Small Craft Advisory 12, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1245 PM AKST THU JAN 3 2013

.ANALYSIS AND UPPER LEVELS...
A DEEP LONGWAVE TROUGH REMAINS ENTRENCHED OVER THE BERING
SEA...SETTING UP DEEP-LAYER SOUTHERLY FLOW ACROSS MAINLAND ALASKA. A
977 MB LOW LOCATED OVER THE EASTERN BERING IS WEAKENING RAPIDLY AND
CURVING WESTWARD TOWARD THE LONGWAVE TROUGH AXIS. THIS IS BRINGING
SCATTERED SNOW SHOWERS TO THE SOUTHWEST MAINLAND. MOST OF THE ACTION
IS FURTHER EAST...WHERE THE ASSOCIATED FRONT IS STALLED OVER THE
NORTHERN GULF AND BRINGING HEAVY RAIN/SNOW TO PRINCE WILLIAM SOUND
AND THE EASTERN SLOPES OF THE KENAI MOUNTAINS. AS THE FRONT INCHES
NORTHWARD...DOWNSLOPING IS BEGINNING TO MANIFEST OVER THE WESTERN
KENAI...LIMITING SNOWFALL TO LITTLE MORE THAN FLURRIES AT THE MOMENT.
WINDS ARE ACCELERATING THROUGH THE FAVORED TERRAIN GAPS OF TURNAGAIN
ARM AND THE KNIK RIVER VALLEY AS THE FRONT BRINGS STRONG SOUTHEAST
FLOW TO SOUTHCENTRAL. THE OVERALL TREND OF BOTH THE LOW AND THE FRONT
IS WEAKENING...AS THE LIMITED JET SUPPORT THE SYSTEM HAD IS RAPIDLY
DIMINISHING. OUT WEST...WINDS OVER THE WESTERN ALEUTIANS HAVE BECOME
SOUTHEASTERLY AS A WEATHER FRONT APPROACHES FROM THE SOUTHWEST.

.MODEL DISCUSSION...
THE MODELS ARE IN GOOD SYNOPTIC AGREEMENT...BUT ARE STRUGGLING WITH A
FEW DETAILS WITHIN THE OVERALL PATTERN. SATELLITE IMAGERY SHOWS A LOW
SPINNING UP WELL SOUTH OF THE GULF OF ALASKA AND MOVING TO THE
NORTHEAST. AS THIS LOW TRACKS INTO THE SOUTHEAST GULF FRIDAY
NIGHT...THE ECMWF IS TAKING THE ENERGY TOWARD THE NORTHERN
GULF...WHILE THE NAM IS MUCH FURTHER SOUTH AND TAKES THE ENERGY
TOWARD SOUTHEAST ALASKA. GIVEN THE PERSISTENCE OF THE LONGWAVE TROUGH
OUT WEST...AND THE JET REMAINING FAR TO THE SOUTH...THE MOST LIKELY
SCENARIO IS THAT THE LOW WILL SPLIT INTO TWO CIRCULATIONS AS IT
WEAKENS...WITH ONE GOING NORTH AND ONE GOING EAST. THE GFS IS A
MIDDLE-OF-THE-ROAD SOLUTION WITH THIS EVOLUTION...AND WAS FAVORED FOR
THE AFTERNOON FORECAST PACKAGE. OUT WEST...ANOTHER LARGE AND COMPLEX
LOW DEVELOPS BY THIS WEEKEND OVER THE CENTRAL BERING. THE ECMWF WAS
THE FAVORED MODEL AS IT SUGGESTS MULTIPLE WEAKER LOWS AS OPPOSED TO
ONE STRONGER LOW...A SOLUTION THAT HAS BEEN VERY COMMON IN THIS
PATTERN LATELY.

.SHORT TERM FORECAST...
SOUTHCENTRAL...PRIMARY FORECAST CHALLENGE WILL BE WATCHING THE
GRADUAL DEMISE OF THE FRONT CURRENTLY IMPACTING THE AREA. MODELS
DISAGREE ON WHETHER DOWNSLOPING WILL KEEP MUCH OF THE WESTERN KENAI
AND ANCHORAGE BOWL DRY OVERNIGHT. BASED ON RADAR AND SATELLITE
TRENDS...DOWNSLOPE DRYING IS HOLDING FIRM AS THE FRONT INCHES
NORTHWARD. WILL RUN WITH GENERALLY A DRIER FORECAST FOR NOW...BUT
CANNOT RULE OUT A LIGHT DUSTING OF SNOW IN THE AREA LATER TONIGHT AS
THE FRONT CONTINUES TO FALL APART. WINDS THROUGH TURNAGAIN ARM AND
THE KNIK RIVER VALLEY WILL BE SLOW TO DECREASE THIS EVENING...BUT
SHOULD DROP SIGNIFICANTLY BY FRIDAY MORNING. ACTIVE WEATHER ACROSS
THE REGION WILL LARGELY ABATE ON FRIDAY AS NO LOWS OR FRONTS WILL
MOVE BACK IN UNTIL SATURDAY MORNING.

SOUTHWEST...ANOTHER DAY...ANOTHER LOW WEAKENING ALONG THE COAST AND
DRIFTING BACK INTO THE BERING SEA. THIS WILL KEEP SCATTERED SNOW
SHOWERS OVER MUCH OF THE REGION OVERNIGHT AND INTO FRIDAY MORNING.
SOUTHEAST WINDS WILL INCREASE AGAIN BY FRIDAY EVENING AS A FRONT
MOVES IN FROM THE BERING SEA AND BRINGS WIDESPREAD PRECIPITATION BY
LATE FRIDAY NIGHT. TEMPERATURES WILL NOT WARM SIGNIFICANTLY AHEAD OF
THIS NEXT LOW...AND NORTHERN COASTAL LOCATIONS WILL LIKELY SEE
BLOWING SNOW DEVELOPING WITH THE APPROACH OF THE FRONT.

BERING SEA AND ALEUTIANS...FAIRLY STRONG LOW APPROACHING THE WESTERN
ALEUTIANS WILL BRING GENERALLY GALE-FORCE WINDS TO THE WESTERN HALF
OF THE ALEUTIANS AND BERING SEA THROUGH SATURDAY. THIS LOW WILL BE
HEADING INTO THE CENTER OF THE AFOREMENTIONED LONGWAVE TROUGH...AND
WILL BREAK UP INTO MULTIPLE (WEAKER) LOW PRESSURE CENTERS BY SATURDAY
MORNING.

.LONG TERM FORECAST...
THE OVERALL WEATHER PATTERN WILL REMAIN INTACT THROUGH AT LEAST EARLY
NEXT WEEK. THIS MEANS SOUTHERLY FLOW WILL CONTINUE ACROSS MAINLAND
ALASKA BRINGING COOLER...BUT STILL ABOVE-AVERAGE...TEMPERATURES TO
MOST AREAS. SEVERAL MORE WEATHER FRONTS WILL MOVE ACROSS SOUTHWEST
AND SOUTHCENTRAL ALASKA THROUGH EARLY NEXT WEEK...BRINGING A
RAIN/SNOW MIX TO THE COASTLINES...WITH DRIER CONDITIONS INLAND.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...STORM 175
         GALE 150 155 172 176 185
         HEAVY FREEZING SPRAY 185
FIRE WEATHER...NONE

AMD JAN 13