Blizzard Watch 25, NWS Anchorage, AK

411 
WWAK42 PAFC 200900
WSWALU

URGENT - WINTER WEATHER MESSAGE
NATIONAL WEATHER SERVICE ANCHORAGE AK
1200 AM AKST TUE DEC 20 2011


AKZ161-210100-
/X.UPG.PAFC.BZ.A.0025.111220T1500Z-111220T2100Z/
/X.NEW.PAFC.BZ.W.0048.111220T1500Z-111221T0100Z/
BRISTOL BAY-
INCLUDING THE CITIES OF...KING SALMON...DILLINGHAM...NAKNEK...
PILOT POINT
1200 AM AKST TUE DEC 20 2011

...BLIZZARD WARNING IN EFFECT FROM 6 AM TO 4 PM AKST TUESDAY NORTH
AND WEST OF KING SALMON...

THE NATIONAL WEATHER SERVICE IN ANCHORAGE HAS ISSUED A BLIZZARD
WARNING...WHICH IS IN EFFECT FROM 6 AM TO 4 PM AKST TUESDAY. THE
BLIZZARD WATCH IS NO LONGER IN EFFECT. 


* LOCATION...NORTH AND WEST OF KING SALMON.

* SNOW...TOTAL SNOW ACCUMULATIONS OF 3 TO 6 INCHES WITH ISOLATED
  AMOUNTS TO 8 INCHES...WITH UP TO 3 INCHES ACCUMULATION NORTH AND
  EAST OF KING SALMON. 

* VISIBILITY...VISIBILITY WILL BE REDUCED TO ONE QUARTER MILE OR LESS
  AT TIMES.

* WIND...EAST WIND 25 TO 40 MPH WITH GUST TO 55 MPH IN THE MORNING
  BECOMING SOUTH TO SOUTHWEST 20 TO 30 WITH GUSTS TO 40 MPH DURING
  THE AFTERNOON.

* TIMING...THE MOST WIDESPREAD BLIZZARD CONDITIONS WILL OCCUR
  DURING THE MORNING HOURS...THEN MOVE NORTH THROUGH THE AFTERNOON
  AS WINDS SWITCH TO SOUTH OR SOUTHWESTERLY. SNOW SHOWERS WITH
  AREAS OF BLOWING SNOW WILL CONTINUE THROUGH THE EVENING.

* IMPACTS...SNOWFALL COMBINED WITH STRONG WINDS AND BLOWING SNOW
  WILL PRODUCE WHITE-OUT CONDITIONS AT TIMES. ANY OUTDOOR
  ACTIVITIES SUCH AS DRIVING WILL BECOME VERY DIFFICULT.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A BLIZZARD WARNING MEANS SEVERE WINTER WEATHER CONDITIONS ARE
EXPECTED OR OCCURRING. FALLING AND BLOWING SNOW WITH STRONG WINDS
AND POOR VISIBILITIES ARE LIKELY. THIS WILL LEAD TO WHITE-OUT
CONDITIONS...MAKING TRAVEL VERY DIFFICULT. ALL TRAVEL AND OUTDOOR
ACTIVITY IS STRONGLY DISCOURAGED.

&&

$$

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
105 PM AKST MON DEC 19 2011

.ANALYSIS AND UPPER LEVELS...A STRONG NORTH PACIFIC JET CONTINUES
TO PRODUCE A RAPID SUCCESSION OF STORMS TRACKING ACROSS THE NORTH
PACIFIC AND THEN CURVING NORTHWARD TOWARD MAINLAND ALASKA. A LOOK
AT SATELLITE IMAGERY SHOWS A RELATIVELY SMALL AND WEAK LOW RIDING
NORTH-NORTHEASTWARD ALONG THE ALASKA PENINSULA. THERE IS A FAIRLY
NARROW BAND OF SNOW SURROUNDING THE LOW ACROSS KODIAK ISLAND AND
THE ALASKA PENINSULA WHICH WILL HEAD INTO COOK INLET AND ACROSS
THE KENAI PENINSULA AS WE HEAD THROUGH THE AFTERNOON HOURS. A VERY
NOTABLE CHARACTERISTIC ON INFRARED SATELLITE IMAGERY IS THE CELLULAR
ACTIVITY BEHIND THIS LOW WITH VERY COLD CLOUD TOPS. THE 12 SOUNDING
FROM COLD BAY SHOWS STEEP LAPSE RATES APPROACHING DRY ADIABATIC.
THEREFORE...SOME OF THESE SHOWERS COULD BE INTENSE AS THEY MOVE
ONSHORE ACROSS SOUTHWEST ALASKA AND KODIAK ISLAND THIS AFTERNOON.
MODELS ALSO SHOW A SMALL AREA OF 2 TO 3 MB PER HOUR PRESSURE RISES
DIRECTLY IN THE WAKE OF THE LOW WHICH WILL BRIEFLY ENHANCE WIND
SPEEDS AS THIS LOW PASSES THROUGH.

