Small Craft Advisory 152, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
400 PM AKST SAT FEB 14 2009

.ANALYSIS AND UPPER LEVELS...

ALOFT...THE DOMINANT WEATHER FEATURES ARE A TRIO OF VORTICES
EXTENDING FROM CHINA TO EASTERN SIBERIA TO THE ARCTIC SEA NEAR 80N
140W THAT IS SPITTING OUT SYSTEMS IN RAPID SUCCESSION FROM SOUTHERN
CHINA TOWARDS ALASKA.  WITH THE MEAN RIDGE POSITION OVER EASTERN
AK/WESTERN CANADA THE FLOW IS MOSTLY SOUTHWESTERLY BRINGING IN A MUCH
WARMER AND WETTER WEATHER PATTERN THAN WHAT WE HAVE SEEN MOST OF THIS
WINTER.  A SUBTLE SHORTWAVE CURRENTLY OVER CENTRAL ALASKA IS RAPIDLY
WEAKENING AS IT APPROACHES THE RIDGE AXIS EXTENDING FROM THE GULF OF
ALASKA INTO NORTHWEST CANADA...BUT HAS BROUGHT LIGHT UPSLOPE SNOW TO
THE UPPER SUSITNA VALLEY THIS MORNING.  A STRONG SHORTWAVE IS
CURRENTLY LOCATED OVER THE CENTRAL ALEUTIANS SUPPORTING A LARGE STORM
SYSTEM SEEN ON SATELLITE LOOPS BRINGING CLOUDS TO ALL OF THE AKPEN
AND SOUTHWEST ALASKA.  ANOTHER SHORTWAVE NEAR THE KAMCHATKA PENINSULA
IS MOVING EASTWARD TOWARDS THE ALEUTIANS HOT ON THE HEELS OF THE
CENTRAL ALEUTIANS SHORTWAVE.

AT THE SURFACE...A LARGE 979 MB DOUBLE-PRONGED LOW OVER THE CENTRAL
ALEUTIANS IS BRINGING BLIZZARD CONDITIONS TO THE PRIBILOFS AS IT
CONTINUES TO TREK TOWARDS BRISTOL BAY AND SOUTHWEST AK.  AHEAD OF
THIS LOW...SOUTHERLY FLOW CONTINUES TO PUSH WARM MOIST AIR ONTO TO
THE KENAI PENINSULA AND THE ANCHORAGE BOWL AREAS.  WINDS THROUGH
TURNAGAIN ARM ARE SUBSIDING SOMEWHAT BUT SHOULD PICK BACK UP AS THE
NEXT LOW APPROACHES SOUTHWEST AK WITH AN INCREASE IN THE PRESSURE
GRADIENT.

.MODEL DISCUSSION...

THE NAM CONTINUES TO HANDLE THE DETAILS OF THE PLACEMENT AND
ORIENTATION OF THE 979 MB LOW IN THE CENTRAL ALEUTIANS THE BEST.  IT
KEEPS THE NORTHERN LOW OF THE SET AS THE STRONGEST WHICH MATCHES WELL
SO FAR WITH SATELLITE PRESENTATION. ALL MODELS WANT TO SEND THIS LOW
NORTHWARD TO NEAR THE NORTHWEST AK COASTLINE BY MONDAY AFTERNOON WITH
A TRIPLE POINT LOW FORMING ALONG THE FRONT NEAR KODIAK ISLAND. MODELS
ARE TRENDING WEAKER WITH THIS FEATURE IN THE GULF AND THUS WINDS WERE
TRENDED DOWNWARD IN THE MONDAY-TUESDAY PERIOD TAKING INTO ACCOUNT
THIS WEAKENING TREND IN THE MODELS.

.SHORT TERM FORECAST...

