Small Craft Advisory 232, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
332 PM AKST SAT MAR 12 2011

.SHORT TERM...A 990 MB LOW OVER DIXON ENTRANCE WILL CONTINUE TO
MOVE NORTH INTO THE SOUTH GULF THROUGH THIS EVENING THEN OPEN UP
INTO A TROUGH EXTENDING TO THE NORTHEAST. LEAD OCCLUSION BAND IS
NOW OVER THE FAR NORTH AND WEAKENING RAPIDLY. THE SECOND WRAP IS
JUST NOW PUSHING INTO THE SOUTHERN PANHANDLE AND WILL CONTINUE
NORTH TO BE OVER NORTH CENTRAL EARLY SUNDAY THEN DISSIPATE ACROSS
THE FAR NORTH SUNDAY AFTERNOON. HIGH PRESSURE OVER NORTHWEST
CANADA CONTINUES TO WEAKEN.

 PRECIP ASSOCIATED WITH LEAD OCCLUSION HAS BEEN VERY LIGHT THIS
MORNING AND NOT MUCH MORE THAN FLURRIES LEFT. EVEN HIGHER CLOUDS
ASSOCIATED WITH THIS FEATURE ARE BREAKING UP. THIS DID INCREASE
NORTHERLY OUTFLOW WINDS ACROSS THE NORTH THIS MORNING BUT AREA
EXPECTED TO WEAKEN THIS AFTERNOON AND FALL BELOW ADVISORY LEVELS
IN PAGY THIS AFTERNOON. AN INCREASE IN GRADIENT AHEAD OF SECOND
WRAP WILL KEEP GALES IN LYNN CANAL.

 CLOUDS ASSOCIATED WITH SECOND WRAP ARE QUICKLY SPREADING NORTH
AND WILL BE ACROSS NORTH CENTRAL THIS AFTERNOON AND FAR NORTH BY
THIS EVENING. THIS BAND OF CLOUDS DID PRODUCED A BURST OF SNOW IN
PAPG THIS MORNING AND WILL LIKELY CONTINUE ACROSS PAJN-PAOH AREAS
LATE THIS AFTERNOON AND EVENING. AM EXPECTING SNOWFALL AMOUNTS
ACROSS THE CENTRAL PANHANDLE TO BE JUST BELOW ADVISORY LEVEL WITH
2 TO 4 INCHES FALLING THROUGH SUNDAY MORNING. THE NORTH COAST
WILL REMAIN MAINLY SNOW BUT OVERALL QPF IS LOWER SO JUST THINK
1 TO 3 INCHES TONIGHT. RAIN SNOW LINE WILL PUSH NORTH TONIGHT AND
WILL CUT ACROSS AKZ23-AKZ26 BY MORNING FOR SNOW CHANGING TO RAIN
FROM THE SOUTH THROUGH SUNDAY MORNING. GENERALLY HAVE DIMINISHING
WINDS HERE.

 RAIN HAS RETURNED TO THE SOUTHERN COAST WITH SOME OF THIS
MODERATE AT TIMES. DO EXPECT TO SEE A WIND SHIFT TO THE SOUTHEAST
AS THE FRONTAL TROUGH MOVES INLAND AND HAVE TEMPERATURES
INCREASE. PRECIP WILL BECOME SHOWERY BEHIND FRONT FOR A WHILE BUT
GO BACK A A MORE STEADY RAIN. THINKING MAY USE PERIODS OF
RAIN/SNOW FOR ZONES TONIGHT WITH BANDED STRUCTURE.

 MODELS AGREE WELL ON SYNOPTIC PICTURE BUT THERE ARE A LOT OF
SMALL VARIATIONS IN TIMING AND PLACEMENT OF THE SMALLER FEATURES
THAT WILL AFFECT SENSIBLE WEATHER. DID NOT FAVOR ANY ONE
PARTICULAR MODEL TODAY BUT WENT FOR AN ENSEMBLE APPROACH TO
SMOOTH OUT DIFFERENCE AND STICK WITH THE OCCASIONAL NATURE OF THE
CURRENT PATTERN. DID USE NAM12 FOR PRES AND WIND.

