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000
FXAK67 PAJK 191412
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
612 AM AKDT WED JUN 19 2013

.SHORT TERM...A RIDGE OF HIGH PRESSURE WILL BUILD OVER THE
EASTERN GULF TODAY. THIS IS CURRENTLY CAPPING A MARINE LAYER OVER
THE OUTSIDE WATERS WHICH MOVED INTO SITKA AND NEARBY COASTAL
AREAS OVERNIGHT. AS THE RIDGE BUILDS THIS AFTERNOON THE WINDS
WILL INCREASE OUT OF THE NW AND SHOULD HELP TO MOVE THE MARINE
LAYER OUT OF SITKA. HOWEVER IT COULD PUSH IT FURTHER INTO OTHER
COASTAL AREAS. FOR NOW HAVE KEPT THE MENTION OF FOG TO THE
OUTSIDE WATERS THROUGH THE EVENING THEN HAVE IT MOVING BACK INTO
THE SOUTHERN COASTAL AREAS...SUCH AS CRAIG AND METLAKATLA...LATER
TONIGHT.

 THE OTHER MAIN WEATHER FEATURE WILL BE AN UPPER LEVEL WAVE OF
VORTICITY PASSING OVER THE PANHANDLE FROM CENTRAL B.C. NW TOWARD
TENAKEE THROUGH THE AFTERNOON BRINGING ISOLATED TO SCATTERED
SHOWERS TO THE AREA. CLOUDS ASSOCIATED WITH THIS CAN BE SEEN ON
SATELLITE IMAGERY THIS MORNING JUST EAST OF HYDER. HAVE INCLUDED
A SLIGHT CHANCE OR ISOLATED THUNDERSTORMS THIS AFTERNOON AND
EVENING WITH THIS WAVE AND WHEN IT CORRESPONDED WELL WITH MODEL
BASED CAPE. THE GFS SHOWED THE BEST CAPE OVER KETCHIKAN AND THE
EAST SIDE OF BARANOF ISLAND THIS AFTERNOON OF ABOUT 400J/KG. THE
NAM HAS SOME HIGHER CAPE VALUES SLIGHTLY FURTHER NORTH ALONG THE
MOUNTAINS NEAR JUNEAU AND WILL NEED TO WATCH FOR TCU`S THIS
AFTERNOON IN CASE THIS INSTABILITY "POPS" AS WELL.

 MID LEVEL FLOW IS OFFSHORE AND SHOULD HELP TO CREATE A LOT OF
LONG SUNNY BREAKS TODAY...ESPECIALLY OVER THE INNER
CHANNELS...AND KEEP OUR TEMPERATURES ABOVE NORMAL. THE SUN AND A
GENERALLY WEAK PRESSURE PATTERN WILL CAUSE AFTERNOON SEA BREEZES
TO DEVELOP. THE ONLY PLACE WHERE THIS WORKS WITH THE PRESSURE
GRADIENT IS FOR CROSS SOUND...ICY STRAIT AND THROUGH TO THE SOUTH
SIDE OF DOUGLAS ISLAND. HAVE INCREASED WINDS SLIGHTLY FOR THOSE
AREAS AS A RESULT INCLUDING WEST WINDS TO 20KT FOR CROSS SOUND.
IF THE CLOUDS DISSIPATE EVEN EARLIER AND THE SEA BREEZE IS
STRONGER...A SMALL CRAFT ADVISORY MAY BE NEEDED FOR THAT REGION.
850MB TEMPS ARE PROGGED TO WARM AS WELL. SO TEMPS SHOULD REACH AT
LEAST AS HIGH AS YESTERDAY - EVERYWHERE THAT DOESN`T GET THE
MARINE LAYER. IF THE MARINE LAYER HOLDS IT WILL STAY 10 DEGREES
COOLER. THE SEA BREEZE WILL CAUSE TEMPS TO BE SLIGHTLY COOLER IN
COASTAL AREAS TOO.

