Small Craft Advisory 302, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
355 PM AKDT MON MAY 7 2012

.SHORT TERM...QUIETER WEATHER PATTERN OVER THE PANHANDLE TODAY
WITH MAIN FEATURE BEING A BAROCLINIC CLOUD SHIELD OVER THE
SOUTHERN TWO THIRDS OF THE PANHANDLE. UNDER THIS SHIELD IS THE
MOISTURE PLUME THAT BROUGHT THE HEAVY RAIN TO THE SOUTHERN
PANHANDLE YESTERDAY. IT DRIFTED SOUTH INTO BRITISH COLUMBIA
OVERNIGHT AND HAS DRIFTED BACK TO THE NORTH TODAY AHEAD OF THE
APPROACHING WEAK TROUGH AND SURFACE LOW THAT IS DOWN BY 50N AND
140W. RAIN RATES IN THE SOUTHERN PANHANDLE ARE AGAIN OVERSHADOWED
BY KETCHIKAN WITH AROUND 2 TENTHS OF AN INCH PER HOUR RAIN RATES
OCCURRING THERE FOR THE PAST 5 HOURS. ELSEWHERE RAIN RATES OF A
TENTH OR LESS AN HOUR ARE GENERALLY THE RULE WITH THE HIGHEST
AMOUNTS IN THE SOUTHERN PANHANDLE.

THE MODERATE RAIN IN THE SOUTH WILL FINALLY LIGHTEN UP TONIGHT AS
THE MOISTURE PLUME THAT HAS CONNECTIONS ALL THE WAY DOWN TO THE
AREA NW OF HAWAII, PUSHES OFF INTO CANADA. THE TROUGH AND WEAK LOW
THAT ORIGINALLY BROUGHT THE PLUME BACK INTO THE SOUTHERN PANHANDLE
WILL RAPIDLY MOVE NORTH INTO THE YUKON THIS EVENING, DRAGGING SOME
OF THE MOISTURE NORTH WITH IT. CONSEQUENTLY, POPS REMAIN HIGH FOR
MOST OF THE PANHANDLE THROUGH TONIGHT BUT QPF AMOUNTS WILL START
TO DROP OFF ESPECIALLY IN THE SOUTH AS A SURFACE RIDGE BUILDS IN
BEHIND THE TROUGH TONIGHT. THE STEADY RAIN WILL CHANGE OVER TO
SHOWERS TOMORROW AS A COLD UPPER LOW THAT IS CURRENTLY OVER THE SW
GULF MOVES INTO THE SE GULF. 850 MB TEMPS WILL BE DROPPING TO -6
DEGREES C OVER THE SE GULF TOMORROW PROMOTING THE CONVECTIVE
ENVIRONMENT. WITH SUCH A COLD AIR MASS OVER THE WARMER GULF THE
CHANCE IS THERE FOR SOME ISOLATED THUNDERSTORMS OVER THE SE GULF
AND SOUTHERN OUTER COAST TOMORROW.

WINDS FOR THE MOST PART REMAIN LOW OVER MOST OF THE PANHANDLE
CURRENTLY. WHEN THE TROUGH MOVES INTO THE YUKON THIS EVENING I
EXPECT WINDS IN MOST NORTH-SOUTH CHANNELS TO INCREASE AS IT
RESPONDS TO THE LOWERING PRESSURE IN THE YUKON AND THE BUILDING
RIDGE OVER THE PANHANDLE. WINDS MAY REACH GALE FORCE OUT OF THE
SOUTH IN LYNN CANAL EARLY TOMORROW WITH SMALL CRAFT WINDS IN MANY
OF THE OTHER INNER CHANNELS. WINDS WILL START TO DIMINISH TOMORROW
AFTERNOON AS THE RIDGE IS PUSHED TO THE EAST BY THE APPROACHING
WEAK LOW.

