Heavy Freezing Spray Warning 103, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 PM AKDT SUN MAR 11 2012

.MODEL DISCUSSION...THE BIGGEST MODEL ISSUE MAY BE IN THE VERY SHORT
TERM IN THE GULF OF ALASKA WITH A SECONDARY LOW THAT IS JUST SOUTH OF
MIDDLETON ISLAND. ALL OF THE MODELS RESOLVE THE MAIN LOW BUT THEY ALL
MISSED THE DEVELOPMENT OF THE SECONDARY ONE ON ITS HEELS. THE NAM IS
PROBABLY THE CLOSEST AS IT DOES SHOW A TROUGH IN THE AREA OF THE LOW.

IN THE WEST...MODELS ADEQUATELY CAPTURE THE MAIN PICTURE. THE PACIFIC
LOW WILL TRACK TOWARDS SHEMYA MON MORNING AT PEAK INTENSITY...THEN
DRIFT SOUTHEAST TOWARDS NIKOLSKI LATE MON NIGHT. THE GFS SEEMS TO
SLOW...LAGGING A RESIDUAL LOW AROUND UNALASKA THROUGH TUESDAY NIGHT.
HOWEVER THE 180 KT UPPER JET SUPPORTING THIS SYSTEM CLIPS THE
ALEUTIAN CHAIN AND ADVANCES SOUTHEAST BACK INTO THE NORTH PACIFIC. WE
TEND TO BELIEVE THE ECMWF WHICH SHEARS OUT THE LOBE BY DRAGGING THE
LION'S SHARE OF ENERGY AWAY FROM THE AOR. OUTSIDE OF THIS
THOUGH...MODELS AGREE ON A CONTINUED SHOWERY PATTERN ACROSS THE
BERING SEA/CHAIN THE NEXT SEVERAL DAYS.

.ANALYSIS AND UPPER LEVELS...
A BROAD UPPER LOW ROTATES IN THE GULF OF ALASKA TODAY. FURTHER OUT
WEST...A STRONG KAMCHATKA UPPER LOW/SURFACE LOW COMBO BRINGS STRONG
WINDS AND RAIN TO THE WESTERN ALEUTIANS. BETWEEN THE TWO SYSTEMS A
BRISK NORTHERLY FLOW OVER THE EASTERN ALEUTIANS AND ALASKA PENINSULA
IS AIDING IN THE DEVELOPMENT OF SNOW SHOWERS OVER BRISTOL BAY. THE
CLASH BETWEEN THE WARM AIR BROUGHT NORTH BY THE WESTERN SYSTEM AND
THE COLD AIR SINKING SOUTH BEHIND THE EASTERN TROUGH IS DRIVING THE
JET STREAM IN AN AMPLIFIED PATTERN TODAY.

ACROSS THE SOUTHWEST MAINLAND COLD AND DRY CONDITIONS PERSIST WITH
ARCTIC HIGH PRESSURE PREDOMINANT. BRISK NORTH FLOW OFF OF THE ICE
EDGE CONTINUES TO PRODUCE SNOW SHOWERS ALONG THE AKPEN...THOUGH THESE
LOOK TO DIMINISH AS THE FLOW BECOMES MORE EASTERLY TONIGHT. THE
SIGNIFICANT FEATURE OF CONCERN IS THE PACIFIC LOW AROUND 400 MILES
SOUTHWEST OF SHEMYA. A SLUG OF SNOW AND RAIN ENVELOPS THE ALEUTIAN
CHAIN NOSING EASTWARD. STORM FORCE WINDS ARE ADVANCING AHEAD OF THIS
STRONG LOW.

.SHORT TERM FORECAST...
SOUTHCENTRAL...STRONG WINDS THROUGH CHANNELED TERRAIN REMAINS THE
STORY IN SOUTHCENTRAL ALASKA. THE TIGHT PRESSURE GRADIENT DUE TO THE
LOW IN THE GULF AND HIGHER PRESSURE INLAND CONTINUES TO BRING STRONG
GUSTY WINDS TO AREAS AROUND PRINCE WILLIAM SOUND AND KODIAK ISLAND.
THIS LOW WILL SOON TRACK SOUTH AND WEAKEN AS IT HEADS IN THAT
DIRECTION WHICH WILL WEAKEN THE GRADIENT AND CAUSE THE WINDS TO
DIMINISH. THIS DOWNWARD TREND OF WIND SPEEDS WILL HAPPEN OVERNIGHT
AND THE STRONG GUSTS WILL BE GONE BY MONDAY AFTERNOON.

