Small Craft Advisory 114, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
545 AM AKST WED FEB 6 2013

.ANALYSIS AND UPPER LEVELS...
AN UPPER-LVL LOW OVER THE SOUTHEASTERN KUSKOKWIM VALLEY IS EJECTING
EAST INTO SOUTHCENTRAL AK WHILE OPENING INTO A TROUGH. SNOW IS ENDING
OVER BRISTOL BAY BUT EXPANDING IN COVERAGE ACROSS UPPER COOK INLET AS
THIS OCCURS. BEHIND THE TROUGH/LOW...TRANSITORY UPPER-LVL RIDGING
OVER THE EASTERN BERING IS QUICKLY MOVING EAST INTO SW AK. AT THE
SURFACE...A MID-950 MB PACIFIC LOW CENTERED AROUND 200 MILES SOUTH OF
KISKA IS TRACKING EAST AND FILLING. AN ASSOCIATED FRONT IS DRAPED
FROM THE WESTERN BERING SEA TOWARDS THE EASTERN CHAIN AND APPROACHING
THE PRIBILOF ISLANDS WITH SNOW...WITH POINTS SOUTHEAST INCLUDING
UNALASKA A MIX OF SNOW AND RAIN. A STRONG PRESSURE GRADIENT EXISTS
BETWEEN THIS LOW AND AN ARCTIC HIGH PRESSURE CENTER STAMPED OVER
EASTERN SIBERIA...YIELDING STORM-FORCE WINDS OVER THE FAR WESTERN
BERING/CHAIN...AND SOLID GALE FORCE WINDS ELSEWHERE ALONG AND NEAR
THE FRONT. ALSO OF NOTE IS A VIGOROUS SHORTWAVE TROUGH EJECTING OFF
OF JAPAN MOVING INTO THE PACIFIC.

.MODEL DISCUSSION...
IN THE WEST...MODELS DEPICT THE PACIFIC LOW DRIFTING EAST TO A
POSITION 160 MILES SOUTHEAST OF ATKA AROUND 980 MB EARLY FRI MORNING.
THE ENERGY MOVING OFF JAPAN MOVES ALONG 35N LATITUDE IN THE PACIFIC
OCEAN...AND BEGINS FORMING A SURFACE LOW OVERNIGHT THROUGH THU
SUPPORTED BY A 130 KT JET. THIS NEW LOW INITIALLY MOVING UNDERNEATH
THE ALEUTIAN SYSTEM THEN BEGINS WRAPPING BACK NORTH TO ABSORB IT ON
FRI...WITH THE DEPICTED CENTER AROUND 250 MILES SOUTH OF SAND POINT
EARLY SAT. THERE IS DECENT AGREEMENT WITH THIS DEVELOPMENT...AND HAVE
EMPLOYED A GFS/ECMWF BLEND.

IN THE EAST...MODELS SHOW THE UPPER-TROUGH SWINGING THROUGH
SOUTHCENTRAL TODAY...AND EJECTING EAST OF COPPER RIVER BASIN TO YUKON
TERRITORY TONIGHT. MODEL QPF INITIALIZATION WAS RATHER POOR OVER
UPPER COOK INLET AND KENAI PENINSULA EARLY THIS MORNING...THOUGH A
Q-VECTOR CONVERGENCE ZONE SEEMED TO LINE UP WELL WITH THE
OVERSPREADING SNOW. THE EASTERN PORTION OF THE BERING SEA FRONT IS
SHOWN MOVING TO THE SW MAINLAND AND GULF EARLY THU...AND THEN A
PORTION TRACKING TO THE NORTHERN GULF BY THU EVENING. HINTS OF A
TRIPLE POINT FORMING ALONG IT THU MORNING OVER KODIAK ISLAND AND
MOVING INTO THE KENAI PENINSULA ARE DEPICTED SIMILARLY BY
GFS/ECMWF...WITH THE NAM POSITION FURTHER TO THE EAST. MODELS THEN
SHOW ANOTHER FRONT WORKING UP TO THE SOUTHERN GULF AND KODIAK ISLAND
FRI EVENING. HAVE EMPLOYED A BLEND OF NAM TRANSITIONING TO GFS BY THE
END OF THE FORECAST PERIOD.

.SHORT TERM FORECAST...
SOUTHCENTRAL/GULF...
KODIAK ISLAND IS FAR ENOUGH SOUTH TO NOT BE IMPACTED BY THE MAINLAND
TROUGH TODAY...SO THE CURRENT OFF-SHORE FLOW SHOULD PROMOTE SOME
SUNNY BREAKS. THE FLOW BECOMES MORE ONSHORE TONIGHT AHEAD OF THE
BERING SEA FRONT. THE ONSHORE FLOW SHOULD ALSO HELP WARM TEMPERATURES
SUCH THAT EVEN THOUGH PRECIP MAY START AS SNOW IT SHOULD MIX WITH OR
CHANGE TO RAIN AS TIME WEARS ON. PRECIP TAPERS TO SHOWERS WITH FROPA
THU NIGHT/FRI.

