Blizzard in Alaska, March 25 to 26, 2012

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1140 AM AKDT SUN MAR 25 2012

.ANALYSIS AND UPPER LEVELS...UPPER LEVEL FLOW IS NEARLY ZONAL WHICH
IS PRODUCING A PROGRESSIVE PATTERN ACROSS THE NORTH PACIFIC. THERE
IS A MORE AMPLIFIED TROUGH OVER THE GULF AND NORTHEAST PACIFIC WHICH
WILL CAUSE STORMS MOVING IN FROM THE WEST TO DROP SOUTHEASTWARD AWAY
FROM MAINLAND ALASKA. A LOOK AT SATELLITE IMAGERY THIS MORNING SHOWS
A STRONG LOW (ESTIMATED SURFACE PRESSURE OF 970 MB) TRACKING
EAST-NORTHEAST ACROSS THE WESTERN ALEUTIANS AND INTO THE SOUTHERN
BERING SEA. TEMPERATURES OUT AHEAD OF THIS SYSTEM ARE MUCH WARMER
THAN THEY WERE AHEAD OF THE SYSTEM WHICH CAME THROUGH A FEW DAYS
AGO. IT IS STILL COLD ENOUGH FOR SNOW ALONG THE LEADING EDGE OF
PRECIPITATION...BUT DON'T EXPECT BLOWING SNOW TO BE AS MUCH OF A
PROBLEM.

MEANWHILE...HIGH PRESSURE CENTERED OVER SOUTHWEST ALASKA HAS LED TO
SOME STEEP SURFACE BASED INVERSIONS AS SEEN IN THE BETHEL AND KING
SALMON SOUNDINGS. THUS AREAS OF FOG HAVE FORMED MOST NOTABLY ACROSS
THE KUSKOKWIM DELTA WHERE VISIBILITIES ARE NEAR ZERO.

A LOOK AT SOUTHCENTRAL ALASKA SHOWS A WEAK SHORT-WAVE TROUGH OVER
THE SUSITNA VALLEY MOVING EASTWARD. THERE ARE SOME SHOWERS ALONG
THE NORTH GULF COAST ASSOCIATED WITH A WEAK LOW OVER THE CENTRAL
GULF. THE UPPER TROUGH WILL MAKE USE OF THIS MOISTURE TO PRODUCE
SNOW SHOWERS TODAY FROM EASTERN PRINCE WILLIAM SOUND TO THE COPPER
RIVER BASIN.

.MODEL DISCUSSION...THE ECMWF CONTINUES TO BE THE MOST CONSISTENT
MODEL AND IS PREFERRED. CURRENT FORECAST IS GENERALLY ON TRACK AND
ONLY MINOR CHANGES WILL BE MADE.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...SNOW SHOWERS WILL END ACROSS THE COPPER RIVER
BASIN TONIGHT AS WEAK SHORT-WAVE EXITS TO THE EAST. HOWEVER...EXPECT
LOW LEVEL MOISTURE TO REMAIN IN THE PRINCE WILLIAM SOUND AREA AND
CONTINUE TO PRODUCE A FEW SHOWERS. A WEAK UPPER LEVEL RIDGE WILL
MOVE OVER SOUTHCENTRAL ALASKA AND THE GULF. AS ENERGY FROM THE
BERING STORM DIVES DOWN INTO THE NORTHEAST PACIFIC TONIGHT AND
MONDAY A WARM FRONT WILL MOVE NORTHWARD INTO THE GULF. THIS WILL
BRING LIGHT PRECIP TO PORTIONS OF THE GULF COAST BY MONDAY NIGHT.
AN UPPER LEVEL TROUGH WILL THEN LIFT NORTHWARD UP THE WEST SIDE
OF THE RIDGE TUESDAY...SPREADING MOISTURE NORTHWARD. FAIRLY STRONG
EASTERLY FLOW WILL DOWNSLOPE OUT THE USUAL AREAS...SO THE MAIN
IMPACT WILL BE CLOUD COVER. PRECIP WILL PERSIST THROUGH MID WEEK
ALONG THE COAST KODIAK ISLAND AND THE WEST SIDE OF COOK INLET.
TEMPERATURES WILL STEADILY WARM AND CHANGE PRECIP TO MOSTLY RAIN.

SOUTHWEST ALASKA...THE STRONG STORM OVER THE SOUTHERN BERING WILL
RAPIDLY WEAKEN AS UPPER LEVEL ENERGY DIVES SOUTHEASTWARD INTO THE
PACIFIC ON MONDAY. THIS WILL KEEP THE BRUNT OF THE STORM FROM
REACHING SOUTHWEST ALASKA. DO EXPECT AREAS OF LIGHT SNOW AND A
LITTLE BIT OF WIND TO REACH THE COAST. THE WARM FRONT THAT MOVES
INTO THE GULF MONDAY NIGHT WILL ALSO SPREAD MOISTURE OVER TO
SOUTHWEST ALASKA TUESDAY AND THEN UPPER TROUGH WILL SWING NORTHWARD
AND HELP ENHANCE SNOWFALL. HOWEVER...STRONG EASTERLY FLOW WILL
RESULT IN DOWNSLOPE DRYING ON THE WEST SIDE OF MOUNTAINS.

BERING SEA/ALEUTIANS...BERING SYSTEM WILL TRACK EASTWARD TONIGHT
AND CONTINUE TO PACK A PUNCH WITH HIGH END GALES ON THE FRONT SIDE
OF THE SYSTEM AND STORM FORCE WINDS ON THE BACK SIDE. CONDITIONS
WILL RAPIDLY IMPROVE DURING THE DAY MONDAY AS UPPER LEVEL ENERGY
DIVES SOUTHEASTWARD INTO THE PACIFIC LEAVING A WEAK REMNANT LOW
IN THE BERING. THE NEXT SYSTEM WILL TRACK FARTHER SOUTH PASSING
JUST SOUTH OF THE ALEUTIAN CHAIN MONDAY NIGHT AND TUESDAY AND
THEN SOUTHEASTWARD INTO THE HIGH AMPLITUDE TROUGH OVER THE
NORTHEAST PACIFIC TUESDAY NIGHT. COLD AIR WILL MOVE BACK IN
BEHIND THIS SECOND SYSTEM AND RESUME A SNOW SHOWER REGIME ACROSS
THE REGION.

.LONG TERM FORECAST...LATE NEXT WEEK THE PATTERN WILL BEGIN TO
AMPLIFY WITH THE TROUGH OVER THE NORTHEAST PACIFIC BECOMING EVEN
MORE AMPLIFIED AND A RIDGE BUILDING OUT AHEAD OF A DEVELOPING
PACIFIC SYSTEM. MODELS AGREE ON THE GENERAL EVOLUTION OF THE
PATTERN CHANGE BUT DIFFER ON PLACEMENT OF SYSTEMS WITHIN IT.
UNTIL THIS PATTERN CHANGE TAKES PLACE STORM TRACK WILL REMAIN
ALONG THE SOUTHERN TIER OF THE FORECAST AREA KEEPING MAINLAND
ALASKA ON THE DRY SIDE.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...STORM WARNING...172 175.
         GALE WARNING...155 165 170 176 179 180 185.
FIRE WEATHER...NONE.

SEB MAR 12