INVERTED TROUGHS CIRCULATING AROUND THE LOW IN THE GULF WILL CONTINUE
TO BRING SNOW SHOWERS TO THE PRINCE WILLIAM SOUND AREA THIS EVENING
BUT WILL DIE DOWN AS THE LOW TRACKS TO THE SOUTH. THE LOW WILL ALSO
TAKE MUCH OF THE CLOUD COVER WITH IT CLEARING OUT THE SKIES OVER MANY
AREAS OF SOUTHCENTRAL ALASKA. THIS WILL BRING COLDER TEMPS IN THE
OVERNIGHT AND EARLY MORNING HOURS.

SOUTHWEST...
LOOK FOR COLD AND MOSTLY CLEAR CONDITIONS THE NEXT COUPLE OF DAYS
COURTESY OF A BUILDING RIDGE. ADVISORY LEVEL WIND CHILL THREATS STILL
LOOMS THOUGH AS THE PRESSURE GRADIENT ONCE AGAIN STRENGTHENS ALONG
THE PERIPHERY OF THE BERING/ALEUTIAN SYSTEM MONDAY EVENING. AN
UPPER-LOW OVER THE CENTRAL INTERIOR BEGINS TO DRIFT TOWARDS THE
KUSKOKWIM VALLEY TUESDAY. THIS LOOKS TO BRING AN INCREASED RISK OF
SNOW SHOWERS BACK TO THE REGION. THE INCREASED CLOUDINESS HOWEVER
ALSO SHOULD TEMPER OVERNIGHT LOWS A BIT ACROSS INTERIOR AREAS.

BERING SEA/ALEUTIANS...
SOUTHEAST WINDS WILL BEGIN TO SHIFT TO THE WEST ON MONDAY AS THE
FRONT ASSOCIATED WITH THE PACIFIC LOW MOVES THROUGH. COLD ADVECTION
ON THE BACKSIDE OF THE SYSTEM IS NOT PARTICULARLY STRONG...BUT WHEN
COUPLED WITH VERY STRONG PRESSURE RISES...WE EXPECT HURRICANE FORCE
WINDS THROUGH THE WESTERN CHAIN ON MONDAY...AND STORM FORCE WINDS
ACROSS THE REMAINDER OF THE BERING/CHAIN. THE FRONT WILL ADVANCE TO
NEAR THE PRIBILOF ISLANDS WHERE SNOW AND BLOWING SNOW MAY BRING
BLIZZARD CONDITIONS. THE MAIN UNCERTAINTY IS THE PRECIPITATION
INTENSITY. WILL RE-EVALUATE THE THREAT AFTER TAKING A PEEK AT THE 00Z
RUNS THIS EVENING.
THE AFOREMENTIONED LOW AND FRONT WILL WEAKEN MONDAY NIGHT ENDING THE
STEADIEST PRECIPITATION. A WEAK SHOWERY PATTERN THEN ENSUES FOR
MID-WEEK.

.LONG TERM FORECAST...AFTER A TRANSIENT UPPER LEVEL RIDGE MOVES
THROUGH THE BERING SEA AND SOUTHWEST ALASKA EARLY THIS WEEK THE COLD
CORE UPPER LEVEL TROUGH WILL REASSERT ITSELF OVER THE SOUTHWEST
PORTION OF THE STATE FOR TE MIDDLE TO LATER PART OF THE WEEK. AT THAT
TIME THE SURFACE LOW IN THE GULF OF ALASKA WILL STRENGTHEN AGAIN AND
THESE FEATURES WILL COMBINE TO KEEP COLD TEMPERATURES OVER THE
MAJORITY OF THE FORECAST AREA WITH MUCH BELOW NORMAL TEMPERATURES IN
THE BERING SEA AND SOUTHWEST ALASKA REGION THROUGH THE WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WARNING 191. BLIZZARD WATCH 195.
MARINE...GALE 121 130 132 138 150 155 170 179 185.
  STORM 172.
  HURRICANE FORCE WIND 175 176
  HEAVY FREEZING SPRAY 121 129 130 132 138 140 141 150 155 165 179.
FIRE WEATHER...NONE.

MTL/DWK/JAM/EZ MAR 12