THE NEXT MAJOR STORM IS DEVELOPING SOUTH OF THE CENTRAL ALEUTIANS
IN THE LEFT EXIT REGION OF THE SUBTROPICAL JET. AS THE RIDGE
AMPLIFIES AHEAD OF THIS LOW IT IS BEGINNING TO CURVE TOWARD THE
NORTHEAST. THIS LOOKS LIKE IT WILL BE THE LAST MAJOR STORM TO
AFFECT THE MAINLAND BEFORE A CHANGE OCCURS IN THE LONG-WAVE PATTERN.

.MODEL DISCUSSION...THERE ARE KEY DIFFERENCES IN THE MODEL SOLUTIONS
WITH REGARD TO STRENGTH AND TRACK OF THE LOW DEVELOPING SOUTH OF
THE CENTRAL ALEUTIANS. GFS IS MOST CONSISTENT WITH TRACK AND SHOWS
SMALL SPREAD IN ITS ENSEMBLE MEMBERS IN BOTH TRACK AND DEPTH.
HOWEVER...IT IS ABOUT 10 MB DEEPER THAN THE OTHER MODELS AS IT
MOVES INTO THE EASTERN BERING SEA TUESDAY MORNING. THERE ARE NO
SIGNS OF RAPID DEEPENING OF THIS LOW IN SATELLITE IMAGERY. IT LOOKS
MORE LIKE A MORE GRADUAL STRENGTHENING IS UNDER WAY WHICH WOULD
LEAD AWAY FROM THE DEEPER GFS SOLUTION. FOR NOW WILL STICK CLOSE
TO INHERITED FORECAST AND KEEP A CLOSE EYE ON SATELLITE IMAGERY
TO SEE IF IN FACT THE DEEPER SOLUTION MIGHT BE CORRECT. THERE IS
POTENTIAL FOR HIGH IMPACTS IN SEVERAL AREAS ACROSS THE SOUTHERN
MAINLAND DEPENDING ON THE STRENGTH OF THIS SYSTEM.

