217 
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Southeast Alaska forecast discussion 
National Weather Service Juneau Alaska 
1222 PM akdt Wednesday Jul 23 2008 


Short term...complex surface and upper air pattern across the Gulf 
and adjacent areas at this time. A fairly strong upper vorticity is over the 
y-k Delta and will dig southeast into the far western Gulf late 
tonight...merging with another vorticity currently moving eastward S of the 
akpen. The strong vorticity will then continue to the southwestern/S-cntrl 
Gulf Thursday and close off to an upper low. A weak low near 
50/150 will drift north and intensify late tonight and Thursday...and 
reach the central or north-central Gulf Thursday morning. A weak occluded 
front over the eastern Gulf will dissipate today as a stronger 
occluded front develops over the western Gulf tonight...and moves to 
the eastern Gulf by late Thursday afternoon. 


Main forecast issues will be winds with the stronger occluded 
front and low...and precipitation. Wind wise...strong S flow aloft will 
help enhance the low level upslope ridge along the north Gulf Coast 
later tonight and Thursday...and this will induce/intensify a barrier 
jet over the far northern Gulf area then. Am going to boost winds over 
marine area 52 to 40 knots for Thursday...with GFS actually even a bit 
stronger than that...but that was the most intense solution and 
there are enough differences on the models to not go that far 
yet. Will keep min gales for areas 43 and 51...and 25-30 knots Small Craft Advisory 
for marine zones 41 and 42. Will likely see Small Craft Advisory level east winds 
through Cross Sound by late Thursday afternoon...with remaining Inner 
Channels 20 knots or less through Thursday afternoon. 


Precipitation wise...some light precipitation associated with weak occluded 
front over the far eastern Gulf will move across the northern areas today. 
This should diminish some this evening as upper support moves east 
of the area...but there is enough onshore flow to keep probability of precipitation at 
least in the chance range northern areas tonight. Over the S...probability of precipitation 
will be kept fairly low as they still are relatively close to 
ridge axis aloft. Probably only mention a chance of light rain 
for zone 26 this evening at most...with zones 27 through 29 being 
kept dry. 




Long term...12z Friday a 500h low will be over a point 300 nm south-southwest of 
Yakutat, tracking east and reaching a point 200 nm SW of Sitka 00z 
Sunday. This steering will support a 998 mb low in the central 
Gulf of Alaska that will send an occlusion east to a Sitka to Ketchikan line 
18z Friday. The low will become vertically stacked by the time fills 
to 1002 mb 200 nm SW of Sitka 00z sun. 


The long range pkg closely follows the GFS run from 12z this 
morning, at least through this weekend. This confidence in 
the GFS is largely based on the much improved consensus 
between the GFS and the European model (ecmwf). 12z Friday a 500h low will be 
over a point 300 nm south-southwest of Yakutat. Good consensus between 
European model (ecmwf) and GFS, and better than prior model runs. 00z sun 
both models track the low aloft to be over a point 200 nm SW 
of Sitka, with the GFS height 541 km and the European model (ecmwf) at 544, 
again a close match. Climate will be increasingly filtered 
in especially from sun Onward. 




&& 


Ajk watches/warnings/advisories... 
public...none. 
Marine...Small Craft Advisory for pkz012-042-043. 


&& 


$$ 


Rwt/jbt 

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