Small Craft Advisory 154, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
100 PM AKST TUE FEB 18 2014

.ANALYSIS AND UPPER LEVELS...
AN UPPER LOW IN THE VICINITY OF SOUTHWEST ALASKA HAS BEEN IN CONTROL
OF THE WEATHER ACROSS THE STATE FOR THE PAST WEEK. THIS FEATURE IS
SLOWLY WEAKENING AND HAS NOW BEGUN TO MOVE TO THE NORTHEAST. THE MOST
SIGNIFICANT SURFACE LOW IN THE AREA IS MOVING INTO THE SOUTHERN
PANHANDLE...HOWEVER A ROBUST UPPER TROUGH EXTENDING FROM THE
AFOREMENTIONED UPPER LOW IS PULLING SIGNIFICANT AMOUNTS OF
PRECIPITATION FROM THIS LOW INTO SOUTHERN ALASKA. THIS PRECIPITATION
IS VERY CONVECTIVE IN NATURE...LEADING TO UNUSUALLY HIGH SNOWFALL
RATES IN A NARROW BAND FROM NORTHERN PRINCE WILLIAM SOUND TO THE
EASTERN KENAI PENINSULA. A WINTER STORM WARNING REMAINS IN PLACE AT
THIS TIME. OVERALL SOUTHEASTERLY FLOW IS SO FAR PROTECTING THE
ANCHORAGE BOWL AND MATANUSKA VALLEY FROM ANY SNOWFALL...THOUGH THIS
SHOULD CHANGE AS A WEAKER SURFACE LOW CURRENTLY SOUTH OF SEWARD
CONTINUES TO WEAKEN AND DRIFT WESTWARD INTO COOK INLET THIS EVENING.
MEANWHILE SOUTHWEST ALASKA IS MOSTLY DRY...WITH CLOUDS AND A CHANCE
OF SNOW CREEPING INTO EASTERN SECTIONS OF BRISTOL BAY FROM THE
UNSETTLED WEATHER OVER SOUTHCENTRAL. OUT WEST...COLD NORTHERLY FLOW
CONTINUES ACROSS MUCH OF THE REGION...WITH THE MOST SIGNIFICANT SNOW
SHOWER ACTIVITY ALONG THE ALASKA PENINSULA.

.MODEL DISCUSSION...
THE MODELS ARE IN PRETTY GOOD OVERALL AGREEMENT...BUT ARE STILL
STRUGGLING A BIT WITH THE POSITION OF THE UPPER TROUGH CURRENTLY OVER
THE SOUTHWEST GULF. UNFORTUNATELY IT IS THIS TROUGH THAT WILL BE A
KEY PLAYER IN SNOWFALL TOTALS ACROSS THE ANCHORAGE AREA TONIGHT AND
TOMORROW MORNING. AFTER JUMPING SOUTHWARD WITH THE TROUGH POSITION
WITH THE OVERNIGHT MODEL RUNS MOST OF THE MODELS HAVE NOW CORRECTED
BACK TO A FURTHER NORTH POSITION. THE NAM HAD VERY POOR
INITIALIZATION...FAILING EVEN TO CAPTURE THE SIGNIFICANT CONVECTIVE
BAND CURRENTLY OVER PRINCE WILLIAM SOUND. THE PREFERENCE FOR THE
AFTERNOON PACKAGE IS A COMBINATION OF THE ECMWF/GFS SOLUTIONS.

.SHORT TERM FORECAST...
SOUTHCENTRAL...HEAVY SNOW IS FALLING AS EXPECTED FROM THE
NORTHEASTERN KENAI PENINSULA INTO WESTERN PRINCE WILLIAM SOUND. THE
PRIMARY CONVECTIVE BAND SPENT MUCH OF THE MORNING A BIT FURTHER NORTH
THAN EXPECTED...THUS OVERALL SNOW AMOUNTS IN POPULATED AREAS MAY END
UP COMING IN A BIT LOWER THAN PREVIOUSLY THOUGHT. THE MAIN FORECAST
CHALLENGE WILL BE DETERMINING SNOWFALL AMOUNTS ON THE LEE SIDE OF THE
COAST MOUNTAINS FROM KENAI NORTH TO ANCHORAGE AND THE MATANUSKA
VALLEY. AS THE SURFACE LOW WEAKENS AND ENTERS COOK INLET THIS
AFTERNOON THE CROSS-BARRIER FLOW AND RESULTANT DOWNSLOPE DRYING
SHOULD DISSIPATE. AT THE SAME TIME...THE APPROACH OF THE UPPER TROUGH
WILL CONTINUE TO TAKE ADVANTAGE OF FAVORABLE MIDLEVEL INSTABILITY TO
PRODUCE IMPRESSIVE SNOWFALL RATES AROUND THE AREA...WHICH SHOULD
BLEED THEIR WAY INTO THE ANCHORAGE AREA THIS EVENING. AS MENTIONED
ABOVE...THE BAND OF HEAVIEST SNOW WILL LIKELY CONTINUE TO BE QUITE
NARROW...AND SO WHAT WOULD USUALLY BE CONSIDERED MINOR CHANGES IN
POSITION WILL HAVE A LARGER-THAN-NORMAL IMPACT ON OBSERVED SNOW
AMOUNTS ACROSS THE UPPER COOK INLET REGION TONIGHT INTO TOMORROW
MORNING. OVERALL...CONFIDENCE IS INCREASING THAT THE ANCHORAGE AREA
WILL SEE ACCUMULATING SNOW TONIGHT...WITH THE POTENTIAL FOR A MORE
SIGNIFICANT EVENT IF THE AFOREMENTIONED HEAVY SNOW BAND SETS UP
DIRECTLY OVERHEAD. FURTHER NORTH...A WEAKER BUT LINGERING DRY
NORTHEASTERLY WIND AT THE LOWER LEVELS SHOULD DIMINISH SNOW AMOUNTS A
BIT OVER THE MATANUSKA VALLEY.

