Small Craft Advisory 401, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
243 PM AKDT MON JUL 9 2012

.SHORT TERM...FAST MOVING LOW ALOFT TRACKING N TOWARD BARANOF
ISLAND THIS AFTERNOON HAS A RELATIVELY WEAK EXPRESSION TO THE
BOUNDARY LAYER, BUT IS IN A STRONGLY BAROCLINIC ENVIRONMENT FOR
THIS TIME OF YEAR AND WILL DEVELOP DOWNWARD INTO THE BOUNDARY
LAYER MORE AS IT REACHES DEEPER TOPOGRAPHY IN THE NRN PANHANDLE
THIS EVENING. WHILE IT IS A 1010 MB LOW APPROACHING THE PANHANDLE
NOW, IT WILL BE A 998 MB LOW IN SOUTHERN YUKON TERRITORY ABOUT
12Z MON. THE MODELS, INCLUDING THE NAM AS PRIMARY GUIDANCE, HAVE
A REASONABLE LOCK ON THE THICKNESS GRADIENT AND THEREFORE THE
BAROCLINITY. THE CONFIDENCE IS AVERAGE. FORECAST CHANGES ARE
SMALL.

 THE PARENT LOW IS 240 NM S OF MIDDLETON ISLAND.  THE AXIS TO THE
 LOW ALOFT IS TILTED TO THE N TOWARD THE COLDER THICKNESS AS
DEPICTED IN THE 1000-500 H THICKNESS FIELDS OF THE MODELS. THIS
MORE NORTHERN LOCATION OF THE LOW ALOFT WILL BECOME IMPORTANT
TONIGHT AS IT PROGRESSIVELY INTERACTS WITH A POLAR FRONT ZONE
WAVE TRACKING N TOWARD THE PANHANDLE. UNTIL THIS EVENING, THE OLD
PARENT LOW ACTUALLY INTERFERES WITH THE CYCLOGENESIS OF THE WAVE,
BUT AFTER THE WAVE PASSES MOST OF THE WAY N ALONG THE PANHANDLE
THE TROUGH FROM THE OLD PARENT LOW WILL AID THE CYCLOGENESIS.

 GOES IR LOOP SHOWS A SECTION OF POLAR FRONT ZONE EXTENDING FROM
600 NM S OF KETCHIKAN TO A FRONTAL WAVE ABOUT 200 NM SW OF
KETCHIKAN AT THIS TIME. THIS WAVE HAS TRACKED TOWARD THE N AT
ABOUT 60 KT DURING THE LAST 6 HOURS.

.LONG TERM...MODELS IN BETTER AGREEMENT ON THE MAIN FEATURES
FROM TUE NIGHT INTO FRI. SFC RIDGE WILL BE BUILDING OVER THE ERN
GULF AND SE AK TUE NIGHT INTO WED. THEN A WEAK FRONT WILL MOVE
INTO THE ERN GULF LATE THU AND MAKE SLOW PROGRESS ACROSS THE AREA
THRU FRI NIGHT. ENDED UP USING A GFS/NAM BLEND TO MAKE SOME
ADJUSTMENTS FROM WED NIGHT INTO THU NIGHT...MAINLY TO INCREASE
WINDS OVER THE GULF. DID MAKE OTHER TWEAKS FROM TUE NIGHT INTO
FRI.

 EVEN WITH THE RIDGE BUILDING IN...ENOUGH ONSHORE FLOW WILL BE
GOING ON OVER THE NRN AREAS TO KEEP CLOUDS AND A FEW SHOWERS
AROUND TUE NIGHT INTO WED. THE S SHOULD SEE SOME CLEARING WITH A
MORE NWLY LOW LEVEL FLOW THERE...BUT WILL HAVE TO WATCH FOR SOME
MIDDLE AND HIGH CLOUDS POTENTIALLY STREAMING IN FROM THE WSW WELL
OUT AHEAD OF THAT LATE WEEK FRONT. THE SHOWER THREAT SHOULD
DIMINISH OVER THE N WED NIGHT BUT PRECIP FROM THE LATE WEEK FRONT
SHOULD BE MOVING INTO THE GULF THU...THEN LIKELY ONSHORE OVER THE
NRN AND CENTRAL AREAS THU NIGHT INTO FRI.

 AS FOR WINDS...THE WINDS OVER THE NRN AREA SHOULD DECREASE
SLOWLY TUE NIGHT AND WED MORNING AS MID-LEVEL FLOW VEERS FROM SW
TO W AND LEE SIDE TROFFING OVER THE FAR NRN PANHANDLE AND SRN
YUKON WEAKENS. DID BRING IN SCA LEVEL WINDS TO THE WRN OUTER
MARINE AREAS BEGINNING WED NIGHT AND THIS SHOULD CONTINUE OVER
THE NRN GULF INTO THU NIGHT. WITH THE FRONT WEAKENING AS IT
APPROACHES THE MAIN PANHANDLE AREA DO NOT EXPECT THE SCA LEVEL
WINDS TO REACH THE E-CENTRAL OR SE GULF THU NIGHT OR FRI.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND FROM TUESDAY MORNING THROUGH TUESDAY AFTERNOON FOR
     AKZ018.
MARINE...GALE WARNING FOR PKZ012.
         SMALL CRAFT ADVISORY FOR PKZ011-013-022-031>034-053.

&&

JBT/RWT