Small Craft Advisory 792, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
328 PM AKST FRI DEC 2 2011

.SHORT TERM...SATELLITE IMAGERY SHOWING A SHORT WAVE TROUGH AND
WEATHER FRONT OVER THE AK PANHANDLE TRACKING EAST. THIS FRONT HAS
BROUGHT PERIODS OF RAIN TO THE ENTIRE PANHANDLE WITH A RAIN SNOW
MIX NEAR PETERSBURG, YAKUTAT AND AT HIGHER ELEVATIONS.
PRECIPITATION HAS BEEN FAIRLY LIGHT WITH THE EXCEPTION OF YAKUTAT
WHICH HAS RECEIVED SOME MODERATE TO HEAVY RAIN AS IT IS IN THE
DIRECT PATH OF JET AXIS AND MOISTURE FEED. RAIN WILL BEGIN TO
DIMINISH OVER THE REGION AS THE FRONT EXITS TO THE EAST
OVERNIGHT. NEXT SHORT WAVE MOVES OVER THE SOUTHEASTERN AK GULF
THROUGH SAT MORNING REACHING THE SOUTHERN PANHANDLE SAT
AFTERNOON. HIGH PRESSURE RIDGE OVER THE AK GULF PUSHING IN
546 1000-500MB THICKNESS OVER THE REGION THROUGH SAT WITH RISING
SNOW LEVELS. AS THE WARM AIR ADVECTION CONTINUES PRECIPITATION
WILL BE MOSTLY RAIN WITH SOME MIX OF SNOW AT HIGHER ELEVATIONS
AND NORTHERN REGIONS.

 500 MB HIGH PRESSURE RIDGE OVER THE CENTRAL AK GULF BEGINS TO
MOVE EAST AND TILT TO THE EAST. THE SHORTWAVE TROUGH AND FRONT
HAVE BEEN LIMITED TO THE SURFACE. CONTINUED ONSHORE FLOW AND
MOISTURE FEED AT 850 MB WILL KEEP CHANCE OF PRECIP AND MOSTLY
CLOUDY SKIES. NORTH-SOUTH PRESSURE GRADIENT WILL BEGIN TO WEAKEN
AS SURFACE RIDGE OVER THE PANHANDLE BEGIN TO WEAKEN. GALE FORCE
WINDS OVER N LYNN CANAL AND STRONG WINDS OVER SKAGWAY WILL BEGIN
TO SUBSIDE THROUGH THE NIGHT. FOR SATURDAY WINDS WILL GENERALLY
BE LESS THAN 20 KTS.

 MODELS WERE IN GOOD AGREEMENT AGAIN TODAY WITH OVERALL SYNOPTIC
PATTERN AND THERE WAS LITTLE DIFFERENCE IN INITIALIZATION. LIKED
THE NAM/EC WITH THE DETAIL IN THE SHORTWAVES MOVING ACROSS THE
GULF. 12Z MODELS RUNS SHOWED ONLY MINOR DIFFERENCES FROM THE
CURRENT FORECAST AND OVERALL CHANGES WERE MINOR. DID EXTEND THE
HIGHER WINDS OVER THE NORTHERN REGIONS THROUGH THE EVENING.
FORECAST CONFIDENCE IS ABOVE AVERAGE.

.LONG TERM...NOT MUCH CHANGE IN THE FORECAST FROM THE PREVIOUS
PACKAGE. AT THE BEGINNING OF THE LONG RANGE PERIOD THE AMPLIFIED
UPPER RIDGE OVER THE PACIFIC AND EXTENDING NORTH INTO THE INTERIOR
OF STATE WILL DRIFT TO THE EAST AND INCREASE THE ONSHORE FLOW. THIS
RIDGE WILL KEEP WARM AIR OVER THE AREA ALONG WITH SOUTHERLY WINDS
AT THE SURFACE. A WARM FRONT WILL LIFT NE OUT OF THE NORTH PACIFIC
AND INTO THE NORTHERN GULF BY SUN MORNING AND SLIDE EAST OVER THE
REST OF THE PANHANDLE THROUGH SUN NIGHT. THERE IS A LONG FETCH OF
MOISTURE AND VERY WARM AIR AS A TROF BEHIND THE RIDGE WILL DIG INTO
THE NORTH PACIFIC AND THE SOURCE REGION WILL BE FROM THE SUB-
TROPICS. ALL OF THIS WARM AIR AND MID-LEVEL DYNAMICS WILL ALLOW
THE FRONT TO PRODUCE HEAVY RAIN RAIN OVER THE NORTHERN GULF SUNDAY
AND THEN SPREAD EASTWARD ACROSS THE REST OF THE FORECAST AREA
SUN NIGHT INTO MON. RAIN AMOUNTS WILL RANGE FROM 2 TO 4 INCHES
WITH FREEZING LEVELS NEAR 5000 FEET. THIS MAY CAUSE SOME LOCALLY
FLOODING DUE TO POOR DRAINAGE. THE FRONT WILL PRODUCE STRONG GALE
FORCE WINDS OVER THE NORTHERN GULF WITH MAX SMALL CRAFT OVER THE
REST OF THE EASTERN GULF. OVER THE INNER CHANNELS GALES WILL
DEVELOP THROUGH SUN OVER LYNN CANAL AND SMALL CRAFTS FROM THE
SOUTH OVER THE REST OF THE INNER CHANNELS. NEAR LAND AREAS THERE WILL
BE SOME BREEZY CONDITIONS BUT WINDY CONDITIONS OVER THE FAR
NORTHERN ZONES WITH GUSTS TO 40 MPH.

THE TROF BEHIND THE UPPER RIDGE WILL DRIFT EAST ACROSS THE GULF
AND PUSH A COLD FRONT OVER THE FORECAST AREA LATE MON AFTERNOON
INTO MON NIGHT. THE CAA WILL CHANGE THE RAIN TO SNOW SHOWERS FROM
NORTH TO SOUTH THROUGH MON NIGHT BUT AT THE SAME TIME THERE WILL
BE SOME DRYING DEVELOPING BEHIND THE FRONT SO ATTM THERE IS NOT
MUCH IN THE WAY OF ACCUMULATION. THE UPPER RIDGE OVER THE GULF MON
NIGHT WILL AMPLIFY AS A LOW MOVES INTO THE BERING. THIS WILL
INCREASE THE OFFSHORE FLOW AND THE SKIES WILL CLEAR OUT TO BE
MOSTLY CLEAR THROUGH THURSDAY MORNING. THE RIDGE WILL PUSH TO THE
EAST THURSDAY AFTERNOON AND INCREASE ONSHORE FLOW AND ADVECT
CLOUDS ACROSS THE AREA. THIS WAS A SLIGHT CHANGE FROM PREVIOUS
FORECAST. THERE IS LOWER CONFIDENCE IN THIS PORTION OF THE
FORECAST AS THE TIMING OF THE RIDGE MOVING EAST OF THE AREA IS
STILL A BIT UNCERTAIN.

USED A BLEND OF THE EC/GFS THROUGH TUE MORNING THEN WENT WITH HPC
FOR THE EXTEND PORTIONS.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND UNTIL 6 PM AKST THIS EVENING FOR AKZ018.
MARINE...GALE WARNING FOR PKZ012-022.
         SMALL CRAFT ADVISORY FOR PKZ013-021-031>033-052.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ041>043-051.

&&

PRB/ABJ