Storm Warning 17, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
1237 PM AKST FRI FEB 12 2010

.SHORT TERM...MID MORNING SATELLITE REVEALS A WEAK MID LEVEL
TROUGH OVER THE SOUTHERN PANHANDLE WITH ANOTHER MID LEVEL TROUGH
MOVING INTO THE CHARLOTTES AND SHEARING APART AS IT DOES. THESE
MID LEVEL TROUGHS WILL CONTINUE TO BRING A FEW HIGH AND MID
CLOUDS TO THE CENTRAL AND NORTHERN PANHANDLE WITH BRIEF PERIODS
OF LIGHT RAIN AND SPRINKLES TO THE SOUTHERN PANHANDLE INTO
TONIGHT. THE RAPIDLY DEEPENING STORM FORCE LOW NEAR 43N 148W
REMAINS IN A VERY FAVORABLE BAROCLINIC ENVIRONMENT AND IS HELPING
TO CAUSE WAA AT MID LEVELS ALLOWING THE TWO MID LEVEL SHORTWAVES
OVER THE PANHANDLE TO BE SHEARED APART. THIS WILL ALLOW FOR
PARTLY TO MOSTLY CLOUDY SKIES TONIGHT WITH VERY LITTLE PRECIP
OVER THE PANHANDLE. THE 12Z GFS INITIALIZED THE MID LEVEL
VORTICITY AND UPPER LEVEL JET ENERGY THE BEST THIS MORNING AND
THEREFORE USED ITS SOLUTION FOR THE SHORT TERM PACKAGE. THE 12Z
NAM AND ECMWF INITIALIZED THE SYSTEM A LITTLE SLOWER. THIS
DEVELOPING STORM FORCE LOW IN THE NORTHEASTERN PACIFIC IS THE
MAIN FORECAST PROBLEM THROUGH THE SHORT TERM PERIOD.

 WILL CONTINUE TO SEE PERIODS OF LIGHT RAIN AND SPRINKLES
DIMINISH INTO THE AFTERNOON AND EVENING HOURS ACROSS THE SOUTHERN
PANHANDLE WITH ONLY MID TO HIGH CLOUDS NORTH OF FREDERICK SOUND
AS THE EASTERLY 700 MB TO SURFACE WINDS HAVE DRY PARCEL
TRAJECTORIES FROM BRITISH COLUMBIA. WITH THE RELATIVELY WEAK
SURFACE PRESSURE GRADIENT ACROSS THE PANHANDLE THIS EVENING ADDED
AREAS OF FOG TO THE FORECAST...BUT BY LATER TONIGHT THE SURFACE
PRESSURE GRADIENT RAPIDLY INCREASES AND SO AREAS OF FOG SHOULD
DIMINISH THROUGH THE NIGHT. THE STRONGEST WINDS TONIGHT WILL BE
ACROSS THE SOUTHERN PANHANDLE AS THE 850 MB LLJ WINDS INCREASE
STEADILY INTO SATURDAY MORNING AND COULD SEE WIND ADVY GUSTS NEAR
PRINCE OF WALES ISLAND AFTER MIDNIGHT WITH GALES IN ASSOCIATED
WATERS.

