Blizzard and High Wind in Alaska, March 28 to 30, 2009

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
545 AM AKDT SAT MAR 28 2009

.MODEL DISCUSSION...

MODELS SEEM TO BE MOSTLY IN AGREEMENT ON THE TRACK OF THIS NEXT MAJOR
LOW ACROSS THE EASTERN ALEUTIANS THIS AFTERNOON FOLLOWED BY LANDFALL
NEAR TOGIAK LATE SUNDAY MORNING.  THIS SYSTEM WILL BRING A WIDE
VARIETY OF SIGNIFICANT WEATHER TO THE ENTIRE SOUTHERN HALF OF THE
STATE.

.ANALYSIS AND UPPER LEVELS...

WEAK LOW PRESSURE REMAINS OVER SOUTHCENTRAL ALASKA...WITH A COUPLE OF
SHORTWAVES MOVING NORTHEASTWARD ACROSS THE SOUTHERN MAINLAND ON THE
DOWNSTREAM SIDE OF A NARROW LONGWAVE TROUGH SITUATED FROM THE WEST
COAST OF ALASKA TO THE CENTRAL ALEUTIANS.  A STRONG NORTH PACIFIC
UPPER LOW HAS BECOME ABSORBED INTO THE BASE OF THE LONGWAVE
TROUGH...WHICH IS INDUCING CYCLOGENESIS IN THE NORTH PACIFIC JUST
SOUTH OF THE ALEUTIANS NEAR 50N 170W.  THIS CYCLOGENESIS IS OCCURRING
IN THE FAVORABLE LEFT EXIT REGION OF A STRONG 500 MB JET STREAK.  A
LARGE UPPER HIGH CONTINUES TO DOMINATE THE WEATHER OVER EASTERN
SIBERIA AND THE KAMCHATKA PENINSULA REGIONS.

.SHORT TERM FORECAST...

WEST OF THE ALASKA RANGE...ATTENTION IS FOCUSED FOR THE NEXT COUPLE
OF DAYS ON THE STRONG LOW DEVELOPING IN THE NORTH PACIFIC TO THE
SOUTH OF THE CENTRAL ALEUTIANS.  THIS LOW WILL MOVE ACROSS THE
EASTERN ALEUTIANS TODAY AND THEN MAKE LANDFALL LATE SUNDAY MORNING
NEAR TOGIAK ON THE SOUTHWESTERN MAINLAND....BRINGING LOTS OF
PRECIPITATION AND STRONG WINDS.  FOR RIGHT NOW...IT LOOKS LIKE STRONG
WINDS AND SNOW WILL HELP BRING BLIZZARD CONDITIONS TO MOST AREAS IN
THE VICINITY OF THE LOW...BOTH ON THE FRONT AND BACK SIDE.  EVEN AS
THE LOW MOVES INLAND INTO WEST-CENTRAL ALASKA...WINDS WILL REMAIN
BLUSTERY AND COLD ADVECTION SHOWERS ARE LIKELY TO LINGER WELL INTO
THE FIRST PART OF THE WEEK.

SOUTH AND EAST OF THE ALASKA RANGE...SHOWERY ACTIVITY WILL CONTINUE
ACROSS SOUTHCENTRAL...INCLUDING THE ANCHORAGE BOWL...AS A SERIES OF
SHORTWAVES MOVE ACROSS THE REGION WITH A BROAD DIFFUSE SURFACE LOW
OVER THE MATANUSKA VALLEY AND NORTHERN COPPER RIVER BASIN.  COLD
ADVECTION SHOWERS WILL CONTINUE ON THE BACK SIDE OF THIS LOW UNTIL
THE SECOND SHORTWAVE PASSES OVER THE AREA THIS AFTERNOON.  THIS IS
FOLLOWED BY VERY BRIEF TRANSITORY RIDGING BEFORE THE NEXT MAJOR STORM
SYSTEM MOVES IN FROM THE SOUTH AND WEST TONIGHT.

STRONG WINDS ALOFT COMBINED WITH A TIGHTENING PRESSURE GRADIENT WILL
BEGIN TO CAUSE AN INCREASE IN WINDS LATER TODAY.  AS A STRONG FRONT
MOVES NORTHWARD TOWARDS THE SOUTHERN GULF COAST...A BARRIER JET WILL
FORM AND BRING STORM FORCE WINDS TO THE NORTHERN GULF OF ALASKA. THIS
WILL HAVE AN AFFECT ON WINDS THROUGH PORTAGE VALLEY AND TURNAGAIN ARM
AS WELL AS THE HIGHER ELEVATIONS OF ANCHORAGE.  A FEW STRONG WIND
GUSTS TO 45 MPH ARE POSSIBLE IN THE LOWER ELEVATIONS OF ANCHORAGE AS
WELL...PARTICULARLY ON THE SOUTH AND WESTERN SIDES OF TOWN.  THUS...A
HIGH WIND WATCH IS IN EFFECT FOR EARLY SUNDAY MORNING THROUGH LATE
SUNDAY EVENING FOR TURNAGAIN ARM AND THE HIGHER ELEVATIONS OF
ANCHORAGE.  IN ADDITION...A BLIZZARD WATCH FOR PORTAGE VALLEY AND THE
EASTERN TURNAGAIN ARM AREA IS IN EFFECT FOR THE SAME TIME PERIOD ON
SUNDAY.  A WINTER WEATHER ADVISORY FOR SNOW IS NEEDED FOR HEFTY SNOW
AMOUNTS IN THE WESTERN SUSITNA VALLEY BEGINNING LATE TONIGHT THROUGH
LATE SUNDAY NIGHT...WHERE STRONG FORCING FOR ASCENT FROM THE DYNAMICS
ALOFT WILL BE ENHANCED BY STRONG UPSLOPE FLOW ON THE EAST SIDE OF THE
ALASKA RANGE.

CONDITIONS GRADUALLY IMPROVE MONDAY AS THE LOW EXITS EAST...BUT THERE
WILL CONTINUE TO BE SHOWERY ACTIVITY ACROSS MOST OF THE REGION AS
COLD ADVECTION KICKS IN FROM THE WEST.

.LONG TERM FORECAST...

LATEST HPC GUIDANCE AND THE LATEST GFS MODEL SHOW FAST ZONAL FLOW
SETTING UP JUST TO THE SOUTH OF THE STATE AS SURFACE LOW PRESSURE
OVER SOUTH CENTRAL ALASKA MOVES TOWARDS THE ALCAN BORDER ON MONDAY.
A FAST MOVING SYSTEM WILL PASS THROUGH THE NORTH PACIFIC INTO THE
CENTRAL GULF OF ALASKA TUESDAY...PERHAPS STAYING FAR ENOUGH SOUTH TO
HAVE LITTLE IMPACT ON THE SOUTHERN HALF OF THE STATE.  THIS IS
QUICKLY FOLLOWED BY ANOTHER SERIES OF STORMS THAT WILL KEEP THE
WEATHER MOSTLY UNSETTLED THROUGH MOST OF NEXT WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WATCH...125 155 161
         BLIZZARD WARNING...185 195
         HIGH WIND WATCH...101
MARINE...GALE...125 129 130 132 138 140 141 150 160 170 171 172 175
                179 180
         STORM...120 155 165
         HEAVY FREEZING SPRAY...130 155 165 179
FIRE WEATHER...NONE.

CC MAR 09