Small Craft Advisory 895, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
105 PM ADT SAT SEP 30 2006

.DISCUSSION...

.ANALYSIS...SATELLITE IMAGERY SHOWS A NEARLY VERTICALLY STACKED
LOW SPINNING OVER THE CENTRAL BERING. OCCLUDED FRONT EXTENDS
EASTWARD FROM THE LOW CENTER TO THE PRIBILOFS AND THEN SOUTHWARD
BETWEEN COLD BAY AND DUTCH HARBOR. GALE FORCE WINDS NOTED ALONG
THIS FRONT...MAINLY SOUTH OF THE ALEUTIANS. A STRONG UPPER LEVEL
SHORT-WAVE IS ROTATING AROUND THE BOTTOM OF THE BERING LOW.
SUBSIDENCE ON THE BACK SIDE OF THIS IS LIKELY HELPING TO MIX DOWN
HIGHER WINDS FROM ALOFT. THERE IS ALSO A TIGHT SURFACE PRESSURE
GRADIENT ALONG THE ALEUTIANS. THE COMBINATION OF THESE FACTORS IS
PRODUCING NEAR STORM FORCE WESTERLY GUSTS ALONG THE ALEUTIANS. A
LOW LEVEL RIDGE BUILDING OVER SOUTHCENTRAL HAS PROVIDED MOSTLY CLEAR
SKIES ACROSS THE REGION THIS MORNING WITH A FEW AREAS OF DENSE FOG.
GUSTY WINDS IN THE USUAL PLACES SUCH AS SEWARD AND WHITTIER HAVE
BEGUN TO DECREASE AS THE RIDGE MOVES OVERHEAD. A WEAK SHORT-WAVE
BETWEEN AND UPPER HIGH OVER THE INTERIOR AND AN UPPER LOW NEAR
MIDDLETON ISLAND DROPPED DOWN THROUGH THE EASTERN COPPER RIVER
BASIN THIS MORNING GENERATING SOME SNOW ALONG THE TOK CUT-OFF.
SPOTTER REPORTS INDICATE ACCUMULATIONS OF 1 TO 4 INCHES. SNOW HAS
SINCE LIGHTENED UP AND SHOULD COMPLETELY END BY MID AFTERNOON AS
THE SHORT-WAVE SINKS SOUTH AND EASTWARD OVER THE WRANGELL MOUNTAINS
AND THE UPPER RIDGE BUILDS OVERHEAD.

.MODAL ANALYSIS...ALL MODELS INITIALIZED VERY WELL WITH SYNOPTIC
FEATURES AND SOLUTIONS ARE SIMILAR THROUGH 24 HOURS. MODELS
THEN DIVERGE SIGNIFICANTLY AS HEAD FURTHER OUT IN TIME. PREFER THE
GFS/UKMET SOLUTION WITH EVOLUTION OF LOWS OVER THE EASTERN BERING
ON SUNDAY. UPPER CENTER WILL REPOSITION ITSELF OVER STRONG SHORT-WAVE
CURRENTLY MOVING ALONG ALEUTIANS. THIS SHOULD INDUCE A NEW SURFACE
LOW OVER THE EASTERN BERING LATE SATURDAY NIGHT WHILE OLD LOW FILLS
BACK OVER THE CENTRAL BERING SEA. BEYOND THIS TIME PERIOD PREFER
GFS SOLUTION WITH LOWS ORIGINATING OVER THE FAR WESTERN BERING SEA
AND THE NORTH PACIFIC. DPROG/DT SHOWS GFS HAS CONSISTENTLY TRENDED
WESTWARD WITH TRACK OF DEVELOPING PACIFIC LOW MONDAY AND TUESDAY
SO WILL MAKE THE JUMP TO THE NEW SOLUTION.

.FORECASTS...NEAR ZONAL FLOW ACROSS THE FORECAST AREA WILL KEEP
SYSTEMS PROGRESSING EASTWARD THROUGH MONDAY. THE OCCLUDED FRONT
EXTENDING FROM BERING SEA LOW WILL TRACK ACROSS EASTERN BERING THIS
EVENING AND THEN WEAKEN AS IT MOVES INLAND ACROSS SOUTHERN MAINLAND
LATE TONIGHT INTO SUNDAY. RAIN WILL OVERSPREAD SOUTHWEST ALASKA
TONIGHT AND MOST OF SOUTHCENTRAL ON SUNDAY. AS NEW SURFACE LOW WILL
DEVELOP NORTH OF COLD BAY AND MOVES INTO BRISTOL BAY SUNDAY
AFTERNOON. THE PRESSURE GRADIENT ACROSS SOUTHCENTRAL WILL TIGHTEN
SO STRONG EASTERLY WINDS CAN BE EXPECTED IN THE USUAL PLACES. OF
BIGGEST CONCERN ARE THE WEST TO NORTHWEST WINDS ON BACK SIDE OF
BERING SEA LOW COMPLEX. SUBSIDENCE COMBINED WITH TIGHT PRESSURE
GRADIENT AND WEAK COLD ADVECTION WILL HELP TO ENHANCE WINDSPEEDS
ALONG CENTRAL AND EASTERN ALEUTIANS SATURDAY NIGHT AND SUNDAY. WILL
FORECAST STRONGER WINDS THAN INDICATED BY THE MODELS FOR THESE AREAS
- EXPECT STORM FORCE WINDS OF 50 KT WITH LOCALLY STRONGER GUSTS
THROUGH CHANNELED AREAS. THESE WINDS WILL DROP OFF QUICKLY AS HEAD
THROUGH THE DAY SUNDAY WITH SURFACE LOW MOVING INLAND OVER SOUTHWEST
ALASKA AND DISSIPATING. MEANWHILE A LOW NEAR KAMCHATKA WILL DROP
SOUTHWARD TO THE WESTERN ALEUTIANS SUNDAY AFTERNOON AND BEGIN TO
AMPLIFY THE FLOW. THIS WILL PICK UP AND DEVELOP A NORTH PACIFIC LOW
WHICH WILL AMPLIFY THE PATTERN EVEN MORE. WITH SOME UPPER JET SUPPORT
LOW PACIFIC LOW WILL STRENGTHEN AS IT TRACKS NORTHWARD INTO THE
EASTERN BERING SEA TUESDAY. THE END RESULT IS A CONTINUED WET
PATTERN FOR MOST OF THE ANCHORAGE FORECAST AREA THROUGH THE MIDDLE
OF NEXT WEEK WITH LITTLE BREAK BETWEEN SYSTEMS. WITH THE MEAN TROUGH
POSITION OVER THE BERING SEA WARM AIR WILL CONTINUE TO PUSH NORTHWARD
ACROSS THE SOUTHERN MAINLAND SO THAT PRECIP WILL FALL AS RAIN AT
LOWER ELEVATIONS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...STORM WARNING 170 172.
         GALE WARNING 150 155 165 171 175.

SEB SEP 06