Blizzard and Heavy Snow in Alaska, February 25 to 27, 2012

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKST FRI FEB 24 2012

.ANALYSIS AND UPPER LEVELS...
SURFACE TROUGH ALONG THE NORTHERN GULF COAST THIS MORNING WITH
MODERATE WESTERLY GAP WINDS CONTINUING IN PRINCE WILLIAM SOUND. UPPER
LEVEL TROUGH HAS NOT PUSHED THROUGH SOUTH CENTRAL ALASKA YET.
THEREFORE...FLURRIES CONTINUE AROUND THE KENAI...ANCHORAGE AND MATSU
AREAS. SOUTHWEST ALASKA STILL STUCK IN STRATUS AHEAD OF THE WEAKENING
FRONT IN THE EASTERN BERING. THIS FRONT DOES NOT HAVE GREAT UPPER
LEVEL JET SUPPORT AND THE PRESSURE GRADIENT IS NOT STRONG. BETWEEN
THESE TWO FEATURES...AN AREA OF HIGH PRESSURE TO SWING ACROSS
SOUTHWEST ALASKA INTO SOUTH CENTRAL ALASKA TONIGHT. IN THE NORTH
PACIFIC...THE LARGE LOW IS APPROACHING ATTU ISLAND AND WINDS ARE
INCREASING. THIS LOW IS STACKED VERTICALLY WITH A STRONG JET STREAM
ON THE SOUTHERN EDGE HELPING TO INTENSIFY ITS FRONTAL STRUCTURE WHICH
IS APPROACHING THE WESTERN ALEUTIAN CHAIN.

.MODEL DISCUSSION...
MODELS ARE IN GREAT AGREEMENT IN THE SHORT AND MID TERM AS WOULD BE
EXPECTED WITH A DOMINATING LOW MOVING INTO THE PICTURE THIS WEEKEND.
AHEAD OF THE LARGE LOW IN THE BERING...A WEAKENING FRONT IS IN THE
EASTERN BERING SEA. THE FRONT WILL MOVE ONSHORE TONIGHT. SMALL AREA
OF LOW PRESSURE IN BRISTOL BAY ALONG THE FRONT TO DISSIPATE TONIGHT.
AN AREA OF LOW PRESSURE REMAINS IN THE NORTHERN GULF WITH SOME GOOD
WESTERLY GAP WINDS WILL DISSIPATE TONIGHT AS THE PARENT LOW DRAGS
INTO BRITISH COLUMBIA. THE LARGE LOW WILL DOMINATE THE WEATHER
PATTERN THROUGH THE WEEKEND. THE LOW WILL MOVE THROUGH THE BERING
SLOWLY AND INTO THE GULF OF ALASKA SUNDAY NIGHT AS ANOTHER LOW
DEVELOPS NEAR THE KAMCHATKA PENINSULA. THE GULF LOW WILL REMAIN
THROUGH TUESDAY. OUT NEAR THE KAMCHATKA LOW IS WHERE THE
DISCREPANCIES START TO SHOW THEIR WEARS.

IN THE LONG TERM THE MODELS DIVERGE SIGNIFICANTLY AND OVERALL
CONFIDENCE IS LOW SO HPC GUIDANCE WAS PREFERRED.

.SHORT TERM FORECAST...
SOUTHCENTRAL...
UPPER LEVEL TROUGH SWINGING THROUGH THE AREA THIS AFTERNOON AND
TONIGHT WITH LIGHT SNOW ENDING FROM THE WEST. CLEARER SKIES TONIGHT
MAKING FOR POSSIBLE AREAS OF FOG. THE PRESSURE GRADIENT IN THE AREA
HAS CREATED SOME MODERATE WESTERLY AND NORTHERLY GAP WINDS THROUGH
THE SOUND. THE AREA OF LOW PRESSURE WILL WEAKEN TONIGHT RESULTING IN
LIGHTER WINDS BY MIDNIGHT. A WEAK FRONT IN THE EASTERN BERING TO PUSH
OVER THE AREA TOMORROW AFTERNOON/EVENING WITH A FEW SHOWERS EXPECTED.
THE BIG LOW IN THE BERING WILL THEN BE THE PLAYER FOR THE WEEKEND.
THE ASSOCIATED FRONT TO AFFECT KODIAK ISLAND SATURDAY EVENING THEN
ROLL UP TO THE NORTHER GULF COAST LATE SATURDAY NIGHT. MODERATE TO
STRONG WINDS AND PRECIPITATION ARE ANTICIPATED WITH THIS FRONT AND
LOW PRESSURE SYSTEM. BLIZZARD WATCHES WILL BE IN EFFECT ALONG
TURNAGAIN ARM WITH SOME AREAS OF HEAVY SNOW ALONG THE COAST AND UP
THE MATSU VALLEY. THERE IS GOOD UPPER LEVEL JET SUPPORT WITH THIS
FRONT WITH ABOVE NORMAL MOISTURE. THE SOUTHWEST FLOW ALOFT WILL BRING
ALL THIS MOISTURE FURTHER INLAND AND CREATE AN OPTIMAL UPSLOPE
PATTERN INTO THE SUSITNA VALLEY. FURTHERMORE...THE SOUTHWEST FLOW
WILL ALLOW AN UNUSUAL EVENT TO HAPPEN IN THE ANCHORAGE BOWL TO HAVE
STRONG TURNAGAIN ARM WIND AND SNOW. THE LOW WILL ANCHOR IN THE GULF
MONDAY WITH SNOW WRAPPING THE NORTHERN GULF COAST THROUGH TUESDAY.
THE SNOW OVER THE INLAND AREAS WILL TAPER OFF MONDAY INTO TUESDAY.

