Small Craft Advisory 167, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
100 PM AST FRI FEB 16 2007

.DISCUSSION...

SOME WEAK FEATURES ARE PRODUCING SNOW TODAY ACROSS SOUTHCENTRAL
ALASKA. THE ARCTIC FRONT IS SITTING RIGHT OVER ANCHORAGE...THERE IS
AN UPPER TROUGH SITTING ROUGHLY EAST-WEST OVER THE GULF AND MOVING
NORTHWARD...AND ANOTHER TROUGH OVER THE INTERIOR WITH SOME VORTICITY
ADVECTION INTO NORTHERN PORTIONS OF SOUTHCENTRAL. THIS HAS SET UP
NORTH-SOUTH BANDS OF SNOW FROM THE KENAI MOUNTAINS TO ANCHORAGE TO
THE SOUTHERN SUSITNA VALLEY. AREAS OF SNOW ARE ALSO FALLING FROM
PRINCE WILLIAM SOUND TO THE COPPER RIVER BASIN. THE GULF TROUGH WILL
CONTINUE TO SLIDE NORTHWARD THIS EVENING AND THEN WILL STALL AND BE
PULLED EASTWARD BY A MAJOR LOW HEADED FOR SOUTHEAST ALASKA.
THEREFORE...EXPECT SNOW TO GRADUALLY DIMINISH THIS EVENING AND END
ACROSS SOUTHCENTRAL BY SATURDAY MORNING.

THE MAJOR STEERING LOW THAT HAS BEEN ADVERTISED THE PAST FEW DAYS
HAS NOW ARRIVED AND IS POSITIONED JUST SOUTH OF THE WESTERN
ALEUTIANS TRACKING NORTH-NORTHEASTWARD. GFS HAS VERIFIED QUITE
WELL WITH THE TRACK AND DEPTH OF THIS LOW. OBSERVATIONS FOR ADAK
INDICATE MAX GALE FORCE WINDS WITH STRONGER GUSTS THROUGH CHANNELED
TERRAIN. THESE WINDS WILL SPREAD EASTWARD TONIGHT AND THEN DIMINISH
SATURDAY AS THE FRONT BEGINS TO SHEAR APART AND WEAKEN WITH PARENT
LOW REMAINING NEARLY STATIONARY OVER THE CENTRAL BERING. THE
COMBINATION OF A QUICKLY WEAKENING FRONT COMBINED WITH PLACEMENT OF
RIDGE OVER NORTHERN PORTION OF ALASKA MEANS SOUTHWEST ALASKA WILL
EXPERIENCE MINIMAL IMPACTS...SMALL CRAFT WINDS AND SNOW NEAR THE
COAST. WINDS WILL NOT BE STRONG ENOUGH TO PRODUCE ANY MAJOR BLOWING
SNOW PROBLEMS. KODIAK ISLAND WILL ALSO SEE PRECIP FROM THE FRONT BUT
LOOKS LIKE THE FRONT WILL NOT MAKE IT MUCH FARTHER NORTH AND EAST
SO THAT INLAND SOUTHWEST ALASKA AND MOST OF SOUTHCENTRAL WILL REMAIN
DRY. SATELLITE IMAGERY SHOWS STRONG COLD ADVECTION ON THE BACK SIDE
OF THE ALEUTIAN LOW. AS THE LOW MOVES INTO THE BERING SEA TONIGHT
SOME OF THIS COLD AIR WILL MOVE INTO THE ALEUTIANS. COMBINATION COLD
ADVECTION AND TIGHT PRESSURE GRADIENT WILL RESULT IN STORM FORCE
WINDS LATE TONIGHT THROUGH SATURDAY MORNING FOR THE WESTERN TO
CENTRAL ALEUTIANS. SURFACE TEMPS STILL LOOK LIKE THEY WILL REMAIN
WARM ENOUGH TO KEEP VISIBILITIES ABOVE BLIZZARD LEVELS. EVEN THOUGH
DONT EXPECT BLIZZARD CONDITIONS THERE LIKELY WILL BE OCCASIONAL
MODERATE SNOW AND BLOWING SNOW ALONG BENT BACK OCCLUSION AND IN
COLD ADVECTION GENERATED SNOW SHOWERS. STRONG WINDS/COLD ADVECTION
WILL PERSIST ALONG THE ALEUTIANS THROUGH THE WEEKEND AS LOW SITS
NEARLY STATIONARY OVER THE CENTRAL BERING SEA.

ALSO OF NOTE IN THE SATELLITE IMAGERY IS A LOW NEAR THE BOTTOM OF
THE UPPER TROUGH AT 40N 161E. THIS LOW WILL SWING EASTWARD WITH THE
TROUGH AND THEN BE FORCED NORTHEASTWARD TOWARD THE AKPENN BY THE
UPPER JET. THE MODEL SOLUTIONS ARE QUITE DIVERGENT WITH THE EXACT
TRACK AND STRENGTH OF THIS LOW. WITH GOOD UPPER SUPPORT AND COLD AIR
ADVECTION WILL TEND TOWARD THE STRONGER GFS. HOWEVER...OPERATIONAL
GFS IS 10 OR MORE MILLIBARS STRONGER THAN THE OTHER OPERATIONAL
MODELS SO WILL GO WITH THE ENSEMBLE MEAN WHICH IS ABOUT HALF WAY
BETWEEN THE OPERATIONAL GFS AND THE MUCH WEAKER NAM SOLUTION. WILL
DOWNPLAY THE EFFECTS OF THIS LOW UNTIL WE GAIN A BETTER IDEA OF HOW
IT WILL EVOLVE.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALES 150 155 160 165 170 171 180 185.
         STORMS 172 175.
         HEAVY FREEZING SPRAY 185.

SEB FEB 07