459 
fxak67 pajk 182128 
afdajk 


Southeast Alaska forecast discussion 
National Weather Service Juneau Alaska 
125 PM akdt Thursday Mar 18 2010 


Short term...fairly strong deep layer ridge along western noam will 
weaken slightly through Friday. A complex frontal system over the 
central Gulf will slowly lift NE toward the area and be just 
offshore the central and northern outer coast by late Friday afternoon. 


Main forecast concern is how far southeast precipitation will get with the 
front. This will depend on how strongly the deep layer ridge 
holds in as the upper support for the front moves through...and 
models differ on this. Ended up going with a middle ground 
solution on this...with a rapid drop off in probability of precipitation from 80+ along 
Frederick Sound to less than 20 along Dixon Entrance for Friday. 
This was a slight southeast adjustment to the precipitation area from the 
previous forecast however. 


Otherwise...given cloud cover expected to slowly thicken over 
the area tonight...raised min temperatures most areas. Ptype will be 
mostly rain with this system at sea level although some snow will 
likely fall over the far north area due to low level northwest flow keeping 
it a bit cooler in the chilkat valley. May see some snow mix in 
around paya but model soundings (along with the latest paya 
sounding) suggest precipitation should be mostly rain...even though low 
level flow will be Ely. Cannot rule out a few wet flakes mixing 
in from pajn-pael Friday morning either. 


Strongest winds will be over the northern Gulf ahead of the front. 
Went with maximum gales for the northestern Gulf coastal waters...decreasing 
to min gales for the far southeastern Gulf coastal waters ahead of the 
front. Will see Small Craft Advisory level winds on mainly the east-west Inner Channels 
ahead of the front late tonight and Friday...with lightest winds 
expected in Lynn Canal due to parallel pressure gradient 
orientation. Should be a slow decrease in pre-frontal winds later 
Friday as the upper support moves inland ahead of it and low level 
pressure gradients weaken. Do not think the winds will be strong 
enough along the coast to warrant any wind advisories...but will 
likely have breezy mentioned for most of them especially late 
tonight and Friday. 


&& 


Long term...start of long term has weakening low in the northwest Gulf 
and associated front over the Panhandle shearing apart. Increased 
probability of precipitation for tomorrow night but at this time still expecting a dry 
weekend. Building ridge of high pressure will follow the 
low...location of this ridge is the forecast issue so far. GFS 
was keeping this ridge a bit further to the west than NAM and European model (ecmwf). 
Which in turn decreased the pressure gradient over the weekend 
and lowered winds in northern north-S Inner Channels. Liked the look 
of a NAM ec blend for this time period but panc leaned toward and 
GFS/NAM blend. So used a blend of ec and NAM with some GFS. 
Overall this kept the pattern pretty much the same but did weaken 
the north-S gradient slightly. Did keep the smcr winds for Sat sun 
but now down to 25 kts. 


For day 4 Onward model difference increase. Next low moving up 
form the North Pacific toward the Queen Charlottes on sun into Mon, GFS 
is much faster...further east and track north over the Panhandle. The 
ec keeps the low just west of the charlottes for same time period 
before the next ridge tracks east pushing out the low. HPC guidance used 
mainly the ec and GFS ensembles and felt it was a good compromise 
between the two solutions. HPC guide also dealt well the the next 
middle week low...which ec and GFS were in a bit better 
agreement...before diverging again with frontal band location.. 


Overall forecast confidence in average to a bit below average. 
Felt the forecast would be changed enough by model feature 
position to question any certainty. 


Ajk watches/warnings/advisories... 
public...none. 
Marine...Gale Warning for pkz041>043-051-052. 
Small Craft Advisory for pkz021-022-033>036. 


&& 


$$ 


Rwt/prb 

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