 THE LATEST MODEL RUNS HAVE COME IN STRONGER WITH THE 850 MB LLJ
ACROSS THE SOUTHERN PANHANDLE NOW NEAR 80 TO 85 KNOTS SATURDAY
MORNING AND SO WILL ISSUE A HIGH WIND WATCH FOR AKZ027. KEPT ALL
OTHER WIND ADVY TIMES THE SAME ADDING AKZ028 TO THE MIX AS WINDS
IN AND ALONG CLARENCE STRAIT WILL GUSTS ABOVE 40 MPH THROUGH
TOMORROW. THE STORM FORCE LOW WILL MOVE INTO THE SOUTHERN GULF BY
SATURDAY AFTERNOON...BUT BY THE EARLY MORNING THE SURFACE LOW
WILL BE CUT OFF FROM ITS MID LEVEL BAROCLINIC ENVIRONMENT AND
UPPER LEVEL JET SUPPORT AND SO WITH THIS WILL SEE THE STRONGEST
WINDS REMAIN ALONG THE OUTER COAST THROUGH SATURDAY AFTERNOON.
THERE WILL ALSO BE A STRONG NORTHERLY SURFACE PRESSURE GRADIENT
ACROSS THE CENTRAL AND NORTHERN PANHANDLE WITH THE APPROACHING
LOW TOMORROW AND SO WILL SEE LOCALLY WINDY CONDITIONS ALONG LYNN
CANAL...NEAR SKAGWAY AND OUT OF INTERIOR PASSES. THE ASSOCIATED
FRONTAL BOUNDARY WILL BEGIN MOVING ACROSS THE SOUTHERN PANHANDLE
SATURDAY MORNING SPREADING PERIODS OF RAIN NORTHWARD ACROSS THE
SOUTHERN AND CENTRAL PANHANDLE BY SATURDAY AFTERNOON. HOWEVER THE
EASTERLY 850 MB TO SURFACE WIND COMPONENT WILL LIMIT PRECIP
AMOUNTS NORTH OF FREDERICK SOUND. COULD ALSO SEE SNOW MIX WITH
RAIN BRIEFLY AT THE ONSET OF PRECIP NORTH OF ANGOON BUT 850 MB
TEMPERATURES WILL CONTINUE TO WARM THROUGH THE AFTERNOON AND SO
EXPECT ALL AREAS TO SWITCH QUICKLY TO RAIN ALONG THE ICY STRAIT
CORRIDOR. FORECAST CONFIDENCE IS ABOVE AVERAGE THROUGH THE SHORT
TERM PERIOD.

&&

.LONG TERM...AS THE STORM FORCE LOW CONTINUES TO RETROGRADE WEST
AT THE START OF THE LONG TERM WILL SEE BUILDING RIDGE OVER THE
PANHANDLE WITH UPPER LVL NEGATIVELY TILTED TROUGH TRACING INTO
THE W GULF. EXPECTING THE BLOCKING UPPER LVL RIDGE TO REMAIN IN
PLACE THROUGH MOST OF THE WEEK. AT THE SURFACE WEAK SHORT WAVES
MOVING UP ALONG THE COAST MON WERE WELL DEPICTED BY GFS BUT
SMOOTHED OUT BY OTHER MODELS. NEXT SERIES OF LOW PRESSURE SYSTEMS
TRACKING INTO THE W GULF BREAK DOWN AGAINST THE BLOCKING RIDGE.
MID LEVEL WIND FLOW VARYING FROM SW TO SE SO KEPT HIGHER POPS
ALONG THE COAST. FAIRLY TIGHT PRESSURE GRADIENT REMAINS IN PLACE
THROUGH MID WEEK KEEPING INSIDE CHANNELS AT OR NEAR ADVY LVLS.
LOW TEMPS MID WEEK WITH 850MB TEMPS NEAR -8 C...FOLLOWED BY WAA
AT THE END OF THE WEEK AS 850 TEMPS RAISE TO 4 C OVER THE
SOUTHERN ZONES.

MODELS STARTED IN FAIR AGREEMENT AT THE START OF THE LONG TERM.
CONTINUED WITH THE SHORT TERMS CHOICE OF THE GFS THROUGH DAY 3.
NAM12 WINDS SEEMED A BIT HIGH IN COMPARISON. MODELS THEN DIVERGE
MAINLY IN DETAILS OF SHORT WAVES MOVING UP ALONG THE COAST AND
EXTENT OF THE BLOCKING HIGH OVER THE PANHANDLE. ENSEMBLES WERE IN
GOOD AGREEMENT WITH THE PROBLEMS RESIDING IN THE OPERATIONAL
MODELS. DECIDED A BLEND OF HPC GUID WITH INHERITED GRIDS FOR THE
REMAINDER OF THE TERM. FORECAST CONFIDENCE WAS ABOUT AVERAGE THEN
DROPS SIGNIFICANTLY BY EARLY NEXT WEEK.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...HIGH WIND WATCH FROM SATURDAY MORNING THROUGH SATURDAY
AFTERNOON FOR AKZ027.
         WIND ADVISORY FROM 6 AM SATURDAY TO 5 AM AKST SUNDAY FOR
AKZ022-023.
         WIND ADVISORY FROM 6 AM TO 6 PM AKST SATURDAY FOR
AKZ028.
MARINE...STORM WARNING FOR PKZ041-042.
         GALE WARNING FOR PKZ013-021-022-031>036-043-051-052.
         SMALL CRAFT ADVISORY FOR PKZ011-012.

&&

PSS/PRB