SOUTHWEST ALASKA...
A WEAK FRONT SITS OFF THE WESTERN ALASKA COAST THIS AFTERNOON. THE
FRONT WILL PUSH ONSHORE TONIGHT WITH SOME AREAS OF BLOWING SNOW AND
REDUCED VISIBILITY ALONG THE WESTERN CAPES AND IMMEDIATE KUSKO DELTA
COAST. SNOW WILL SPREAD INLAND OVERNIGHT AND TOMORROW. SNOW AMOUNTS
ARE ANTICIPATED TO BE LIGHT. THE BERING LOW TO MOVE INTO THE WESTERN
BERING SATURDAY AFTERNOON. ITS ASSOCIATED FRONT WILL MOVE TO THE
COAST LATE SATURDAY AFTERNOON/EARLY EVENING. THIS FRONT HAS GREAT JET
SUPPORT AND MODERATE TO STRONG SURFACE WINDS AS IT PUSHES THE HIGH
OVER THE NORTHERN BERING OUT OF THE WAY. HAVE ISSUED A WINTER STORM
WATCH FOR SOUTHWEST ALASKA STARTING LATE TOMORROW AFTERNOON. AS THE
FRONT HITS THE COAST...THERE COULD BE A PERIOD OF STRONG WINDS AND
HEAVY SNOW PRODUCING BLIZZARD CONDITIONS. THERE IS A BIT OF
UNCERTAINTY AS TO THE STRENGTH OF THE WIND. IT IS ANTICIPATED THAT
LARGE AMOUNTS OF SNOW WILL FALL OVER THE AREA SATURDAY NIGHT WITH
GOOD ONSHORE FLOW AND AMPLE MOISTURE AND UPPER LEVEL SUPPORT. SNOW
SHOWERS WILL CONTINUE SUNDAY AND MONDAY AS THE LOW MOVES INTO THE
EASTERN BERING AND INTO THE GULF BY MONDAY MORNING.

BERING SEA AND ALEUTIANS...FRONT IS MOVING THROUGH THE EASTERN
ALEUTIANS THIS AFTERNOON WITH MODERATE SNOW AND RAIN. THIS FRONT WILL
BE OUT OF THE AREA AFTER MIDNIGHT. BIG LOW OVER THE NORTH PACIFIC
APPROACHING THE WESTERN ALEUTIANS THIS AFTERNOON WITH A STRONG FRONT.
GALE FORCE WINDS AND HEAVY PRECIPITATION WILL ACCOMPANY THE FRONT
WHILE IT MOVES TO THE CENTRAL ALEUTIANS TOMORROW. WE DO NOT EXPECT
ANY BLIZZARD CONDITIONS ALONG THE ALEUTIANS ONCE AGAIN AS THE SYSTEM
IS TOO WARM. HOWEVER...BLIZZARD CONDITIONS CAN BE EXPECTED ONCE AGAIN
AS THE FRONT REACHES THE PRIBILOFS LATE TOMORROW MORNING. THE LOW
WILL WEAKEN SLOWLY AS IT MOVES ACROSS THE BERING SATURDAY AND SUNDAY.
EXPECT MODERATE SNOW SHOWERS AROUND THE LOW. ON THE BACKSIDE OF THE
LOW...COLD AIR TO RETURN TO THE NORTHERN BERING AND MODERATE
NORTHWEST FLOW. SO WE CAN EXPECT SCATTERED TO NUMEROUS SHOWERS IN THE
NORTHWEST FLOW IMPINGING ON THE BERING SIDE OF THE ALEUTIAN CHAIN
MONDAY.

.LONG TERM FORECAST...
THE AMPLIFIED PATTERN WE HAVE BEEN SEEING WILL CONTINUE THROUGH MOST
OF THE LONG TERM AS WELL BRINGING A SERIES OF RIDGES AND LOWS THROUGH
THE AREA. FINALLY BY LATE NEXT WEEK THE PATTERN WILL START TO CHANGE
AS A LONG WAVE TROUGH BEGINS TO SETUP OVER THE STATE EXTENDING OVER
THE BERING SEA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING...195
         WINTER STORM WATCH...121 145 152 155 161
         BLIZZARD WATCH...101 125
MARINE...STORM WARNING...172 175 176 185
         GALE WARNING...155 160 165 180 170 171 179
         HEAVY FREEZING SPRAY WARNING...121 126 127 129 130 179
FIRE WEATHER...NONE

JN FEB 12