 &&

 .LONG TERM... WEAK SURFACE LOW CENTERS ARE FORECAST TO MOVE N
ALONG THE PANHANDLE COAST SUN NIGHT THROUGH ABOUT WED CAUSING
SEVERAL EPISODES OF LIGHT PRECIPITATION. BY LATE IN THE WEEK
MODELS SHOW NO ORGANIZED WEATHER SYSTEMS NEAR THE EASTERN GULF.
THE LACK OF PRESSURE GRADIENT LATE IN THE WEEK WILL ALLOW
TEMPERATURES TO BE SEASONAL WHICH WILL FEEL LIKE A WARMING TREND
IN MANY AREAS. FORECAST CONFIDENCE IN LONG RANGE TREND IS AT OR
ABOVE AVERAGE THROUGH MID WEEK. PREDICTED CHANGES IN LONG WAVE
PATTERN AFTER THAT INCREASE THE SPREAD OF MODEL SOLUTIONS AND
LOWERS CONFIDENCE.

 THERE IS A DISTINCT LACK OF JETSTREAM OVER SE AK FOR NEXT WEEK.
A STRONG WESTERLY JET /160 KT CORE/ STAYS NEAR 40N WELL UNDER THE
DOMINANT HIGH PRESSURE RIDGE ALOFT OVER WESTERN AK. UPPER LEVEL
WINDS SPLIT AND FAN OUT NEAR 150W. THIS IS THE FLOW THAT WILL BE
STEERING WEAKING LOW CENTERS N UP THE COAST.

 ONE OF THE LOW CENTERS PUSHES INTO THE SOUTHERN PANHANDLE FROM
COASTAL BC SUN NIGHT AND MONDAY BRINGING CONTINUED LIGHT RAIN FOR
OUR SOUTHERN ZONES. THE CHANCE OF PRECIP DECREASES N OF ABOUT A
PETERSBURG TO SITKA LINE MON-TUES AS THE SYSTEMS WEAKEN AND LOSE
SUPPORT. PRECIP TYPE WILL INCLUDE SNOW FOR LOCATIONS WELL INLAND
WHERE COLDER AIR IS TRAPPED. WIND PATTERNS WILL FLUCTUATE SOME
NEXT WEEK... ESPECIALLY FOR SOUTHERN HALF OF PANHANDLE. SFC WINDS
WILL BE N-E NORTH OF THE LOW CENTERS AND SWITCH TO S-SE AFTER
FRONTAL WAVES PASS BY HEADING NORTH.

 GLOBAL MODELS APPEAR TO BE INITIALIZED WELL THIS MORNING AND
HAVE VERY SIMILAR SOLUTIONS THROUGH MID WEEK. DIFFERENCES SHOW UP
THURS TO SAT COINCIDING WITH PREDICTED CHANGES IN LONG WAVE
PATTERN FEATURES OVER THE N PACIFIC. THE PERSISTENT UPPER LEVEL
RIDGE OVER WESTERN AK IS PREDICTED TO SHIFT EAST IN RESPONSE TO A
VERY STRONG AND PROGRESSIVE STORM SYSTEM COMING OFF OF ASIA.
500 MB HEIGHT RISES ASSOCIATED WITH THE UPPER RIDGE SHIFTING
CLOSER TO EASTERN AK SHOULD MAKE FOR GRADUAL WARMING DURING THE
WEEK OF BOTH DAY TIME MAX TEMPS AND OVERNIGHT MIN TEMPS. THESE
CHANGES WILL BE MORE EVIDENT OVER THE NORTHERN 2/3 OF PANHANDLE
WHERE POCKETS OF UNSEASONABLY COLD AIR STILL EXIST ESPECIALLY IN
THE NORTHERN INNER CHANNELS. THE ECMWF HANDLES THIS CHANGE WITH
FLATTER RIDGING AND MORE ONSHORE FLOW FRI-SAT. THE GFS HAS MUCH
SHARPER HIGH AMPLITUDE RIDGING AND NORTHERLY FLOW INTO PANHANDLE.
NATIONAL CENTER GUIDANCE FOR LATE IN WEEK OVER AK SHOWS A FLATTER
RIDGE BUT ALSO REVEALS LARGE UNCERTAINTY. END OF WEEK FORECASTS
WILL BE DIFFICULT UNTIL MODELS GET A HANDLE ON THE VERY DEEP
STORM /940MB/ FORMING OFF OF ASIA MID- LATE WEEK.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING FOR PKZ011>013-022.
         SMALL CRAFT ADVISORY FOR PKZ021-031>034-036-041>043-051.

&&

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