Area Forecast Discussion
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FXAK67 PAJK 232311
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
311 PM AKDT SAT MAY 23 2015

.SHORT TERM...COMPLEX WEATHER STORY OVER THE PANHANDLE TODAY. PART
ONE IS AN UPPER LOW OVER THE SOUTHERN PANHANDLE THAT HAS SPARKED
OFF SOME ISOLATED THUNDERSTORMS THIS MORNING. ONE CELL FORMED JUST
AFTER DAYBREAK ON THE PENINSULA BETWEEN PORTLAND CANAL AND BEHM
CANAL BUT PROMPTLY COLLAPSED AS IT TRIED TO MOVE W OVER WATER. A
FEW OTHER T-STORMS HAVE POPPED UP NEAR PRINCE RUPERT, BC BUT THOSE
ALSO COLLAPSED AS THEY MOVED NW OVER PORTLAND CANAL. PART TWO IS
FARTHER NORTH AND TAKES THE FORM OF A SHIELD OF MID TO HIGH LEVEL
CLOUDS STREAMING INTO THE CENTRAL AND NORTHERN PANHANDLE FROM THE
BC INTERIOR. THESE CLOUDS HAVE CURTAILED DAYTIME TEMPERATURES
COMPARED TO YESTERDAY. MOST PLACES ARE STILL SHOWING TEMPS IN THE
50S AND 60S AROUND NOON. FINALLY PART THREE IS THE PERSISTENT
MARINE LAYER CLOUDS AND FOG ALONG THE OUTER COAST AND SOUTHERN
PANHANDLE. YAKUTAT HAD VISIBILITY AS LOW AS A QUARTER MILE THIS
MORNING. THE LOW CLOUDS ARE HAVING A TOUGH TIME BURNING OFF DUE TO
THE HIGHER CLOUDS AND SOME DEVELOPING WEAK ONSHORE FLOW.

THE UPPER LOW OVER THE SOUTHERN PANHANDLE DOES NOT STICK AROUND
LONG AS IT IS FORECAST TO SLIP SE THIS EVENING TAKING MOST OF ITS
VORTICITY WITH IT. STILL IT WILL STICK AROUND LONG ENOUGH THAT
MORE ISOLATED THUNDERSTORMS ACROSS THE SOUTHERN PANHANDLE THIS
AFTERNOON AND EVENING ARE POSSIBLE. THEY ARE MAINLY EXPECTED
ACROSS THE HIGHER TERRAIN AS LINGERING CLOUD COVER THIS MORNING IS
INHIBITING TEMPERATURES FROM GETTING HIGH ENOUGH TO INITIALIZE
CONVECTION FROM SEA LEVEL. GENERAL MOTION OF THESE STORMS WILL BE
FROM THE E AND SE TO THE W AND NW. EXPECT MORE LIGHTNING AND SOME
HEAVY RAIN AS THESE STORMS DEVELOP.

FARTHER NORTH THE MID TO HIGH LEVEL CLOUD COVER HAS STUNTED
AFTERNOON TEMPERATURES BOTH IN THE PANHANDLE AS WELL AS UPSTREAM
IN BC. AS SUCH THUNDERSTORMS ARE NOT EXPECTED THIS EVENING FROM
AROUND PETERSBURG NORTHWARD. OTHERWISE MOSTLY CLOUDY SKIES WILL
CONTINUE FOR THE CENTRAL AND NORTHERN PANHANDLE AS THE VORTICITY
THAT IS RESPONSIBLE FOR THE CLOUDS STICKS AROUND AND EVEN DRIFTS
NORTH THROUGH TONIGHT. TOMORROW MOST OF THAT VORTICITY STARTS TO
DRIFT BACK EAST AHEAD OF THE NEXT TROUGH IN THE GULF SO THE CLOUD
SHIELD SHOULD START BANKING BACK TO THE EAST TOMORROW BUT ENOUGH
WILL LINGER FOR HIGH TEMPS TO NOT GET OUT OF THE 60S FOR THE MOST
PART.

SPEAKING OF THE NEXT TROUGH, IT IS STILL OVER IN THE WESTERN GULF
RIGHT NOW AND WILL START HEADING EAST TONIGHT. IT WILL BRING
CLOUDS AND RAIN TO THE CENTRAL GULF AND NORTHERN OUTER COAST WEST
OF YAKUTAT BY TOMORROW AFTERNOON. IT DOES NOT QUITE GET TO THE
REST OF THE PANHANDLE BY THE END OF THE SHORT RANGE BUT SOME
HIGHER LEVEL CLOUDS COULD BE OBSERVED ALONG THE NE GULF COAST BY
TOMORROW AFTERNOON.

