Blizzard in Alaska, February 22 to 23, 2013

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1212 PM AKST FRI FEB 22 2013

.ANALYSIS AND UPPER LEVELS...A VERY LARGE AND DEEP LOW IS PASSING
JUST WEST OF ADAK THIS MORNING WITH FRONTAL SYSTEM TRACKING NORTH
AND EASTWARD ACROSS THE CENTRAL BERING AND CENTRAL TO EASTERN
ALEUTIANS. THE STRONGEST WINDS WITH THIS SYSTEM ARE ASSOCIATED
WITH ARCTIC AIR WRAPPING AROUND THE SOUTH SIDE OF THE LOW CENTER.
A SATELLITE SCATTEROMETER IMAGE FROM OVERNIGHT SHOWED AN AREA OF
50 TO 70 KTS SOUTH TO SOUTHWEST OF THE LOW CENTER. THESE HAVE
LIKELY STRENGTHENED A BIT SINCE THEN AS THE LOW HAS CONTINUED TO
DEEPEN.

MEANWHILE...DOWNSTREAM OF THIS SYSTEM A SERIES OF SHORT-WAVES ARE
PROGRESSING EAST-NORTHEAST ACROSS SOUTHCENTRAL ALASKA AND THE GULF
OF ALASKA. THIS IS PRODUCING AREAS OF LIGHT SNOW PRIMARILY FROM
ANCHORAGE NORTHWARD TO THE MATANUSKA AND SUSITNA VALLEYS. DOWNWARD
MOMENTUM TRANSFER WITH THE UPPER TROUGH IS COMBINING WITH LOW LEVEL
COLD ADVECTION AND A TIGHT PRESSURE GRADIENT IN THE WAKE OF A STRONG
LOW NEAR SOUTHEAST ALASKA TO PRODUCE WIDESPREAD STRONG WINDS ACROSS
THE GULF.

.MODEL DISCUSSION...MODELS HAVE REALLY BEEN STRUGGLING WITH THE
TRACK OF SYSTEM ALONG THE ALEUTIANS...DISPLAYING SIGNIFICANT
RUN-TO-RUN INCONSISTENCIES. FOR THE 12Z MODEL CYCLE THE
GFS/NAM/GEMGLB ARE ALL VERIFYING TOO FAR WEST WITH THE LOW CENTER.
THE ECMWF AND UKMET ARE RIGHT ON SPOT. INTERESTINGLY...MODELS ARE
IN GOOD AGREEMENT IN FRONTAL PROGRESSION TO MAINLAND ALASKA AND
DEVELOPMENT OF A WEAK TRIPLE POINT LOW JUST NORTH OF KODIAK ISLAND.
SOLUTIONS DO DIVERGE WITH TRACK OF THE LOW AS IT REACHES SOUTHWEST
ALASKA SATURDAY NIGHT. BASED ON THE BETTER INITIALIZATION OF THE
ECMWF PLAN TO TREND TOWARD IT THROUGH THE WEEKEND. UNCERTAINTY
GROWS MUCH LARGER WITH NEXT SYSTEM TRACKING SOUTH OF THE ALEUTIANS
AND ALASKA PENINSULA SUNDAY AND MONDAY. CURRENT FORECAST DOES NOT
REFLECT A STRONG LOW IN THIS AREA SO WILL MAKE SOME SIGNIFICANT
CHANGES IN THIS TIME PERIOD TO INDICATE STRONGER WINDS (EVEN WITH
UNCERTAINTY IN THE EXACT LOW TRACK).