SOUTHWEST...COLD AND MOSTLY DRY CONDITIONS CONTINUE AS THE UPPER LOW
SLOWLY DRIFTS AWAY TO THE NORTHEAST OVER THE NEXT FEW DAYS. SOME
SPILLOVER OF SNOW ALONG THE ALASKA AND ALEUTIAN RANGES WILL CONTINUE
THIS EVENING...THOUGH ONLY MINOR ACCUMULATIONS ARE EXPECTED.

BERING SEA AND ALEUTIANS...A ZONAL JET REMAINING SOUTH OF THE
ALEUTIANS WILL KEEP THE STATUS-QUO LARGELY INTACT THROUGH WED NIGHT.
THIS MEANS FLOW GENERALLY OUT OF THE NORTH WITH WEAK COLD AIR
ADVECTION AND SNOW SHOWERS IN MOST AREA. AS THE LONGWAVE PATTERN
BEGINS TO CHANGE APPRECIABLY ON THURSDAY A SERIES OF LOWS WILL MOVE
INTO THE AREA FROM THE SOUTH. THE INCREASINGLY AMPLIFIED UPPER-LEVEL
PATTERN WILL ALLOW A LOW NEAR THE EASTERN ALEUTIANS ON THURSDAY TO
BECOME STRONGER THAN THE OTHER SYSTEMS SEEN RECENTLY IN THE
AREA...WITH A LARGE AREA OF GALE-FORCE WINDS AND MODERATE TO HEAVY
PRECIPITATION LIKELY FOR THE LATTER HALF OF THE WEEK. DEPENDING HOW
FAR NORTH THIS STORM TRACKS THE PRIBILOF ISLANDS WILL NEED TO BE
MONITORED FOR BLOWING SNOW POTENTIAL ON THURSDAY WITH INCREASINGLY
NORTHEASTERLY WINDS.

.LONG TERM FORECAST...
CONFIDENCE IS HIGH IN A WHOLESALE CHANGE OF THE LONGWAVE PATTERN BY
THIS WEEKEND. THE NEW PATTERN WILL FEATURE A DEEP TROUGH OVER THE
BERING SEA AND A RETURN TO MUCH MORE ACTIVE WEATHER.
MEANWHILE...DEEP-LAYER SOUTHERLY FLOW WILL USHER IN WHAT LOOKS LIKE
ANOTHER PERIOD OF ABOVE-NORMAL TEMPERATURES TO MUCH OF MAINLAND
ALASKA THAT PERSISTS WELL INTO NEXT WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...WINTER STORM WARNING 125
MARINE...GALE 178
         HEAVY FREEZING SPRAY 130 139 150 160 165 179
FIRE WEATHER...NONE

AMD FEB 14

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1123 PM AKST TUE FEB 18 2014

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0940 PM     SNOW             5 SSE ANCHORAGE         61.15N 149.81W
02/18/2014  M3.9 INCH                           AK   TRAINED SPOTTER

            SNOW BEGAN ACCUMULATING 445 PM.

1000 PM     SNOW             2 SE EAGLE RIVER        61.30N 149.53W
02/18/2014  M6.0 INCH                           AK   NWS EMPLOYEE

            SNOW BECOMING LIGHTER

1005 PM     SNOW             1 NNE POTTER MARSH      61.07N 149.77W
02/18/2014  M7.5 INCH                           AK   CO-OP OBSERVER

            STILL COMING DOWN

&&

KUTZ