THROUGH ALL OF THIS, THE MARINE LAYER CLOUDS AND FOG WILL CONTINUE
THEIR ADVANCE AND RETREAT ALONG THE OUTER COAST AND INNER
CHANNELS. DEVELOPING ONSHORE FLOW THIS AFTERNOON AND TONIGHT WILL
LIKELY CAUSE THE LOW CLOUDS AND FOG TO ADVANCE FARTHER INTO THE
INNER CHANNELS TONIGHT THEN WHAT HAS BEEN SEEN IN THE LAST FEW
DAYS. QUITE A FEW AREAS THAT HAVEN`T SEEN THE LOW CLOUDS LIKELY
WILL TONIGHT INCLUDING MANY AREAS ALONG CLARENCE STRAIT, ICE
STRAIT, CHATHAM STRAIT, SUMNER STRAIT AND POSSIBLY EVEN FARTHER
INLAND. THE CLOUDS WILL THEN BURN OFF AGAIN TOMORROW BUT HIGHER
LEVEL CLOUD COVER IN SOME AREAS MAY DELAY THE BURN OFF UNTIL LATER
IN THE DAY OR NOT AT ALL.

SHORT RANGE MODELS WERE IN GOOD AGREEMENT THOUGH SOME DISAGREEMENT
ON EXACTLY HOW MUCH UPPER LEVEL ENERGY IS LEFT OVER THE PANHANDLE
AFTER THE SOUTHERN PANHANDLE UPPER LOW RETREATS WAS NOTED. ALL IN
ALL THAT DOES NOT AFFECT THE FORECAST TOO MUCH ASIDE FROM HOW MUCH
SHOWER ACTIVITY AND CLOUDS WILL LINGER OVER THE SOUTHERN OUTER
COAST. GENERALLY FAVORED THE NAM FOR GUIDANCE TODAY.

.LONG TERM...WEAKENING SHORT WAVE IN THE NORTHERN AK GULF AND
ASSOCIATED FRONT WILL PUSH INTO THE AK INTERIOR AND YUKON THROUGH
MONDAY AS HIGH PRESSURE BEGINS TO REBUILD OVER THE CENTRAL AK
GULF. PRECIPITATION WILL MAINLY BE OVER THE NORTHERN GULF AND
YAKUTAT REGION AS ANY ENERGY FROM THE WAVE DISSIPATES PUSHING THE
RIDGE CURRENTLY OVER THE PANHANDLE EASTWARD. CLOUD COVER FROM THE
FRONT WILL MOVE ACROSS THE PANHANDLE SUNDAY NIGHT SO EXPECTING
LESS DIURNAL TEMPERATURE VARIATION. AS THE HIGH PRESSURE RIDGE
BUILDS OVER THE GULF BY MONDAY WE RETURN TO A SIMILAR WEATHER
PATTERN SEEN THE PAST FEW DAYS WITH WARM DAY TIME TEMPS, CLEARER
SKIES, AFTERNOON SEA BREEZE DEVELOPMENT, MARINE STRATUS FORMING
AND POTENTIAL EASTERLY WAVES MOVING IN FROM BRITISH COLUMBIA LATER
IN THE WEEK. DIFFERENCES WILL BE THE RIDGE AXIS MAY HAVE MORE
ONSHORE FLOW WHICH WOULD KEEP IN MORE CLOUD COVER AND THUS SUBDUE
TEMPERATURES. PLUS WHILE MODEL 500 MB HEIGHTS HAD POTENTIAL FOR
ANOTHER STRONG BLOCKING PATTERN THEY WERE NOT AS ROBUST AS THE
PREVIOUS OMEGA BLOCK. IN ADDITION AN UPPER LEVEL LOW WILL DEVELOP
NEAR KODIAK FROM A PARENT LOW IN THE BERING SEA TUESDAY THEN CROSS
OVER THE NORTHERN GULF WEDNESDAY. NOT SEEING A CORRESPONDING
SURFACE FEATURE SO THIS MAY BRING JUST MORE CLOUD COVER TO THE
NORTHERN PANHANDLE. BUT HIGH UNCERTAINTY WITH THE TRACK OF THIS
SYSTEM. FEEL THE 00Z ECMWF SOLUTION MOVING IT INTO NORTHERN B.C.
SEEMED MORE REASONABLE, BUT THE 12Z RUNS STARTED TO SLOW DOWN ITS
EASTWARD PROGRESSION. BY THE END OF THE WEEK HIGHER UNCERTAINTY
WITH WAVES ADVANCING FROM THE WEST. THE GFS KEEPS A BLOCKING
PATTERN IN PLACE THROUGH MOST OF THE LONG RANGE KEEPING ALONG LOW
WEST OF THE AK GULF WHILE THE ECMWF IN THE PAST TWO RUNS BREAKS
DOWN THE RIDGE BY SATURDAY ALLOWING THESE SYSTEMS INTO THE CENTRAL
GULF.

