Snow Advisory 14, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
500 AM ADT FRI MAR 23 2007

.DISCUSSION...
MODELS ARE IN FAIR AGREEMENT THIS MORNING ALTHOUGH NAM HAS A SLIGHT
EDGE OVER GFS REGARDING PLACEMENT AND STRENGTH OF NORTHERN GULF LOW.
MORE SIGNIFICANT DIFFERENCES SURROUND HANDLING OF BERING SEA LOW OVER
THE WEEKEND AS IT APPROACHES BRISTOL BAY. GFS HAS BEEN REMARKABLY
CONSISTENT WITH THIS FEATURE SO FAVORED THE NAM FOR THE FIRST 24
HOURS BUT QUICKLY BLEND WITH AND THEN SWITCH TO GFS FOR THE REMAINDER
OF THE FORECAST PACKAGE.

SURFACE...972 MB LOW LOCATED JUST WEST OF MIDDLETON ISLAND EARLY THIS
MORNING WITH OCCLUDED FRONT EXTENDING NORTHEAST TOWARD THE COPPER
RIVER DELTA AND THEN EAST ALONG THE GULF COAST. SNOW BEING REPORTED
ALL ALONG THE COAST WITH THE EXCEPTION OF VALDEZ WHO IS GETTING
DOWNSLOPED AND LEFT OUT AT THIS POINT. SOME FLAKES SLIPPED OVER THE
CHUGACH MOUNTAINS AS A RESULT OF THE SURFACE LOW LOCATED A BIT
FURTHER WEST THAN PREVIOUS MODEL RUNS INDICATED. GRADIENT ALSO
TIGHTENING UP BRINGING SOME 35 TO 50 MPH GUSTS THROUGH THE NORMAL
CHANNELED AREAS. FRESH SNOW FROM WEDNESDAYS EVENT IS EASILY BEING
LIFTED AND BLOWN AROUND TEMPTING US INTO A BLIZZARD WARNING FOR
THOMPSON PASS THIS MORNING. OUT WEST...MOSTLY CLEAR SKIES OVER THE
INTERIOR AND A SERIES OF WEAK LOWS ACROSS THE BERING SEA.

UPPER AIR...LONG RANGE TROF AXIS OVER THE CENTRAL BERING SEA WITH
SHORTWAVES LOCATED OVER SOUTHCENTRAL...SOUTHWEST...AND CENTRAL
BERING. THE ANCHOR UPPER LOW CURRENTLY LOCATED OVER EASTERN SIBERIA
WILL SWING SOUTHEAST AND DEEPEN THE TROF OVER SOUTHWEST ALASKA BY
SUNDAY AFTERNOON AND EVENTUALLY INTO THE NORTHERN GULF BY TUESDAY.
BEHIND IT...A RIDGE WILL BUILD OVER THE BERING SEA.

SOUTHCENTRAL SURFACE...SOME QUESTION REMAINING AS TO WHERE NRN GULF
LOW IS GOING TO TRACK THIS MORNING AND ITS EVENTUAL AFFECTS ON
ANCHORAGE BOWL. ALTHOUGH THE SURFACE LOW IS IN A SEMI FAVORABLE
POSITION FOR SNOW IN ANCHORAGE...UPPER FEATURES ARE LACKING. WOULD
LIKE TO SEE A MORE NEGATIVELY TILTED TROF OVERHEAD AND MORE MOISTURE
AT THE MID LEVELS. COLD AIR ADVECTION WILL KICK IN LATER THIS MORNING
AT 850 MB BUT IS RELATIVELY WEAK. HAVE OPTED TO INCLUDE SNOW AMOUNTS
IN THE FIRST PERIOD BUT FEEL MOST SNOW THAT FALLS WILL BE LIMITED TO
HIGHER ELEVATIONS WITH WEST ANCHORAGE SEEING LITTLE ACCUMULATION...IF
ANY.

HAVE ALSO MADE A LAST SECOND DECISION TO INCLUDE A BLOWING SNOW
ADVISORY FOR 125. TWO VERY UNTIMELY OUTAGES AT PATO AND PAWR LEFT US
IN A BIND BUT FEEL THERE ARE LIKELY AREAS OF SNOW AND BLOWING SNOW
REDUCING VISIBILITY TO ONE QUARTER MILE OR LESS.

NRN GULF LOW WILL SLOWLY DISSIPATE INLAND WITH A WEAK RESIDUAL LOW
REMAINING IN THE PWS VICINITY. SNOW SHOWERS IN PWS COASTAL AREAS AND
COPPER RIVER BASIN LINGER THROUGH THE EARLY WEEKEND WHILE WEST OF THE
CHUGACH AND TALKEETNA RANGES ENJOY A PLEASANT WEEKEND. SUNDAY EVENING
BRINGS THE NEXT SHORT WAVE AND SURFACE LOW ACROSS THE ALASKA RANGE
AND WITH IT CLOUDS AND ANOTHER CHANCE OF SNOW FOR SOUTHCENTRAL.

SURFACE WEST OF ALASKA RANGE...WEAK SURFACE LOWS ASSOCIATED WITH
UPPER AND MID LEVEL IMPULSES WILL CONTINUE TO MOVE ACROSS THE CENTRAL
AND EASTERN BERING SEA THROUGH THE WEEKEND BRINGING OCCASIONAL SNOW
SHOWERS. THE INTERIOR WILL ENDURE CONTINUED COLDER THAN AVERAGE
TEMPERATURES...IN THE RANGE OF 15 TO 20 DEGREES BELOW NORMAL. BY
SATURDAY AFTERNOON 850 WINDS BECOME SOUTHWESTERLY AHEAD OF THE
DEEPENING TROF ALLOWING FOR WARM AIR ADVECTION AND THE CHANCE OF SNOW
FOR MOST OF THE INTERIOR BY SUNDAY. THE RELIEF IS SHORT LIVED AS COLD
AIR SLIPS SOUTHWARD AGAIN MONDAY AS THE TROF CROSSES THE ALASKA RANGE
AND NORTHERLY FLOW RETURNS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 131
         BLOWING SNOW ADV 125.
MARINE...GALE 120 130.
         HEAVY FREEZING SPRAY 121 129 130 138 141 150.
FIRE WEATHER...NONE.

AB MAR 07