SOUTHCENTRAL...SUBTLE SURFACE RIDGING TODAY BETWEEN THE TWO LOWS OVER
NORTHWEST ALASKA AND THE LARGE 979 MB LOW IN THE CENTRAL ALEUTIANS
HAS LESSENED THE PRESSURE GRADIENT ENOUGH TO LOWER WINDS THROUGH
TURNAGAIN ARM INTO EARLY THIS EVENING.  AS THIS SURFACE RIDGING GIVES
WAY TONIGHT TO PRESSURE FALLS WINDS SHOULD BEGIN TO PICK BACK UP
SUNDAY MORNING IN TURNAGAIN ARM AND LAST INTO THE AFTERNOON HOURS
BEFORE BEGINNING TO SUBSIDE DURING THE EVENING HOURS.  PRECIPITATION
SHOULD BE FAIRLY LIMITED IN THE ANCHORAGE BOWL DUE TO DOWNSLOPE FLOW
BUT THE FAVORED UPSLOPE AREAS OF PRINCE WILLIAM SOUND AND THE WESTERN
SUSITNA VALLEY SHOULD SEE HEFTIER AMOUNTS.  WITH TEMPERATURES
STRADDLING THE FREEZING MARK IN LOWER ELEVATIONS ALONG PRINCE WILLIAM
SOUND AND THE KENAI PENINSULA...RAIN WILL BE POSSIBLE.

SOUTHWEST AK...STRONG WINDS ASSOCIATED WITH THE 979 MB LOW ACROSS THE
CENTRAL ALEUTIANS AND THE PRIBILOFS WILL APPROACH SOUTHWEST ALASKA
TONIGHT.  BLIZZARD CONDITIONS MAY BE POSSIBLE ALONG THE SOUTHWEST
COASTLINE MUCH LIKE THE PREVIOUS SYSTEM BROUGHT THOSE CONDITIONS FROM
DILLINGHAM NORTH.  WE ALSO HAVE TO BE CONCERNED WITH BLIZZARD
CONDITIONS POSSIBLE ON THE BACK SIDE OF THE LOW NEAR SAINT PAUL AS
COLD ADVECTION WINDS APPROACHING 35-40 MPH AND LIGHT SNOW COULD MAKE
FOR NEAR WHITEOUT CONDITIONS.  OTHERWISE EXPECT HIGHER PRECIPITATION
TOTALS TOWARDS THE LOWER KUSKOKWIM VALLEY AND AKPEN TONIGHT THROUGH
SUNDAY NIGHT CLOSE TO WHERE THE LOW TRACKS...WITH LESSER AMOUNTS IN
THE UPPER KUSKOKWIM VALLEY DUE TO DOWNSLOPE FLOW OFF THE ALASKA
RANGE.

IN THE ALEUTIANS...A FRONT WILL CONTINUE TO BE SITUATED ALONG THE
ALEUTIAN CHAIN WITH THE NEXT WEATHER SYSTEM MOVING ALONG THIS FRONT
CONTINUING TO BRING RAIN AND SNOW TO MOST OF THE CHAIN THROUGH MONDAY
NIGHT.

.LONG TERM FORECAST...MODELS CONTINUE TO HINT AT A MORE AMPLIFIED
WEATHER PATTERN IN THE EXTENDED.  A VERY LARGE AND DEEP CUT-OFF LOW
WILL ESTABLISH ITSELF NEAR 40N 140W...WHILE THE LARGE VORTEX NEAR
EASTERN SIBERIA WILL PERSIST AND GROW STRONGER.  THIS WILL ALLOW FOR
A STRONG JET TO KEEP FAST SOUTHWEST FLOW ALOFT MOVING TOWARDS ALASKA
AS RIDGING TRIES TO BUILD OVER THE STATE.  THUS EXPECT A CONTINUED
ACTIVE WEATHER PATTERN.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 161 AND 195. BLIZZARD WATCH 155.
MARINE...GALE WARNING...120 130 132 136 137 150 155 160 165 170 172
                        175 176 179 180 352 412 413 414
         STORM WARNING...NONE
         HEAVY FREEZING SPRAY WARNING...179 412 414
FIRE WEATHER...NONE.

CC FEB 09