SNOW LOOKS TO BE RATHER STEADY TODAY...BUT NOT NECESSARILY HEAVY. THE
TRANSITORY NATURE OF THE UPPER-TROUGH MOVING THROUGH SHOULD HELP
TEMPER OVERALL SNOW ACCUMULATIONS AS WELL. WITH UPPER-TROUGH
PASSAGE...RIDGING ALOFT BUILDS INTO THE REGION FROM THE WEST.
SUBSIDENCE ASSOCIATED WITH IT COUPLED WITH RESIDUAL LOW LVL MOISTURE
REMAINING FROM THE SNOWFALL SHOULD ALLOW FOR SOME FOG DEVELOPMENT...
PARTICULARLY AROUND COOK INLET/TURNAGAIN/KNIK ARMS OVERNIGHT TONIGHT.
THE UPPER-RIDGE AXIS MOVES TO THE COPPER BASIN/ALCAN BORDER THU
AFTERNOON. THE FLOW ALOFT FOR AREAS ON IT'S UPSTREAM SIDE WILL BECOME
SOUTHERLY AND MOIST...LEADING TO ANOTHER ROUND OF SNOW. WHILE THERE
ARE SOME MODEL DIFFERENCES WITH TRIPLE-POINT DEVELOPMENT ALONG THE
FRONT...THERE IS ENOUGH CONFIDENCE THAT THE COMBINATION OF SNOW
INTENSITY AND STRENGTHENING WINDS THROUGH GAPS WILL LEAD TO REDUCED
VISIBILITY IN BLOWING SNOW. THE WORST CONDITIONS ARE EXPECTED THROUGH
PORTAGE VALLEY/TURNAGAIN ARM...WITH A BLIZZARD WATCH ISSUED FOR THIS
AREA. UPPER RIDGING BUILDS INTO SOUTHCENTRAL ON FRI LEADING TO A
RESPITE IN THE ACTION.

SOUTHWEST/AKPEN...
SNOW MIXED WITH RAIN LOOMS FOR THE AKPEN AS THE FRONT MOVES THROUGH.
SOME LOCAL GALE FORCE GUSTS ARE POSSIBLE ALONG FAVORED
NORTHWEST-SOUTHEAST ORIENTED BAYS AND PASSES ALONG THE NORTHERN
AKPEN. ACROSS THE SW MAINLAND...LOOK FOR SOME MORNING FOG/STRATUS
AIDED BY SUBSIDENCE FROM THE APPROACHING RIDGE. SNOW FROM THE BERING
FRONT ADVANCES TO THE REGION TONIGHT. AIR TEMPERATURES SUFFICIENTLY
COLD THAT FALLING SNOW WILL BE RATHER LIGHTWEIGHT AND EASY TO BLOW
AROUND. HAVE INTRODUCED BLOWING SNOW ADVISORIES FOR THE CAPES/COASTAL
AREAS WHERE WINDS WILL BE STRONGEST. THE COMBINATION OF A WEAKENING
ARRIVING FRONT AND ONLY MARGINALLY STRONG WINDS SEEMED TO POINT TO
VISIBILITY NOT QUITE REACHING BLIZZARD IN THESE AREAS...BUT
ACKNOWLEDGE THAT A LOW TO MODEST CHANCE DOES EXIST FOR THINGS TO BE
WORSE THAN CURRENTLY FORECAST. A SLOWER MOVING FRONT COULD ALSO LEAD
TO HIGHER SNOW ACCUMULATION THAN CURRENTLY ADVERTISED AS WELL IN
BRISTOL BAY. CONDITIONS TAPER TO SHOWERS WITH FROPA LATE THU.

BERING SEA/ALEUTIANS...
THE ADVANCE OF THE BERING FRONT AND IT'S ASSOCIATED SNOW AND WIND
SHOULD LEAD TO RAPIDLY DETERIORATING CONDITIONS OVER THE PRIBILOF
ISLANDS TODAY...IMPROVING ONLY WITH FROPA TONIGHT. ELSEWHERE ALONG
THE CHAIN...WINDS REMAIN AT GALE FORCE DUE TO THE LOW JUST NOW
STARTING TO WEAKEN...WITH PRECIPITATION MAINLY SHOWERY IN THE WAKE OF
THE FRONT.

.LONG TERM FORECAST...
FORECAST CHALLENGES THIS WEEKEND SURROUND IMPACTS FROM A PACIFIC LOW
THAT APPROACHES THE AKPEN AND BRISTOL BAY. ALOFT...A RESIDUAL
UPPER-LOW REMAINS CENTERED NEAR WEST CENTRAL AK WELL INTO NEXT
WEEK...ALLOWING LOBES OF ENERGY ROTATING AROUND IT TO MIGRATE THROUGH
MUCH OF THE FORECAST AREA...FROM THE ALEUTIAN CHAIN TO THE SOUTHERN
MAINLAND. CONDITIONS LOOK TO REMAIN RATHER ACTIVE.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING...195
         BLIZZARD WATCH...125
         WINTER WEATHER ADVISORY FOR BLOWING SNOW...155 161
MARINE...STORM...176 411
         GALE...120 125 130 170 172 175 179 185 352 412 413 414
         HEAVY FREEZING SPRAY...179 411 412
FIRE WEATHER...NONE

MALOY