Blizzard and High Wind in Alaska, November 18 to 19, 2012

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1235 PM AKST SUN NOV 18 2012

.ANALYSIS AND UPPER LEVELS...BUILDING RIDGE OUT AHEAD OF TROUGH
MOVING OUT OF ASIA IS BEGINNING TO PHASE WITH STATIONARY RIDGE OVER
EASTERN SIBERIA AND THE NORTHERN BERING SEA. MEANWHILE ON THE
DOWNSTREAM SIDE OF THE RIDGE AN UPPER LEVEL CLOSED LOW IS DIGGING
SOUTHWARD ACROSS BRISTOL BAY AND INTO THE NORTH PACIFIC. THIS UPPER
LOW IS PART OF A MUCH LARGER CYCLONIC CIRCULATION WHICH ENCOMPASSES
MUCH OF MAINLAND ALASKA...WESTERN CANADA...THE GULF OF ALASKA AND
NORTHEAST PACIFIC. THE UPPER LOW IS DRAGGING ARCTIC AIR SOUTHWARD
ACROSS SOUTHWEST ALASKA THE EASTERN BERING AND ALASKA PENINSULA.
THE COMBINATION OF COLD ADVECTION...A TIGHT PRESSURE GRADIENT
BETWEEN BERING HIGH AND GULF LOW...AND DOWNWARD MOMENTUM TRANSFER
ASSOCIATED WITH UPPER LOW IS PRODUCING VERY STRONG WINDS ALONG THE
SOUTHERN ALASKA PENINSULA (WHERE A HIGH WIND WARNING IS IN EFFECT )
AND EASTERN ALEUTIANS. COLD AIR MOVING ACROSS THE RELATIVELY WARMER
WATERS OF THE EASTERN BERING IS ALSO PRODUCING WIDESPREAD SNOW
SHOWERS ACROSS THE REGION. WEB CAMS SHOWS VISIBILITIES IN BLOWING
SNOW ARE NOT ALL THAT BAD...ALTHOUGH KING COVE IS OCCASIONALLY
OBSERVING NEAR WHITE OUT CONDITIONS IN HEAVIER SHOWERS. SINCE THIS
DOES NOT APPEAR TO BE WIDESPREAD WILL STICK WITH HIGH WIND WARNING
AND HIGHLIGHT THE LOCALIZED LOW VISIBILITIES IN THE FORECAST.

THERE ARE MULTIPLE SURFACE LOWS IN THE GULF. THE MORE IMPORTANT
FEATURE HOWEVER IS AN UPPER WAVE AND SURFACE TROUGH WHICH ARE
ROTATING FROM THE NORTHERN GULF SOUTHWESTWARD TOWARD KODIAK ISLAND.
MIDDLETON ISLAND RADAR SHOWS SOME MODERATE TO HEAVY BANDS OF SNOW
ALONG THIS TROUGH. SOME AREAS IN WESTERN PRINCE WILLIAM SOUND
PICKED UP 6 TO 12 INCHES OF SNOW OVERNIGHT. A BLIZZARD WARNING
IS IN EFFECT FOR KODIAK ISLAND AS SNOW ARRIVES THIS EVENING.
SKIES ARE BEGINNING TO CLEAR OVER INTERIOR SOUTHCENTRAL AND SHOWERS
ARE DIMINISHING ALONG THE COAST AS THE TROUGH AND UPPER WAVE MOVE
OFF TO THE SOUTH.

.MODEL DISCUSSION...NAM HAS BEST HANDLE ON SURFACE TROUGH AND UPPER
WAVE HEADED TOWARD KODIAK ISLAND AND WILL BE USED AS GUIDANCE FOR
TIMING AND INTENSITY OF WINDS AND PRECIP AS IT CROSSES KODIAK ISLAND
TONIGHT INTO MONDAY. OTHERWISE MODELS ARE GENERALLY PRETTY SIMILAR
WITH HANDLING OF SYNOPTIC FEATURES AND SHOW GOOD RUN-TO-RUN
CONSISTENCY. THUS FORECAST CONFIDENCE IS ABOVE AVERAGE AND ONLY
MINOR ADJUSTMENTS WILL MADE TO EXISTING FORECASTS.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE FOCUS FOR TONIGHT WILL BE ON KODIAK ISLAND.
WINDS AND SNOW WILL BOTH BE ON THE INCREASE AS SURFACE TROUGH AND
UPPER WAVE APPROACH THIS AFTERNOON AND EVENING. AS THE SURFACE
TROUGH CROSSES FLOW LOW LEVEL FLOW WILL VEER SLIGHTLY TOWARD THE
NORTH TO NORTH-NORTHEAST. THIS SHOULD PROVIDE JUST ENOUGH FLOW OFF
THE WATER TO CAUSE SURFACE TEMPERATURES AND DEWPOINTS TO RISE TO
AROUND FREEZING ALONG THE EAST COAST OF KODIAK ISLAND. THUS...LOW
VISIBILITIES IN BLOWING SNOW WILL NOT BE AS MUCH OF A PROBLEM FOR
KODIAK CITY. HOWEVER STILL EXPECT AREAS AWAY FROM THE COAST AS WELL
AS HIGHER ELEVATIONS TO EXPERIENCE BLIZZARD CONDITIONS. BASED ON
INTENSITY OF RETURNS ON MIDDLETON ISLAND RADAR AND THE FACT THAT
SNOW FALL COULD BE ENHANCED BY UPSLOPE FLOW ON THE NORTHEAST SIDE
OF KODIAK ISLAND...HAVE UPPED SNOW TOTALS FOR KODIAK TONIGHT.

