Small Craft Advisory 925, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
145 PM ADT FRI NOV 2 2007

.ANALYSIS AND UPPER LEVELS...IN THE UPPER LEVELS THERE IS A
SHORT-WAVE RIDGE CENTERED OVER THE SOUTHERN MAINLAND...SHORT-WAVE
RIDGE OVER THE CENTRAL BERING...AND A SHORT-WAVE TROUGH OVER THE
WESTERN BERING. A NEARLY ZONAL 180 KT JET EXTENDS OUT OF ASIA
BETWEEN 40N AND 50N LATITUDE. THIS JET IS DRIVING THE WESTERN BERING
SHORT-WAVE EASTWARD INTO THE BASE OF THE SHORT-WAVE RIDGE. THIS IS
RESULTING IN FAIRLY FAST PROGRESSION OF THE SURFACE FRONT ACROSS
THE ALEUTIANS. A STRONG SURFACE LOW HAS DEVELOPED ALONG THE FRONT
JUST NORTHWEST OF THE WESTERN ALEUTIANS. SURFACE OBSERVATIONS AS WELL
AS QUICKSCAT WINDS VERIFY STORM FORCE WINDS ALONG THE FRONT AND MAX
GALES IN THE VICINITY OF THE LOW. COLD ADVECTION IS PRODUCING GUSTY
WINDS AND SNOW SHOWERS ON THE EAST SIDE OF THE CENTRAL BERING RIDGE
OVER THE EASTERN BERING AND SOUTHWEST ALASKA COASTAL REGION. AN
UPPER LEVEL LOW CENTER IS DROPPING THROUGH BRISTOL BAY AND HEADED
TOWARD KODIAK ISLAND AND THE WESTERN GULF. THE REMNANTS OF THE STRONG
LOW THAT MOVED INTO SOUTHCENTRAL ON THURSDAY HAVE MOVED INTO INTERIOR
SOUTHCENTRAL. SATELLITE IMAGERY SHOWS SEVERAL WEAK UPPER LEVEL WAVES
ROTATING ACROSS THE REGION AS WELL AS A COUPLE WEAK SURFACE LOWS
OVER SOUTHCENTRAL. ALL OF THIS IS LEADING TO AREAS OF MAINLY LIGHT
PRECIPITATION. COLDER AIR HAS SLOWLY FILTERED INTO SOUTHCENTRAL...
HOWEVER PRECIPITATION IS STILL PREDOMINANTLY RAIN ALONG THE COAST.
ANCHORAGE AND VICINITY OBSERVED PERIODS OF SNOW THIS MORNING...WITH
MODERATE TO HEAVY SNOW IN SOME PLACES. AS SOON AS THE PRECIPITATION
LIGHTENED UP IT SWITCHED BACK TO RAIN. ATMOSPHERE WILL CONTINUE TO
SLOWLY COOL SO ANY REMAINING PRECIPITATION SHOULD SWITCH BACK TO
SNOW LATER TODAY. WEB CAMS SHOW AREAS OF FOG HAVE STARTED TO FORM
ACROSS SOUTHCENTRAL. WITH LOTS OF LOW LEVEL MOISTURE IN PLACE AND
LIGHT WIND REGIME EXPECT DENSE FOG WILL LIKELY FORM IN SOME AREAS
TONIGHT.

