Gale Warning 225, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1245 PM AKST TUE MAR 5 2013

.ANALYSIS AND UPPER LEVELS...A HIGH AMPLITUDE PATTERN IS IN PLACE
WITH A TROUGH CENTERED OVER SIBERIA AND THE WESTERN BERING SEA AND
A RIDGE CENTERED OVER MAINLAND ALASKA AND THE GULF OF ALASKA. AN
OLD FRONTAL BOUNDARY IS STRETCHED OUT ALONG THE WEST SIDE OF THE
RIDGE OVER WESTERN ALASKA. THERE WAS LITTLE PRECIP WITH THIS FRONT
OVERNIGHT...BUT A SHORT-WAVE TROUGH IS LIFTING NORTHWARD ACROSS
SOUTHWEST ALASKA THIS MORNING PRODUCING STEADIER AND HEAVIER AREAS
OF PRECIP. MOST OF THIS IS IN THE FORM OF RAIN ALTHOUGH COLDER AIR
IS SLOWLY WORKING ITS WAY IN FROM THE WEST. BENIGN CONDITIONS
DOMINATE THE REST OF THE FORECAST AREA WITH WEAK COLD ADVECTION
SHOWERS OVER MUCH OF THE BERING SEA AND CLEAR SKIES ACROSS
SOUTHCENTRAL ALASKA.

THE NEXT MAJOR STORM SYSTEM WILL COME FROM THE NORTH PACIFIC WHERE
A LOW IS BEGINNING TO DEEPEN IN THE EXIT REGION OF A 175KT PLUS
UPPER LEVEL JET.

.MODEL DISCUSSION...THERE CONTINUES TO BE MINOR TRACK ISSUES WITH
THE DEVELOPING PACIFIC SYSTEM. WITH THE CENTRAL PRESSURE EXPECTED
TO DROP INTO THE 960S PREFER THE SLOWER MOVEMENT AS DEPICTED BY
THE ECMWF/GFS/UKMET MODELS. THIS IS CLOSE TO THE INHERITED FORECAST
SO WILL NOT MAKE MANY CHANGES.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE SHORT-WAVE TROUGH MOVING INTO SOUTHWEST
ALASKA THIS MORNING WILL LIFT NORTHEASTWARD TONIGHT AND WEDNESDAY
WITH THE TAIL END PRODUCING WEAK LIFT OVER SOUTHCENTRAL ALASKA.
THIS WILL RESULT IN AREAS OF LIGHT SNOW OR FLURRIES WITH LITTLE
OR NO ACCUMULATION. THE LOW CURRENTLY DEVELOPING OVER THE NORTH
CENTRAL PACIFIC WILL TAKE A TRACK TOWARD SOUTHWEST ALASKA PUSHING
A STRONG FRONT ACROSS THE GULF THURSDAY AND THURSDAY NIGHT. THIS
IS A CLASSIC SET-UP FOR STRONG GAP WINDS AND DOWNSLOPE WINDS. MODEL
FORECAST PRESSURE GRADIENT INDICATE A GOOD CHANCE FOR REACHING HIGH
WIND THRESHOLDS ALONG WESTERN TURNAGAIN ARM...SO WILL ISSUE A WATCH
WITH THE AFTERNOON PACKAGE. THE STRONG DOWNSLOPING WINDS MEANS THE
BULK OF PRECIP WILL FALL IN PRINCE WILLIAM SOUND AND THE WEST SIDE
OF COOK INLET AND THE SUSITNA VALLEY. THE FRONT WILL BE MOVING
QUICKLY SO HEAVIEST PRECIP WILL BE OVER A FAIRLY SHORT PERIOD OF
TIME. THERE IS POTENTIAL FOR ADVISORY LEVEL SNOW AMOUNTS OVER THE
WESTERN SUSITNA WITH ENHANCEMENT FROM UPSLOPE FLOW. THE OTHER
POTENTIAL HAZARD WILL BE BLIZZARD CONDITIONS THROUGH THOMPSON PASS.
EVEN THOUGH FRONT WILL BE OCCLUDING AS IT REACHES SOUTHCENTRAL
EXPECT COMBINATION OF STRONG WINDS AND DOWNSLOPING TO PRODUCE WARM
TEMPERATURES ACROSS MUCH OF THE REGION. IT DOES LOOK LIKE COLDER AIR
WILL MOVE BACK IN BEHIND THE SYSTEM FRIDAY NIGHT AND SATURDAY.

SOUTHWEST ALASKA/BERING SEA...ASIDE FROM STRONG WINDS THE MAIN THREAT
FROM THIS DEVELOPING SYSTEM WILL BE BLIZZARD CONDITIONS. THE AIR MASS
AHEAD OF THE FRONTAL SYSTEM WILL BE COLD ENOUGH TO INITIALLY SUPPORT
SNOW. WITH GOOD UPPER LEVEL SUPPORT EXPECT STRONG UPWARD VERTICAL
MOTION TO PRODUCE MODERATE TO HEAVY PRECIP WHEN IT FIRST ARRIVES.
THE SYSTEM WILL BE MOVING AT A PRETTY GOOD PACE WHEN IT FIRST REACHES
SOUTHWEST ALASKA SO WARMER AIR WILL ALSO MOVE IN. THE QUESTION IS
WHETHER THERE IS WILL BE A LONG ENOUGH PERIOD OF SUB-FREEZING
TEMPERATURES TO PRODUCE A BRIEF BLIZZARD. THE MOST LIKELY AREAS ARE
THE WESTERN CAPES OF BRISTOL BAY UP TO THE KUSKOKWIM DELTA COAST
WHERE AIR MASS WILL START OUT A LITTLE COLDER AND WHERE NORTHERLY
WINDS WILL HOLD IN LONGER. AREAS ON THE BACK SIDE OF THE SYSTEM
(FROM THE PRIBILOF ISLANDS TO THE EASTERN ALEUTIANS) WILL HAVE A
MUCH HIGHER PROBABILITY OF BLIZZARD CONDITIONS AS ARCTIC AIR ADVECTS
SOUTHWARD.

.LONG TERM FORECAST...THE STORM SYSTEM TRACKING TO SOUTHWEST ALASK
WILL EXIT TO THE NORTH THIS WEEKEND. MODELS THEN INDICATE A STRONG
BLOCKING RIDGE SETTING UP SHOP OVER MAINLAND ALASKA EARLY NEXT WEEK.
THIS MEANS STORM TRACK WILL BE HELD WEST OF THE RIDGE OVER THE
WESTERN BERING SEA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WATCH 185.
MARINE...STORM WARNING...132 150 155 160 170.
         GALE WARNING 130 138 165 171 172 179 180.
FIRE WEATHER...NONE.

SEB MAR 13