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...CONDITIONS WILL BRIEFLY DRY OUT THIS AFTERNOON
AND EVENING ACROSS SOUTHCENTRAL AS THE LAST IN A LINE OF UPPER
SHORT-WAVES EXITS TO THE NORTHEAST. WITH DECREASING CLOUDS AND
A SHORT-WAVE RIDGE MOVING OVERHEAD THERE WILL BE A THREAT OF FOG
ACROSS THE REGION. HOWEVER...THIS WILL BE SHORT-LIVED AS THE
FRONTAL SYSTEM FROM THE ALEUTIAN SYSTEM MOVES TO THE WESTERN GULF
OVERNIGHT AND INTO SOUTHCENTRAL ON SATURDAY. THIS WILL BE A FAST
MOVING FRONT AND IT WILL RAPIDLY WEAKEN AS IT APPROACHES SOUTHCENTRAL
SO GENERALLY EXPECT A SHORT DURATION OF PRECIP AND WINDS. THERE IS
SOME UNCERTAINTY IN THE LOCATION AND STRENGTH OF THE TRIPLE POINT
LOW. BASED ON THE CURRENT EXPECTED TRACK FROM THE BARREN ISLANDS
NORTHWARD ACROSS THE KENAI PENINSULA EXPECT SOME GUSTY EASTERLIES
THROUGH PORTAGE VALLEY AND TURNAGAIN ARM WHICH WILL CAUSE SOME
TEMPORARY LOW VISIBILITIES IN SNOW AND BLOWING SNOW. THE EXACT
TRACK OF THE LOW WILL AFFECT THE STRENGTH OF THESE WINDS AND
DETERMINE HOW LOW VISIBILITIES DROP. RIGHT NOW IT DOES NOT LOOK
FAVORABLE TO REACH ADVISORY OR WARNING THRESHOLDS. AFTER THE FRONTAL
SYSTEM WEAKENS THE REMNANTS OF THE ALEUTIAN SYSTEM WILL MOVE INTO
THE GULF AND SOUTHCENTRAL ON SUNDAY PRODUCING AREAS OF GENERALLY
LIGHT SNOW WITH MINOR ACCUMULATION. A MUCH MORE SIGNIFICANT STORM
WILL HEAD INTO THE GULF EARLY NEXT....BUT THERE IS HIGH UNCERTAINTY
IN THE TRACK OF THIS SYSTEM SO ITS A BIT TOO EARLY TO IDENTIFY WHICH
AREAS WILL EXPERIENCE THE GREATEST IMPACTS.

SOUTHWEST ALASKA...FRONTAL SYSTEM CROSSING THE BERING TODAY WILL
MOVE ACROSS SOUTHWEST ALASKA TONIGHT AND SATURDAY. THERE WILL
INITIALLY BE SOME GUSTY WINDS AS SNOW FIRST ARRIVES WHICH WILL
CAUSE BLOWING SNOW AND VISIBILITIES AS LOW AS ONE HALF MILE.
HOWEVER...THE FRONT WILL BE MOVE THROUGH QUICKLY AND WEAKEN AS IT
HEADS INLAND. THEREFORE THE PERIOD OF REALLY LOW VISIBILITIES WILL
BE SHORT-LIVED. THE LOW CENTER WILL ARRIVE IN THE REGION SATURDAY
NIGHT MAINTAINING AREAS OF LIGHT SNOW. AS THIS SYSTEM EXITS THE
NORTH AND EAST SUNDAY AND SUNDAY NIGHT STRONG COLD ADVECTION WILL
KICK IN BEHIND IT. THIS WILL COMBINE WITH STRONG PRESSURE RISES
TO PRODUCE GUSTY WINDS...PRIMARILY ALONG AND NEAR THE COAST. WILL
LIKELY NEED A WIND CHILL ADVISORY FOR THE KUSKOKWIM DELTA BEGINNING
SUNDAY NIGHT. THE PATTERN WILL REMAIN ACTIVE EARLY NEXT WEEK AS
ANOTHER STRONG STORM SYSTEM TRACKS SOUTH OF THE ALASKA PENINSULA.
THERE IS QUITE A BIT OF UNCERTAINTY IN THE TRACK OF THIS SYSTEM...
BUT THERE IS A GOOD CHANCE SNOW WILL SPREAD NORTHWARD INTO BRISTOL
BAY AND NORTHERLY WINDS WILL STRENGTHEN ACROSS SOUTHWEST ALASKA.
BOTTOM LINE...ITS LOOKING COLD AND WINDY.