 MODELS WERE IN GOOD AGREEMENT ON THE PRESSURE PATTERN TODAY.
USED THE NAM12 FOR ADJUSTMENTS TO THAT AND WINDS. THERE WERE
DIFFERENCES WITH EACH MODEL ON THE PLACEMENT OF SHOWERS. MOST
SHOWED A SIMILAR PATH FOLLOWING THE UPPER LEVEL FEATURE AS
MENTIONED...HOWEVER MAJORITY OF THEM HAD VERY LIMITED AMOUNTS.
LIKELY DUE TO THE OFFSHORE/DOWNSLOPING EFFECTS. THE ECMWF HAD THE
GREATEST LIKELIHOOD OF PRECIP. TOOK MORE OF A CONSENSUS APPROACH
WITH THE GREATEST CHANCES IN THOSE AREAS WITH GREATEST
INSTABILITY AS STATED ABOVE. FORECAST CONFIDENCE IS AVERAGE.

 &&

 .LONG TERM.../THU THROUGH TUE/ PATTERN CHANGE INDICATED FOR SE
AK PANHANDLE FOR WEEKEND AND EARLY NEXT WEEK. HOWEVER THERE ARE
SOME UNCERTAINTIES WITH DETAILS...PARTICULARLY WITH HOW MUCH
PRECIP AND WHEN. FORECAST CONFIDENCE HIGHER THAT TEMPS WILL COOL
CLOSER TO NORMAL BUT CONFIDENCE WITH PRECIP TIMING AND AMTS IS
LOW.

 IN THE BIG PICTURE HIGH PRESSURE PRETTY MUCH STAYS IN PLACE OVER
INTERIOR AK AND NW CANADA DURING THIS PERIOD. WEST JET STREAM AND
STORM TRACK REMAIN SOUTH OF PANHANDLE AROUND 50N LATITUDE. THE
PATTERN CHANGE IS RELATED TO THE CUMULATIVE EFFECTS OF SEVERAL
DIFFERENT COMPONENTS. FIRST... SURFACE HIGH PRESSURE BUILDS OVER
THE OFFSHORE WATERS THU-FRI AND ULTIMATELY A WEAK ONSHORE PUSH OF
COOLER AND MOIST OCEAN AIR MOVES ALL THE WAY IN TO THE INNER
CHANNELS FRI. SECOND...MOISTURE ASSOCIATED WITH SHOWERS AND
THUNDERSHOWERS FORMING IN BRITISH COLUMBIA WILL DRIFT WEST TO
COASTAL MOUNTAINS AND OUR CENTRAL AND SOUTHERN ZONES. LAST...AN
UPPER LOW CENTER AND SURFACE FRONT MOVE EAST TOWARD BC COAST FRI-
SAT AND WEAKEN. THIS LOW FEATURE IS PREDICTED TO TAKE A TURN TO
THE N-NE TOWARD THE SOUTHERN PANHANDLE BRINGING WEAK FRONTAL
DYNAMICS AND MOISTURE WITH IT. THE NET RESULT WILL BE A REGION OF
STEADY LIGHT RAIN AND COOLER AIR SPREADING NORTH OVER THE SOUTHERN
2/3 PANHANDLE FRI NIGHT-EARLY SAT.

 THE FORECAST UNCERTAINTIES ARE CONNECTED TO THE WEEKEND LOW
CENTERS STALLING W-SW OF HAIDA GWAII IN PART BECAUSE OF THE UPPER
HIGH PRESSURE OVER INTERIOR AK AND NW CANADA. IF THIS WERE TO
HAPPEN A E-SE FLOW ALOFT WOULD LIKELY SET UP OVER THE PANHANDLE.
TYPICALLY THIS PATTERN IS CLOUDY BUT CHANCES OF PRECIP ARE HIGHER
OVER SRN HALF PANHANDLE. AREAS NORTH OF ROUGHLY FREDERICK SOUND MAY
SEE A BIT LESS CLOUD COVER AND TEMPS WARMING TO MID 60S...ESP SUN-
MON. NAM SOLUTION IS RAINIEST. GFS SOLUTION HOLDS LOW CENTERS
FARTHER SOUTH. EC AND UK MET ARE SLOWER IN GENERAL AND HOLD
WEEKEND LOWS A BIT FARTHER WEST. USED AN ENSEMBLE APPROACH TO
ARRIVE AT THE AVE SOLUTION IN THE GRAPHIC PRECIPITATION FORECASTS.
DID COOL MAX TEMPS DOWN SUN-TUES TO AROUND CLIMATOLOGICAL
NORMALS...UPPER 50S AND 60S.

 &&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.

&&

$$

FERRIN/TA