Heavy Snow in Alaska, February 4 to 5, 2008

SOUTHEAST ALASKA FORECAST DISCUSSION
1100 AM AST MON FEB 4 2008

.SYNOPSIS...
.SHORT RANGE...COMPLICATED PATTERN THROUGH THIS EVENING
CONTINUING OVER SOUTHEAST ALASKA ... HOWEVER IT BECOMES A LITTLE
MORE SIMPLE THROUGH TUESDAY AS THE STRONG LOW SPREADS OUT OF THE
NORTH CENTRAL PACIFIC AND ACROSS THE QUEEN CHARLOTTE / SOUTHERN
PANHANDLE REGION TUESDAY DEPENDING ON THE TRACK.

A TROUGH IN THE NORTHERN STREAM OVER THE YUKON-KUSKOKWIM DELTA
OVER SOUTHWEST ALASKA ROTATING INTO THE NORTHWEST GULF WHILE THE
LARGER TROUGH IN THE SOUTHERN STREAM MOVES NORTHEAST TO THE
EASTERN GULF.  A BROAD FLAT RIDGE OVER THE EASTERN PACIFIC TO THE
SOUTHEASTERN GULF HAS QUITE A BIT OF MOISTURE IN THE FLOW
SPREADING OVER THE COLDER PANHANDLE RESULTING IN OVERRUNNING SNOW
ACROSS THE ENTIRE AREA. AS SUCH...SEVERAL AREAS HAVE SNOW
ADVISORIES OR HEAVY SNOW WARNINGS THROUGH TODAY AND INTO TONIGHT.
THE SOUTHERN PORTIONS DO HAVE SOME AREA WITH THE TEMPERATURES
AROUND THE FREEZING MARK WHICH COULD LEAD TO SOME MIXED
PRECIPITATION.

PARTIALLY COMPLICATING THE ENTIRE PATTERN IS THAT THERE ARE ABOUT
3 DIFFERENT LOWS IN/NEAR THE GULF. THE FIRST IS NEAR CAPE
SUCKLING THAT WILL STAY WHERE ITS AT AND WILL STRENGTHEN THROUGH
TUESDAY AS THE NORTHERN STREAM TROUGH LENDS SOME SUPPORT ALONG
WITH COLD AIR SPILLING OUT INTO THE NORTHERN GULF FROM THE
CENTRAL GULF COAST. A SECOND LOW OVER THE CENTRAL GULF AROUND
54/138 OR SO. AND THIS SEEM TO PARTIALLY CONNECTED LIKE A TRIPLE
POINT ALMOST TO THE THIRD STRONGER LOW THAT MOVES TO THE SOUTHERN
PANHANDLE TUESDAY MORNING.

THE GRADIENT OVER THE NORTHERN PANHANDLE HAS PICKED UP A LITTLE
FASTER IN THE SKAGWAY AREA SO WE ARE STARTING THAT WIND ADVISORY
A LITTLE SOONER THAN EXPECTED. NOT SEEING MUCH ELSE OF CHANGES TO
THE WARNING SITUATIONS.

AFTER THE LOW MOVES ACROSS THE SOUTHERN PANHANDLE A TRAILING
TROUGH WILL PERSIST ACROSS THE CENTRAL PANHANDLE TO THE LOW OVER
THE NORTHEAST GULF IT A TIGHT NORTH PRESSURE GRADIENT OVER THE
NORTHERN PANHANDLE THAT WILL RESULT IN VERY WINDY CONDITIONS. BMB

