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000
FXAK67 PAJK 071450
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
550 AM AKST SAT DEC 7 2013

.SHORT TERM...A HIGH PRESSURE RIDGE OVER THE GULF OF ALASKA
EXTENDING FROM THE KENAI PENINSULA SOUTHEAST WEST OF HAIDA GWAII
TO THE EASTERN PACIFIC IS STILL HOLD UP AND VERY SLOWLY GIVING
WAY TO THE BATTERING OF SHORT WAVES IN THE UPPER LEVEL FLOW
PATTERN. A COMPLEX LOW PRESSURE SYSTEM QUASI STATIONARY ABOUT
500 NM SOUTH OF COLD BAY HAS A FRONTAL BOUNDARY EXTEND FROM THE
EASTERN ALEUTIANS TO ABOUT 40N/140W. MEANWHILE IN THE UPPER LEVEL
FLOW WEAK SHORT WAVES ARE TRACKING SOUTHWARD FROM THE EASTERN
PORTION OF THE STATE AND YUKON TERRITORY ACROSS THE PANHANDLE AND
BRITISH COLUMBIA. THE MAIN IMPACT OF THESE TROUGHS HAS BEEN TO
SPREAD CLOUDS IN THE REGION AND SLOWLY MOISTEN THE LOWER
ATMOSPHERE THROUGH TIME. A FEW FLURRIES OR SPRINKLES COULD BE
FOUND AS WELL WITH THE TROUGHS.

 SOME OF MODEL GUIDANCE TRYING TO HINT AT SOME FOG DEVELOPMENT AS
WELL. I DID NOT TRY TO HIT IT TOO HARD YET AS AM CONCERN ABOUT
THE LACK OF WET GROUND SURFACES TO TO ASSIST IN THE FOG FORMATION
AND THE FACT THE LOWER LEVELS OF THE PANHANDLE ARE NOT YET
SATURATED.

 WIND MAINLY UNDER 20 KT ACROSS THE REGION AND THIS SHOULD
PERSIST THROUGH SATURDAY NIGHT. ONLY A FEW MINOR ADJUSTMENTS TO
THE FORECAST THAT WAS OUT ALREADY BUT USED A BIT OF THE NAM AND A
SHADE OF THE ECMWF FOR WINDS.

 &&

 .LONG TERM...CHANGE IS COMING. THE RESENT COLD AND DRY WEATHER
IS COMING TO AN END AS THE BLOCKING RIDGE IN THE GULF FALLS APART
SUN INTO MON. THE UPPER RIDGE BECOMES MUCH FLATTER BY MON
PROMOTING MORE WESTERLY FLOW OFF THE GULF FOR MUCH OF NEXT WEEK.
HOWEVER THE COLD DRY AIR MASS IN THE PANHANDLE WILL NOT JUST GO
AWAY WITHOUT A FIGHT. IT WILL STAY ENTRENCHED IN THE INNER
CHANNELS WHILE THE WARMER MOISTER WESTERLY FLOW OVERRUNS IT
STARTING SUN NIGHT.

