Small Craft Advisory 884, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
348 PM AKST TUE DEC 27 2011

.SHORT TERM...SATELLITE IMAGERY THIS AFTERNOON SHOWING A
DEVELOPING LOW IN THE NORTHERN PACIFIC WITH A HIGH PRESSURE RIDGE
MOVING EAST OVER BRITISH COLUMBIA. SNOW SHOWERS OVER THE
PANHANDLE BECAME SCATTERED THROUGH THE DAY WITH THOSE OVER THE
NORTHERN REGIONS LASTING THE LONGEST. A FEW CLEAR BREAKS SEEN
THROUGH THE DAY WERE FAIRLY SHORT LIVED. WINDS OVER SKAGWAY
DECIDED TO REMAIN STRONG THROUGH THE DAY BUT ARE EXPECTED TO
DIMINISH THIS EVENING AS THE PRESSURE GRADIENT WEAKENS AS THE
RIDGE MOVES EAST. OVERALL THE DAY HAVE BEEN A TRANSITION FROM THE
VERY ACTIVE WEATHER MONDAY INTO ANOTHER ACTIVE PERIOD STARTING
TUE NIGHT.

 THE 967 MB LOW IN THE NORTH PACIFIC WILL TRACK INTO THE
SOUTHEAST GULF TONIGHT THEN MOVE OVER SITKA BY WEDNESDAY
AFTERNOON AND WEAKEN THROUGH THE DAY. FRONT ASSOCIATED WITH THE
LOW WILL PUSH OVER THE SOUTHERN PANHANDLE THIS EVENING WITH
PRECIP DEVELOPING THROUGH THE EVENING. WITH COLD AIR ALREADY IN
PLACE PRECIP SHOULD BEGIN MOSTLY AS SNOW THEN TRANSITION TO ALL
RAIN OVERNIGHT AS WARM AIR BEHIND THE FRONT MOVES IN. KEEPING
ACCUMULATIONS FOR THE SOUTHERN AREAS JUST BELOW ADVISORY LEVELS
DUE TO THE SNOW RAIN MIX. AS THE FRONT MOVES NORTH NOT EXPECTING
THE WARM AIR TO PUSH AS FAR NORTH WITH SNOW AMOUNTS OF 3 TO
6 INCHES EXPECTED BETWEEN FREDERICK SOUND AND ICY STRAIT. COULD
SEE HIGHER AMOUNTS WITH WARMER MID LEVEL AIR OVER THE COLDER
SURFACE AIR RESULTING IN A BETTER OVER RUNNING EVENT. SOME RAIN
WILL MIX IN WED AFTERNOON BUT SHOULD BE LIMITED AND NOT EXPECTED
TO EFFECT SNOW AMOUNTS GREATLY. FOR HAINES SNOW WILL CONTINUE
INTO WED EVENING THUS SNOW AMOUNTS ARE EXPECTED TO REACH WARNING
CRITERIA.

 WINDS WILL REACH GALE FORCE OVER THE COASTAL WATERS AND SOUTHERN
INNER CHANNELS BY WEDNESDAY. SMALL CRAFT WINDS OVER THE REMAINING
INNER CHANNELS WILL DEVELOP THROUGH THE EVENING. WINDS WILL SHIFT
FROM THE SOUTH TO NORTH THROUGH WED EVENING OVER THE NORTHERN
REGIONS. WITH EASTERLY GRADIENT TIGHTENING ON WEDNESDAY AS THE
LOW MOVES TOWARD SITKA WITH HIGH PRESSURE OVER BRITISH COLUMBIA
EASTERLY OUTFLOW WINDS WILL INCREASE THROUGH THE DAY. DOWNTOWN
JUNEAU AND OTHER INTERIOR PASSES MAY SEE SOME HIGHER GUSTS.

 MODELS WERE IN GOOD AGREEMENT THIS MORNING. LIKED THE EC
INITIALIZATION COMPARING FEATURES TO SATELLITE BUT GFS WAS A
CLOSE SECOND. NAM IS NOT BRINGING THE PRECIP BAND AS FAR NORTH
COMPARED TO THE EC AND GFS BUT OVERALL SYNOPTIC PATTERNS WERE
SIMILAR. USED A BLEND OF 00Z EC WITH INHERITED GRIDS. INCREASED
SOME WINDS OVER THE INNER CHANNELS BUT MAIN CHANGE WAS INCREASE
IN SNOW AMOUNTS FOR WEDNESDAY. MODEL SNOW GUIDANCE WAS FAIRLY
CONSISTENCY WITH THE 3 TO 5 INCHES OF SNOW WITH OVERRUNNING
GUIDANCE JUST NEARING 8 INCHES. FORECAST CONFIDENCE IS JUST ABOVE
AVERAGE.

