Small Craft Advisory 1059, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
500 PM AST SUN DEC 16 2007

.ANALYSIS AND UPPER LEVELS...
HEMISPHERIC PATTERN IN A STRONG 2 WAVE WHICH IS INHERENTLY UNSTABLE.
DOMINANT FEATURE IS HIGH LATITUDE BLOCK OVER NORTHWEST EUROPE WHICH
REMAINS LOCKED IN WELL INTO NEXT WEEKEND. DEEP LOW IN THE GULF OF
ALASKA VERTICALLY STACKED AND QUASISTATIONARY. WEAK EASTERLY WAVES
ROTATING ACROSS SOUTH CENTRAL LEADING TO BANDS OF SNOW SHOWERS THAT
MADE IT AS FAR NORTH AS TURNAGAIN ARM. STRONG MID LEVEL NORTHWEST
JETSTREAM ON THE BACKSIDE LED TO STRONG COLD ADVECTION WINDS ACROSS
SOUTHWEST ALASKA AND THE ALASKA PENINSULA WITH GALES IN THE COASTAL
MARINE AREAS. NEXT UPPER LEVEL LOW DROPPING OUT OF THE POLAR
EASTERLIES INTO THE LONG WAVE TROUGH POSITION ACROSS ALASKA SHOULD
FUJIWARA.

.MODEL DISCUSSION...
NCEP MODELS NOW GENERAL AGREEMENT...THOUGH DIVERGING WITH BOTH THE
UKMET AND THE ECMWF. THE MAIN AREA OF CONTRAST IS THE HANDLING OF THE
LOW FORECAST TO MOVE NORTH ACROSS THE WESTERN ALEUTIANS EARLY IN THE
WEEK. NCEP MODELS TAKE SURFACE LOW TO THE NORTHWEST WHILE THE
EUROPEAN MODELS ARE MORE PROGRESSIVE. THIS INDICATES THAT THERE IS A
FUNDAMENTAL DIFFERENCE IN THE DOMINANT WAVE NUMBER BETWEEN THE NCEP
MODELS AND THE EUROPEAN MODELS.

GFS ENSEMBLES APPEAR CLOSELY CLUSTERED THROUGH 120 HOURS WITH MINIMAL
VARIANCE CONSIDERING THE SEASON. RUN TO RUN VARIANCE HAS ALSO
DECREASED IN THE GFS BEYOND HOUR 84 ESPECIALLY OVER THE LAST TO
CONSECUTIVE RUNS. HOWEVER ECMWF AND GFS DIVERGENCE INCREASES IN THE
LONGER RANGE THUS NOT READY TO JUMP ON THE GFS SOLUTION YET.

.SHORT TERM FORECAST...
LOOKING AT WINDS GUSTING TO 50 MPH IN THE MATSU LATER TONIGHT THROUGH
MONDAY PRODUCING WIND CHILLS TO 35 BELOW ZERO. THIS IN THE WAKE OF
THE EASTERLY WAVE MOVING THROUGH. COLD ADVECTION NORTHWEST WINDS TO
REMAIN IN THE WEST SLOWLY DIMINISHING TUESDAY MORNING. REGARDLESS OF
THE TRACK OF THE LOW IN THE WESTERN ALEUTIANS LOOKING FOR STORM FORCE
WINDS AND RAIN BEGINNING TONIGHT THROUGH EARLY MONDAY NIGHT.
TEMPERATURES TO REMAIN BELOW NORMAL INTO THE EASTERN BERING IN THE
NORTHWEST FLOW WITH ONLY THE WEST ABOVE NORMAL TO THE WEST OF THE
RIDGELINE.

.LONG TERM FORECAST...
STILL UNSETTLED BEYOND DAY 3 UNTIL THE ANCHOR POINT FOR THE LONG WAVE
TROUGH IS IDENTIFIED. RIDGE APPEARS LIKELY TO BREAK DOWN BY THE END
OF THE WEEK AND ORIENT MORE EAST WEST JUST NORTH OF THE ALASKA RANGE
ALLOWING A BRIEF RETURN TO SOUTH FLOW IN SOUTH CENTRAL AND SOUTHWEST.
HEIGHTS REMAIN LOW ENOUGH TO MAINTAIN PRECIPITATION TYPE AS SNOW INTO
NEXT WEEKEND.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE 121 130 132 172 179 185. STORM 175 176.
FIRE WEATHER...NONE.

CAS DEC 07