR.

SUBSTANTIAL DIFFERENCES EXIST WITH THE ORIENTATION OF THIS LOW
AND HOW IT OR RESIDUAL LOBES OF ENERGY ASSOCIATED WITH IT IMPACT
THE MAINLAND THE LATTER PART OF NEXT WEEK. THE GFS TENDS TO KEEP
A LARGER UPPER LOW IN THE BERING SEA WHICH BECOMES INCREASINGLY
COMPLEX AS IT DRIFTS TO THE EASTERN PORTION OF THE BERING SEA AND
ALEUTIAN CHAIN. THE ECMWF TENDS TO KEEP THE PRIMARY UPPER LOW OUT
BY THE WESTERN ALEUTIAN CHAIN...BUT SPAWNS OFF SIZABLE LOBES
THAT PUSH TOWARDS SW AK AND THE GULF OF AK. THE EVOLUTION OF AND
TIMING OF THESE DETAILS WILL POSE CONSIDERABLE FORECAST
CHALLENGES IN THE AOR. SUFFICE TO SAY...IT APPEARS THE TREND WILL
BE FROM DRIER TO WETTER AS WE HEAD TOWARDS NEXT WEEKEND. THE
THREAT OF STRONGER STORMS IS LOOMING AS WELL AS THE CORE OF THE
JET STREAM BEGINS IMPACTING MORE OF THE AOR.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...FLOOD ADVISORY...121
MARINE...GALE...119 125
FIRE WEATHER...NONE.

&&

PERCY/JAM