Blizzard in Alaska, February 9, 2013

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE ANCHORAGE AK
520 AM AKST SAT FEB 9 2013

.ANALYSIS AND UPPER LEVELS...
AN UPPER-LVL RIDGE OVER THE EASTERN GULF IS AMPLIFYING AND RETREATING
EAST AS A PACIFIC LOW PUSHES AGAINST IT FROM THE SOUTHWEST AND AN
UPPER-LOW SLIPS SOUTH OF THE BERING STRAIT. THE PACIFIC LOW 250 MILES
SOUTH OF CHIGNIK IS MOVING NORTH TOWARDS SOUTHERN BRISTOL BAY. IT'S
ASSOCIATED PRECIP SHIELD WITH THE FRONT IS TRAVERSING INTERIOR
BRISTOL BAY AND SLOWING AS IT NEARS THE KUSKOKWIM DELTA. THE EASTERN
PORTION OF THE FRONT HAS CLEARED KODIAK ISLAND AND MOVES TO THE
NORTHERN GULF COAST...WITH A SLUG OF SNOW/RAIN AND WIDESPREAD SOUTH
TO EAST GALES. A BARRIER JET SUPPORTS STORM-FORCE WINDS OVER COASTAL
WATERS FROM CAPE SUCKLING TO GORE POINT...WITH SOME LOCAL
ACCELERATION ALSO OVER KAMISHAK BAY. WINDS HAVE ALSO PICKED UP
CONSIDERABLY THROUGH TURNAGAIN ARM AND PORTAGE VALLEY WHERE HIGH WIND
WARNINGS ARE POSTED. ON THE OTHER SIDE OF THE PACIFIC LOW...COLD AIR
BLEEDS DOWN THE EASTERN BERING SEA...WITH AMPLE SNOW SHOWERS THROUGH
THE PRIBILOF ISLANDS AND OFFSHORE WATERS. SOME OF THE COLD AIR IS
JUST NOW POKING TO THE AKPEN WHERE PRECIP IS MIXING WITH OR CHANGING
TO SNOW. FURTHER WEST...A COMPLEX LOW 500 MILES SOUTHWEST OF ATTU
IS DRIFTING EAST. AN ASSOCIATED FRONT IS STALLING OVER THE FAR
WESTERN CHAIN...WITH THE SQUEEZED GRADIENT PRODUCING SNOW AND BLOWING
SNOW.

.MODEL DISCUSSION...
MODELS SATISFACTORILY CAPTURE THE MAIN WEATHER PICTURE...WITH THE
ECMWF STILL PERFORMING BEST OUT WEST. THE PACIFIC LOW MOVES ASHORE
EAST OF CHIGNIK TONIGHT AND TRACKS UP TOWARDS NOME ON SUN. THERE
APPEARS TO BE LESS PHASING OF THIS SYSTEM WITH THE UPPER-LOW SWINGING
DOWN FROM THE BERING STRAIT COMPARED TO PREVIOUS DAYS...WITH ALSO
LESS QPF ACROSS THE FRONT DRAPED OVER THE MAINLAND. THE TREND TO PUSH
THE FRONT BACK EAST THROUGH BRISTOL BAY AND EAST THROUGH COOK INLET
AND THE NORTHERN GULF ON SUN STILL IS STILL LOOKING SIMILAR THOUGH.
MODELS ALSO STILL AGREE THAT THE UPPER-LOW WILL HANG IN THE VICINITY
OF THE BERING STRAIT FOR A PERIOD OF SEVERAL DAYS WITH VARIOUS
DISTURBANCES ROTATING AROUND IT THROUGH THE AOR. MODELS ALSO SHOW A
WAVE FORMING IN THE PROGRESSIVE FLOW AROUND 100 MILES SOUTH OF
NIKOLKSI TONIGHT...QUICKLY TRACKING IT TO 200 MILES SOUTHWEST OF
SITKINAK SUN MORNING AND TO NEAR MIDDLETON ISLAND EARLY MON. THE
ECMWF AN UKMET HAVE THIS WAVE TRACKING FURTHER NORTH CLOSER TO PRINCE
WILLIAM SOUND THAN NAM...WITH THE GFS A COMPROMISE SOLUTION IN
BETWEEN. THE BIGGEST DIFFERENCE OF THE EUROPEAN MEMBERS TRACK
VERIFYING WOULD BE A BETTER SHOT OF STEADY SNOW BACK THROUGH
SOUTHCENTRAL SUN NIGHT INTO MON. IN THE EAST...HAVE LEANED ON THE NAM
INITIALLY WITH A TREND TO GFS BY LATE SUN NIGHT.

