Small Craft Advisory 309, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
100 PM ADT SUN APR 1 2007

.DISCUSSION...

ANALYSIS...A HIGH AMPLITUDE UPPER RIDGE EXTENDS FROM THE GULF OF
ALASKA NORTHWARD ACROSS MAINLAND ALASKA INTO THE BEAUFORT
SEA...PROVIDING CLEAR AND CALM CONDITIONS OVER SOUTHCENTRAL ALASKA.
A SHORT-WAVE TROUGH OVER THE BERING STRAIT REGION THIS MORNING IS
PUSHING UP AGAINST THE TOP OF THE RIDGE...FORCING IT TO SLIDE
EASTWARD A BIT TOWARD THE YUKON. HEADING FURTHER UPSTREAM...A MATURE
CLOSED LOW WEST OF THE ALEUTIANS IS TRACKING WESTWARD TOWARD
KAMCHATKA. THE UPPER TROUGH AXIS EXTENDING EASTWARD FROM THIS LOW
IS MOVING NORTHWESTWARD AND HELPING TO AMPLIFY SHORT-WAVE RIDGE
OVER THE CENTRAL BERING. THE COMBINATION OF THIS RIDGE AND REMNANT
MOISTURE FROM SHORT-WAVE THAT MOVED THROUGH SATURDAY HAS RESULTED IN
AREAS OF STRATUS AND DENSE FOG FROM THE EASTERN BERING SEA TO THE
SOUTHWEST COAST. IR SATELLITE/WATER VAPOR IMAGERY SHOW A LOT OF UPPER
LEVEL MOISTURE STREAMING FROM 50N TO KODIAK ISLAND AND THE AKPENN.
THIS MOISTURE IS JUST AHEAD OF A TROUGH THAT EXTENDS FROM THE WESTERN
AKPENN SOUTHEASTWARD INTO THE PACIFIC AND IS DRIFTING TO THE
NORTHEAST. FINALLY...AS PER SATELLITE IMAGERY THERE IS A STRONG
ZONAL JET SHOOTING EASTWARD OUT OF RUSSIA ALONG 40N TO ABOUT 180
WITH DEVELOPING SURFACE LOW NEAR 42N 165E(AT 18Z).

THIS PATTERN IS EVOLVING. THE UPPER JET WILL CONTINUE TO DRIVE
EASTWARD...EXTENDING UPPER TROUGH EASTWARD JUST SOUTH OF THE CHAIN
AND CAUSING THE CENTRAL BERING RIDGE TO CUT-OFF AND RETREAT NORTHWARD
A BIT. THIS IN TURN WILL ALLOW THE SHORT-WAVE TROUGH CURRENTLY OVER
THE BERING STRAIT TO COME BACK SOUTHWARD TUESDAY THROUGH THURSDAY IN
THE FORM OF A CLOSED LOW OVER THE BERING SEA. MEANWHILE...A LARGE
ANCHOR LOW WILL SET UP SOUTH OF THE GULF OF ALASKA. SO...AS WE HEAD
TO THE END OF THE WEEK...WEATHER ACROSS MOST OF ALASKA WILL BE A BIT
MORE UNSETTLED UNDER THE INFLUENCE OF MULTIPLE UPPER LOWS.

MODEL DISCUSSION...MODELS IN FAIR AGREEMENT THROUGH ABOUT 60 HOURS
AND ONLY MINOR ADJUSTMENTS WILL BE MADE TO CURRENT FORECASTS. AFTER
THIS POINT THERE IS VERY POOR CONSISTENCY FROM PREVIOUS MODEL RUNS
FOR THE NEXT SYSTEM SOUTH OF THE ALEUTIANS. GFS RUN FROM YESTERDAY
AFTERNOON DEPICTED A SINGLE LOW BOMBING OUT TO 955 MB THURSDAY NIGHT
WHILE THE LATEST GFS SOLUTION SHOWS MULTIPLE WEAKER LOWS. THE 12Z
ECMWF CONTINUES TO SHOW A SINGLE DEEP LOW AS DOES THE GFS ENSEMBLE
MEAN. THEREFORE...WILL DISCOUNT THE LATEST GFS SOLUTION FOR THIS TIME
PERIOD AND STICK WITH CURRENT FORECAST. THE MODELS ARE MUCH MORE
CONSISTENT WITH THE LARGE LOW SETTING UP SOUTH OF THE GULF...SO HAVE
MORE CONFIDENCE THERE...AND AGAIN ONLY MINOR ADJUSTMENTS WILL BE
MADE.

SOUTHCENTRAL FORECAST...MOISTURE WILL GRADUALLY INCREASE MONDAY AND
TUESDAY AS RIDGE WEAKENS AND SLIDES EASTWARD AND FLOW SHIFTS TO
SOUTHEAST. THIS WILL FORCE SHORT-WAVE TROUGH CURRENTLY PRODUCING HIGH
CLOUDS AROUND AKPENN AND KODIAK ISLAND NORTHWARD ACROSS WESTERN GULF
RESULTING IN A CHANCE OF SHOWERS ALONG THE COAST MONDAY NIGHT AND
TUESDAY. INLAND LOCATIONS WILL REMAIN DRY. LARGE-SCALE LOW WILL MOVE
NORTHWARD TOWARD THE GULF AS WE HEAD TO THE END OF THE WEEK. EASTERLY
WAVES WILL BRING PRECIP TO COASTAL REGIONS AND A CHANCE OF PRECIP
INLAND NEXT WEEKEND. TEMPS DURING THIS PERIOD ARE EXPECTED TO REMAIN
CLOSE TO AVERAGE...SO THE DAILY FREEZE/THAW CYCLE WILL CONTINUE.

SOUTHWEST ALASKA/AKPENN/EASTERN BERING SEA FORECAST...AREAS OF FOG
AND STRATUS WILL PERSIST THROUGH TONIGHT AND THEN DIMINISH MONDAY AS
EASTERLY (OFFSHORE) FLOW DEVELOPS. CHANCE OF PRECIP WILL INCREASE BY
MID WEEK AS SHORT-WAVE DROPS DOWN FROM THE NORTH.

ALEUTIANS/CENTRAL BERING FORECAST...OCCLUDED FRONT ASSOCIATED WITH
LOW WEST OF THE ALEUTIANS CONTINUES TO SHEAR APART. ASSOCIATED
MOISTURE WILL MAKE IT AS FAR EAST AS UNALASKA TONIGHT. EAST-WEST
UPPER TROUGH AXIS WILL HELP BRING MOISTURE ASSOCIATED WITH STORMS
TRACKING TO THE SOUTH BACK WESTWARD ACROSS THE REGION. SO OCCASIONAL
PRECIP WILL BE THE NORM AS WE HEAD THROUGH THE WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALES 170 171 172 176.
FIRE WEATHER...NONE

SEB APR 07