Small Craft Advisory 339, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
500 AM ADT WED APR 11 2007

.DISCUSSION...SATELLITE THIS MORNING INDICATES A VERY DISORGANIZED
PATTERN OVER THE STATE.  06Z SURFACE ANALYSIS INDICATES A WEAK RIDGE
HAS BUILT IN OVER THE PANHANDLE WHILE THE DISSIPATING SURFACE LOW
LIES SOUTHWEST OF MEKORYUK.  THIS LEAVES A COL OVER THE SOUTHCENTRAL
REGION...ALTHOUGH RADAR ALSO INDICATES A VERY WEAK SURFACE LOW LYING
JUST SOUTH OF THE PRINCE WILLIAM SOUND.  THE COMBINATION OF THIS
SURFACE LOW...DAYTIME SURFACE HEATING...AND COLDER UPPER AIR
TEMPERATURES LEND WEAK INSTABILITY OVER THE REGION AND ALL FOUR
REGIONAL RADARS SHOW SHOWERS LINGERING THROUGH THE OVERNIGHT HOURS.

UPPER AIR SHOWS A 120 KT JET MAX MOVING INTO THE LONGWAVE TROUGH
SOUTH OF THE ALEUTIANS.  THIS IS ACCOMPANIED BY A STRONG VORT MAX AND
AS IT PROGRESSES INTO THE TROUGH IT PROVIDES THE UPPER LEVEL SUPPORT
NEEDED TO RAPIDLY DEVELOP THE SURFACE LOW. AS THE JET MAX MOVES
FURTHER EASTWARD THE UPPER LEVEL LOW DEVELOPS FURTHER EASTWARD AS
WELL...WHICH WILL PUSH THE SURFACE LOW INTO THE GULF OF AK RATHER
RAPIDLY. A SECOND FEATURE OF INTEREST IS A STRONG VORT MAX THAT LIES
EAST OF THE ALASKA BORDER JUST TO THE NORTH OF THE ST ELIAS MTS IN
CANADA.  THIS FEATURE IS EXPECTED TO DEVELOP INTO AN UPPER LEVEL
LOW...WHICH WILL SUPPORT THE WEAK INVERTED TROUGH ON THE SURFACE.

.SOUTH AND EAST OF THE ALASKA RANGE...SHOWERS ARE EXPECTED TO
CONTINUE THROUGH THIS MORNING IN PARTICULAR WITH THE REMNANTS OF THE
VERY WEAK SURFACE LOW IN THE NORTHERN GULF.  WITH THE DEVELOPMENT OF
THE UPPER LOW OVER WESTERN CANADA LIGHT PRECIP CAN BE EXPECTED TO
SNEAK OVER THE BORDER AND PERVADE THE EASTERN COPPER RIVER BASIN
THROUGH FRIDAY MORNING. COLD TEMPERATURES IN THE REGION WILL BRING
SNOW TO THE TOWNS EAST OF GULKANA THROUGH WEDNESDAY NIGHT. FOR AREAS
WEST OF GULKANA...AS THE LOW BEGINS TO DEVELOP SOUTH OF THE ALEUTIANS
WEAK RIDGING WILL DEVELOP ALOFT AND CONDITIONS WILL IMPROVE ACROSS
THE REGION WEDNESDAY NIGHT AND INTO THURSDAY.  BY FRIDAY MORNING THE
LOW WILL HAVE PROGRESSED EASTWARD INTO THE GULF OF ALASKA...HOWEVER
SINCE IT REMAINS SO FAR SOUTH THE STRONGEST WINDS WILL REMAIN IN THE
GULF WITH KODIAK SEEING GUSTY WINDS WITH THE ONSHORE FLOW.  THE NORTH
GULF COAST...INCLUDING THE PRINCE WILLIAM SOUND...CAN ALSO EXPECT
SOME PRECIP ON FRIDAY AS THE INVERTED TROUGH ROTATES THROUGH THAT
REGION.

.WEST OF THE ALASKA RANGE INCLUDING THE ALEUTIANS...NOT MUCH CHANGE
ANTICIPATED IN THE NEXT FEW DAYS AS MOST OF THE ACTION WILL BE
SURROUNDING THE SURFACE LOW SOUTH OF THE ALEUTIANS.  WITH THE GENERAL
INSTABILITY IN THE AREA SHOWERS CAN BE EXPECTED THROUGHOUT THE
DURATION BUT SOME BREAKS IN THE CLOUDS WILL ALLOW SURFACE HEATING
DURING THE DAY AND TEMPERATURES WILL CONTINUE TO BE SEASONABLY WARM.
THE AK PEN WILL EXPERIENCE A BRIEF PERIOD OF WINDY CONDITIONS AND
NORTHERLY FLOW THURSDAY MORNING AND FRIDAY...HOWEVER THERE IS NOT
MUCH COLD AIR ADVECTION AND TEMPERATURES ARE NOT EXPECTED TO DROP
SIGNIFICANTLY.  THIS SHOWERY PATTERN WILL CONTINUE THROUGH FRIDAY AND
INTO SATURDAY MORNING WHEN AN INVERTED TROUGH ASSOCIATED WITH THE
NEXT LOW MAY BRING MORE STRATIFORM TYPE PRECIPITATION TO THE BERING.

.MODEL DISCUSSION...FOR THE FIRST 72 HOURS NAM AND GFS SEEM TO BE IN
GOOD AGREEMENT.  BOTH MODELS ARE A LITTLE FASTER THAN YESTERDAYS RUNS
BUT STILL FALL BEHIND THE ECMWF AND THE UKMET. NCEP PREFERS THE ECMWF
SOLUTION BUT CURRENT FORECAST IS BASED ON THE GFS FOR CONSISTANCYS
SAKE.  AFTER 72 HOURS MODELS CONTINUE TO BRING A SECOND LOW PRESSURE
SYSTEM INTO THE REGION ON SUNDAY.  CURRENT GFS RUN STILL LOOKS VERY
SIMILAR TO LAST NIGHTS SOLUTION...HOWEVER ENSEMBLES CONTINUE TO SHOW
QUITE A BIT OF VARIABILITY ON STRENGTH AND PLACEMENT.  DUE TO THIS
UNCERTAINTY DECIDED NOT TO VARY FROM LAST NIGHTS FORECAST UNTIL THE
MODEL RUNS BEGIN TO CONVERGE A LITTLE BIT MORE.

.EXTENDED...THE CURRENT THREE WAVE HEMISPHERIC PATTERN LOOKS TO
TRANSITION INTO A SPRING-TIME PATTERN OF SHORTENED WAVELENGTHS OVER
NORTHERN PORTIONS OF THE WESTERN HEMISPHERE. OVER THE NORTHERN
PACIFIC THE STORM TRACK LOOKS TO STAY ANCHORED OVER 50N AND LOOKS TO
CONTINUE THE UNSETTLED WEATHER ACROSS MUCH OF THE STATE.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALE 132 138 150 155 AND 350
FIRE WEATHER...NONE

LEWF APR 07