Blizzard Watch 20, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1225 PM AKDT THU MAR 14 2013

.ANALYSIS AND UPPER LEVELS...A LARGE CLOSED UPPER LEVEL LOW IS
TRACKING WESTWARD ACROSS MAINLAND ALASKA UNDERNEATH A CLOSED HIGH
CENTERED OVER THE BEAUFORT SEA. A WEAK UPPER LEVEL WAVE ON THE EAST
SIDE OF THE LOW ALONG WITH A SURFACE LOW OVER THE NORTHWEST GULF
ARE BRINGING AREAS OF SNOW TO SOUTHCENTRAL ALASKA...PRIMARILY IN
COASTAL AREAS. A TROUGH EXTENDING SOUTHWARD FROM THE LOW CENTER IS
ROTATING EAST-NORTHEASTWARD. AREAS OF SNOW HAVE DEVELOPED OUT AHEAD
OF THIS TROUGH FROM BRISTOL BAY TO THE SOUTH END OF KODIAK ISLAND.

MEANWHILE AN ANCHOR (UPPER LEVEL) LOW IS CENTERED NEAR THE KAMCHATKA
PENINSULA. A DEEP SURFACE LOW IS NEARLY STATIONARY UNDERNEATH THE
UPPER CENTER WHILE A STRONG FRONTAL SYSTEM IS PROGRESSING EASTWARD
ACROSS THE WESTERN BERING AND ALEUTIANS.

.MODEL DISCUSSION...MODELS ARE INCONSISTENT WITH HANDLING OF WEAK
LOWS OVER THE NEXT COUPLE DAYS. THE DIFFERENCES IN POSITION WON'T
HAVE A HUGE IMPACT ON THE FORECAST...SO WILL GENERALLY TREND THE
FORECAST TOWARD A MIDDLE GROUND SOLUTION.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE SURFACE LOW OVER THE NORTHWEST GULF WILL
DISSIPATE THIS AFTERNOON OVER THE KENAI PENINSULA WHILE THE UPPER
LEVEL WAVE EXITS TO INTERIOR ALASKA. AS A RESULT SNOW WILL TAPER
OFF ACROSS SOUTHCENTRAL THIS AFTERNOON AND EVENING. MEANWHILE THE
UPPER TROUGH AXIS ALONG THE ALASKA PENINSULA WILL SLOWLY PIVOT
NORTHEASTWARD AS THE UPPER LOW CONTINUES A WESTWARD MOVEMENT TOWARD
THE EASTERN BERING. THIS WILL CAUSE AN INCREASE IN SNOW OVER KODIAK
ISLAND AS WE HEAD THROUGH THIS AFTERNOON AND EVENING. THIS TROUGH
WILL SHEAR APART FRIDAY AND FRIDAY NIGHT AS THE NORTHERN HALF IS
FORCED NORTHWARD AND THE SOUTHERN HALF IS FORCED EASTWARD. BY THE
TIME IT REACHES SOUTHCENTRAL THERE VERTICAL MOTION WILL BE VERY
WEAK SO DON'T EXPECT MORE THAN A FEW SHOWERS ALONG THE COAST.

MEANWHILE A LOW OVER THE NORTHEAST PACIFIC WILL CROSS THE EASTERN
GULF TONIGHT AND FRIDAY AND DISSIPATE SOMEWHERE OVER THE NORTHEAST
GULF FRIDAY NIGHT. THE LOW WILL BE WEAK AND HAVE A SMALL AREA OF
INFLUENCE SO EXPECT LITTLE IMPACT ON SOUTHCENTRAL...PERHAPS A
LITTLE BIT OF SNOW IN THE FAR EASTERN COPPER BASIN AND SOUTHEAST
PRINCE WILLIAM SOUND AREAS (DEPENDING ON THE EXACT TRACK OF THE LOW).