BEHIND THIS SYSTEM MODELS DIVERGE SIGNIFICANTLY AND FORECAST
CONFIDENCE IS VERY LOW. PLAN TO MAKE LITTLE CHANGE TO THE INHERITED
FORECAST WHICH WAS BASED ON THE 00Z ECMWF.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...MOST OF THE REGION WILL SEE A QUICK SHOT OF
SNOW TONIGHT INTO EARLY TUESDAY MORNING AS THE LOW ALONG THE ALASKA
PENINSULA AND THE ASSOCIATED UPPER LEVEL TROUGH MOVE THROUGH. THE
SMALL SIZE OF THE SYSTEM ALONG WITH THE FAST SPEED MEANS THE BULK
OF ACCUMULATING SNOW WILL FALL OVER A 3 OR 4 HOUR PERIOD. THERE WILL
THEN BE ANOTHER BRIEF BREAK BETWEEN SYSTEMS BEFORE A MUCH STRONGER
STORM AFFECTS THE AREA. SIMILAR TO THE LAST MAJOR STORM THIS PAST
WEEKEND THIS LOW WILL TRACK INTO THE EASTERN BERING SEA AND WESTERN
ALASKA. THERE ARE SOME KEY DIFFERENCES WITH THIS STORM AND THE ONE
THIS PAST WEEKEND WHICH WILL RESULT IN LESS IMPACT IN THE ANCHORAGE
AREA. THIS ONE IS EXPECTED TO BE WEAKER AND TRACK FURTHER WEST. THE
UPPER LEVEL JET WHICH MOVES OVER SOUTHCENTRAL MAXES OUT AROUND 80 KTS
WHICH IS NOT VERY IMPRESSIVE. THE SOUTHEASTERLY FLOW LOOKS TO BE
SHALLOWER - EXTENDING THROUGH ABOUT 4000 FEET WITH A MORE SOUTHERLY
COMPONENT ABOVE THAT. FINALLY...THE FRONT WILL OCCLUDE LONG BEFORE
IT GETS HERE SO THERE WILL BE LITTLE IN THE WAY OF WARM AIR
ADVECTION. ALL OF THIS POINTS TOWARD A MORE TYPICAL HIGH WIND
WARNING FOR TURNAGAIN ARM AND HIGHER ELEVATIONS. THE NAM...WHICH
HAS THE RESOLUTION TO MORE ACCURATELY DEPICT WEATHER IN THE BOUNDARY
LAYER...SHOWS THE CORE OF WINDS CENTERED AT 4000 FEET WHICH SUPPORTS
THIS IDEA THAT THE HIGH WINDS WILL NOT MAKE IT DOWN TO LOWER
ELEVATIONS. THE SOUTHERLY FLOW AND COLDER AIR ALSO MEANS THERE
SHOULD BE SOME SNOWFALL AS THE FRONT MOVES THROUGH. COLD ADVECTION
AND INSTABILITY BEHIND THE FRONT MEANS SOUTHERLY WINDS WILL ONCE
AGAIN GET INTO ALL OF ANCHORAGE TUESDAY NIGHT INTO WEDNESDAY.

THE FRONT WILL BE QUICK TO MOVE ACROSS SOUTHCENTRAL ALASKA TUESDAY
EVENING THROUGH WEDNESDAY MORNING SO THE GREATEST IMPACT WEATHER
WILL BE FAIRLY SHORT-LIVED ACROSS THE REGION. OTHER IMPACTS WILL
BE A PERIOD OF MODERATE TO HEAVY SNOW IN THE SUSITNA VALLEY AND
THE PRINCE WILLIAM SOUND REGION. STILL SOME UNCERTAINTY WITH TRACK
OF LOW OUT WEST AND TIMING OF FRONT AS IT CROSSES SOUTHCENTRAL SO
PLAN TO WAIT UNTIL THE NEXT MODEL CYCLE BEFORE ISSUING ANY ADVISORIES
OR WARNINGS FRO SNOWFALL. THERE IS A LIKELIHOOD THOMPSON PASS WILL
SEE ANOTHER BLIZZARD AS THE FRONT MOVES THROUGH SO HAVE ISSUED A
BLIZZARD WATCH FOR TUESDAY NIGHT.

SOUTHWEST ALASKA...UNCERTAINTY IN THE STRENGTH AND TRACK OF THE
NEXT STORM SYSTEM AS IT APPROACHES SOUTHWEST ALASKA MAKES IT HARD
TO PINPOINT WINDS AND SNOW AMOUNTS. AT THE MOMENT IT APPEARS THE
GREATEST IMPACT WILL BE FROM SNOWFALL AND WINDS NORTH AND WEST OF
KING SALMON. THERE MIGHT BE JUST ENOUGH WIND FOR BLIZZARD
CONDITIONS...BUT BASED ON THE RAPID SPEED OF THE FRONT DO NOT THINK
WILL SEE THREE STRAIGHT HOURS OF 1/4 MILE VISIBILITY.
THEREFORE...WILL SIDE WITH A SNOW AND BLOWING SNOW ADVISORY FOR
VISIBILITIES DOWN TO ONE HALF MILE AT TIMES BEGINNING EARLY TUESDAY
MORNING. THERE WILL BE BLOWING SNOW ACROSS THE KUSKOKWIM DELTA ON
THE NORTH SIDE OF THIS SYSTEM...BUT IT DOES NOT LOOK LIKE ENOUGH
WIND OR FALLING SNOW TO CAUSE A SUSTAINED PERIOD OF REDUCED
VISIBILITIES. SOME WARMER AIR WILL MAKE IT INTO EASTERN PORTIONS
OF BRISTOL BAY WHERE RAIN COULD MIX WITH SNOW. HOWEVER...COLD AIR
BEHIND THE SYSTEM WILL CHANGE ANY REMAINING PRECIPITATION BACK TO
SNOW TUESDAY NIGHT. ALSO EXPECT GUSTY SOUTHWESTERLIES BEHIND THE
LOW DUE TO COLD ADVECTION AND INSTABILITY.

