Brisk Wind Advisory 23, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
130 PM AKST MON FEB 25 2013

.ANALYSIS AND UPPER LEVELS...THERE ARE TWO MAJOR STORM SYSTEMS
AFFECTING THE ALASKA REGION THIS MORNING. A TRIPLE POINT LOW
INTENSIFIED OVERNIGHT SOUTH OF THE ALASKA PENINSULA AND IS NOW
BEGINNING TO STALL SOUTH OF KODIAK ISLAND AS THE UPPER JET
CONTINUES OFF TO THE EAST. THE GREATEST IMPACT FROM THIS SYSTEM IS
BEING FELT ON THE BACK SIDE ACROSS THE SOUTHERN ALASKA PENINSULA.
STRONG VERTICAL MOTION FROM THIS STORM AND A SHORT-WAVE TROUGH
MOVING EASTWARD ACROSS THE EASTERN BERING IS COMBINING WITH COLD
AIR ADVECTION AND STRONG NORTHERLY WINDS TO PRODUCE WIDESPREAD
BLIZZARD CONDITIONS. CONDITIONS ARE SLOWLY IMPROVING FROM WEST
TO EAST. THERE IS ALSO A BAND OF SNOW AHEAD OF THE BERING TROUGH
FROM AROUND BETHEL SOUTHWARD ALONG THE WESTERN CAPES OF BRISTOL BAY
PRODUCING SNOW AND LOCALIZED AREAS OF BLOWING SNOW. SNOW IS ALSO
SPREADING SLOWLY NORTHWARD FROM THE LOW CENTER ACROSS KODIAK ISLAND
AND INTO BRISTOL BAY.

ANOTHER DEEP LOW IS TRACKING SOUTH OF THE WESTERN ALEUTIANS WITH
AN OCCLUDED FRONT HEADED NORTHWARD FROM THE LOW CENTER.

.MODEL DISCUSSION...ECMWF INITIALIZED A TAD BETTER THAN OTHER MODELS
WITH LOW SOUTH OF THE ALASKA PENINSULA. IT ALSO SHOWED GREAT
RUN-TO-RUN CONSISTENCY AND WILL BE USED AS GUIDANCE FOR THE FIRST
THREE DAYS OF THE FORECAST. THERE HAD BEEN QUITE A BIT OF UNCERTAINTY
WITH REGARD TO LOW POSITIONS IN THE GULF. MODELS SEEMED TO HAVE A
BETTER HANDLE ON THE SITUATION NOW AND FORECAST CONFIDENCE IS ABOVE
AVERAGE.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE LOW SOUTH OF KODIAK ISLAND WILL BACK ITS
WAY TOWARD KODIAK ISLAND TONIGHT AS THE UPPER TROUGH LIFTS NORTHWARD
INTO THE GULF TAKING ON AN EAST-WEST ORIENTATION. THE AFFECT OF THIS
WILL BE TO STALL THE OCCLUDED FRONT OVER THE NORTHERN GULF...KEEPING
MOST OF THE IMPACTS FROM WIND AND PRECIP CONFINED TO KODIAK ISLAND
AND THE GULF COAST. AS THE LOW CENTER MOVES WESTWARD TONIGHT INTO
TUESDAY MORNING THE REMNANTS OF THE FRONT WILL PUSH WESTWARD JUST
SOUTH OF THE KENAI PENINSULA. ALTHOUGH LOW LEVEL FLOW IS NOT
FAVORABLE FOR A BIG SNOW...IT DOES LOOK LIKE THERE WILL BE A
PERIOD OF STRONG LOW LEVEL CONVERGENCE IN THE KACHEMAK BAY AREA.
THEREFORE...WILL CONSIDER ISSUING A WINTER WEATHER ADVISORY FOR
SNOW FOR THIS AREA. THE UPPER TROUGH WILL LIFT NORTHWARD ACROSS
SOUTHCENTRAL TUESDAY NIGHT AND WEDNESDAY. VERTICAL MOTION WILL BE
DISORGANIZED AND LOW LEVEL FLOW WILL BE UNFAVORABLE FOR MUCH PRECIP
INLAND...SO ONCE AGAIN EXPECT MOST OF THE IMPACTS TO REMAIN ALONG
THE COAST.

SOUTHWEST ALASKA...SNOW WILL BECOME MORE WIDESPREAD AS LOW SETTLES
IN NEAR KODIAK ISLAND THIS EVENING WITH MOISTURE ADVECTING ACROSS
THE MOUNTAINS INTO BRISTOL BAY. THE TROUGH OVER THE EASTERN BERING
WILL STALL ALONG THE WESTERN ALASKA COAST THIS EVENING AND THEN
HEAD BACK WESTWARD AS TROUGH OVER GULF BECOMES EAST-WEST ORIENTATED
RESULTING IN STRENGTHENING EASTERLY FLOW. INITIALLY THE HEAVIEST
SNOW WILL BE ALONG THE LOW LEVEL TROUGH AXIS EXTENDING FROM THE
LOW CENTER NORTHWESTWARD TO AROUND DILLINGHAM. AS EASTERLY FLOW
STRENGTHENS TUESDAY AFTERNOON AND EVENING SNOW WILL PUSH WESTWARD
AND THEN TAPER OFF TUESDAY NIGHT AS THE LOW DISSIPATES.

BERING SEA/ALEUTIANS...THE ALEUTIANS WILL SEE ANOTHER ROUND OF SNOW
AND BLOWING SNOW AS LOW TO THE SOUTH APPROACHES TONIGHT. HOWEVER AIR
MASS IS TOO WARM TO CAUSE REALLY LOW VISIBILITIES. THERE MIGHT EVEN
BE ENOUGH WARM AIR ADVECTION TO CAUSE A CHANGE TO RAIN ALONG THE
CENTRAL ALEUTIANS FOR A WHILE. THE SYSTEM WILL ULTIMATELY REMAIN
SOUTH OF THE CHAIN. COLDER AIR SNOW SHOWERS AND GUSTY WINDS WILL
MOVE IN BEHIND THE LOW ON TUESDAY NIGHT AND WEDNESDAY. MEANWHILE...
THE TROUGH OVER THE EASTERN BERING WILL HEAD BACK WESTWARD TUESDAY
NIGHT AND WEDNESDAY...LIKELY BRINGING SNOW TO THE PRIBILOF ISLANDS.
WITH AN ARCTIC AIR MASS IN PLACE AND SAINT PAUL ISLAND SURROUNDED
BY SEA ICE CONDITIONS ARE VERY FAVORABLE FOR BLOWING SNOW.
THEREFORE...WILL ISSUE A BLIZZARD WATCH FOR TUESDAY NIGHT AND
WEDNESDAY.

.LONG TERM FORECAST...LOOKS LIKE PATTERN WILL REMAIN ACTIVE BUT THAT
THERE WILL BE A CHANGE IN THE HEMISPHERIC WAVE PATTERN. OVER THE
PAST WEEK THERE HAS BEEN A HIGHLY ZONAL JET OVER THE NORTH PACIFIC.
MEDIUM RANGE MODELS INDICATE A SHIFT TO A MORE AMPLIFIED JET AND WAVE
PATTERN WHICH WOULD PROVIDE LONGER BREAKS IN BETWEEN STORM SYSTEMS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 181. BLIZZARD WATCH 195.
MARINE...STORM WARNING...120 130 150 155 172 175
         GALE WARNING...132 136 137 138 140 160 165 170 176 180 185.
         HEAVY FREEZING SPRAY WARNING...140 150 155 165 170 179.
FIRE WEATHER...NONE.

SEB FEB 13