.MODEL DISCUSSION...NAM VERIFIES BEST WITH LOCATION OF DEVELOPING
LOW OVER THE WESTERN BERING SEA (ALTHOUGH A BIT TOO WEAK). THE OTHER
MODELS DEVELOPED THE LOW A LITTLE TOO LATE AND NORTH AND WEST OF
THE ACTUAL CENTER. HOWEVER BY 00Z ALL THE MODELS HAVE THE LOW IN
THE SAME LOCATION. BASED ON SATELLITE TRENDS THIS POSITION LOOKS
GOOD. MODEL WIND FIELDS AROUND LOW AND ALONG FRONT ALSO MATCH UP
FAIRLY WELL WITH OBSERVED WINDS. NAM IS THE OUTLIER IN TRACKING THIS
STORM TO THE CENTRAL BERING. WILL STICK WITH THE REST OF THE MODELS
WHICH TRACK THE LOW NORTHEASTWARD TONIGHT AND THEN BACK WESTWARD
SATURDAY AND SUNDAY. MODELS ARE IN GOOD AGREEMENT ELSEWHERE THROUGH
SUNDAY AND MATCH UP WELL WITH PREVIOUS SOLUTIONS...SO ONLY MINOR
TWEAKS WILL BE MADE TO THE FORECAST THROUGH THIS TIME PERIOD. BEYOND
SUNDAY THE MODEL SOLUTIONS DIVERGE SIGNIFICANTLY. WITH LOW MOVING
INTO THE GULF SUNDAY NIGHT WILL TREND TOWARD GFS/NAM/UKMET SOLUTION
WHICH TRACKS THE LOW TO THE EASTERN GULF. THE ECMWF IS AN OUTLIER
WITH ITS TRACK FARTHER WEST. ELSEWHERE...THERE ARE LARGE DIFFERENCES
AND LARGE SPREAD IN THE ENSEMBLES SO WILL LEAVE ALONE FOR NOW. LOOKS
LIKE THE MODELS MAY CONTINUE TO HAVE PROBLEMS ACROSS THE BERING
REGION HEADING INTO NEXT WEEK AS A LARGE CLOSED CYCLONIC CIRCULATION
SETS UP WITH MULTIPLE SYSTEMS EMBEDDED WITHIN THE FLOW. MODELS
TYPICALLY HAVE DIFFICULTY IN THE DETAILS OF THESE MULTIPLE SYSTEMS.

.SHORT TERM FORECAST...

SOUTHCENTRAL...UPPER TROUGH WITH WEAK EMBEDDED WAVES WILL SIT OVER
SOUTHCENTRAL AND THEN MOVE INTO CANADA SATURDAY INTO SATURDAY NIGHT
AS THE BERING SEA SYSTEM HELPS TO PUSH EVERYTHING EASTWARD. SO LIGHT
AREAS OF RAIN AND SNOW WILL CONTINUE THROUGH SATURDAY
MORNING...CHANGING TO ALL SNOW TONIGHT FOR MOST LOCATIONS. WITH WEAK
DYNAMICS SNOW WILL REMAIN LIGHT SO DO NOT EXPECT MAJOR ACCUMULATION
ANYWHERE. SNOW SHOWERS WILL TAPER OFF SATURDAY AFTERNOON. AS
MENTIONED ABOVE AREAS OF FOG ARE LIKELY TONIGHT. THE THREAT OF FOG
WILL CONTINUE INTO SATURDAY NIGHT AS THE UPPER LEVELS BEGIN TO DRY
OUT LEAVING LOTS OF LOW LEVEL MOISTURE AND POSSIBLY PARTIAL CLEARING
TO HELP PRODUCE RADIATIONAL FOG. THE FRONT MOVING ACROSS THE BERING
SEA WILL WEAKEN SIGNIFICANTLY AS IT APPROACHES SOUTHCENTRAL LATE
SATURDAY NIGHT INTO SUNDAY. BEST CHANCE OF PRECIPITATION WILL BE
KODIAK ISLAND AND THE GULF COAST. LOOKS LIKE FRONT WILL COMPLETELY
FALL APART NEAR THE AKPEN SO PRECIPITATION WILL LIKELY NOT SPREAD
TO INTERIOR SOUTHCENTRAL. BY MONDAY THERE MAY BE JUST A FEW SHOWERS
LEFT FROM THE OLD FRONT IN COASTAL REGIONS. OTHERWISE...CONTINUED
DRY ACROSS THE REST OF SOUTHCENTRAL BUT WITH THE LIKELIHOOD OF
CLOUDS.