BERING SEA/ALEUTIANS...MODELS SHOW A STRONG THERMAL GRADIENT
AROUND THE PACIFIC LOW CENTER...INDICATIVE OF A STRONG FRONT.
THEREFORE...EXPECT STRONG WINDS IN ALL SECTORS OF THE STORM AS
IT CROSSES INTO THE EASTERN BERING TONIGHT. THE STRONGEST WINDS
THOUGH MAY BE ON THE BACK SIDE OF THE LOW. THE NAM SHOWS 60 KT
AT 1000 FEET ABOVE DUTCH HARBOR EARLY TUESDAY MORNING SO WILL
TREND TOWARD STRONGER WINDS BEHIND THE LOW. WITH UNCERTAINTY IN
THE ULTIMATE STRENGTH OF THE LOW WILL HAVE TO RE-EVALUATE POTENTIAL
FOR REACHING HIGH WIND THRESHOLD OF 75 MPH ONCE THE NEW MODEL RUNS
COME IN LATE THIS AFTERNOON. THERE IS A LOT OF UNCERTAINTY AFTER
THIS SYSTEM MOVES THROUGH...BUT LOOKS LIKE ANOTHER PACIFIC SYSTEM
COULD AFFECT THE ALEUTIANS MID WEEK.

.LONG TERM FORECAST...THE EXTENDED FORECAST PERIOD APPEARS TO BE
ONE OF TRANSITION TO A NEW PATTERN. THINGS APPEAR QUITE CHAOTIC
DURING THIS TRANSITION AND MODELS SHOW LITTLE IN THE WAY OF
CONSISTENCY. THEREFORE...FORECAST CONFIDENCE IS VERY LOW.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WATCH ZONE 101. BLIZZARD WATCH ZONE 131.
MARINE...STORM WARNING...130 150 155 170.
         GALE WARNING...120 125 132 138 140 141 160 165 171 172 180.

         HEAVY FREEZING SPRAY WARNING...185.
FIRE WEATHER...NONE.

SEB DEC 11

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE ANCHORAGE AK
152 PM AKST MON DEC 19 2011

AKZ101-200900-

...ONE MORE CHINOOK WIND EVENT EXPECTED BEFORE THE PATTERN CHANGES...

ANOTHER STRONG PACIFIC STORM IS EXPECTED TO TRACK TO WESTERN ALASKA
ON TUESDAY BRINGING ANOTHER ROUND OF CHINOOK WINDS TO ANCHORAGE.
IT APPEARS THAT THIS STORM WILL BE MARGINALLY WEAKER THAN THE STORMS
WHICH HAVE AFFECTED ANCHORAGE THE PAST THREE WEEKENDS. MORE
NOTABLY...THE HIGHEST WINDS OF 75 MPH OR GREATER ARE EXPECTED TO
REMAIN CONFINED TO THE MORE TYPICAL HIGHER ELEVATIONS OF AROUND
2000 FEET AND HIGHER. AREAS FURTHER DOWN THE HILLSIDE AND ALONG
MOUNTAIN GAPS WILL STILL SEE SOME WIND...LIKELY IN THE 40 TO 60 MPH
RANGE. AFTER THE FRONT MOVES THROUGH SOMETIME TUESDAY NIGHT GUSTY
SOUTHERLY WINDS WILL MOVE INTO ALL OF ANCHORAGE.

ALL INDICATIONS ARE THAT A PATTERN CHANGE IS IN STORE AFTER THIS
STORM MOVES THROUGH. THEREFORE...THIS WILL LIKELY BE THE LAST BIG
CHINOOK WIND FOR A WHILE. COLDER AIR IS EXPECTED TO SETTLE IN BEHIND
THIS STORM IN THE MIDDLE TO END OF THIS WEEK.

SEB