SHORT RANGE MODELS ARE IN FAIR AGREEMENT WITH SOME DIFFERENCES ON
DETAILS. MAIN DIFFERENCE WAS IN WHERE THEY DEPICTED THE UPPER LOW
TO BE TOMORROW AFTERNOON. EC WAS THE FARTHEST SOUTH WITH THE NAM A
BIT TOO FAST. GFS AND UK WERE FAIRLY CLOSE TO EACH OTHER AND
PROVIDED A GOOD STARTING POINT. DECIDED ON USING A BLEND TO EC/NAM
FOR THE TONIGHT PERIOD DUE TO BETTER RIDGE POSITION AND THEN USING
MORE GFS TOWARD TOMORROW FOR ITS MIDDLE GROUND APPROACH FOR THE
UPPER LOW. FORECAST CONFIDENCE IS ABOVE AVERAGE.

&&

.LONG TERM...WEATHER PATTERN TO REAMAIN ACTIVE INTO NEXT WEEKEND
AS FIRST SYTEM BECOMS REPLAQCED WITH SECOND LATE IN THE WEEK. HAVE
POTENTIAL FOR HEAVY RAIN STARTING THURSDAY IN NE GULF AND
GRADUALLY SPREADING TO SOUTHERN BY FRIDAY NIGHT.

COLD UPPER LEVEL LOW MOVES ACROSS SOUTHERN HALF OF
THE PANHANDLE TUESDAY NIGHT AND SPREADS OUT ACROSS NORTHERN
PANHANDLE WEDNESDAY MORNING. 85H TEMPS DROP TO AS COLD AS -7C AND
LOWERS SNOW LEVELS TO AROUND 500 FEET THROUGH INNER CHANNELS AND
AROUND 1000 FEET ACROSS SOUTHERN. THIS WILL GREATLY LOWER
STABILITY AND HAVE ADDED A SLIGHT CHANCE OF THUNDERSTORMS WITH
SMALL HAIL OR EVEN MIXING WITH SNOW.

A FLAT RIDGE AT SURFACE AND ALOFT BUILDS INTO THE EASTERN GULF
WEDNESDAY...SHARPENS UP A BIT OVER SOUTHEAST ALASKA WEDNESDAY
NIGHT...AND MOVES INTO WESTERN CANADA THURSDAY. AS THIS BUILDS IN
WILL SEE SMCR SLY WINDS IN LYNN CANAL THAT DIMINISH AS RIDGE MOVES
OVERHEAD. POPS DIMINISH BUT STILL EXPECT SHOWERS ALONG MOUNTAINS
WITH WESTERLY FLOW IN LOWER LEVELS.

A NEW UPPER LOW DROPS SOUTH INTO THE SOUTHWEST GULF THURSDAY AND
SPINS UP A 980 MB LOW NEAR KODIAK. THE ASSOCIATED FRONT MOVES INTO
THE EASTERN GULF THURSDAY NIGHT. A SERIES OF WAVES MOVING ALONG
THE FRONT SLOW EASTWARD PROGRESSION ACROSS SOUTHEAST ALASKA FRIDAY
AND SATURDAY. SOLID SE GALES EXPECTED FOR EASTERN GULF THURSDAY-
FRIDAY AHEAD OF FRONT AND DIMINISHING QUICKLY AS THEY BECOME
WESTERLY BEHIND THE FRONT. HAVE GALES DEVELOPING IN CLARENCE ON
FRIDAY WITH MAX SMCR FOR CENTRAL INNER CHANNELS. THERE IS A LONG
FETCH OF MOISTURE WITH THE FRONT AND WITH THE SLOW MOVEMENT HAVE
POTENTIAL FOR HEAVY RAIN ACROSS NE GULF THURSDAY SPREADING INTO SE
ALASKA FRIDAY.

MODELS HAD GOOD GENERAL AGREEMENT BUT LIKED EC FOR RIDGE MOVEMENT
AND WINDS FOR INNER CHANNELS EARLY ON BUT LIKED GFS FOR HANDLING
OF UPPER LEVEL LOW AND NEXT SYSTEM. STARTED WITH A NUDGE TO EC AND
WENT TO A GFS/EC BLEND BY DAY 3.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING FOR PKZ012.
         SMALL CRAFT ADVISORY FOR PKZ011-013-021-031>034-036-041.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ042-043-051-052.

&&

EAL/MM