Small Craft Advisory 640, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
213 PM AKDT MON AUG 25 2014

.ANALYSIS AND UPPER LEVELS...

BROAD UPPER TROUGH EXTENDS FROM EASTERN RUSSIAN TO THE ALCAN THIS
AFTERNOON WITH ONE LOBE DIVING SOUTH FROM RUSSIA INTO THE
BERING...AND THE OTHER BECOMING AN OPEN WAVE AS IT MOVES ACROSS
SOUTHCENTRAL AND THE GULF OF AK. ANOTHER WEAK WAVE IS SWEEPING
ACROSS THE CENTRAL BERING. AT THE SURFACE...A BROAD AREA OF LOW
PRESSURE IS OVER THE NORTHWESTERN GULF WHILE ANOTHER LOW IS OVER
THE WESTERN AND CENTRAL ALEUTIANS...AND THIRD LOW IS OVER EASTERN
RUSSIA. A RIDGE OF HIGH PRESSURE IS OVER THE EASTERN ALEUTIANS
AND BERING. SIGNIFICANT CONVECTIVE ACTIVITY IS DEVELOPING ON THE
EASTERN HALF OF THE SOUTHCENTRAL WAVE OVER THE KENAI AND CHUGACH
MOUNTAINS.

&&

.MODEL DISCUSSION...

MODELS ARE IN FAIRLY GOOD AGREEMENT.

THE UPPER LOW OVER SOUTHCENTRAL AND THE NORTHERN GULF WILL BECOME
AN OPEN WAVE TUE AND THEN COMPLETELY FLATTEN...WITH SUBSEQUENT
VERY WEAK UPPER RIDGING ADVANCING ACROSS THE MAINLAND TUE NIGHT
INTO WED. MEANWHILE THE UPPER LOW OVER EASTERN RUSSIA DIVES
SOUTHEAST ACROSS THE BERING AND REACHES THE AKPEN WED AFTERNOON
BEFORE MOVING INTO THE GULF THROUGH THU AFTERNOON.

THE REFLECTION OF THESE EVENTS AT THE SURFACE IS A BROAD AREA OF
LOW PRESSURE OVER THE NORTHERN GULF THROUGH TUE AFTERNOON THAT
WEAKENS ON WED. WED NIGHT INTO THU A LOW THAT HAD BEEN MOVING
ALONG THE ALEUTIANS MERGES WITH ONE DIVING SOUTH FROM EASTERN
RUSSIA...JUMPS THE AKPEN...AND MOVES HALFWAY ACROSS THE GULF.

THE FORECAST UTILIZES GFS AND EC WITH THE LATTER BECOMING THE
MAIN CHOICE WITH ITS MORE NORTHERLY PATH OF THE LOW AFTER IT
CROSSES THE AKPEN. THE INTERMEDIATE MODEL RUNS ARE INDICATING EVEN
LESS OF A DIFFERENCE IN THAT TRACK.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...

AS THE LAST VORTMAX MOVES AROUND THE SOUTHCENTRAL
TROUGH...SHOWERS ARE EXPECTED THIS EVENING...WITH ISOLATED
THUNDERSTORMS ALONG THE KENAI AND CHUGACH MOUNTAINS...AND NEAR THE
ALASKA RANGE. THE OPENING OF THE WAVE ON TUE WILL REDUCE THE
POSSIBILITY OF LIGHTNING...BUT KEEP SHOWERS IN FOR ANOTHER DAY.
SHOWERS WILL PERSIST ON WED BEFORE COVERAGE INCREASES AS THE LOW
JUMPS THE AKPEN INTO THE GULF INTO THU.

SOUTHWEST ALASKA...

SHOWERS WILL SLOWLY DIMINISH TONIGHT. A FRONT ASSOCIATED WITH THE
LOW DIVING SOUTH FROM RUSSIA WILL CAUSE PRECIPITATION TO INCREASE
TUE AND WED AND THEN PERSIST INTO THU.

BERING SEA/ALEUTIANS...

RAIN AND SHOWERS PERSISTING INTO WED WILL BE ASSOCIATED WITH THE
LOW MOVING ACROSS THE ALEUTIANS AS WELL AS THE LOW DIVING SOUTH
THROUGH THE BERING. ON THU PRECIPITATION AND A NEW FRONT WILL
ARRIVE OVER THE WESTERN ALEUTIANS.

&&

.LONG TERM FORECAST...

AN UPPER LEVEL WEAK RIDGE WILL CONTINUE TO BUILD OVER THE
NORTHERN GULF OF ALASKA COASTLINE RESULTING IN TURNAGAIN ARM
WINDS PICKING UP THROUGH THIS UPCOMING WEEKEND. AN INVERTED TROUGH
WILL EXTEND THROUGH THE GULF OF ALASKA ASSOCIATED WITH A LOW
PRESSURE SYSTEM TRACKING NEAR HAIDA GWAII BY FRIDAY. THIS SYSTEM
WILL BRING RAIN/STRATUS/FOG THROUGHOUT THE GULF THROUGH FRIDAY
NIGHT. THE INTERIOR SOUTHEAST MAINLAND WILL HAVE SOME REMNANTS OF
MOISTURE LEFT FROM AN EXITING SYSTEM PRODUCING SCATTERED SHOWERS
GOING INTO THE WEEKEND. A FRONTAL BOUNDARY WILL APPROACH THE
ALASKA PENINSULA AND MOVE NORTHEAST UP THROUGH COOK INLET
BRINGING RAIN TO THE REGION THROUGH THIS UPCOMING WEEKEND. A LOW
PRESSURE SYSTEM WILL BE POSITIONED OVER THE WESTERN BERING SEA
FRIDAY MORNING AND TRACK TO THE EASTERN BERING SEA BY SATURDAY.
THIS SYSTEM WILL MOVE INLAND THROUGH THE BRISTOL BAY AREA BRINGING
MORE CLOUDS AND RAIN TO THE SOUTHWEST ALASKA REGION THROUGH THE
WEEKEND.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.
&&

DS/PLD AUG 14