Small Craft Advisory 476, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
404 PM AKDT WED AUG 29 2012

.SHORT TERM...THE LATEST SATELLITE IMAGERY SHOWS MOST OF THE
FORECAST AREA ALONG WITH THE EASTERN GULF UNDER MOSTLY SUNNY
SKIES FROM UPPER HIGH OVER THE GULF PRODUCING OFFSHORE FLOW.
THERE IS SOME CLOUDS OVER THE SOUTHERN THIRD FROM THE LINGERING
UPPER LOW. THERE IS AN AREA OF SEA STRATUS OVER THE WESTERN GULF
THAT WILL DRIFT EAST INTO THE EASTERN GULF BY THURSDAY AFTERNOON
AS THE UPPER RIDGE DRIFTS EAST. THE STRONG WINDS FROM THE NORTH
OVER THE NORTHERN HALF IS CONTINUING TO DIMINISH BUT SMALL CRAFT
WINDS ARE STILL HAPPENING NEAR NORTHERN LYNN. THE REST OF THE
AREA IS SEEING NORTH WINDS 15 TO 10 KT EVEN OVER THE EASTERN
GULF.

FOR TONIGHT...THE WINDS WILL BECOME LIGHT ACROSS THE ENTIRE AREA
AS THE HIGH OVER THE YUKON DRIFTS EAST AND THE PRESSURE GRADIENT
RELAXES. THIS WILL ALLOW PATCHY FOG TO FORM THROUGH TONIGHT AS
BOUNDARY LAYER IS STILL ON THE MOIST SIDE WITH ALL THE RAIN
YESTERDAY. LOW TEMPS WILL DROP SIGNIFICANTLY THROUGH TONIGHT WITH
THE CLEAR SKIES AND THERE WILL BE PATCHY FROST FORMING IN LOW
LYING AREAS OVER THE NORTHERN THIRD OF THE PANHANDLE AWAY FROM THE
WATER.

THROUGH THURSDAY SKIES WILL BE MAINLY MOSTLY CLEAR AS THE UPPER
HIGH MOVES OVER THE THE FORECAST AREA. IN DOING SO THE SEA STRATUS
OVER THE GULF UNDER THE HIGH WILL DRIFT EAST TO BE OVER THE
EASTERN GULF BUT REMAIN OFFSHORE. A WEAK SURFACE HIGH WILL BUILD
OVER THE INNER CHANNELS THROUGH TOMORROW AND WINDS WILL INCREASE
SOME FROM THE SOUTH. THE STRONGEST WINDS WILL BE OVER NORTHERN
LYNN WITH MIN SMALL CRAFT AND 15 TO 10 KT OVER THE REST OF THE
INNER CHANNELS.

THERE IS MUCH BETTER FORECASTER CONFIDENCE THAN YESTERDAY FOR THE
NEXT 24HRS AND USED A BLEND OF THE NAM AND PREVIOUS FORECAST.

 &&

.LONG TERM...THURSDAY NIGHT BEGINS WITH THE RIDGE ALOFT OVER THE
PANHANDLE MOVING EAST INTO CANADA ON FRIDAY AS A TROUGH OVER THE
WESTERN GULF DELIVERS THE NEXT SHOT OF PRECIPITATION STARTING IN
YAKUTAT FRIDAY AFTERNOON. TWO THINGS IMPORTANT IN THIS TRANSITION,
MARINE STRATUS PENETRATION INTO THE INSIDE PASSAGE AND THE ONSET
OF PRECIPITATION FRIDAY THROUGH SATURDAY TIMEFRAME. WE THINK THE
MARINE STRATUS WILL BEGIN ENCROACHING INTO CROSS SOUND AND
SOUTHERN CHATHAM THURSDAY NIGHT AS RH VALUES TYPICALLY INCREASE
DURING NIGHTTIME BUT WILL LEAVE AT LEAST MOSTLY CLOUDY CONDITIONS
PENETRATING TO GUSTAVUS FROM THE WEST AND TO FREDERICK SOUND FROM
THE SOUTH IN THE MORNING AS SURFACE RIDGE ORIENTS WINDS MORE
TOWARD THE WEST OVER THE PANHANDLE.

THE SURFACE FRONT ACTUALLY SLOWS DOWN AND TILTS FRIDAY AS IT
APPROACHES THE COAST...SO EVEN AS YAKUTAT WILL LIKELY BEGIN RAINING
LATE FRIDAY...INSIDE CHANNELS WILL NOT RECEIVE RAIN UNTIL AS LATE AS
SATURDAY AFTERNOON AS THE RIDGE ALONG THE COAST STUBBORNLY RESISTS
THE FRONT.

WE ALSO INCREASED WINDS NEARSHORE TO SMALL CRAFT LEVELS AHEAD OF
FRONT FRIDAY AS MODELS SUGGESTED A STRONGER TROUGH THAN PREVIOUSLY
THOUGHT. WE ALSO ACCELERATED EAST WINDS OUT OF CROSS SOUND.  BUT AS
YUKON HIGH MOVES EAST, GRADIENT RELAXES TO THE NORTH AND DECREASED
WINDS IN LYNN CANAL TO BELOW SMALL CRAFT CRITERIA THURSDAY NIGHT.
FINALLY ADDED SOME MORE STRENGTH TO SOUTHEAST WINDS CHANNELING
THROUGH CLARENCE STRAIT SATURDAY.

LOW TEMPERATURES FRIDAY MORNING WILL BE WARMER THAN THURSDAY
MORNING...ESPECIALLY ALONG THE COAST AS MARINE LAYER MODIFIES DRIER
AIR MASS FROM DAY BEFORE.  INLAND...EXPECTING SOME HIGH CLOUDS TO
DROP SOUTHEAST FROM THE RIDGE TO MODIFY TEMPERATURE DROPS A BIT.

LOOKING BEYOND SATURDAY...EXPECTING MORE ZONAL FLOW WITH SOME WEAK
RIDGING AND TROUGHING AT VARIOUS TIMES AS MODELS IN MORE
DISAGREEMENT.  SO WILL CALL FOR MODERATE TEMPERATURES LEANING TOWARD
CLIMATOLOGY...MOSTLY CLOUDY SKIES WITH AT LEAST A CHANCE OF RAIN
DURING MOST TIME PERIODS.

THE MODELS WERE CONSISTENT DURING THE MID-RANGE BRINGING THE FRONT
INTO THE PANHANDLE...ALTHOUGH THE GFS WAS AROUND 6 HOURS LATER THAN
THE EC AND NAM. STILL DIFFERENCES WERE SMALL, AND THEREFORE USED A
BLEND OF ALL THREE WITH AN EMPHASIS ON THE NAM FOR BETTER TERRAIN
HANDLING. BEYOND DAY 5...WE USED MAINLY HPC WITH A BLEND OF OTHER
MODELS.  FOR POPS WE USED A BLEND MAINLY OF GFS, EC, AND SREF BUT
LEFT OUT NAM BECAUSE NAM WANTED TO BRING PRECIPITATION INTO ELFIN
COVE EARLIER THAN THE OTHERS.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...FROST ADVISORY FROM 4 AM TO 8 AM AKDT THURSDAY FOR AKZ017-
     019>021-025.
MARINE...SMALL CRAFT ADVISORY FOR PKZ012.

&&

ABJ/EAL/JWA