Gale Warning 915, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1150 AM AKST SUN DEC 30 2012

.ANALYSIS AND UPPER LEVELS...A VERY LARGE AND STRONG MATURE LOW IS
CENTERED JUST SOUTH OF THE ALASKA PENINSULA THIS MORNING IS SLOWLY
WEAKENING AS IT TRACKS NORTHWESTWARD TOWARD BRISTOL BAY. A WARM
OCCLUSION IS PUSHING WESTWARD ALONG THE WESTERN ALASKA COAST WHILE
THE REST OF THE FRONTAL SYSTEM HAS GONE ALOFT AND LOST ITS STRUCTURE.
RADAR IMAGERY SHOWS RAIN OVER SOUTHCENTRAL ALASKA IS FOCUSED ALONG
THE COAST AND EXHIBITS A CONVECTIVE AND WAVELIKE CHARACTER. THIS IS
DUE TO THE PRESENCE OF VERY STRONG WINDS IN THE LOW LEVELS ALONG WITH
MOUNTAIN WAVE ACTIVITY. WINDS ARE CURRENTLY TRANSITIONING FROM A
GEOSTROPHIC WIND ALONG TURNAGAIN ARM (WHICH FAVORS STRONGER WINDS
THROUGH PORTAGE VALLEY AND EASTERN TURNAGAIN ARM) TO AN AGEOSTROPHIC
WIND (WHICH FAVORS STRONGER WINDS OVER WEST TURNAGAIN ARM AND
ANCHORAGE) AS THE LOW MAKES MORE PROGRESS NORTH AND WEST CAUSING AN
INCREASE IN THE EAST-WEST PRESSURE GRADIENT. COINCIDENT WITH THIS
TRANSITION...WINDS HAVE COME DOWN OVER HIGHER ELEVATIONS OF ANCHORAGE
THIS MORNING...BUT EXPECT THEM TO TREND BACK UP AS WE HEAD INTO THE
AFTERNOON.

MEANWHILE ANOTHER LOW IS BEGINNING TO DEVELOP OVER THE NORTH-CENTRAL
PACIFIC. IT WILL BE THE THIRD IN A RAPID SERIES OF VERY STRONG STORMS
TO AFFECT THE REGION.

.MODEL DISCUSSION...THERE ARE SOME POSITION DIFFERENCES WITH THE
TRACK OF THE DEVELOPING LOW OVER THE NORTH-CENTRAL PACIFIC ALTHOUGH
THEY ARE ALL GROUPED IN THE SAME GENERAL REGION. PREFER THE ECMWF
WHICH SHOWS VERY GOOD RUN-TO-RUN CONSISTENCY AND IS SUPPORTED BY
THE GEMGLB SOLUTION. MORE SIGNIFICANT MODEL DIFFERENCES DEVELOP
WITH DEVELOPMENT OF TRIPLE POINT LOW SOUTH OF THE ALEUTIANS TUE.
WITH SUCH LARGE SPREAD IN SOLUTIONS WILL USE A BROAD-BRUSH APPROACH
FOR NOW.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...STILL EXPECTING WINDS TO PEAK IN THE ANCHORAGE
AREA THIS AFTERNOON AS PRESSURE GRADIENTS CONTINUE TO STRENGTHEN.
THE LOW DID REALLY STALL OUT SOUTH OF KODIAK ISLAND LAST NIGHT AND
THIS MORNING. THIS SLOWER MOVEMENT MEANS THAT HIGH WINDS LIKELY WON'T
BE AS WIDESPREAD ACROSS THE ANCHORAGE BOWL AS PREVIOUSLY THOUGHT.
AREAS MOST LIKELY TO STILL OBSERVE SOME POTENTIALLY DAMAGING WIND
GUSTS ARE ALONG AND NEAR THE MOUNTAINS. WEST ANCHORAGE WON'T SEE
STRONG SOUTHEASTERLIES MOVE IN UNTIL MID TO LATE AFTERNOON. WINDS
WILL STILL BE STRONG AND GUSTY...BUT NOT NEARLY AS STRONG AS WINDS
NEAR TURNAGAIN ARM AND THE MOUNTAINS. STRONG PRESSURE RISES WILL
OCCUR BEHIND THE LOW WHICH WILL MAINTAIN STRONG WINDS IN THE WAKE
OF THE LOW INTO THE OVERNIGHT HOURS. PRECIP IS FALLING MAINLY AS
RAIN AT THE MOMENT...BUT DO EXPECT GRADUAL COOLING OVERNIGHT WHICH
WILL LOWER SNOW LEVELS OVER PRINCE WILLIAM SOUND...POSSIBLY DOWN
NEAR SEA LEVEL TOWARD MORNING.