AS WE HEAD INTO THE WEEKEND THE FRONT CROSSING THE BERING WILL
REACH THE SOUTHWEST GULF. HOWEVER...ALL MODELS INDICATE FORMATION
OF A LOW SOUTH OF KODIAK ISLAND AND A PROGRESSIVE UPPER TROUGH...
BOTH OF WHICH WILL KEEP MOISTURE FROM MAKING IT TO THE REST OF
SOUTHCENTRAL. THUS THE GENERAL DRY AND COOL PATTERN WILL PERSIST
FOR MUCH OF SOUTHCENTRAL ALASKA (ESPECIALLY INLAND AREAS).

SOUTHWEST ALASKA...AS THE UPPER LOW CONTINUES WESTWARD THIS
AFTERNOON AND EVENING AND THE TROUGH EXTENDING SOUTHWARD PIVOTS
TOWARD SOUTHWEST ALASKA SNOW WILL SPREAD NORTH AND WESTWARD.
THE SNOW WILL SET UP IN A ZONE RIGHT AHEAD OF THE TROUGH FROM
BRISTOL BAY TO INTERIOR KUSKOKWIM DELTA. AREAS NORTH OR SOUTH
OF THIS ZONE WILL STAY DRY. THIS ZONE OF SNOW WILL PUSH INLAND
AND TAPER OFF ON FRIDAY AS THE UPPER TROUGH SHEARS APART. THE
FRONT CROSSING THE BERING SEA WILL BRING ANOTHER ROUND OF SNOW
AS IT REACHES THE SOUTHWEST COAST FRIDAY NIGHT. EXPECT A TRIPLE
POINT LOW TO DEVELOP NORTH OF THE PRIBILOF ISLANDS AND TRACK JUST
WEST OF THE KUSKOKWIM DELTA. THIS MIGHT STRENGTHEN WINDS JUST
ENOUGH TO CAUSE BLIZZARD CONDITIONS. WILL ISSUE A BLIZZARD WATCH
WITH THE AFTERNOON PACKAGE. EXPECT ANOTHER TRIPLE POINT LOW TO
DEVELOP SOUTH OF THE ALASKA PENINSULA FRIDAY NIGHT AND TRACK INTO
THE GULF. WITH THE TWO LOWS MOVING IN OPPOSITE DIRECTIONS SNOW
WILL DIMINISH AS IT HEADS INLAND OVER SOUTHWEST ALASKA SATURDAY
AND SATURDAY NIGHT.

BERING SEA/ALEUTIANS...THE BERING SEA AND ALEUTIANS WILL INITIALLY
SEE A PERIOD OF WESTERLIES ALOFT...WITH ENERGY EXITING THE SOUTH
SIDE OF THE ANCHOR LOW OVER KAMCHATKA. AS WE HEAD INTO THE WEEKEND
ONE OF THESE SHORT-WAVES WILL DIG SOUTHEASTWARD INTO THE NORTH
PACIFIC AND CAUSE AMPLIFICATION OF THE UPPER LEVEL PATTERN. THIS
WILL RESULT IN DEVELOPMENT OF A DEEP LOW OVER THE NORTH PACIFIC ON
SUNDAY...POSSIBLY IMPACTING THE ALEUTIANS AS WE HEAD INTO MONDAY.

.LONG TERM FORECAST...A HIGH AMPLITUDE RIDGE WILL BECOME
RE-ESTABLISHED OVER THE EASTERN BERING SEA LATE THIS WEEKEND INTO
EARLY NEXT WEEK. MEDIUM RANGE MODELS INDICATE WEAKENING OF THIS
RIDGE AS WE HEAD THROUGH NEXT WEEK...BUT REMAINING STRONG ENOUGH
TO KEEP STORMS CONFINED TO THE CENTRAL TO WESTERN BERING SEA AND
ALEUTIANS. MAINLAND ALASKA WILL BE COLD AND DRY AS ARCTIC AIR MOVES
DOWN THE EAST SIDE OF THE RIDGE. THIS WILL LIKELY RESULT IN ANOTHER
STRONG WIND EVENT ALONG THE GULF COAST BY THE MIDDLE OF NEXT WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING...130 172 175 176 179 180 185.
         HEAVY FREEZING SPRAY WARNING...126 127 128 130 140 141
                                        160 165 179.
FIRE WEATHER...NONE.

SEB MAR 13