BERING SEA/ALEUTIANS...BASED ON THE LATEST TRACK OF THE LOW JUST
WEST OF ADAK AND EXPECTED FUTURE TRACK EASTWARD...THE STRONGEST
CORE OF WINDS ON THE SOUTH SIDE OF THE LOW WILL STAY JUST SOUTH OF
THE ALEUTIAN CHAIN. THERE MAY BE JUST A FEW SOUTHWESTERLY GUSTS
APPROACHING WARNING LEVEL IN ATKA THIS AFTERNOON BEFORE THESE WINDS
SHIFT EASTWARD. MEANWHILE...EXPECT BLIZZARD CONDITIONS TO DEVELOP
ON THE PRIBILOF ISLANDS THIS AFTERNOON AS SNOW ARRIVES WITH THE
OCCLUDED FRONT. WINDS WILL DIMINISH SIGNIFICANTLY ON ST GEORGE
ISLAND AS THE FRONT NEARS...BUT WILL REMAIN STRONG ON ST PAUL ISLAND.
THE FRONT NEVER ACTUALLY REACHES THE ISLAND - IT COMES CLOSE AND
THEN HEADS EASTWARD. THERE WILL LIKELY BE A PERIOD OF IMPROVED
VISIBILITIES TONIGHT...BUT BLIZZARD CONDITIONS WILL RE-DEVELOP AS
STRONG COLD ADVECTION KICKS IN ON THE BACK SIDE OF THE SYSTEM. AS
THE LOW BEGINS TO PROGRESS EASTWARD TONIGHT AND SATURDAY THE FOCUS
WILL SHIFT TO THE BACK SIDE WHERE COLD ADVECTION AND STRONG PRESSURE
RISES WILL PRODUCE VERY STRONG AND GUSTY WINDS. LOW LEVEL WINDS DO
NOT APPEAR QUITE STRONG ENOUGH TO REACH WARNING LEVELS...BUT AS
WINDS ACCELERATE THROUGH GAPS IN THE EASTERN ALEUTIANS AND ALASKA
PENINSULA THEY MAY COME VERY CLOSE. THE OTHER THREAT WILL BE BLOWING
SNOW AS SNOW SHOWER GENERATION KICKS INTO GEAR OVER THE BERING SEA.
ALTHOUGH STRONG ADVECTION IS MODERATE TO STRONG AND SNOW SHOWERS
WILL BE HEAVY AT TIMES...DON'T SEE ANY UPPER LEVEL FEATURE TO HELP
PRODUCE A STEADY SNOW. THEREFORE...DO NOT THINK SUSTAINED BLIZZARD
CONDITIONS WILL DEVELOP ALONG THE EASTERN ALEUTIANS OR ALASKA
PENINSULA. THERE WILL BE SHORT DURATIONS OF WHITE-OUT CONDITIONS
IN HEAVIER SNOW SHOWERS.

.LONG TERM FORECAST...THE UPPER LEVEL JET WILL PERSIST SOUTH OF THE
ALEUTIAN CHAIN AND CONTINUE TO SUPPORT FAST MOVING AND STRONG STORM
SYSTEMS THROUGH THE MIDDLE OF NEXT WEEK. IT LOOKS LIKE THERE WILL
THEN BE A LITTLE BIT OF CHANGE IN THE PATTERN AS A LARGE UPPER LEVEL
LOW SETS UP OVER THE FORECAST AREA AND THE UPPER JET SINKS SOUTHWARD.
THIS WILL SLOW DOWN THE PROGRESSION OF STORMS...AT LEAST FOR TWO OR
THREE DAYS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 195.
MARINE...HURRICANE FORCE WIND WARNING...172.
         STROM WARNING...170 175.
         GALE WARNING 150 155 160 165 171 176 179 185.
FIRE WEATHER...NONE.

SEB FEB 13