Small Craft Advisory 1050, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
100 PM AST THU DEC 13 2007

.ANALYSIS AND UPPER LEVELS...THERE ARE THREE VERY DISTINCT SHORT-WAVE
TROUGHS NOTED ON WATER VAPOR IMAGERY THIS MORNING. ONE IS CENTERED
OVER BRISTOL BAY AND THE ALASKA PENINSULA WITH A WEAK LOW DOWN AT
THE SURFACE JUST SOUTH OF KODIAK ISLAND. AS PER KING SALMON RADAR
THERE IS AN AREA OF PERSISTENT LIGHT SNOW SHOWERS OVER THE BRISTOL
BAY ZONE. RAIN AND SNOW SHOWERS EXTEND SOUTH AND WEST ALONG THE
AKPEN. THERE IS ANOTHER SHORT-WAVE TROUGH JUST EAST OF THE BASE OF
THE BRISTOL BAY TROUGH (OVER THE NORTH PACIFIC). COMBINATION OF THIS
TROUGH AND UPPER JET ON DOWNSTREAM SIDE OF TROUGH IS PRODUCING AN
INTENSIFYING SURFACE LOW WHICH IS TRACKING NORTHEASTWARD TOWARD
SOUTHEAST ALASKA. THE THIRD SHORT-WAVE TROUGH IS SOUTH OF THE
WESTERN ALEUTIANS WHERE A MODERATE LOW HAS FULLY OCCLUDED. THE LOW
IS TRACKING EAST-NORTHEAST...SO EXPECT WINDS AND PRECIPITATION TO
MOVE INTO THE WESTERN TO CENTRAL ALEUTIANS THIS AFTERNOON.
FINALLY...THERE IS  A VERY WEAK UPPER WAVE MOVING NORTHWARD ACROSS
SOUTHCENTRAL PRODUCING LOTS OF MID LAYER CLOUDS BUT VERY LITTLE IN
THE WAY OF PRECIPITATION. JUST A FEW FLURRIES OR ISOLATED SHOWERS
ARE DETECTABLE ON RADAR. MUCH OF THE FOG THAT WAS OVER SOUTHCENTRAL
DISSIPATED AS MID LEVEL CLOUDS MOVED IN. THERE IS STILL SOME FOG IN
THE COPPER BASIN...BUT IT IS NOT DENSE. ALL OF THESE SHORT-WAVES ARE
EMBEDDED WITHIN A ZONAL LONG-WAVE...SO THAT EVERYTHING IS PROGRESSING
EASTWARD.

.MODEL DISCUSSION...MODELS INITIALIZED WELL AND ARE IN VERY GOOD
AGREEMENT THROUGH THE SHORT-TERM. WITH HIGH CONFIDENCE IN THE
MODELS SOLUTION WILL ADD A LOT OF DETAIL TO FORECAST THROUGH THIS
WEEKEND...PARTICULARLY WITH REGARD TO THE COLD ADVECTION WINDS
SETTING UP ACROSS SOUTHCENTRAL...THE GULF WATERS...AND THE AKPEN.

.SHORT TERM FORECAST...

SOUTHCENTRAL...CLOUDS WILL GRADUALLY DECREASE TONIGHT AS THE
SHORT-WAVE CURRENTLY OVERHEAD MOVES OFF TO THE NORTH AND EAST. THE
REMNANTS OF THE BRISTOL BAY WAVE WILL EVENTUALLY MOVE THROUGH LATE
FRIDAY...BUT MOST OF ENERGY WILL MOVE EASTWARD OVER GULF SO DONT
EXPECT ANY NOTABLE IMPACT. MEANWHILE...THE SURFACE PRESSURE GRADIENT
WILL REALLY TIGHTEN UP TONIGHT AND FRIDAY AS THE INTENSIFYING
PACIFIC LOW TRACKS TOWARD SOUTHEAST ALASKA. COLDER AIR WILL ALSO
ADVECT INTO SOUTHCENTRAL. THE COMBINATION OF SURFACE PRESSURE
GRADIENT AND COLD ADVECTION WILL PRODUCE GUSTY GAP WINDS ALONG THE
NORTHERN AND WESTERN GULF...ESPECIALLY FOR RESURRECTION BAY/PASSAGE
CANAL/THOMPSON PASS/COPPER RIVER DELTA/AND KAMISHAK BAY. THIS FIRST
SURGE OF COLD AIR IS RELATIVELY WEAK. MUCH STRONGER ADVECTION WILL
ENSUE LATE FRIDAY NIGHT AND CONTINUE THROUGH SATURDAY NIGHT AS A
RIDGE BUILDS OVER THE WESTERN BERING AND A SHORT-WAVE DROPS
SOUTHEASTWARD ACROSS SOUTHWEST ALASKA INTO THE GULF. THIS WILL SET
UP A JET ACROSS SOUTHWEST ALASKA AND THE KODIAK ISLAND WATERS
RESULTING IN STRONG COLD ADVECTION. THEREFORE...EXPECT MAX GALE
TO STORM FORCE WINDS TO SET UP THROUGH THIS REGION. ALTHOUGH NOT AS
STRONG...GAP WINDS WILL ALSO INCREASE ACROSS THE REST OF SOUTHCENTRAL
ON SATURDAY. THIS WILL LIKELY BE THE BEGINNING OF A PROLONGED COLD
AND WINDY PERIOD FOR SOUTHCENTRAL AS ANOTHER LOW MOVES INTO THE GULF
AND THE COLD ADVECTION OVER WARMER WATERS HELPS MAINTAIN LOW PRESSURE
OVER THE GULF.

