649 
fxak67 pajk 202309 
afdajk 


Southeast Alaska forecast discussion 
National Weather Service Juneau Alaska 
209 PM akst Friday Nov 20 2009 


Short term...surface observation and satellite images this morning are 
showing a 987 mb low moving north just east of Prince Rupert, British Columbia. 
A secondary low is visible in the surface observation and visible 
satellite just to the SW of Prince of Wales Island as well. Short 
term models are having a tough time initializing the secondary 
low today with only the UKMET, the Gem, and our local WRF model 
giving any hint that it is there. The other models feature a 
trough in the same area. Also the UKMET and to some extent the 
GFS match the observed surface winds around the secondary low 
rather well. 


For tonight and tomorrow, the low just east of Prince Rupert will 
continue north into British Columbia and dissipate today. Onshore flow will set 
up once again tonight bringing the showers of snow for the north 
and rain and snow for the south. By Saturday we will start seeing 
the effects of a 988 mb low moving into the eastern Gulf. The 
associated front will bring steadier precipitation into the southern 
Panhandle and the central and southern outer coast Saturday 
afternoon. 


Precipitation type will remain snow for most of the northern Panhandle 
through Saturday with areas farther south seeing a mix to all 
rain. Winds are generally light with a few places reporting small 
craft winds at the moment. Winds will be picking up to small craft 
criteria for the southern three coastal marine zones and the 
southern and central Inner Channels Saturday afternoon as the 
front comes onshore. 


For the short term forecast today, went with mostly the UKMET 
with a bit of the GFS thrown in. Differences between these two 
were very small with the low moving into the eastern Gulf 
Saturday, but the GFS was used to get more of the cold high in 
Canada that the UKMET was a little lacking on. Forecast confidence 
is above average due to good initialization of the model of choice 
and good model agreement for the next Gulf low. 




Long term...note the winds for Sun night and Monday are being 
increased by 10 to 20 knots. The result will be numerous zones with 
gales or storms. The fetch associated with the sea state will 
tend to be short due to the offshore component of flow. 


GFS five wave hemispheric shows low-amplitude trough extending 
from near pole and S over a pabr to padq line and extend S to the 
S. The amplitude will increase over the npac and Gulf of Alaska as 
it retrogrades about 10 degree west through 00z Tuesday. This retrograde and 
amplitude gain is that the waves on the polar front zone in 
the npac will change from near zonal to tracking NE into the Gulf of Alaska. 


The first of these cyclogentic waves should track NE toward the 
Gulf sun and reach 965 mb 300 nm S of pamd as it moves north 12z Monday. 
The low will turn to the northwest thereafter but send an occluded front into the 
eastern Gulf of Alaska early Monday. The model consensus and confidence 
for this solution is good. Note the gales and storm force winds 
are being prepared for marine forecasts as this product is being 
written. Note this wind event will be associated with a polar 
front zone feature traceable to about 1200 nm SW of pasy, so the 
details will become more clear as the system approaches. 


Ajk watches/warnings/advisories... 
public...none. 
Marine...Small Craft Advisory for pkz021-022-032>036-041>043. 


&& 


$$ 


Eal/jbt 

National Weather Service Glossary of Abbreviations

Non-Expanded Version (with abbreviations)