273 
fxak67 pajk 062103 
afdajk 


Southeast Alaska forecast discussion 
National Weather Service Juneau Alaska 
103 PM akdt Sat Sep 6 2008 


Short term...the latest satellite imagery shows most of the 
Panhandle under mostly cloudy skies with low clouds and patchy 
fog. The low clouds and fog will slowly dissipate through the 
late morning hours but high clouds will begin to move over Southeast Alaska 
as a front from a strong low over the western Gulf drifts across 
the central Gulf this afternoon. Winds this morning are light but 
they will increase to 15 knots through the afternoon as the high 
pressure over the panhandled at this time strengthens. 


The upper level high pressure over the eastern Gulf this morning 
will continue to sharpen up as the upper low south of the Alaska Peninsula 
lifts north to be just south of Kodiak by late tonight. The 
offshore northwest flow from the upper high will continue through today 
to keep the Panhandle partly cloudy over the northern half to 
mostly clear over the southern half. As the upper high axis 
drifts east high clouds will begin to move over the area late 
this afternoon into the evening. Clouds will continue to thicken 
through tonight and the paya area will see rain developing by 
late tonight as the weather front associated with the 989mb low 
over the western Gulf drifts across the Gulf tonight. The cold 
front will move through the paya area by Sun afternoon but will 
continue to see moderate to heavy rain as there will be a strong 
southerly jet over them. The rest of the forecast area will see 
rain developing from northwest to southeast through Sunday as the front moves 
over the Panhandle. The north central Panhandle will see the rain 
become moderate by the afternoon in the advance of the cold front 
with strong positive vorticity advection. The far southern inside areas may see some 
patchy fog develop late tonight into Sun morning as they will 
cool to saturation with just high thin clouds over them tonight. 
The fog will dissipate through morning hours and will have a 
chance of rain by the afternoon as most of the upper and middle 
level dynamics and jet support will remain over the northern two 
thirds of Southeast Alaska. 


The weather front will increase the winds over the central and 
northern Gulf to maximum small craft tonight. These winds will 
persist into Sun morning as there will be weak barrier jet 
developing just west of the Cape Suckling to keep the winds up 
longer. The rest of the Gulf will see winds increase to 20 knots by 
the morning as the front moves over the area. The increase waters 
and land areas will see the southeast winds increase to 15 knots with some 
higher gusts as the front moves over the area in the late 
afternoon. 


Long term...GFS this morning was a little more progressive in 
moving a ridge and upper low east across the Gulf middle week next 
week than the 00z European model (ecmwf). Likewise with a short wave in the upper levels 
late next week. At the surface...some differences regarding the 
placement of a low on Wednesday in the northern Gulf but have little 
impact on the eastern Gulf and Panhandle. At the end of the long 
range forecast period...GFS is placing a front in the central Gulf 
whereas European model (ecmwf) locates this same feature farther north in the 
northern and eastern Gulf. Overall...good agreement between GFS 
and 00z European model (ecmwf) through next Sunday. Even better agreement between 
GFS and the new 12z European model (ecmwf) so forecaster confidence in this long 
range forecast is above average. Used GFS for primary guidance. 


The extended range forecast begins with an occluded front over the 
coastal waters and rain over all of the Panhandle. A surface ridge 
will build in behind this front but the usual surface ridge 
precipitation will keep Panhandle probability of precipitation at chance or better through 
Monday night. The next developing system will spread rain into the 
western portions of zone 17 Tuesday morning Sep 09th and spread south 
down the Panhandle through Wednesday afternoon. Models have sped 
this front up since yesterday so have advanced this feature and 
the associated precipitation accordingly. A surface trough approaches the 
Panhandle Thursday night September 11th and looks like it will 
spread showers over the central and southern zones through the day 
Friday. Upper level support for this is not that strong nor is it 
phased well with this feature so confidence in this particular 
aspect of the extended range forecast is not as good as other 
portions. 


In terms of winds...nothing significant until the approach of the 
front on Tuesday 09 September. At that time...small craft 
southeasterly winds expected to build in from the west across zone 
310 and the coastal marine zones in advance of the surface front. 
May see marginal gales north of Cape Spencer by Wednesday morning 
10 September and also am expecting pre-frontal small craft winds 
over the southern Inner Channels by this time. Still far too early 
to issue a Wind Advisory...but indications are that this may be 
necessary for zone 27 for next Wednesday...so will watch this 
closely. Do not expect things to pick up over Lynn Canal until 
after frontal passage Wednesday night when a strong northerly 
pressure gradient will set up between the Panhandle and a surface 
low over the Yukon. The surface trough that approaches the outer 
coast Thursday night September 11th does not have a lot of wind 
associated with it and so marginal small craft winds are currently 
forecast over the northern Inner Channels. As indicated 
above...however...forecaster confidence in this particular feature 
is not that good so will have to monitor over the next several days. 




&& 


Ajk watches/warnings/advisories... 
public...none. 
Marine...Small Craft Advisory for pkz042-043-051-052. 


&& 


$$ 


Abj/fritsch 

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