Small Craft Advisory 389, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
200 PM ADT THU APR 27 2006

.DISCUSSION...

.MODELS...
MODELS ARE STILL NOT RESOLVING THE SEVERAL VORTICES ROTATING AROUND
THE PARENT LOW IN THE GULF OF ALASKA WELL.  FORECASTS ARE BEING
TWEAKED TO ACCOUNT FOR THE PRECIPITATION AROUND PRINCE WILLIAM
SOUND...AND THE OCCASIONAL PUSHES UP THE CHUGACH MOUNTAINS.  THE MAIN
CAUSE FOR CONCERN WILL BE THE FRONT CURRENTLY MOVING UP THE
ALEUTIANS.  GFS AND PARALLEL NAM ARE INITIALIZING IT BEST.  TIMING
BECOMES THE MAIN ISSUE...AS ETA WANTS TO BRING IN PRECIPITATION TO
KENAI PENINSULA BY MIDDAY MONDAY...WHEREAS GFS HOLDS OFF ON PRECIP
UNTIL EARLY TUESDAY MORNING.  GFS SEEMS TO OFFER THE MOST VIABLE
SOLUTION...AS IT HAS THE PAST FEW DAYS.

.UPPER AIR...
THE HIGH AMPLITUDE BLOCKING RIDGE IN PLACE OVER THE BERING SEA THE
LAST SEVERAL DAYS HAS BEEN CLOSED OFF AND RETREATED TO SIBERIA BY THE
UPPER LOW OVER THE ALEUTIANS TODAY.  AS THIS UPPER LOW INCHES
EASTWARD...IT WILL MERGE WITH AN UPPER LOW MOVING OFF THE INTERIOR TO
THE SOUTHWEST TODAY. THE UPPER LEVEL LOW OVER THE GULF OF ALASKA
WILL BE LIFTED NORTH INLAND TOMORROW WITH THE INCOMING SURFACE FRONT.
AT THAT POINT...THE UPPER LOW WILL REMAIN NEARLY STATIONARY OVER
BRISTOL BAY THROUGH THE REST OF THE WEEK...AND SET THE STAGE FOR A
BROAD AREA OF POSITIVE VORTICITY ADVECTION OVER MUCH OF SOUTHCENTRAL
ALASKA. ANOTHER LOW OFF THE SOUTHERN TIP OF THE KAMCHATKA PENINSULA
WILL SEND A SHORT WAVE TROUGH UNDERNEATH THE BRISTOL BAY LOW TUESDAY
AND INTO THE GULF WEDNESDAY. IN ADDITION...THE UPPER LOW NEAR
KAMCHATKA WILL BEGIN TO SWING EAST WEDNESDAY. THE RESULT WILL BE THE
BRISTOL BAY LOW MOVING INLAND THURSDAY AS THE KAMCHATKA LOW TAKES ITS
PLACE FRIDAY.

.EAST OF THE ALASKA RANGE...
AIRMASS REMAINS POTENTIALLY UNSTABLE.  TEMPERATURES ALOFT ARE STILL
RELATIVELY COLD...AND THE PRESENCE OF MIDLEVEL MOISTURE WILL ALLOW
FOR SOME TOWERING CUMULUS TO DEVELOP TODAY AND TOMORROW WITH DAYTIME
HEATING.  CONVECTIVELY ACTIVATED SHOWERS WILL DEVELOP OVER THE
ELEVATED TERRAIN AND DRIFT INTO VALLEYS.  LIGHTNING STILL SEEMS
UNLIKELY...AS CAPE AND VERTICAL MOTION SEEM UNIMPRESSIVE.  A MINOR
COOK INLET SEA BREEZE MAY DEVELOP...AS THE INLET REMAINS RELATIVELY
CHILLY AND THE LAND SURFACE CONTINUES TO WARM.  THE APPROACH OF THE
STORM SYSTEM CURRENTLY OVER THE ALEUTIANS
WILL END TALK OF CUMULUS WITH VERTICAL EXTENT FOR A FEW DAYS STARTING
TUESDAY.  THE LOW WILL BECOME NEARLY STATIONARY OVER THE ALASKA
PENINSULA BY TUESDAY...WITH ITS FRONT EXTENDING EASTWARD THROUGH
KODIAK ISLAND AND INTO THE GULF.  THE TURNAGAIN ARM AND PORTAGE
VALLEY WINDS LOOK TO KICK UP IN THIS TIMEFRAME...AND MAY BLOW FOR A
FEW DAYS.  850 MB TEMPERATURES DONT INDICATE A SIGNIFICANT DEPARTURE
FROM AVERAGE IN SURFACE TEMPS IN THE SHORT TERM. HOWEVER...THEY DO
SPEAK TO MOST PRECIPITATION BEING RAIN FROM THIS STORM SYSTEM. THE
ENTIRE SYSTEM WILL LIFT NORTH THURSDAY THROUGH SOUTH CENTRAL.

.WEST OF THE ALASKA RANGE...
THE LATEST SCATTEROMETER IMAGES ARE VERIFYING THE GFS GALE FORCE
WINDS AROUND THE ALEUTIAN LOW WELL.  THE STORM SYSTEM LOOKS TO FORM A
TRIPLE POINT LOW LATE TODAY SOUTH OF THE EASTERN ALEUTIANS...AND WILL
MOVE ONSHORE OVER THE AKPEN MONDAY MORNING. STRONG WINDS WILL MOVE
ONSHORE TUESDAY OVER SOUTHWEST ALASKA WITH AREAS OF PRECIPITATION
MAINLY ON UPSLOPE AREAS. THE LOW WILL SLOWLY DISSIPATE TUESDAY
THROUGH WEDNESDAY.  BY THAT TIME...WINDS WILL BE SMALL CRAFT LEVEL AT
BEST.  BEHIND THE LOW...NORTHERLY WINDS WILL BE BLOWING OFF THE ICE
COVER IN THE NORTHERN BERING SEA...AND KEEPING CONDITIONS OVERCAST
UNTIL THE NEXT SYSTEM APPROACHES THE WESTERN ALEUTIANS WEDNESDAY.
GALE TO STORM FORCE WINDS WILL ACCOMPANY THIS WESTERN ALEUTIAN LOW.
THE LOW NEAR BRISTOL BAY LIFTS TO THE NORTH WEDNESDAY NIGHT AND OVER
SOUTH CENTRAL ALASKA THURSDAY. IN THE MEANTIME...THE LOW OVER THE
WESTERN ALEUTIAN TRAVELS TO THE EASTERN ALEUTIANS BY FRIDAY MORNING.
THE LOW WILL WEAKEN ON THIS TREK WITH WINDS DIMINISHING TO SMALL
CRAFT LEVELS. RAIN WILL ACCOMPANY THIS LOW THROUGH THE ALEUTIAN
CHAIN.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE 120 130 132 138 150 155 160 172 175
FIRE WEATHER...NONE.

TD/JN APR 06