Snow Advisory 9, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
1100 AM AST TUE DEC 18 2007

.SYNOPSIS...
.SHORT RANGE...THE 1900 UTC SATELLITE IMAGERY INDICATES SNOW
SHOWERS ARE CLUSTERED OVER THE SOUTHERN HALF OF THE PANHANDLE
MOVING NORTHWARD. SOME OF THE STRONGER SNOW SHOWERS HAVE BEEN
MODERATE TO HEAVY BUT THE MOVEMENT IS NORTHWARD AROUND 20 KT SO
THE DURATION IS SHORT.

THE AREA OF MORE NUMEROUS SHOWERS IS ASSOCIATED WITH A MINOR
TROUGH THAT IS ROTATING NORTHWARD AROUND A QUASI-STATIONARY UPPER
LOW IN THE GULF OF ALASKA. SNOW SHOWERS SHOULD INCREASE IN THE
CENTRAL PANHANDLE THIS AFTERNOON AS THE TROUGH MOVES NORTH BUT
NOT AS MUCH AS IN THE SOUTH SINCE THE TROUGH IS WEAKENING.

LATER TONIGHT ANOTHER WEAK TROUGH APPROACHES THE SOUTHERN
PANHANDLE SO EXPECT THE SNOW SHOWER FREQUENCY TO INCREASE AGAIN.
THE UPPER LEVEL LOW IS PROGRESSING SLOWLY EASTWARD AND IS FINALLY
PUSHED ONSHORE BY LATE WED.

.LONG RANGE...CONTINUED COMPLICATED WEATHER PATTERN THROUGH THE
LONG RANGE.  VERY POOR RUN TO RUN CONSISTENCY REMAINS AS WELL AS
VERY LITTLE AGREEMENT BETWEEN EACH MODEL.  GIVEN THIS LOW
CONFIDENCE SCENARIO...WILL NOT ADJUST CURRENT FORECAST EXCEPT TO
BLEND ALONG THE BORDER BETWEEN US AND ANCHORAGE.

A TROUGH WILL SIT OVER THE PANHANDLE WEDNESDAY NIGHT AND WEAKEN
AS A RIDGE QUICKLY BUILDS OVER THE GULF.  AS THE RIDGE PUSHES THE
TROUGH EASTWARD SHOWERS WILL DISSIPATE BRIEFLY OVERNIGHT.
HOWEVER...FLOW ONCE AGAIN RETURNS TO AN ONSHORE COMPONENT
THURSDAY AFTERNOON.

SEVERAL DIFFERENT SOLUTIONS BEGIN TO APPEAR THURSDAY AFTERNOON.
MODELS DO AGREE WITH A COMPLICATED SET OF LOWS DUMBBELLING
ABOUT AN UPPER LEVEL LOW FORMING IN WESTERN INTERIOR AK/BERING
SEA.  THE STRENGTH AND TIMING OF SURFACE FEATURES REVOLVING ABOUT
THIS UPPER LOW IS THE TRICKY PART.  THE ECMWF IS THE MOST
AGGRESSIVE MODEL AND MOVES A STRONG LOW INTO THE NORTHERN GULF
THURSDAY NIGHT.  THE GFS WEAKENS THIS LOW IN FAVOR OF A MUCH
SLOWER MOVING SYSTEM THAT ARRIVES INTO THE NORTHERN GULF SATURDAY
AND BRINGS A LEADING FRONT INTO THE GULF FRIDAY EVENING.

AM THINKING THAT THERE WILL LIKELY BE GALE FORCE WINDS AND WIND
ADVISORY CONDITIONS ONCE A FRONT ASSOCIATED WITH THE STRONGEST OF
THESE LOWS MAKES IT INTO THE EASTERN GULF/PANHANDLE.
ADDITIONALLY...THERE WILL BE A STRONG LIKELIHOOD FOR SIGNIFICANT
SNOWFALL IN THE NORTHERN PANHANDLE WITH COLD AIR IN PLACE.
HOWEVER...TIMING THESE FEATURES IS STILL UP IN THE AIR.  WILL
LEAVE CURRENT FORECAST AS IS RATHER THAN FLIP-FLOP WITH THE
MODELS.

THE UPPER LEVEL TROUGH MOVING THESE WAVES INTO THE GULF WEAKENS
THROUGH SATURDAY NIGHT AS A NEW CUT OFF UPPER LEVEL LOW DEVELOPS
IN THE NORTHERN PACIFIC ON SATURDAY.  LONG RANGE MODELS DO POINT
AT A STRONG SURFACE LOW SLIDING TO THE NORTHEAST TOWARDS THE
QUEEN CHARLOTTE ISLANDS ON SUNDAY NIGHT. BEHIND THIS...ANOTHER
COMPLICATED UPPER LOW RAPIDLY FORMS IN THE SOUTHWESTERN GULF ON
MONDAY NIGHT.  THIS LOW QUICKLY TRACKS TOWARDS THE CENTRAL
PANHANDLE TUESDAY THROUGH TUESDAY NIGHT.  WHILE THE MODELS ARE IN
GOOD AGREEMENT WITH THESE SYSTEMS...THE PROGRESSIVE NATURE AND
THE RUN TO RUN INCONSISTENCIES KEEP CONFIDENCE LOW HERE.

.AJK...WATCHES/WARNINGS/ADVISORIES
PUBLIC...NONE

MARINE...NONE