Heavy Freezing Spray Warning 131, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
135 PM AKST FRI MAR 9 2012

.ANALYSIS AND UPPER LEVELS...
A BROAD UPPER LEVEL TROUGH IS IN PLACE OVER MAINLAND ALASKA WITH
SEVERAL WEAKENING LOWS ROTATING AROUND ITS PERIPHERY. THE REMNANTS OF
WHAT USED TO BE A GALE FORCED LOW CAN BE SEEN ON SATELLITE AND THE
MIDDLETON ISLAND RADAR NEAR MONTAGUE ISLAND. A LOW THAT WAS CROSSING
THE ALASKA PENINSULA THIS TIME YESTERDAY IS ROUNDING THE BASE OF THE
TROF IN THE NORTHEASTERN PACIFIC AND WILL HEAD TOWARD THE GULF LATER
TONIGHT THROUGH SATURDAY. HIGH PRESSURE AND COLD AIR ADVECTION IS
DOMINATING THE CENTRAL AND EASTERN BERING SEA WHILE A WEAK LOW TRIES
TO DEVELOP SOUTH OF THE ALEUTIANS.

.MODEL DISCUSSION...
OVERALL THE MODELS ARE IN EXCELLENT AGREEMENT ON ALL OF THE MAJOR
FEATURES...ONLY MINOR DIFFERENCES THROUGH THE SHORT TERM WITH THE
EXACT LOCATION OF THE UPPER SHORTWAVES ROTATING AROUND THE UPPER
TROF. THESE SHORTWAVES AND THEIR ASSOCIATED SURFACE REFLECTIONS WILL
BE DIFFICULT TO PIN DOWN AS THEY MEANDER AROUND THE NORTHERN GULF
THROUGH THE WEEKEND. VERY LITTLE CHANGES ARE BEING MADE TO THE
FORECAST OVER THE EASTERN DOMAIN WHILE THE WEST WILL NUDGE TOWARD THE
12Z GFS WITH THE PURPOSE OF INCREASING WINDS ASSOCIATED WITH A
DEVELOPING LOW TOWARD THE END OF THE WEEKEND.

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...A COLD CORE UPPER LOW IS CURRENTLY POSITIONED
NEAR THE ALASKA RANGE WHILE A WEAK SURFACE LOW IS MEANDERING AROUND
WESTERN PRINCE WILLIAM SOUND. SNOW SHOWERS ARE CURRENTLY LIMITED TO
THE COPPER RIVER BASIN AND THE COASTAL AREAS AROUND PRINCE WILLIAM
SOUND. MEASURABLE SNOW WOULD BE FALLING OVER THE INTERIOR PORTIONS OF
SOUTHCENTRAL IF IT WERE NOT FOR THE POSITION OF THE UPPER LOW AND
LACK OF ANY SIGNIFICANT SHORTWAVE MOVING THROUGH THE REGION. AS IT
IS...A FEW FLURRIES HAVE BEEN FALLING OVER EASTERN PORTIONS OF
ANCHORAGE AND THE MATSU VALLEY. THIS WILL LIKELY CONTINUE THROUGH
TONIGHT AS THE SURFACE LOW DROPS SOUTH AND EVENTUALLY DISSIPATES
TONIGHT.

THE NEXT AREA OF LOW PRESSURE WILL TAKE ITS PLACE OVER THE WEEKEND
AND BRING ANOTHER CHANCE OF LIGHT SNOW TO SOUTHCENTRAL BY THE END OF
THE WEEKEND. AT THIS TIME...THE BEST CHANCE OF MEASURABLE SNOW IN
ANCHORAGE AND THE MATSU VALLEY LOOKS TO BE SUNDAY NIGHT WITH A WEAK
EASTERLY IMPULSE MOVING THROUGH THE REGION. UNTIL THEN...PARTLY TO
MOSTLY CLOUDY SKIES WILL PREVAIL WITH CONTINUED COLDER THAN AVERAGE
TEMPERATURES.

THE OTHER FORECAST CHALLENGE AROUND SOUTHCENTRAL IS THE TIGHTENING
PRESSURE GRADIENT ALONG THE GULF COAST. THIS WILL LEAD TO GUSTY WINDS
OUT OF THE NORMAL CHANNELED AREAS INCLUDING VALDEZ AND WHITTIER. THE
WAVE THAT MAY BRING ANCHORAGE SNOW SUNDAY NIGHT WILL ALSO TIGHTEN UP
THE GRADIENT AND BRING THE CHANNELED AREAS THE STRONGEST WINDS. AT
THIS TIME...LOOKS LIKE THE GRADIENT IS GREATEST ALONG THE COAST
SATURDAY AFTERNOON AND CONTINUES TO BE STRONG THROUGH THE REST OF THE
WEEKEND. WITH THE HIGHER CONFIDENCE WITH THE TIMING OF THIS
FEATURE...WE WILL BE NUDGING THE WIND SPEEDS UP THROUGH VALDEZ
THROUGH THE WEEKEND.

SOUTHWEST ALASKA...
FOR AVIATION PURPOSES...THE CONTINUED CHALLENGE ACROSS SOUTHWEST
ALASKA IS CEILINGS AND VISIBILITY RESTRICTIONS IN FLURRIES AND FOG. A
VERY SLOW IMPROVEMENT IS EXPECTED DURING THE WEEKEND AS COLD DRY AIR
FILTERS IN OVER THE REGION. THE COLD AIRMASS IS SUBSTANTIAL ENOUGH TO
LEAD TO SOME IMPRESSIVE WIND CHILLS FOR EARLY MARCH. WILL BE
CONSIDERING A WIND CHILL ADVISORY FOR THE DELTA TONIGHT AS
TEMPERATURES SHOULD CONTINUE TO DROP WHILE WIND SPEEDS ONLY SLOWLY
DIMINISH. BY MONDAY...HIGH PRESSURE WILL BE CENTERED OVER SOUTHWEST
ALASKA PROVIDING PLEASANT ALBEIT COLD CONDITIONS. PATCHY FOG IN LOW
LYING AREAS WILL CONTINUE TO BE A THREAT.

BERING SEA AND ALEUTIANS...SNOW SHOWERS PERSISTING ALONG THE ALASKA
PENINSULA WHILE THE REST OF THE ALEUTIANS EXPERIENCE BENIGN WEATHER.
A WEAK LOW WILL DEVELOP SOUTH OF THE WESTERN ALEUTIANS TONIGHT BUT
THE ZONAL FLOW ALOFT WILL QUICKLY SHEAR IT APART AS IT DIES OVER THE
NORTH PACIFIC. THE NEXT LOW AND ASSOCIATED FRONT LOOK TO BE A BIT
MORE IMPRESSIVE BY THE END OF THE WEEKEND. THE AFTERNOON FORECAST
WILL BE STRENGTHENING THE WINDS OVER THE WESTERN ALEUTIANS TO STORM
FORCE SUNDAY. THIS LOW WILL LIKELY MAKE IT TO THE CENTRAL BERING
BEFORE WEAKENING AND SHIFTING TO THE SOUTHEAST.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...WIND CHILL ADVISORY 155
MARINE...HEAVY FREEZING SPRAY 150 155 165 179 412
         GALE 130 138 132 129 150 155 160 165 172 175 413
FIRE WEATHER...NONE

AB MAR 12