.LONG TERM...THE FORECAST MODELS ARE IN GOOD AGREEMENT THROUGH
THURSDAY NIGHT THEN THEY DIVERGE QUICKLY WITH LOW FORECASTER
CONFIDENCE FOR THIS WEEKEND INTO EARLY NEXT WEEK. CONTINUED TO USE
THE EC THROUGH THE MID RANGE THEN REFRESHED THE EXTENDED PORTIONS
WITH THE LATEST HPC GUIDANCE.

AT THE START OF THE LONG RANGE A LOW PRESSURE SYSTEM WILL BE
ROLLING UP THE EASTERN GULF AND WILL MOVE OVER THE NORTHERN INNER
CHANNELS THROUGH THURSDAY NIGHT. THE LOW WILL PRODUCE RAIN OVER
THE COASTAL AND FAR SOUTHERN AREAS IN THE EVENING BUT AS THE COLD
FRONT PASSES TO THE EAST THE RAIN WILL CHANGE OVER TO SNOW SHOWERS
WITH MINOR ACCUMULATIONS. SNOW OVER THE CENTRAL AREAS WILL MIX
WITH SOME RAIN IN THE EARLY EVENING AS SOME WARMER AIR MAY MAKE IT
TO THE SURFACE BUT THE COLD FRONT WILL MOVE THROUGH QUICKLY AND
SNOW SHOWERS WILL MOVE ACROSS THE AREA. SNOW AMOUNTS WILL VARY
WITH ACCUMULATIONS RANGING FROM 1 TO 4 INCHES. THE FAR NORTHERN AREAS
WILL REMAIN ALL SNOW AND WITH SIGNIFICANT ACCUMULATIONS OF 5 TO 8
INCHES NEAR PAHN. SO WITH THAT SAID AN WINTER STORM WARNING IS IN
EFFECT THROUGH THURSDAY MORNING AS THE ONCE THE UPPER TROF LIFTS
OVER THE AREA THE SNOW SHOWERS WILL BECOME SCATTERED WITH MINOR ACCUMULATIONS.

THE WINDS WITH THIS LOW WILL BE STRONG FROM THE NORTH IN THE EARLY
EVENING ON WED BUT AS THE LOW WEAKENS AND LIFTS INTO THE INTERIOR
THE SOUTHERLY WINDS WILL INCREASE TO BE GALES OVER LYNN AND SMALL
CRAFTS OVER THE REST OF THE INNER CHANNELS WED NIGHT. LAND AREAS
WILL SEE THE SOUTHERLY WIND INCREASE OVERNIGHT TO BE ON THE BREEZY
SIDE BUT THE FAR NORTHERN AREAS WILL SEE SOUTH WINDS 20 TO 30 WITH
GUSTS TO 40 MPH DEVELOPING AFTER MIDNIGHT. THESE WINDS WILL SLOWLY
DIMINISH THROUGH THURSDAY AS THE PRESSURE GRADIENT RELAXES. OVER
THE GULF AS THE LOW LIFTS INLAND THERE WILL BE A BURST OF STRONG
WESTERLY WINDS TO GALES WED NIGHT BUT THEY WILL DECREASE TO LESS
THAN SMALL CRAFT THROUGH THURSDAY. SOME OF THESE STRONG WESTERLY
WINDS MAY AFFECT THE COASTAL AREAS SO THERE IS GUSTS TO 40 MPH FOR
THOSE AREAS WED NIGHT.

FOR THE REST OF THE WEEK...WITH THE POLAR JET SOUTH OF THE AREA
AND A MEAN UPPER TROF OVER THE GULF SNOW SHOWERS WILL PERSIS
THROUGH MOST OF THE WEEK WITH SOME RAIN MIXING IN OVER THE
SOUTHERN THIRD. THERE LOOKS TO BE ANOTHER PATTERN SHIFT WITH THE
POLAR JET MOVING BACK NORTH AND MORE ABOVE NORMAL TEMPS TO MOVE
BACK INTO THE ARE. SO WITH THAT SAID WARMED THE TEMPS SOME FROM
SUN THROUGH EARLY NEXT WEEK.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER WEATHER ADVISORY FROM 11 PM THIS EVENING TO 4 PM AKST
     WEDNESDAY FOR AKZ024-026.
         WINTER WEATHER ADVISORY FROM 5 AM TO 4 PM AKST WEDNESDAY FOR
     AKZ020-021-025.
         WINTER STORM WARNING FROM 9 AM WEDNESDAY TO 9 AM AKST THURSDAY
     FOR AKZ019.
         STRONG WIND UNTIL 9 PM AKST THIS EVENING FOR AKZ018.
MARINE...GALE WARNING FOR PKZ022-033-035-036-041>043.
         SMALL CRAFT ADVISORY FOR PKZ011>013-021-031-032-034-051-052.

&&

PRB/ABJ