Small Craft Advisory 20, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
1245 PM AST SUN JAN 6 2008

.ANALYSIS AND UPPER LEVELS...OMEGA BLOCK IS FIRMLY ENTRENCHED WITH
A HIGH AMPLITUDE RIDGE OVER THE CENTRAL BERING AND CLOSED LOWS
OVER KAMCHATKA AND SOUTHWEST ALASKA. THE KAMCHATKA LOW IS LIFTING
NORTHWARD UP THE WEST SIDE OF THE RIDGE. SURFACE FRONT EXTENDS
SOUTHWARD FROM THIS LOW TO A WEAK SURFACE LOW JUST NORTH OF THE
WESTERN ALEUTIANS AND THEN SOUTH INTO THE PACIFIC. THE LOW OVER
SOUTHWEST ALASKA IS SINKING SOUTHEASTWARD. SHORT-WAVES ROTATING
AROUND THE LOW ARE HELPING TO ENHANCE COLD ADVECTION SNOW SHOWERS
AND WINDS ON THE BACK SIDE OF THE LOW (EASTERN BERING/ALASKA
PENINSULA) AND CONTRIBUTING TO LIGHT SNOW AHEAD OF THE LOW (OVER
SOUTHCENTRAL). A SURFACE LOW OVER THE NORTHERN GULF IS DRIFTING
SLOWLY NORTHWESTWARD TOWARD THE KENAI PENINSULA IN RESPONSE TO THE
UPPER LOW DROPPING SOUTHWARD. MOISTURE IS ON THE INCREASE ACROSS
SOUTHCENTRAL WITH AREAS OF LIGHT SNOW OR SNOW SHOWERS OVERSPREADING
THE PRINCE WILLIAM SOUND REGION AS WELL AS THE WESTERN KENAI AND
ANCHORAGE. FINALLY THERE IS A LARGE MATURE LOW NEAR 45N 170W...BUT
IT IS NOT IMPACTING THE FORECAST AREA. HOWEVER...SATELLITE IMAGERY
SHOWS A WELL DEFINED TRIPLE POINT WHICH SHOULD DEVELOP INTO A LOW
BY LATER THIS AFTERNOON.

.MODEL DISCUSSION...MODEL DISAGREEMENTS BEGIN TO SHOW UP AS THE
TRIPLE POINT LOW MENTIONED ABOVE TRACKS TOWARD SOUTHEAST ALASKA.
THE GFS IS THE ODD MODEL OUT IN STALLING THE LOW FARTHER SOUTH AND
WEST AND PUSHING TROUGH NORTH AND WEST OF LOW CENTER FARTHER WEST
ACROSS THE GULF. THE GFS THEN MAINTAINS A LOW OVER THE MIDDLE OF
THE GULF THROUGH WEDNESDAY. THE ECMWF/UKMET/NAM ARE ALL IN FAIR
AGREEMENT ON BRINGING THE ORIGINAL LOW FARTHER EAST WITH TROUGH
EXTENDING TO NORTHERN GULF WHERE A NEW LOW FORMS. THE KEY IS IN
THE UPPER LEVELS WHERE THE GFS HOLDS BACK THE UPPER TROUGH WHILE
THE OTHER MODELS SWING IT NORTHWARD. HAVE COORDINATED WITH JUNEAU
WFO TO GO WITH THE MODEL CONSENSUS ON THIS ONE. OTHERWISE...NO MAJOR
CHANGES IN THE SHORT-TERM. THE MAIN CHANGES WILL BE FINE-TUNING OF
PRECIPITATION FORECAST OVER SOUTHCENTRAL.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...NORTHERN GULF LOW WILL MOVE OVER THE KENAI
PENINSULA TONIGHT AND DISSIPATE WHILE ANOTHER SURFACE LOW FORMS
BACK OVER THE GULF AND AGAIN TRACKS TOWARD THE KENAI PENINSULA.
MEANWHILE...UPPER LEVEL SHORT-WAVES WILL CONTINUE TO ROTAET ACROSS
SOUTHCENTRAL AS THE UPPER LOW CENTER DROPS TO KODIAK ISLAND ON
MONDAY. ALL OF THESE FACTORS WILL PRODUCE PERIODS OF SNOW ACROSS
SOUTHERN PORTIONS OF SOUTHCENTRAL. INLAND AREAS WILL REMAIN
DRIER...BUT WEAK UPPER LIFT MAY PRODUCE AREAS OF LIGHT SNOW OR
FLURRIES WITH LITTLE ACCUMULATION. CONDITIONS WILL DRY OUT TUESDAY
WITH SNOW CHANCES MAINLY ALONG THE COAST.

SOUTHWEST ALASKA/ALASKA PENINSULA...STRENGTH OF COLD ADVECTION AND
SURFACE PRESSURE GRADIENT WILL GO THROUGH PERIODS OF STRENGTHENING
AND WEAKENING...BUT GENERAL PATTERN WILL REMAIN THE SAME IN THE
SHORT-TERM. SO COLD ADVECTION SHOWERS AND GUSTY WINDS WILL CONTINUE
OVER THE EASTERN BERING/SOUTHWEST COAST/ALASKA PENINSULA. INLAND
AREAS WILL REMAIN MOSTLY DRY WITH MID TO HIGH CLOUDS ACCOSIATED WITH
UPPER LOW DROPPING THROUGH. SOME AREAS OF LIGHT SNOW ARE POSSIBLE
ALONG THE ALASKA AND ALEUTIAN RANGES AS MOISTURE ADVECTS OVER THE
MOUNTAINS FROM THE EAST AND COLD AIR CONTINUES TO ADVECT IN FROM
THE WEST.

BERING SEA/ALEUTIANS...WITH BLOCKING RIDGE OVERHEAD AND JET WELL
TO THE SOUTH DO NOT EXPECT ANY MAJOR SYSTEMS TO AFFECT THE REGION
IN THE SHORT-TERM. THE FRONT OVER THE WESTERN ALEUTIANS IS NEARLY
STATIONARY AND WILL REMAIN SO AS IT SLOWLY ELONGATES AND SHEARS
APART ALONG THE WEST SIDE OF THE RIDGE.

.LONG TERM FORECAST...OMEGA BLOCK WILL HOLD IN PLACE FOR A WHILE
SO DO NOT EXPECT ANY SIGNIFICANT CHANGES THROUGH THE EXTENDED
FORECAST PERIOD.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALES 130 132.
         HEAVY FREEZING SPRAY 130 132 138 150 155 160 165 179 180
                              185.
FIRE WEATHER...NONE.

SEB JAN 08