842 
fxak67 pajk 072012 
afdajk 


Southeast Alaska forecast discussion 
National Weather Service Juneau Alaska 
1212 PM akdt Thursday Aug 7 2008 


Short term...a weakening ridge is slowly drifting east along 
the Coast Mountains with its main axis over eastern British 
Columbia. A long fetch of moisture over western periphery of the 
ridge is connecting to an incoming low in the south eastern Gulf. 
Pacg radar with super resolution depicts spotty light rain moving 
from the south across the area...a bit more concentrated over the 
outside waters from Port Alexander northward. Numerous pilot 
reports and spotters indicated dense fog across southern most 
Inner Channels early this morning with fog bank near Yakutat Bay 
and areas of fog over the northern Panhandle. Fog layers have 
been lifted by middle morning except around Annette Island and 
southern half of Clarence Strait. Morning satellite loop depicts 
two main synoptic scale upper lows...one over interior Alaska and 
the other in the south eastern Gulf. The southern system is 
slowly moving east with its surface low getting closer to 
southwest of the Queen Charlottes islands...pushing the ridge 
farther eastward. An associated pre-frontal boundary is forming 
southwest of Dixon Entrance ahead of the low as of this writing. 


Models are well initialized and in good agreement for tonight and 
Friday with a 1008 mb low southwest of the Queen Charlottes. The 
low will slightly deepen through Friday afternoon. A weak front 
associated with the low will move slowly across Southeast Alaska 
through early Friday afternoon before dissipating by early evening 
hours. Due to more middle level clouds with the frontal boundary 
moving across the area...expect no fog layers forming tonight. 
Based on the model consensus...will go with chance probability of precipitation forecast 
in general for tonight and Friday across the Panhandle except 
Hyder area Friday when the low moves farther east. No significant 
winds and seas are expected over the coastal waters with this weak 
frontal boundary for the short term forecast periods. 


Long term...at the beginning of the long term period three middle 
level vorticity lows are located in southern Alaska and associated waters. 
The first middle level vorticity low near the charlottes will advect 
eastward into western British Columbia late Friday through 
Saturday. This will bring a chance of scattered showers to the 
southern Panhandle as weak middle level vorticity bands rotate 
counterclockwise around the main middle level low in British 
Columbia organizing the shower activity. The 2nd middle level vorticity 
low located northeast of Anchorage will continue to rotate and 
slowly weaken and advect northeastward through late Sunday. This 
middle level low will continue to encourage the marine layer to push 
onshore with the southwesterly low and middle level flow across the 
central and northern Panhandle through the weekend. Expecting 
cloudy skies with areas of drizzle...fog and light rain across 
the central and northern Panhandle through the weekend especially 
near Yakutat. Yakutat will be located beneath a middle level 
deformation band that will locally enhance precipitation and 
shower activity within the marine layer. The 3rd middle level low now 
near 50 north 170 west will advect eastward through the weekend and 
approach the Panhandle Monday. While the locally breezy conditions 
with this low on Monday will mix out the marine layer...the 
positive vorticity advection ahead of the low will allow for 
continued rainy conditions across the majority of the Panhandle 
early next week. 


The 5-wave 500mb geopotential height pattern begins to change 
into early next week. An Omega block begins to form across the 
western United States and as it strengthens...the southwesterly 
height gradient across the Panhandle tightens. With this expect 
next week to be rather wet and locally breezy along coastal 
locations with successive surface lows/fronts advecting eastward 
across the Gulf into the Panhandle Monday...Tuesday...late 
Wednesday and Thursday. 


Through the weekend expect relatively light winds with no strong 
surface pressure gradients across the Panhandle. Winds will reach 15 knots 
in the afternoons and early mornings as the sea/land breezes will 
remain active in the Panhandle. By Monday the aforementioned middle level low 
and associated front will bring locally breezy conditions to 
coastal locations. At this time it is unclear how far inland these locally 
breezy conditions will progress as the front will begin to shear 
out over the mountainous terrain. 


Used the 12z GFS early in the long term as it had a better handle 
on the progression of the middle level low for Monday. Coordinated 
with HPC to use more of the 00/12z European model (ecmwf) from Tuesday through day 9 
with the middle level pattern shift. Confidence is high that next 
week will be rather wet across the Panhandle but at this time it is 
difficult pin down the exact timing of each successive front as 
timing differences in the 12z GFS/European model (ecmwf) remain. Expect 
temperatures to be below normal next week with the wet conditions. 


&& 


Ajk watches/warnings/advisories... 
public...none. 
Marine...none. 


&& 


$$ 


Sja/pss 

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