SOUTHWEST ALASKA...THERE ARE A FEW AREAS OF SNOW SHOWERS ACROSS
SOUTHWEST ALASKA ASSOCIATED WITH UPPER TROUGH AND UPPER LOW DROPPING
THROUGH BRISTOL BAY REGION. THESE WILL GRADUALLY TAPER OFF TONIGHT
INTO SATURDAY MORNING AS TROUGH MOVES EASTWARD AND WHAT IS LEFT OF
THE CENTRAL BERING RIDGE MOVES TOWARD SOUTHWEST ALASKA. THE BERING
SEA FRONT WILL APPROACH THE COAST SATURDAY AFTERNOON AND THEN WEAKEN
AS IT MOVES INLAND SATURDAY NIGHT AND SUNDAY. THERE WILL BE ENOUGH
COLD AIR IN PLACE THAT INITIAL PRECIPITATION TYPE WILL BE ALL SNOW.
HOWEVER...SOUTHERLY WINDS AHEAD OF THE FRONT WILL TRANSPORT WARM AIR
NORTHWARD AND CHANGE PRECIPITATION TO RAIN (AT LEAST FOR A BRIEF
TIME) ALONG THE COAST. COLDER AIR WILL QUICKLY MOVE BACK IN BEHIND
THE FRONT AND CHANGE PRECIPITATION BACK TO SNOW. REMNANTS OF THE
FRONT MAY PROVIDE A CHANCE OF SHOWERS MONDAY...OTHERWISE A BRIEF
DRYING TREND WILL ENSUE.

BERING SEA/ALEUTIANS...THE CENTRAL BERING SHORT-WAVE RIDGE WILL
CAUSE THE SHORT-WAVE TROUGH TO LIFT NORTHWARD ACROSS THE BERING SEA
TONIGHT AND SATURDAY WHICH WILL KEEP THE SURFACE LOW BACK OVER THE
WESTERN BERING. MEANWHILE..THE SURFACE FRONT WILL PUSH EASTWARD AND
GRADUALLY WEAKEN AS IT STRETCHES OUT FARTHER AND FARTHER FROM THE
LOW CENTER. BASED ON WHAT HAS BEEN OBSERVED ALONG THE FRONT THUS FAR
WILL CARRY STORMS EASTWARD ACROSS THE CENTRAL ALEUITIANS TONIGHT AND
THEN MAX GALES FOR THE EASTERN ALEUTIANS TO PRIBILOFS WITH MIN GALES
BY THE TIME IT REACHES THE SOUTHWEST COAST AND. PRECIPITATION AHEAD
OF THE FRONT MAY START AS SNOW BUT WILL QUICKLY CHANGE TO RAIN WITH
STRONG SOUTHERLY FLOW. COLD ADVECTION ON THE BACK SIDE OF THE LOW
WILL CONTRIBUTE TO STORM FORCE WINDS SOUTH OF THE LOW CENTER TONIGHT
AND SATURDAY. THE LOW WILL THEN SLOWLY WEAKEN. COMBINATION OF THE
COLD ADVECTION AND WEAK UPPER WAVES BEHIND THE FRONT WILL PROVIDE
A CONTINUED CHANCE OF SHOWERS BEHIND THE FRONT. COLD ADVECTION DOES
NOT APPEAR STRONG ENOUGH TO CHANGE PRECIPITATION TO ALL SNOW ACROSS
THE BERING SEA AND ALEUTIANS...BUT MAY SEE SOME SNOW MIXED IN WITH
THE RAIN AT TIMES. BY MONDAY A LARGE COMPLEX CYCLONIC CIRCULATION
BEGINS TO SET UP WITH MULTIPLE SHORT-WAVES ROTATING AROUND THE
BERING SEA REGION. SO EXPECT UNSETTLED WEATHER TO CONTINUE.

.LONG TERM FORECAST...A LARGE COMPLEX CYCLONIC CIRCULATION WILL
DOMINATE THE WEATHER ACROSS THE ENTIRE FORECAST AREA THROUGH THE
EXTENDED PERIOD...RESULTING IN UNSETTLED WEATHER.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...STORMS 172 175 176.
         GALES 150 155 160 165 170 171 179 180 185.
FIRE WEATHER...NONE.

SEB NOV 07