THE TROUGH WILL CONTINUE SOUTHWARD INTO THE PACIFIC ON MONDAY AS
THE ENTIRE LOW CIRCULATION RE-CENTERS OVER THE NORTHEAST PACIFIC.
COLDER AIR WILL ONCE AGAIN FILTER SOUTHWARD FROM INTERIOR
SOUTHCENTRAL INTO THE GULF. THE ADVECTION WILL NOT BE STRONG BUT
ENOUGH TO PRODUCE AN INCREASE IN GAP WINDS ACROSS THE REGION.
OTHERWISE...DRY AND COLD CONDITIONS WILL PERSIST OVER SOUTHCENTRAL
FOR THE REST OF THE WEEK. THE GULF COAST MAY SEE ANOTHER CHANCE OF
SNOW MID WEEK AS ENERGY ROTATES AROUND THE PERIPHERY OF THE
NORTHEAST PACIFIC LOW.

SOUTHWEST ALASKA...ADDITIONAL UPPER LEVEL WAVES EMBEDDED IN THE
NORTHERLY FLOW BEHIND THE UPPER LOW WILL CROSS SOUTHWEST ALASKA AND
THE ALASKA PENINSULA TONIGHT INTO MONDAY MORNING. THIS MAY BE ENOUGH
TO KEEP HIGH WINDS GOING THROUGH THE SOUTHERN ALASKA PENINSULA...SO
WILL HAVE TO CONSIDER EXTENDING THE HIGH WIND WARNING BEYOND
MIDNIGHT. AFTER THESE UPPER WAVES MOVE THROUGH COLD ADVECTION WILL
THEN WEAKEN. HOWEVER...THE SURFACE PRESSURE GRADIENT WILL BE SLOW
TO SLACKEN OVER THE NEXT FEW DAYS. THEREFORE...EXPECT WINDS TO
GRADUALLY DIMINISH MONDAY THROUGH WEDNESDAY. SNOW SHOWERS WILL
PERSIST ALONG THE ALASKA PENINSULA WHILE THE REST OF SOUTHWEST
WILL SETTLE INTO A COLD AND DRY PATTERN.

BERING SEA/ALEUTIANS...HIGH PRESSURE WILL PERSIST ACROSS THE CENTRAL
BERING SEA. THIS MEANS THE STORM TRACK WILL REMAIN TO THE WEST...
FROM THE NORTHWEST PACIFIC NORTHWARD ACROSS THE WESTERN BERING
TO SIBERIA.

.LONG TERM FORECAST...MEDIUM RANGE MODELS CONTINUE TO DEPICT A
VERY STABLE PATTERN FOR ALASKA IN THE DAY 4 THROUGH 7 PERIOD WITH
A STRENGTHENING RIDGE OVER THE BERING SEA. THUS...EXPECT MORE OF
THE SAME...COLD AND DRY OVER MUCH OF THE FORECAST AREA. THE ONLY
EXCEPTION WILL BE THE WESTERN ALEUTIANS WHICH WILL CONTINUE TO
SIT ON THE PERIPHERY OF STRONG STORMS TRACKING JUST TO THE WEST.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 171. HIGH WIND WARNING 181.
MARINE...STORM WARNING...155 170 176.
         GALE WARNING...120 127 128 130 132 150 160 165 171 175 180.
         HEAVY FREEZING SPRAY...121 126 127 128 130 140 150 155 160
                                165 180.
FIRE WEATHER...NONE.

SEB NOV 12