 OUR FIRST CHANCE OF PRECIP COMES SUN NIGHT AS A WEAK UPPER
TROUGH MOVES THROUGH WHAT IS LEFT OF THE RIDGE AND HELPS
REINFORCE THE OVERRUNNING WARM AIR. POPS HAVE BEEN LEFT AT A
CHANCE FOR MOST AREAS AS THERE ISN`T MUCH MOISTURE TO WORK WITH
AND THE FEATURES ARE WEAK. HOWEVER IF PRECIP DOES HAPPEN AMOUNTS
WILL BE LIGHT AND THE TYPE WILL BE SOMEWHAT TRICKY TO PIN DOWN
ESPECIALLY SUN NIGHT. MODEL FORECAST SOUNDINGS PAINT A PICTURE OF
A LOW LEVEL SATURATED LAYER THAT IS NEAR OR JUST BELOW FREEZING
WITH A DRY ATMOSPHERE ALOFT THAT REACHES 33 OR 34 DEGREES AT
ABOUT 3000 OR 4000 FT. THIS IS SUGGESTING THAT THERE WILL BE A
LOW LEVEL CLOUD LAYER WITH SUPERCOOLED WATER DROPLETS IN IT WITH
EITHER NO HIGHER LEVEL CLOUDS OR A VERY DRY LAYER BELOW THE HIGH
CLOUDS WHICH WILL CAUSE NO ICE CRYSTALS TO BE ABLE TO SEED THE
LOWER LEVEL CLOUDS. THE RESULT IS THE POSSIBILITY OF SOME LIGHT
FREEZING DRIZZLE SUN NIGHT IN THE NORTHERN HALF OF THE PANHANDLE.
SURFACE TEMPERATURES SUN NIGHT WILL BE HOVERING AROUND THE
FREEZING MARK FOR MOST PLACES SO IT IS STILL QUESTIONABLE IF IT
WILL BE COLD ENOUGH FOR THIS POSSIBILITY. ALSO WHILE THE NAM IS
THE MAIN ONE SUGGESTING THIS SCENARIO THE GFS AND SREF SOUNDINGS
ARE NOT AS COLD IN THE LOWER LEVELS (RESULTING IN PLANE RAIN OR
DRIZZLE) AND THE UPPER LEVEL ATMOSPHERE IS A BIT MORE MOIST
ALLOWING FOR THE POSSIBILITY OF SOME SEEDING OF THE LOWER LEVEL
CLOUD LAYER (RESULTING IN A CHANCE OF SNOW INSTEAD OF DRIZZLE).
AS SUCH FOR SUN NIGHT I HAVE MAINLY CALLED FOR A CHANCE OF RAIN
AND SNOW IN MOST AREAS WITH A CHANCE OF LIGHT FREEZING DRIZZLE IN
THE NORTHERN INNER CHANNELS AND NORTHERN OUTER COAST SUN NIGHT.

 INTO MID WEEK COLDER AIR FILTERS BACK INTO THE NORTHERN
PANHANDLE AS A MOISTER UPPER LEVEL ENVIRONMENT SETS UP OVER MOST
OF THE PANHANDLE ALLOWING FOR SEEDING OF THE LOWER LEVEL CLOUD
LAYER FOR SNOW AND/OR RAIN. CHANCES OF PRECIP RAMP UP ON WED AS
OUR FIRST MAJOR SYSTEM IN A WHILE MOVES INTO THE PANHANDLE FROM
THE SOUTHWEST. TIMING, STRUCTURE, AND STRENGTH ARE STILL UP FOR
DEBATE BY THE MODELS AS THE ECMWF BRINGS THE ONSET OF THE HEAVIER
PRECIP TO THE PANHANDLE A GOOD 12 TO 18 HOURS BEFORE THE GFS
DOES. THE ECMWF ALSO HAS A FARTHER NORTH TRACK AND CENTRAL
PRESSURE 5 MB LOWER THAN THE GFS. IN ANY CASE IT LOOKS LIKE A
DECENT PRECIP EVENT IS IN THE WORKS FOR WED. WHETHER IT WILL BE A
HEAVY SNOW EVENT FOR THE NORTH DEPENDS ON HOW MUCH COLD AIR
REMAINS AFTER THE MODERATION OF THE SURFACE TEMPS BY THE
OVERRUNNING WARMER AIR EARLIER IN THE WEEK. LIKELY HAINES AND
SKAGWAY HAVE THE BEST CHANCE FOR THIS BUT MODEL INCONSISTENCIES
KEEP THINGS UNCERTAIN AT THE MOMENT. THERE IS ANOTHER STORM
COMING FOR LATE WEEK TO NEXT WEEKEND BUT MODEL AGREEMENT IS EVEN
WORSE THAT FAR OUT.


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

&&

$$

BEZENEK/EAL