Small Craft Advisory 223, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKDT FRI MAR 23 2012

.ANALYSIS AND UPPER LEVELS...THE LARGE LOW STEERING THE WEATHER
ACROSS THE STATE IS ANCHORED JUST OFF OF THE KAMCHATKA PENINSULA
COAST. A STRONG FRONT EXTENDS FROM THIS LOW ACROSS SOUTHWEST ALASKA
AND INTO THE WESTERN GULF OF ALASKA. AN IMPRESSIVE FETCH OF MOISTURE
CAN BE SEEN ON THE SATELLITE EXTENDING WELL INTO THE SUBTROPICS. SNOW
ASSOCIATED WITH THIS SYSTEM HAS BEEN MODERATE TO HEAVY OVER SOUTHWEST
ALASKA. A TRIPLE POINT LOW IS DEVELOPING RIGHT ALONG THE ALASKA
PENINSULA AND OVER KODIAK ISLAND. OVERRUNNING MOISTURE IS EVIDENT ON
RADAR AHEAD OF THIS FEATURE REACHING UP COOK INLET...APPROACHING
KENAI EARLY THIS AFTERNOON. A VERY WEAK RESIDUAL LOW THAT HAS BEEN
LINGERING OVER THE NORTHERN GULF IS MOVING INLAND NEAR CORDOVA WITH
SCATTERED SNOW SHOWERS ASSOCIATED WITH IT.

.MODEL DISCUSSION...THE NAM CONTINUES TO BE THE OUTLIER REGARDING THE
DEVELOPING TRIPLE POINT LOW. CAN NOT SEE ANY OBVIOUS REASONS FOR THE
DISCREPANCY AS ALL MODELS APPEAR TO INITIALIZE WELL ON THE MAJOR
FEATURES...BUT THE NAM CONTINUES TO SEND THE LOW ABOUT 60 NM NORTH OF
ANY OTHER SOLUTION LATER TONIGHT. THE GFS AND ECMWF HAVE BEEN MUCH
MORE CONSISTENT WITH THIS LOW SO WE WILL BE MAKING VERY FEW CHANGES
AS EVERYTHING APPEARS ON TRACK.

OUT WEST THERE ARE A FEW MORE DISCREPANCIES LATE IN THE WEEKEND WITH
THE NEXT SYSTEM DEVELOPING WEST OF THE ALEUTIANS AND MOVING TOWARD
THE CENTRAL BERING SEA. THE LAST FEW RUNS OF THE GFS HAS BEEN
TRENDING SLOWER WHILE THE ECMWF HAS SLIGHTLY SPED UP THE SYSTEM.
CONFIDENCE IS GROWING IN A SOLUTION NEAR THE MIDDLE OF THESE TWO
MODEL CHOICES...SO A BLEND OF THE 12Z GFS AND ECMWF WAS USED OUT WEST
THROUGH EARLY NEXT WEEK.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...
LIGHT SNOW IS SPREADING NORTH AS EXPECTED UP COOK INLET. THERE IS A
SLIGHT DELAY IN THE ONSET OF THIS MOISTURE BUT OTHERWISE THE FORECAST
IS LOOKING GOOD.

WEBCAMS AND AUTOMATED OBSERVATIONS FROM THE KACHEMAK BAY AREA HAVE
BEEN LESS THAN IMPRESSIVE AS THE SNOW ARRIVED A FEW HOURS AGO. THIS
LIGHT SNOW SHOULD ARRIVE IN ANCHORAGE IN A FEW HOURS WITH STILL ONLY
MINOR ACCUMULATION EXPECTED.

THE OVERRUNNING MOISTURE WILL ONLY LAST BRIEFLY BEFORE SOUTHEASTERLY
WINDS INCREASE ACROSS THE CHUGACH MOUNTAINS. THIS CROSS BARRIER FLOW
WILL HELP TO DOWNSLOPE ANCHORAGE AND MOST OF THE WESTERN KENAI
PENINSULA BY THIS EVENING. A MID LEVEL JET MAX MOVING OVER THE REGION
THIS EVENING WILL BRIEFLY PROVIDE ADDITIONAL LIFT...BUT AGAIN ONLY
EXPECTING A BRIEF PERIOD OF LIGHT SNOW WITH ACCUMULATION OVER
ANCHORAGE TO BE LESS THAN 1 INCH.

THAT IS NOT THE CASE FOR THE SUSITNA VALLEY WHERE SOUTH TO
SOUTHEASTERLY FLOW WILL PROVIDE UPSLOPE CONDITIONS FOR THE WESTERN
HALF OF THE VALLEY. THE LATEST MODEL RUNS HAVE BACKED OFF ON SNOW
TOTALS SO WE MAY NEED TO SCALE BACK OR CANCEL THIS WITH THE AFTERNOON
FORECAST PACKAGE.

PORTAGE VALLEY AND EASTERN TURNAGAIN ARM WILL LIKELY SEE BLIZZARD
CONDITIONS LATER THIS EVENING AS THE FRONT ARRIVES. NO CHANGES
EXPECTED WITH THIS WARNING.

THE TRIPLE POINT LOW FULLY OCCLUDES AND BEGINS TO WEAKEN LATER
TONIGHT. AS THIS FEATURE BECOMES ISOLATED FROM THE MAIN FLOW IT WILL
LOSE MOMENTUM AND SLOWLY WEAKEN IN THE CENTRAL GULF OF ALASKA DURING
THE WEEKEND. SHOWERS WILL LINGER ALONG THE COAST BUT GENERALLY EXPECT
CONDITIONS TO IMPROVE WITH PARTLY CLOUDY TO MOSTLY CLEAR SKIES
RETURNING BY THE END OF THE WEEKEND.

SOUTHWEST ALASKA...SIGNIFICANT SNOW FALLING OVER PORTIONS OF THE
BRISTOL BAY ZONE AND UPPER KUSKOKWIM VALLEY. VISIBILITY IN MANY AREAS
IS RESTRICTED TO ONE HALF MILE OR LESS IN MODERATE TO HEAVY SNOW WITH
WINDS GENERALLY UNDER 25 MPH. LOCAL GUSTS ARE RESULTING IN SOME
WHITE-OUT CONDITIONS.

AS THE FRONT MOVES FARTHER INLAND...SOUTHWEST FLOW WILL CONTINUE TO
USHER IN LOW LEVEL MOISTURE OFF OF THE BERING SEA. THIS WILL RESULT
IN PERIODS OF LOW CLOUDS AND FOG FOR MUCH OF THE COASTAL AREAS
THROUGH THE WEEKEND WHILE THE INTERIOR CLEARS OUT UNDER UPPER LEVEL
RIDGING.

BERING SEA/ALEUTIANS...RELATIVELY BENIGN WEATHER OUT WEST WITH PARTLY
CLOUDY SKIES AND SCATTERED SNOW SHOWERS PREVAILING OVER MOST OF THE
BERING SEA. ONE WAVE THAT IS ALREADY EVIDENT ON THE REGIONAL
SATELLITE IMAGE WILL DEVELOP SOUTH OF THE CHAIN BUT ZONAL FLOW WILL
NOT ALLOW FOR THIS SYSTEM TO CROSS THE ALEUTIANS. THE NEXT SYSTEM HAS
MUCH MORE UPPER LEVEL SUPPORT BY THE END OF THE WEEKEND AND WILL
LIKELY BRING MUCH OF THE BERING SEA GALE FORCE WINDS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 125.
         WINTER WEATHER ADVISORY 145 161
MARINE...STORM WARNING...185.
         GALE WARNING...120 130 132 175 176 411.
FIRE WEATHER...NONE.

AB MAR 12