ONCE AGAIN THERE WILL BE A BRIEF BREAK BETWEEN STORM SYSTEMS AS
THE THIRD IN A STRING OF STRONG STORMS ARRIVES OVER THE GULF MONDAY
AFTERNOON AND THE REST OF SOUTHCENTRAL MONDAY NIGHT. ALL INDICATIONS
ARE THAT THIS SYSTEM WILL NOT BE AS STRONG AS THE CURRENT ONE. THERE
IS STILL POTENTIAL FOR HIGH WINDS ALONG TURNAGAIN ARM AND HIGHER
ELEVATIONS...WHICH WILL BE DEPENDENT ON THE EXACT LOW TRACK AND
STRENGTH. WILL WAIT UNTIL THE CURRENT WARNINGS EXPIRE BEFORE ISSUING
ANYTHING FOR THE NEXT SYSTEM.

SOUTHWEST ALASKA...PRECIP WILL GRADUALLY BECOME MORE WIDESPREAD
ACROSS SOUTHWEST ALASKA THIS AFTERNOON THROUGH TONIGHT AS THE
LOW TRACKS THROUGH THE AREA AND DOWNSLOPING WINDS DIE DOWN.
PRECIP-TYPE WILL REMAIN PRIMARILY RAIN IN BRISTOL BAY WHILE THE
KUSKOKWIM VALLEY AND KUSKOKWIM DELTA WILL CONTINUE TO SEE A MIX
OF SNOW AND FREEZING RAIN. DON'T EXPECT FREEZING RAIN TO BE LONG
LASTING IN ANY ONE LOCATION...SO EXPECT LITTLE OR NO ICE
ACCUMULATION. CONDITIONS WILL DRY OUT BRIEFLY ON MONDAY BEFORE
THE NEXT SYSTEM...WHICH WILL TAKE A NEARLY IDENTICAL TRACK TO
THE CURRENT ONE...MOVES IN MONDAY AFTERNOON AND EVENING. THE SYSTEM
WILL BE A LITTLE WEAKER...BUT OTHERWISE THE OBSERVED WEATHER OVER
SOUTHWEST ALASKA WILL BE VERY SIMILAR TO WHAT IS OCCURRING TODAY.

BERING SEA/ALEUTIANS...MOST OF THE BERING AND ALEUTIANS WILL BE
UNDER BROAD NORTHWEST FLOW ON THE BACK SIDE OF THE LOW MOVING INTO
SOUTHWEST ALASKA. WEAK COLD ADVECTION WILL CONTRIBUTE TO SNOW
SHOWERS AND GUSTY WINDS PRIMARILY FROM THE CENTRAL BERING TO
EASTERN ALEUTIANS. THE PATTERN WILL CHANGE ON MONDAY AS A SYSTEM
MOVING INTO THE NORTHWEST PACIFIC PUSHES A STRONG FRONTAL BOUNDARY
EASTWARD TO THE WESTERN ALEUTIANS. THIS FRONT WILL CONTINUE TO
PROGRESS EASTWARD AND PASS UNDERNEATH THE NEXT LOW WHICH TRACKS TO
SOUTHWEST ALASKA ON TUESDAY. THERE WILL BE TRIPLE POINT DEVELOPMENT
ALONG THIS FRONT SOMEWHERE IN THE VICINITY OF THE EASTERN ALEUTIANS
ON TUESDAY...BUT THERE IS QUITE A BIT UNCERTAINTY IN THE LOCATION
AND STRENGTH.

.LONG TERM FORECAST...THE SERIES OF VERY STRONG LOWS TRACKING TO
SOUTHWEST ALASKA LOOKS LIKE IT WILL END WITH THE ONE MOVING THROUGH
ON MONDAY AND TUESDAY. A VERY LARGE CYCLONIC CIRCULATION WILL SET UP
OVER THE BERING THROUGH THE EXTENDED PERIOD WITH WEAKER LOWS TRACKING
ALONG THE ALEUTIANS AND THEN ROTATING NORTHWARD TOWARD THE ALASKA
PENINSULA/BRISTOL BAY. THUS...EXPECT MORE ACTIVITY OUT WEST WITH
RELATIVELY QUIETER CONDITIONS OVER THE GULF AND SOUTHCENTRAL ALASKA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WARNING 101 125.
MARINE...STORM WARNING...120 132 138 150 155.
         GALE WARNING...125 130 140 160 165 170 172 175 176 185.
         HEAVY FREEZING SPRAY WARNING...185.
FIRE WEATHER...NONE.

SEB DEC 12