SOUTHWEST ALASKA...SNOW IN BRISTOL BAY/AKPEN WILL TAPER OFF THIS
AFTERNOON/EVENING AS SHORT-WAVE MOVES EASTWARD INTO GULF. ONSHORE
FLOW AND WEAK UPPER WAVES WILL PROVIDE A SLIGHT CHANCE OF SNOW FOR
THE KUSKOKWIM DELTA ALONG WITH AREAS OF LOW CLOUDS AND FOG. AS A
MORE SIGNIFICANT SHORT-WAVE DROPS SOUTHWARD ACROSS SOUTHWEST ALASKA
FRIDAY NIGHT AND SATURDAY COLD ADVECTION AND WINDS WILL PICK
UP...ESPECIALLY THROUGH THE AKPEN. EXPECT AIR MASS TO BE VERY COLD
AND DRY...BUT COLD ADVECTION OVER WATER WILL GENERATE SNOW SHOWERS
OVER THE EASTERN BERING/BRISTOL BAY ACROSS THE AKPEN INTO THE
PACIFIC.

BERING SEA/ALEUTIANS...THE LOW SOUTH OF THE ALEUTIANS WILL TRACK
SOUTH OF THE ALEUTIANS...LIMITING THE AMOUNT OF WARM ADVECTION SO
THAT PRECIPITATION WILL BE MIX OF RAIN AND SNOW FOR MOST PLACES.
THE SYSTEM WILL QUICKLY MOVE OFF TO THE SOUTHEAST LATE FRIDAY.
MEANWHILE...AN UPPER LEVEL RIDGE WILL BEGIN TO BUILD OVER THE
WESTERN BERING AHEAD OF THE NEXT SYSTEM MOVING OUT OF ASIA AND
SLIDE OVER THE CENTRAL BERING SEA BY SATURDAY. MULTIPLE FRONTS/LOWS
WILL THEN ROTATE ALONG THE WESTERN SIDE OF THE RIDGE INTO THE
WESTERN BERING/ALEUTIANS AS WE HEAD INTO NEXT WEEK.

.LONG TERM FORECAST...GFS 500MB 5-WAVE SHOWS LONG-WAVE TROUGH
REMAINING OVER GULF/MAINLAND THROUGH MUCH OF NEXT WEEK. BY THE END
OF NEXT WEEK LOOKS FAIRLY ZONAL AS PRESSURE FROM THE EAST AND WEST
OF BERING SEA RIDGE BREAK IT DOWN LEAVING A CLOSED RIDGE TO THE
NORTH OVER FAR EASTERN RUSSIA. SO...EXPECT MAINLY COLD AND DRY
CONDITIONS FOR MAINLAND ALASKA WITH THE CHANCE THAT SOME OF THE GULF
LOW ENERGY MAY ROTATE INLAND LATE IN THE WEEK. AND OUT WEST LOOK FOR
A STEADY STREAM OF SYSTEMS TO MOVE ACROSS THE REGION THROUGH NEXT
WEEK. WITH SUBTROPICAL JET WELL TO THE SOUTH THE STRONGEST SYSTEMS
WILL REMAIN SOUTH OF THE FORECAST AREA ALONG WITH THE REALLY WARM
AIR.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALES 130 150 155 170 171 172 175 176.
FIRE WEATHER...NONE.

SEB DEC 07