Small Craft Advisory 914, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
500 AM AKST FRI NOV 21 2008

.MODEL DISCUSSION...
THE LATEST MODEL RUNS ARE BEGINNING TO COME TOGETHER ON THEIR
SOLUTIONS.  THE 00Z GFS HAS INCREASED THE SPEED OF THE LOW IN THE
BERING UNTIL IT IS CONSISTENT WITH THE ECMWF. ALTHOUGH THE ECMWF HAS
BEEN MORE CONSISTENT OVER THE PAST FEW DAYS THE GFS WAS STILL THE
PREFERRED SOLUTION FOR TODAY SINCE IT DOES NOT VARY TOO DIFFERENTLY
AND THE GFS HAS SLIGHTLY MORE DETAIL THAN THE ECMWF.  THE MODELS
CONTINUE TO BE IN SURPRISINGLY GOOD AGREEMENT ALL THE WAY OUT THROUGH
THE EXTENDED FORECAST SO CONFIDENCE IS SLIGHTLY HIGHER THAN IT HAS
BEEN FOR SEVERAL DAYS.

.ANALYSIS AND UPPER LEVELS...
THE LONGWAVE TROUGH THAT HAS BEEN CENTERED OVER THE MAINLAND FOR THE
PAST SEVERAL DAYS HAS BECOME MORE NEGATIVELY TILTED AND IS BEGINNING
TO RETROGRADE TO THE WEST AS THE RIDGE IN THE BERING BREAKS DOWN.
THIS SHIFT IN THE PATTERN IS AIDED BY THE STRENGTHENING OF THE UPPER
LEVEL TROUGH CURRENTLY SITUATED OVER EASTERN RUSSIA.  THIS LOW IS
CURRENTLY SUPPORTED BY A 140 KNOT JET MAX JUST TO THE SOUTH OF THE
ALEUTIANS...AS THIS JET MAX MOVES EASTWARD THE UPPER LEVEL LOW WILL
ALSO PROGRESS EASTWARD AND COMBINE WITH THE LOW MOVING OVER THE
WESTERN MAINLAND.  AT THE SURFACE THE LOW IN THE BERING IS STILL VERY
STRONG WHILE THE LOW IN THE GULF OF ALASKA CONTINUES TO WEAKEN SLOWLY.
 AS THE ZONAL JET SOUTH OF THE ALEUTIANS PUSHES THE FRONTAL SYSTEM
ACROSS THE REGION THE FRONT WILL WEAKEN RAPIDLY.  THE SHIFT OF THE
LONGWAVE TROUGH OVER THE WESTERN MAINLAND WILL ALLOW THE WESTERN
SURFACE LOW TO MOVE RAPIDLY EASTWARD AND MERGE WITH THE AREA OF LOW
PRESSURE OVER THE GULF.  THIS WILL BRING AN AREA OF INSTABILITY TO THE
ENTIRE MAINLAND OVER THE WEEKEND.

.SHORT TERM FORECAST...
EAST OF THE ALASKA RANGE...TWO MAIN AREAS OF PRECIP CAN BE SEEN ON
RADAR THIS MORNING...A LIGHT BAND OF SNOW MOVING UP THE COOK INLET AND
MAINLY AFFECTING THE SOUTHERN KENAI PENINSULA...AND A HEAVIER AREA OF
SHOWERS OVER THE EASTERN PRINCE WILLIAM SOUND.  BOTH OF THESE FEATURES
ARE ASSOCIATED WITH THE LOW CURRENTLY IN THE GULF OF ALASKA.  THE AREA
OF GREATEST INSTABILITY IS THE ONE TO THE EAST...AS THE LOW SLOWLY
BROADENS AND DRIFTS OFF TO THE NORTHEAST CONDITIONS ON THE KENAI WILL
IMPROVE AND THE ANCHORAGE BOWL WILL GET ITS FIRST SHOT OF SNOW IN
QUITE A WHILE.  THE LOW IS BRINGING SOME WARMER AIR TO THE EASTERN
PRINCE WILLIAM SOUND AREA AND A MIX OF RAIN AND SNOW IS EXPECTED IN
CORDOVA TODAY.  HOWEVER ELSEWHERE ACROSS THE REGION THE PRECIP WILL
REMAIN SNOW.

WEST OF THE ALASKA RANGE...CONDITIONS ON THE WESTERN MAINLAND WILL
REMAIN CLEAR AND COLD FOR A FEW SHORT HOURS THIS MORNING BUT WILL
RAPIDLY CLOUD OVER AS THE TWO LOW PRESSURE SYSTEMS BEGIN TO MERGE.
THE WARM FRONT MOVING THROUGH THE ALEUTIANS IS EXPECTED TO MOVE UP THE
ALASKA PENINSULA TODAY BEFORE MOVING INTO THE GULF OF ALASKA.
CONDITIONS WILL GET RAPIDLY COLDER AGAIN AS COLD AIR ADVECTION MOVES
IN BEHIND THE LOW.  WHILE WINDS HAVE DECREASED AS THE FRONT WEAKENS
GALES ARE STILL EXPECTED ACROSS THE ALEUTIANS AND STORM FORCE WINDS
ARE EXPECTED THROUGH THE BERING STRAIT WHERE COLD AIR ADVECTION IS
ENHANCING THE NORTHERLY FLOW.  THIS LOW MOVING THROUGH THE ALEUTIANS
IS THE FIRST OF SEVERAL SYSTEM EXPECTED TO MOVE THROUGH THE AREA AND
CONDITIONS WILL REMAIN STORMY THROUGH THE WEEKEND.

.LONG TERM FORECAST...THE SHIFT IN THE PATTERN WILL BRING A ZONAL JET
TO THE ALEUTIANS WHICH WILL CAUSE STORMS TO CONTINUE TO MOVE RAPIDLY
THROUGH THE REGION.  GALE FORCE WINDS AT LEAST CAN BE EXPECTED IN THE
MARINES AND SNOW SHOULD FALL OVER THE MAINLAND AS IT APPEARS THE WARM
AIR ADVECTION WILL REMAIN TO THE SOUTH.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALE 150 155 165 170 172 175 176 179 180
         STORM 185
         HEAVY FREEZING SPRAY 121 160 180
FIRE WEATHER...NONE

LEWF NOV 08