Blizzard in Alaska, April 5, 2010

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
1210 PM AKDT SUN APR 4 2010

.ANALYSIS AND UPPER LEVELS...A NEAR ZONAL UPPER JET EXTENDS EASTWARD
ACROSS THE ALEUTIANS BEFORE DIVING SOUTHWARD AS IT REACHES THE
GULF...HEADING AROUND A POTENT SYSTEM SITTING OFF THE NORTHWEST
U.S. COAST. A DEEP COLD LOW IS CENTERED OVER THE NORTH CENTRAL
BERING WITH A TROUGH AXIS EXTENDING SOUTHEASTWARD ALONG THE
SOUTHWEST ALASKA COAST AND KODIAK ISLAND INTO THE NORTHEAST PACIFIC.
THE STRONG JET AND ZONAL FLOW ARE PRODUCING A VERY PROGRESSIVE
PATTERN. THE TROUGH AXIS IS LIFTING NORTHWARD HELPING TO PULL BACK
A WEAK SURFACE LOW OVER THE GULF NORTHWESTWARD TOWARD THE KENAI
PENINSULA. THERE IS A BAND OF STEADY SNOW RIGHT AHEAD OF THE TROUGH
AXIS FROM THE NORTH END OF KODIAK ISLAND TO INTERIOR BRISTOL BAY.
ELSEWHERE ACROSS SOUTHCENTRAL...SHOWERS ASSOCIATED WITH WEAK WAVES
EMBEDDED IN THE UPPER FLOW CONTINUE TO MOVE ACROSS THE
REGION...MAINLY AFFECTING COASTAL AND UPSLOPE AREAS. MEANWHILE...A
COUPLE SURFACE LOWS CONTINUE TO RIDE THE JET EASTWARD ACROSS THE
BERING. THE MOST SIGNIFICANT OF THESE IS THE ONE NEAR THE PRIBILOF
ISLANDS THIS MORNING. A TIGHT THERMAL GRADIENT ON THE BACK SIDE OF
THIS LOW IS HELPING TO KICK WINDS UP TO 35 TO 40 KT.

.MODEL DISCUSSION...MODELS ARE IN GOOD AGREEMENT THROUGH TUESDAY
AND SHOW GOOD RUN-TO-RUN CONSISTENCY...SO CHANGES TO THE FORECAST
WILL BE MINOR. AFTER THAT POINT SOLUTIONS DIVERGE WITH TRACK OF
DEEP LOW SOUTH OF THE ALEUTIANS TUESDAY NIGHT THROUGH THURSDAY
WITH THE GFS/NAM NOTABLY FASTER THAN THE EC/UKMET. BECAUSE STRONG
JET REMAINS IN PLACE PREFER TO GO WITH THE FASTER SOLUTION FOR NOW.

.SHORT TERM FORECAST...AS THE UPPER TROUGH AXIS CONTINUES TO MOVE
NORTHWARD TONIGHT STEADY PRECIP...MAINLY IN THE FORM OF SNOW...SILL
MOVE INTO WESTERN PRINCE WILLIAM SOUND...SOUTH OF CLAM GULCH ON THE
WESTERN KENAI...AND OVER TO INTERIOR SOUTHWEST ALASKA. THIS TROUGH
WILL THEN QUICKLY FALL APART AS IT ROTATES NORTHWESTWARD AROUND THE
BERING LOW CENTER MONDAY. SO PRECIPITATION WILL ALSO BREAK UP AND
BECOME MORE SHOWERS AGAIN BEFORE IT MAKES MUCH PROGRESS INLAND
ACROSS SOUTHCENTRAL. THE UPPER LOW WILL GRADUALLY MOVE TO THE GULF
BY MID WEEK. AS IT DOES SO UPPER WAVES EMBEDDED WITHIN ITS CYCLONIC
FLOW WILL CONTINUE TO ROTATE ACROSS THE REGION FROM THE GULF AND
SOUTHCENTRAL TO SOUTHWEST ALASKA AND THE EASTERN BERING. THE
CHALLENGE WILL BE IN TRYING TO TIME INDIVIDUAL WAVES. MOST OF THE
PRECIP WILL BE ALONG THE COAST AND IN UPSLOPE AREAS...BUT OTHER
EVERYONE WILL HAVE A CHANCE OF PRECIP AS EACH WAVE MOVES THROUGH.

OUT WEST...THE SURFACE LOW NEAR THE PRIBILOF ISLANDS WILL DISSIPATE
TONIGHT AS IT TRACKS TOWARD THE ALASKA PENINSULA. HOWEVER...A BROAD
AREA OF WEAK COLD ADVECTION WILL CONTINUE ACROSS THE BERING INTO
TUESDAY...RESULTING IN CONTINUED GUSTY WINDS AND SNOW SHOWERS. THE
NEXT LOW MOVING OUT OF RUSSIA WILL THEN MOVE ACROSS THE WESTERN
BERING TUESDAY...BUT A DEEP LOW FROM THE TROPICS WILL BE THE MAJOR
PLAYER AS WE HEAD THROUGH MID WEEK...WITH AN EXPECTED TRACK JUST
SOUTH OF THE ALEUTIANS.

.LONG TERM FORECAST...THE SYSTEM TRACKING SOUTH OF THE ALEUTIANS
MID WEEK SHOULD REMAIN SAFELY SOUTH OF THE GULF AND MAINLAND ALASKA
AS IT CONTINUES TO TRACK EASTWARD LATE NEXT WEEK. MEDIUM RANGE
MODELS THEN INDICATE AMPLIFICATION OF THE PATTERN AS A TROUGH DIGS
SOUTHEASTWARD OUT OF EASTERN RUSSIA WEDNESDAY AND THURSDAY CAUSING
A RIDGE TO BUILD OVER THE BERING SEA. ALTHOUGH THERE IS HIGH
UNCERTAINTY IN THE DETAILS OF THIS...THERE IS MODERATE CONFIDENCE
IN THE EVOLUTION OF THE LONG-WAVE. SO...WITH THE BUILDING RIDGE
MAINLAND ALASKA SHOULD CLEAR OUT AT THE END OF NEXT WEEK WHILE A
MAJOR STORM MOVES INTO THE BERING ON THE WEST SIDE OF THE RIDGE.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING 120 125 129 155 165 170 171 172 175 176.
         HEAVY FREEZING SPRAY WARNING...165.
FIRE WEATHER...NONE.

SEB APR 10