.SHORT TERM FORECAST...
SOUTHCENTRAL/GULF...
ACROSS KODIAK ISLAND...PRECIP IS EBBING A TOUCH AS THE FIRST FRONT
PUSHES NORTH BUT ONSHORE FLOW PERSISTS. THE LOW MOVING INTO SW AK
WILL PASS JUST WEST OF THE ISLAND TONIGHT BUT CLOSE ENOUGH TO KEEP
RAIN AROUND WITH A SECOND FROPA EXPECTED OVERNIGHT TONIGHT. THE FAST
MOVING WAVE TRACKING SOUTH OF THE CHAIN TONIGHT SWINGS UP SUN
AFTERNOON.

STRONG DOWNSLOPING SHOULD GENERALLY TEMPER PRECIPITATION TO PASSING
SHOWERS/FLURRIES ACROSS THE POPULATION CENTERS FROM THE MATANUSKA
VALLEY DOWN THROUGH THE NORTHWESTERN KENAI PENINSULA UNTIL THE
RESIDUAL LOW MOVES TO THE KUSKOKWIM DELTA AND THE SECONDARY FRONT
SWINGS EAST OUT OF BRISTOL BAY ON SUN WITH THE FLOW ALOFT GOING
MOIST/SOUTHWESTERLY. IN THE INTERIM...EXPECT THE BULK OF THE HEAVIEST
PRECIP TO FALL ACROSS SOUTHERN TO EASTERN KENAI PENINSULA...PRINCE
WILLIAM SOUND...AND NORTHERN TO WESTERN REACHES OF THE SUSITNA
VALLEY. COMMENSURATE WITH THE SECONDARY FROPA COMING FROM THE SW
MAINLAND WILL BE A REVERSING OF THE PRESSURE GRADIENT THAT WAS
INITIALLY DOWN INLET...AND SHOULD ENABLE A QUICK SHOT OF BRISK SOUTH
FLOW ENVELOPING COOK INLET/WESTERN KENAI PENINSULA AND THE ANCHORAGE
BOWL. THERE IS ANOTHER ROUND OF SNOW POSSIBLE EARLY MON AS THE WAVE
SWINGING TO THE NORTHERN GULF APPROACHES.

SOUTHWEST/AKPEN...
THE PRECIPITATION SHIELD WITH THE FRONT INCHING NORTH THROUGH
SOUTHWEST AK HAS BEEN A TAD WEAKER THAN FORECAST BASED ON SURFACE
OBSERVATIONS...PERHAPS BECAUSE THERE HAS BEEN LESS PHASING OF THE
UPPER-ENERGY FROM THE NORTH. NEVERTHELESS...THE SHIELD IS ON THE MOVE
AND STILL EXPECTED TO ENVELOP THE KUSKOKWIM DELTA/VALLEY THROUGH
TODAY. COLD AIR IS WRAPPING DOWN THE AKPEN...AND THIS COLD ADVECTION
WILL WORK EAST TONIGHT TO ENVELOP BRISTOL BAY AND ALLOW ALL PRECIP TO
END AS SNOW THERE. THE PLUMMETING TEMPERATURES WILL ALLOW THE SNOW TO
BECOME LOWER DENSITY AND A BIT EASIER TO BLOW AROUND SO THERE WILL
STILL BE SOME BLOWING SNOW TO CONTEND WITH.

BERING SEA/ALEUTIANS...
CONDITIONS SHOULD IMPROVE OVER THE WESTERN CHAIN AS THE STALLING
FRONT WEAKENS TONIGHT. PRECIPITATION WILL NOT GO AWAY COMPLETELY
THOUGH AS THE PARENT LOW CONTINUES TO ADVANCE EAST...ALLOWING THE
PRECIPITATION SHIELD TO ENCOMPASS MORE OF THE CENTRAL CHAIN. THE
PRIBILOFS LIKEWISE SHOULD SEE IMPROVEMENTS TO VISIBILITY AS WINDS
DIMINISH IN THE WAKE OF THE LOW MOVING FURTHER UP INTO THE SW
MAINLAND.

.LONG TERM FORECAST...
MUCH OF THE AOR STILL LOOKS TO BE DOMINATED BY LOW HEIGHTS ALOFT...
INITIALLY FROM THE UPPER-LOW NEAR THE BERING STRAIT. BY MID WEEK A
DEEPENING PACIFIC LOW BEGINS TO AMPLIFY RIDGING THROUGH THE GULF AND
SOUTHERN MAINLAND BRIEFLY...BUT AS IT TRACKS NORTHEAST TOWARDS THE SW
AK IT REINFORCES THE LARGE LONGWAVE TROUGH OVER THE FORECAST AREA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING...131 155 191 195
         HIGH WIND WARNING...101 125
         WINTER WEATHER ADVISORY FOR SNOW...141 145
MARINE...STORM...120 130
         GALE...125 129 132 137 138 140 150 155 160 165 170 172 176
                179 180 185 351 352 411 412 413 414
         HEAVY FREEZING SPRAY...160 165 179 411 412 413 414
FIRE WEATHER...NONE

MALOY