High Wind in Alaska, January 8 to 9, 2011

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1220 PM AKST SAT JAN 8 2011

.ANALYSIS AND UPPER LEVELS...HEIGHTS ARE ON THE RISE OVER THE
EASTERN BERING AND MAINLAND ALASKA AS AN UPPER RIDGE BUILDS OUT
AHEAD OF A HIGH AMPLITUDE TROUGH EXTENDING FROM RUSSIA TO THE
NORTHWEST PACIFIC AND WESTERN BERING SEA. THE RIDGE IS PROVIDING
CALM CONDITIONS ACROSS ALL BUT THE WEST COAST OF MAINLAND ALASKA.
SUBSIDENCE ALOFT COMBINED WITH LIGHT WINDS HAS RESULTED IN AREAS
OF FOG...MOST NOTABLY IN THE ANCHORAGE AREA WHERE DENSE FOG HAS
SETTLED IN. WARMER AIR MOVING UP THE WEST SIDE OF THE RIDGE IS
STARTING TO MAKE ITS WAY OVER TOP OF THE RIDGE INTO WESTERN ALASKA.
THIS IS EVIDENT IN THE STEEP INVERSIONS AT KING SALMON AND MCGRATH
ON THEIR 12Z SOUNDINGS. THIS IS JUST THE BEGINNING OF WHAT IS
EXPECTED TO BE VERY SIGNIFICANT WARMING OF TEMPERATURES AT
MOUNTAIN LEVEL ACROSS MAINLAND ALASKA THE NEXT FEW DAYS.

AN ACTIVE PATTERN HAS SET UP OVER THE CENTRAL TO WESTERN BERING
AND ALEUTIANS WITH STORMS TRACKING UP THE WEST SIDE OF THE RIDGE
SUPPORTED BY A 130KT+ SOUTHERLY JET. ONE STORM FORCE LOW IS EXITING
OVER THE NORTHWEST BERING THIS MORNING WHILE ANOTHER DEVELOPS ALONG
THE FRONTAL BOUNDARY SOUTH OF THE CENTRAL ALEUTIANS. THERE IS A
CORRIDOR ALONG AND AHEAD OF THE FRONT FROM THE CENTRAL TO EASTERN
BERING AND ALEUTIANS WHERE WINDS WILL REMAIN AT MAXIMUM GALE FORCE
LEVELS BETWEEN SYSTEMS DUE THE CONTINUED TIGHT PRESSURE GRADIENT
BETWEEN HIGH PRESSURE OVER MAINLAND ALASKA AND THE MULTIPLE LOWS
OUT WEST.

.MODEL DISCUSSION...THERE ARE SOME MINOR DIFFERENCES WITH LOW
POSITIONS OUT WEST THE NEXT COUPLE DAYS...BUT THESE DIFFERENCES
HAVE LITTLE IMPACT ON THE OPERATIONAL FORECAST. MORE SIGNIFICANT
DIFFERENCES EVOLVE MONDAY AND BEYOND WITH SYSTEMS OVER THE
NORTHWEST PACIFIC WHICH AFFECTS THE FORECAST FOR THE WESTERN
ALEUTIANS. WILL STICK CLOSE TO INHERITED FORECAST ON THIS UNTIL
MODELS GAIN A BETTER HANDLE ON TRACK AND STRENGTH OF THESE SYSTEMS.

.SHORT TERM FORECAST...

SOUTHERN MAINLAND...UPPER RIDGE WILL DEVELOP A CLOSED CENTER
TONIGHT AS IT MOVES OVER SOUTHWEST ALASKA AND THEN STRENGTHEN
AS IT TRACKS TO NORTHERN ALASKA LATE SUNDAY. A THE RIDGE BUILDS
INTO SOUTHWEST ALASKA TONIGHT A VERY WEAK SHORT-WAVE WHICH IS
CURRENTLY ORIENTED NORTH-SOUTH RIGHT DOWN THE MIDDLE OF THE
STATE WILL BE FORCED TO TAKE A SOUTHWARD TURN AS IT PUSHES
THROUGH SOUTHCENTRAL. MORE IMPORTANTLY THAN THE WAVE ITSELF IS
A NORTHERLY JET STREAK BEHIND IT WHICH WILL KICK UP WINDS A BIT
IN THE THOMPSON PASS/VALDEZ REGION. UNLIKE MOST OF THESE SCENARIOS...
THE AIR MASS BEHIND THE SHORT-WAVE IS VERY SIMILAR TO THAT AHEAD
OF IT. THEREFORE...WINDS WON'T BE NEARLY AS STRONG AS THEY USUALLY
ARE WHEN COLD AIR ADVECTION IS INVOLVED. THE COMBINATION OF WARM
AIR ADVECTION AROUND THE TOP OF THE RIDGE WITH WARMING DO TO
SYNOPTIC SCALE SUBSIDENCE WILL RESULT IN A CONTINUAL WARMING OF
LOW LEVEL TEMPERATURES THE NEXT FEW DAYS. LIGHT WINDS AND MOSTLY
CLEAR SKIES AT SEA LEVEL WILL KEEP TEMPERATURES GENERALLY AT OR
BELOW FREEZING ACROSS THE REGION. HOWEVER...TEMPERATURES A COUPLE
THOUSAND FEET UP WILL WARM INTO THE 40S AND PERHAPS EVEN INTO THE
LOWER 50S MONDAY AND TUESDAY. A PERSISTENT STEEP TEMPERATURE
INVERSION MEANS FOG WILL REMAIN A THREAT OVER THE NEXT FEW DAYS.

BERING SEA/ALEUTIANS...AS THE UPPER RIDGE OVER THE MAINLAND
STRENGTHENS IT WILL PUSH THE STORM TRACK FARTHER SOUTH AND WEST.
THE CORRIDOR OF STRONG WINDS BETWEEN THE HIGH AND LOWS (REFERENCED
IN THE ANALYSIS SECTION ABOVE) WILL ALSO GRADUALLY SHIFT SOUTH AND
WEST...BECOMING NEARLY PARALLEL TO THE ALEUTIAN CHAIN BY TUESDAY.
THERE IS A CHANCE THAT THE CENTRAL ALEUTIANS MAY SEE WARNING LEVEL
WINDS AS LOW PASSES BY EARLY THIS EVENING. HOWEVER...IT IS BORDERLINE
AND ANY WARNING LEVEL GUSTS WOULD BE VERY BRIEF...SO WILL NOT ISSUE
A WARNING.

.LONG TERM FORECAST...MODELS ARE CONSISTENT IN DEPICTING A GRADUAL
RETROGRESSION OF THE UPPER RIDGE FROM NORTHWEST ALASKA ON TUESDAY
TO THE CHUKCHI SEA BY THE END OF THE WEEK...AND FORECAST CONFIDENCE
IS HIGH. THE STRENGTH AND INFLUENCE OF THIS RIDGE WILL KEEP MAINLAND
ALASKA DRY. THE WESTWARD MOVEMENT OF THE RIDGE WILL ALLOW ARCTIC AIR
TO SURGE WESTWARD FROM NORTHWEST CANADA AND ACROSS THE MAINLAND...
SETTING UP LOCALLY WINDY CONDITIONS. MEANWHILE...THE STORM TRACK
WILL BE SUPPRESSED TO SOUTH OVER THE NORTH PACIFIC...BUT THE
CORRIDOR OF STRONG WINDS WILL PERSIST ALONG THE ALEUTIANS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...STORM WARNING...172.
         GALE WARNING...127 155 170 171 175 176 179 180 185.
FIRE WEATHER...NONE.

SEB JAN 11