Gale Warning 179, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
400 PM AKST THU FEB 14 2013

.ANALYSIS AND UPPER LEVELS...A STRONG JET THAT IS MOVING OFF THE
ASIAN CONTINENT OVER JAPAN SPLITS IN TWO NEAR 35N 170E. THE NORTHERN
LOBE OF THE JET REMAINS WELL SOUTH OF THE ALEUTIAN ISLANDS BUT THEN
TURNS SHARPLY NORTHEAST AROUND A TROUGH NEAR 40N 150W AND THEN
EXTENDS INTO THE EASTERN GULF OF ALASKA. THIS JET IS PROVIDING ENERGY
FOR A LOW IN THE NORTHERN GULF OF ALASKA TODAY.
OTHER THAN THE LOCATION OF THE JET STREAM THE OTHER UPPER LEVEL
FEATURES ARE NOT TOO EXCITING WITH A FLATTENED RIDGE OVER THE
ALEUTIANS AND BERING SEA. THERE IS ALSO AN UPPER LEVEL TROUGH
EXTENDING OUT OF THE CHUKCHI SEA OVER SOUTHWEST ALASKA AND THEN
SOUTHEASTWARD TO NEAR 40N 150W.
AT THE SURFACE THERE IS A LARGE LOW CENTERED OVER THE NORTHERN GULF
OF ALASKA THAT ENCOMPASSES THE MAJORITY OF THE MAINLAND PART OF THE
STATE. THIS LOW IS RAPIDLY SLOWING ITS FORWARD MOVEMENT AND WEAKENING
AT THE SAME TIME. AS THIS HAPPENS A SECONDARY LOW WILL DEVELOP THIS
EVENING OVER THE SEWARD PENINSULA AND THE MAIN LOW WILL MOVE INTO
PRINCE WILLIAM SOUND. ALTHOUGH THE SURFACE LOW WILL REMAIN IN PRINCE
WILLIAM SOUND UNTIL IT DISSIPATES SATURDAY MORNING THE UPPER LEVEL
SUPPORT WILL CONTINUE TO MOVE TO THE NORTHEAST WHICH WILL CAUSE THE
LOW THE SOUND TO WEAKEN.
SOUTHWEST OF THE WESTERN ALEUTIANS THERE IS ANOTHER STRONG LOW WHICH
IS HEADING TOWARD THE AREA. THE FRONT ASSOCIATED WITH THIS LOW IS
ALREADY SENDING HIGHER CLOUDS OVER THE WESTERN ALEUTIANS AND IT WILL
MOVE OVER THE ALEUTIAN CHAIN FROM LATE TONIGHT INTO SATURDAY. THE
CENTER OF THE LOW LOOKS TO REMAIN SOUTH OF THE ALEUTIAN CHAIN.

.MODEL DISCUSSION...MODELS ARE DOING WELL WITH THE OVER PATTERN AND
SEEM TO BE LOCKED IN PRETTY GOOD THE THE MOVEMENT OF THE MAJOR
FEATURES. THERE ARE SOME SUBTLE DIFFERENCES IN MODELS THAT WILL MAKE
A DIFFERENCE IN THE FORECASTS THOUGH. IN SOUTH CENTRAL ALASKA THE
NAM, ECMWF, AND CANADIAN MODELS ALL HAVE A MESO LOW DEVELOPING IN
COOK INLET OVERNIGHT AS THE MAIN LOW IN THE NORTHERN GULF WEAKENS.
THE GFS IS WEAKENING THE LOW AS WELL BUT DOES NOT CATCH THE EXTENT
THAT THE LOW IS BECOMING MORE DIFFUSE AND KEEPS THE ENERGY TOO
CONSOLIDATED AROUND A SINGLE CENTER. THE SATELLITE IMAGERY IS ALREADY
SHOWING THAT NOT TO BE THE CASE SO THE GFS IS NOT BEING USED IN THE
SHORT TERM FOR THE EASTERN PARTS OF THE FORECAST AREA.
THE OTHER MODEL DIFFERENCE OF NOTE IS THE SPEED AT WHICH THE MODELS
PUSH THROUGH THE TROUGH WHICH WILL END THE SNOWFALL. THE NAM MOVES IT
EAST OF THE ANCHORAGE AREA BY LATE FRIDAY AFTERNOON WHILE THE GFS AND
ECMWF ARE A LITTLE SLOWER WHICH WOULD KEEP SOME SNOW IN THE ANCHORAGE
AND MAT-SU AREAS THROUGH MOST OF THE EVENING FRIDAY.

OUT WEST THE GFS AND ECMWF LOOKS TO HAVE A VERY SIMILAR SOLUTION TO
THE MOVEMENT OF THE FRONT THAT WILL BRING PRECIPITATION AND SOME
BLOWING SNOW TO THE ALEUTIAN ISLANDS TOMORROW AND TOMORROW NIGHT. THE
NAM IS A BIT TOO SLOW IN MOVING THIS LOW AND WAS NOT USED FOR THAT
FEATURE.