USED SOME 12Z NAM/GEM ON SUNDAY NIGHT FOR THE ADVANCING BUT
DISSIPATING SHORT WAVE WHICH THE ECMWF WAS NOT PICKING UP AS MUCH.
MODELS FELL IN LINE WITH EACH OTHER BY MONDAY FOR SURFACE
PRESSURE, BUILDING HIGH AND DID NOT SHOW TOO MUCH DIFFERENCE FROM
PREVIOUS FORECAST. MODEL CHOICE FOR THAT TIME IS 00Z ECMWF. LATER
IN THE WEEK WENT WITH ENSEMBLE APPROACH USING NEW WPC GRIDS.
OVERALL CHANGES TO THE CURRENT FORECAST WERE MINOR BUT WITH MODEL
DIFFERENCES AND RUN TO RUN INCONSISTENCY STARTING WEDNESDAY EXPECT
FORECAST TO VARY. FORECAST CONFIDENCE IS AVERAGE INITIALLY THEN
DROPS BELOW AVERAGE.


&&

.FIRE WEATHER...ELEVATED FIRE DANGER IS A BIT MORE LIMITED IN
SCOPE TODAY. MID TO HIGH LEVEL CLOUDS OVER THE NORTHERN AND
CENTRAL PANHANDLE HAS LIMITED TEMPERATURES TO THE 60S SO FAR THIS
AFTERNOON. LESS CLOUD COVER HAS BEEN OBSERVED OVER THE EXTREME
NORTHERN PANHANDLE AND AS A RESULT RELATIVE HUMIDITY VALUES HAVE
ONLY GONE BELOW 40 PERCENT IN THE TAIYA RIVER AND CHILKAT RIVER
VALLEYS SO FAR. A FEW OTHER AREAS AWAY FROM THE WATER CHANNELS AND
IN AREAS OF LOW CLOUD COVER MAY FOLLOW SUIT LATER THIS AFTERNOON
AND EVENING BUT WILL LARGELY BE LIMITED IN AREA. FIRE WEATHER WILL
IMPROVE OVER THE NEXT FEW DAYS AS CLOUD COVER LINGERS BOTH AT LOW
AND HIGH LEVELS AND ONSHORE FLOW DEVELOPS TONIGHT. MIN RH VALUES
WILL ONLY BE IN THE 40 TO 60 PERCENT RANGE FOR SUN AND MON. FUELS
STILL REMAIN VERY DRY HOWEVER SO EXTRA CARE IS STILL ENCOURAGED
FOR ANY OPEN AIR FIRES. AS HIGH PRESSURE REBUILD OVER THE GULF
NEXT WEEK THERE IS POTENTIAL TO RETURN TO FIRE WEATHER PATTERN
WITH LOWER DAYTIME RELATIVE HUMIDITY. AS THERE IS NO SIGNIFICANT
RAINFALL EXPECTED THROUGH THE LONG RANGE FORECAST FUEL WILL REMAIN
VERY DRY.

&&

.HYDROLOGY...THE REALLY WARM TEMPERATURES OVER THE LAST SEVERAL
DAYS HAVE CAUSED WATER LEVELS IN SOME AREA RIVERS TO RISE DUE TO
MELTING SNOW IN THE HIGHER ELEVATIONS. NO FLOODING IS EXPECTED AT
THIS TIME BUT THE TAIYA RIVER DID APPROACH BANKFULL LAST NIGHT AND
WILL LIKELY DO SO AGAIN TONIGHT AND SUN NIGHT AS WARMER
TEMPERATURES CONTINUE.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ012-021-022-042.

&&

$$

EAL/PRB

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