Small Craft Advisory 686, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKDT SUN SEP 8 2013

.MODEL DISCUSSION...
MODELS ARE ALL IN RELATIVELY GOOD SYNOPTIC AGREEMENT ON THE MAIN
FEATURES. MINOR DIFFERENCES DO OCCUR WITH THE LOW COMPLEX NEAR THE AK
PEN AND THE NEXT CENTER TO MOVE ACROSS THE ALEUTIANS...HOWEVER
PRESSURE GRADIENTS AND PRECIPITATION TIMING ARE SIMILAR.

.ANALYSIS...
.UPPER LEVELS...
WATER VAPOR IMAGERY SHOWS A TROUGH OVER COPPER RIVER BASIN/SUSITNA
VALLEY LIFTING NORTH. A TIGHTLY WRAPPED CENTER IS EVIDENT SOUTH OF
THE EAST ALEUTIANS WITH THE ASSOCIATED FRONTAL TROUGH EXTENDING NORTH
ACROSS THE AK PEN THEN SOUTH ALONG 155W. THE THIN NOSE OF A RIDGE
EXTENDS ACROSS THE EASTERN BERING BETWEEN A WAVE OVER THE DELTA AND A
PRONOUNCED TROUGH IN THE WEST CENTRAL BERING SEA.

THE TROUGH ASSOCIATED WITH THE LOW NEAR THE AK PEN DIGS AS IT PHASES
WITH THE LOW CENTER OVER EASTERN RUSSIA AND COLD AIR SPILLING OUT OF
THE BERING SEA. THE RIDGE IN RESPONSE BUILDS OVER SE AK/WESTERN
CANADA. THIS AMPLIFIED PATTERN IS SHIFTS EAST SOME TUE AS THE LONG
WAVE MOVES OVER WESTERN AK/WEST GULF. ANOTHER SURGE OF COLD AIR OUT
OF EASTERN RUSSIA PHASES WITH A SHORT WAVE MOVING ACROSS THE NORTH
PACIFIC TUE EVENING AND AMPLIFIES THE RIDGE MOVING OVER THE EASTERN
BERING SEA.

.SHORT TERM FORECAST...
.SOUTHCENTRAL...
RAIN ACROSS THE REGION THIS MORNING HAS CHANGED TO SHOWERS AND IS
LIFTING NORTH WITH THE TROUGH. PRESSURE RISES ON THE BACKSIDE WILL
CONTINUE LOCALLY GUSTY SOUTH WINDS INTO THIS FAVORED
AREAS...ESPECIALLY COOK INLET AND COPPER RIVER BASIN. SW GALES SHOULD
END OVER THE NORTH GULF WATERS THIS AFTERNOON. PRESSURE GRADIENTS
WILL AGAIN INCREASE ACROSS THE GULF AND MAINLAND OVERNIGHT AND MON
WITH THE APPROACH OF THE LOW NEAR THE AK PEN AND AS ITS ASSOCIATED
FRONT HEADS TOWARD THE NORTH GULF COAST. SE GALES ARE EXPECTED TO
SPREAD NORTH AND EAST ACROSS THE GULF AHEAD OF THE FRONT...WITH MUCH
LIGHTER WINDS ON THE BACKSIDE. GAP FLOWS ARE ALSO EXPECTED TO
INCREASE FOR THE SAME TIME-FRAME ACROSS TURNAGAIN ARM/PORTAGE
VALLEY...AND OTHER FAVORED AREAS. A BARRIER JET IS EXPECTED TO
DEVELOP AHEAD OF THE FRONT ALONG THE NORTH GULF COAST MON AND
CONTINUE INTO TUE AFTERNOON...THEN WEAKEN TUE NIGHT.

RAIN IS EXPECTED TO SPREAD TO KODIAK ISLAND THIS AFTERNOON AND TO THE
NORTH GULF TONIGHT. DOWNSLOPE CONDITIONS INITIALLY WILL PREVAIL
INLAND...THOUGH THERE MAY BE A LITTLE MORE SPILL OVER AS THIS SYSTEM
WAS OF TROPICAL ORIGIN. RAIN WILL PROBABLY BECOME MORE WIDESPREAD
INLAND AS THE CROSS BARRIER FLOW DIMINISHES TUE.

SOUTHWEST ALASKA...A WEATHER FRONT ASSOCIATED WITH THE SURFACE LOW
MOVING THROUGH THE ALASKA PENINSULA WILL CONTINUE TO BRING STEADIER
RAINFALL TO SOUTHWEST ALASKA AS IT CONTINUES TO PROPAGATE INLAND. THE
LOW MOVES INLAND AND DISSIPATES TUE. HOWEVER...THE REMNANTS OF
THE UPPER TROUGH WILL PROVIDE ENOUGH VERTICAL MOTION TO CONTINUE THE
THREAT OF SHOWERS ACROSS THE SOUTHWEST MAINLAND THROUGH MID-WEEK.
STRONG GAP FLOW IS EXPECTED TO DEVELOP ALONG THE ALEUTIAN RANGE
TONIGHT THEN WEAKEN TUE AFTERNOON.

BERING SEA AND ALEUTIANS...THE SURFACE LOW AND ASSOCIATED WEATHER
FRONT TRACK TO THE NORTHEAST THIS AFTERNOON AND CONTINUE TO BRING
SHOWERS AND GUSTY WINDS TO THE EASTERN ALEUTIANS THROUGH MONDAY
NIGHT. AS THE LOW CONTINUES TO TRACK INLAND TUE MORNING...SHOWERS
AND GUSTY WINDS WILL BEGIN TO TAPER OFF. HIGH PRESSURE BUILDS INTO
THE WESTERN BERING MON MORNING...GIVING THE CENTRAL AND WESTERN
ALEUTIANS A BREAK IN PRECIPITATION THROUGH TUE MORNING. THE NEXT
LOW PRESSURE SYSTEM WILL TRACK EASTWARD JUST SOUTH OF THE WESTERN
ALEUTIANS BY TUE MORNING...BRINGING WET AND WINDY CONDITIONS TO
THE THE WESTERN AND CENTRAL ALEUTIANS.

.LONG TERM FORECAST...
THE RIDGE OVER THE EASTERN BERING SEA WILL SHIFT TOWARDS THE EAST AS
THE LONG-WAVE PATTERN BECOMES MORE AMPLIFIED. A DEEPENING SIBERIAN
LOW PRESSURE SYSTEM WILL PASS TO THE SOUTH OF THE ALEUTIAN CHAIN
THROUGHOUT THE WEEK. THIS WILL BRING ANOTHER ROUND OF RAIN AND WIND
TO SOUTHWEST AND SOUTHCENTRAL ALASKA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...
MARINE...GALE 120 125 130 132 138 140 150.
FIRE WEATHER...

RMC SEP 13