.SHORT TERM FORECAST...
SOUTH CENTRAL ALASKA...THE LOW IN THE NORTHERN GULF IS WEAKENING AND
WILL BECOME LESS ORGANIZED OVERNIGHT AND IT LOSES ITS UPPER LEVEL
SUPPORT. THIS WILL ALLOW A MESO-LOW TO DEVELOP IN THE SOUTHERN PART
OF COOK INLET OVERNIGHT WHICH WILL HELP TO REDUCE THE PRESSURE
GRADIENT AT THE SURFACE. THE BIG IMPACT FROM THAT IS THAT IT WILL
KEEP ANY DOWN SLOPE EFFECT TO A MINIMUM FROM THE KENAI PENINSULA
THROUGH THE SUSITNA VALLEY. THE VERY COLD AIR IN SOUTHWEST ALASKA
WILL GET PACKED UP ALONG THE ALASKA AND ALEUTIAN RANGES BUT WILL
BEGIN TO SPILL OVER INTO SOUTH CENTRAL ALASKA OVERNIGHT. THIS IS A
GOOD SCENARIO FOR SNOWFALL OVER THE MAJORITY OF SOUTH CENTRAL ALASKA
OVERNIGHT. AS THE UPPER LEVEL TROUGH CURRENTLY IN SOUTHWEST ALASKA
MOVES THROUGH THE AREA THE SNOWFALL SHOULD STOP AND THERE WILL THEN
BE CLEARING FROM THE SOUTHWEST. THERE WILL BE A THREAT OF FOG SHORTLY
AFTER AN AREA CLEARS BUT THERE MAY BE ENOUGH MIXING OF THE AIR BEHIND
THIS TROUGH TO KEEP WIDESPREAD FOG FROM DEVELOPING.

SOUTHWEST ALASKA...AN UPPER LEVEL TROUGH IS MOVING SLOWLY EASTWARD
ACROSS THE KUSKOKWIM VALLEY AND THE BRISTOL BAY REGION THAT WILL
BRING SNOWFALL OVERNIGHT. BEHIND THIS TROUGH THERE IS MUCH COLDER AIR
WHICH HAS PLUNGED TEMPERATURES IN THE KUSKOKWIM DELTA BELOW BELOW
ZERO. THIS COLD AIR IS PROGRESSING EASTWARD AND BRING IN COLDER
TEMPERATURE THAN HAVE BEEN SEEN IN A FEW WEEKS TO MOST OF SOUTHWEST
ALASKA.

ALEUTIANS AND BERING SEA...THE WEATHER FRONT MOVING TO THE AREA WILL
BRING STRONG WINDS AND SNOW STARTING WITH THE WESTERN ALEUTIANS LATE
TONIGHT AND THEN SPREADING TO THE EASTERN ALEUTIANS BY LATE FRIDAY
AFTERNOON. THE BIG QUESTION IN REGARDS TO THE SYSTEM IS HOW MUCH
BLOWING SNOW THERE WILL BE. THE AREA FROM KISKA EASTWARD TO NEAR
NIKOLSKI WILL LIKELY SEE VISIBILITIES REDUCED TO SOME EXTEND THROUGH
THE DAY FRIDAY UNTIL IT WARMS ENOUGH TO TURN TO RAIN. AT THIS TIME
THE WARM AIR ADVECTION LOOKS LIKE IT WILL BE ENOUGH TO KEEP
VISIBILITIES FROM DROPPING DOWN TO BLIZZARD LEVELS. THE BEST CHANCE
FOR THIS TO HAPPEN WILL BE IN THE UNALASKA REGION FRIDAY EVENING.
THEREFORE THERE IS A BLIZZARD WATCH IN EFFECT FOR THIS AREA FOR
FRIDAY EVENING.
THE PRIBILOF ISLANDS ARE NOT EXPECTED TO SEE ANY BLOWING SNOW FROM N
FALLING SNOW AS THE PRECIPITATION WILL MOST LIKELY REMAIN SOUTH OF
THAT AREA. HOWEVER THERE COULD STILL BE SOME REDUCED VISIBILITIES AT
TIMES FROM RE-SUSPENDED SNOW.

.LONG TERM FORECAST...
MODEL DISAGREEMENTS IN THE LONG RANGE CONTINUE TO BE IMPACTED BY A
SIBERIAN RIDGE SLIDING INTO THE BERING. THIS WILL PREVENT THE
EASTWARD PROGRESSION ON THE ALEUTIAN LOW TRACK STARTING SUNDAY. THERE
IS ALSO GOOD MODEL AGREEMENT THAT THIS RIDGE WILL THEN MOVE OVER TO
THE WESTERN MAINLAND...WHICH WILL LOOKS TO BRING CLEAR AND COOLER
WEATHER TO THE SOUTHWEST MAINLAND EARLY NEXT WEEK.
THIS WILL ALSO LIKELY KEEP SOUTH CENTRAL ALASKA IN THE STORM TRACK
AND BRING A NUMBER OF CHANCES FOR SNOW NEXT WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WATCH 185.
MARINE...GALE 120 130 155 160 165 170 171 172 175 176 179.
         HEAVY FREEZING SPRAY 130 138 140 150 155 160 165 179.
FIRE WEATHER...NONE.

FEB 13