.LONG RANGE...NAM AND GFS BOTH INITIALIZED VERY WELL WITH REGARD
TO UPPER LEVEL WINDS ALTHOUGH BOTH MODELS UNDER FORECAST THE
STRENGTH OF THE ASCENDING LEG OF THE JET NEAR 160W. HAVE A SLIGHT
PREFERENCE FOR GFS BASED ON OVERALL PATTERN WHERE SATELLITE WIND
DATA NOT AVAILABLE. LIKEWISE...BOTH NAM AND GFS INITIALIZED VERY
WELL WITH REGARD TO WATER VAPOR IN SO FAR AS IT AFFECTS THE LOCAL
FORECAST AREA. HOWEVER...THE GFS INITIALIZATION IS FAR SUPERIOR
TO NAM OVER THE NORTHERN BERING SEA...THE NORTH SLOPE...AND
SIBERIA. THEREFORE...PREFER THE GFS SOLUTION HERE AS WELL. AT THE
SURFACE...12Z DATA FIT THE NAM SLIGHTLY BETTER...ESPECIALLY OVER
THE PANHANDLE. HOWEVER...BY 18Z THE DATA WAS A BETTER FIT TO GFS.
GOOD AGREEMENT IN THE EARLY PORTION OF THE LONG RANGE FORECAST
PERIOD BETWEEN THE GLOBAL MODELS. SIGNIFICANT DIFFERENCES BETWEEN
GFS AND ECMWF BEGIN TO APPEAR BY 08/00Z WITH GFS INITIALLY
DEVELOPING A MUCH STRONGER LOW SOUTH OF THE GULF ALONG 150W AND
TRACKING IT NORTHEAST TOWARDS THE CENTRAL PANHANDLE COAST BY
10/12Z. THE 04/12Z ECMWF RUN IS DEPICTING THE SAME
FEATURE...DEVELOPING IT MORE SLOWLY AT FIRST. BUT BY
09/12Z...ECMWF RAPIDLY DEEPENS THIS LOW AND ACCELERATES THE TRACK
TO THE SOUTH CENTRAL PANHANDLE BY 10/00Z. IMPORTANT TO NOTE HERE
IS THAT THIS IS A MAJOR CHANGE SINCE THE 04/00Z MODEL RUN.
DIFFERENCES BETWEEN ECMWF AND GFS NOT TOO PRONOUNCED FOR
PANHANDLE CONCERNS THROUGH 09/12Z. THEREAFTER...HAVE A CLEAR
PREFERENCE FOR SLOWER GFS SOLUTION DUE PRIMARILY TO THE RUN TO
RUN CHANGES BEING EXHIBITED IN THE CURRENT ECMWF RUN.

THE LONG RANGE FORECAST PERIOD BEGINS WITH A BROAD AREA OF LOW
PRESSURE EXTENDING ACROSS BRITISH COLUMBIA...THE PANHANDLE...AND
THE GULF AND A MAJORITY OF THE SHOWER ACTIVITY IN THE SOUTHERN
HALF OF THE PANHANDLE. BY WEDNESDAY AFTERNOON...A TRIPLE POINT
LOW WILL BE APPROACHING THE SOUTHERN COASTAL ZONE FROM THE GULF.
QPF ASSOCIATED WITH THIS LOW IS FAIRLY SUBSTANTIAL BUT...BASED ON
THE CURRENT TRACK...SOUTH OF THE DIXON ENTRANCE. A MORE NORTHERLY
TRACK SUCH AS IS BEING DEPICTED BY UKMET COULD PRODUCE A
SUBSTANTIAL AMOUNT OF SNOW AND RAIN SO IT WILL HAVE TO BE WATCH
CLOSELY. AFTERWARDS...HIGH PRESSURE BUILDS IN FROM THE NORTH
WHICH SHOULD DRY MOST LOCATIONS OUT THROUGH FRIDAY AFTERNOON AS
WELL AS GIVE US SOME COLD TEMPERATURES. EARLY NEXT WEEKEND...A
FRONT WILL LIFT NORTH ACROSS THE PANHANDLE BRINGING A LOT OF
MOISTURE WITH IT. AT THIS POINT... IT LOOKS LIKE ALL ZONES EXCEPT
HAINES AND SKAGWAY WILL SEE AT LEAST SOME MIXED PRECIP WITH
STRAIGHT RAIN POSSIBLY MAKING IT AS FAR NORTH AS
SITKA...ANGOON...AND FIVE FINGERS. THE RAIN SNOW LINE WILL
ADVANCE TO THE SOUTH AGAIN LATE IN THE WEEKEND AS THE LOW TRACKS
NORTHEAST OVER THE CENTRAL PANHANDLE. FCF

.AJK...WATCHES/WARNINGS/ADVISORIES
PUBLIC...HEAVY SNOW WARNING AKZ024>026-029
      ...SNOW ADVISORY AKZ019-021>023-027-028
      ...WIND ADVISORY AKZ018>020

MARINE...GALE WARNING PKZ011>13-031-032-036
      ...SMALL CRAFT PKZ021-022-034-035-041>043-051-052