Weather

028 
fxak67 pajk 212115 
afdajk 


Southeast Alaska forecast discussion 
National Weather Service Juneau Alaska 
115 PM akdt Thursday Aug 21 2008 


Short term...extensive low clouds with areas of fog across the 
northern Panhandle during the early morning hours have lifted a 
little by middle morning. A weak ridge of high pressure across the 
southern Panhandle had also caused patchy fog along the immediate 
coast before lifting by middle morning. In the wake of the weakening 
ridge across the local region...Southeast Alaska has entered into 
a transition time from a couple of days pleasant weather to a wet 
pattern. Winds across the forecast area remain relatively light. 
Satellite loop shows a weakening surface trough slowly drifting 
northeast across the Panhandle and pre-frontal boundary forming 
ahead of a developing low in the northeast Pacific. The pre- 
frontal boundary looks like to split as it approaches to central 
Panhandle coast as of this writing. 


Latest models are in good agreement with a better initialization 
of NAM family. Prefer to select the NAM solution for the short 
term forecast package. While the weakening ridge of high pressure 
remaining across the southern Panhandle through Friday...a 
developing low in the northeast Pacific will enter the south 
eastern Gulf on Friday morning and deepen. This low will continue 
to intensify slightly as it drifts northward across the eastern 
Gulf through late Friday afternoon. A leading edge of frontal 
boundary associated with the deepening low will sweep across the 
eastern Gulf and Southeast Alaska on Friday. Ahead of the incoming 
system...the marine stratus is expected to return to the northern 
Panhandle this evening then spread southeast across the Panhandle 
late tonight...along with the increasing probability of precipitation. 


In between the remaining weak ridge over the southern Panhandle 
and the incoming system...pressure gradient will gradually 
increase late tonight from the southern outside waters to meet 
small craft winds with building seas...and spread north through 
Friday. Inside waters open to the ocean will experience small 
craft winds as well with a slight building of seas on Friday. With 
enhanced marine layer over the area through early Friday 
morning...likely to categorical probability of precipitation will be the forecast for the 
most zones on Friday. Coastal zones will have breezy to windy 
conditions on Friday. Will not issue a Wind Advisory for the 
central and southern coastal zones with the afternoon package but 
need to keep an eye on for any possible development. 


Long term...upper level model initialization and agreement looks 
good through next Tuesday with GFS building a slightly stronger 
upper level ridge than European model (ecmwf) over the eastern Gulf. After this 
time frame...GFS tracks a somewhat deeper upper low east along the 
northern Gulf and effectively displaces the ridge to the south by 
Wednesday morning. By next weekend...30 August...European model (ecmwf) builds in 
a significant upper ridge from the southwest that is stronger and 
about 24 hours faster than GFS. At the surface at the beginning of 
the long range forecast period...both GFS and European model (ecmwf) are still 
deepening a surface low in the eastern Gulf. European model (ecmwf) however...is 
much more aggressive in deepening this parent feature and 
tracking it northwest to the northern Gulf by Saturday morning. 
GFS...on the other hand...invests a lot more energy into a second 
low that forms along the frontal boundary and approaches the 
southwest Panhandle Saturday afternoon. Based on jet strength and 
location being depicted by both GFS and European model (ecmwf)...prefer the GFS 
solution for the long range forecast. 


As indicated in the short range discussion...a moist weather 
pattern has resumed over the Panhandle with the first round of 
widespread rain coming from a low that will be west of Sitka 
Friday evening. The front associated with this low will become 
disorganized along the outer coast so southwestern and central 
Panhandle locations may see a break in the precipitation late Friday 
night into Saturday morning. Soon thereafter...another low will 
approach the coast from the south-southwest and spread more widespread rain 
from south to north Saturday through Sunday morning that will be 
moderate to heavy at times especially over the southern half of 
the Panhandle. As the heaviest of the rain tracks north across the 
Panhandle...rain rates will diminish but still expect to see 
moderate rain over Yakutat through early Monday morning. For 
Monday...expect widespread shower activity as a surface trough 
pushes over the top of a weak ridge that sets up over the 
Panhandle. By Tuesday morning...the ridge will dominate Panhandle 
weather with onshore flow...marine stratus...and light rain. 


By middle week next week...a fairly deep surface low with a well 
organized front will approach the coast and displace the ridge to 
the east. Model differences on the timing...intensity...and track 
of this low and its associated front make the specifics of this 
system a low confidence forecast. At this point...it is sufficient 
to say that a well organized dynamic front will impact Panhandle 
weather in the latter half of next week. 


In terms of wind...am expecting small craft conditions Friday 
night from Cape Decision north to Yakutat Bay which should 
moderate as the associated low west of Sitka weakens. Easterly 
winds will increase on Saturday as the next low approaches from 
the south-southwest and am expecting 25 to as much as 30 kts in the southern 
coastal zones and the Dixon Entrance. Should also see small craft 
conditions build north over most of the Inner Channels by Saturday 
afternoon and remain for much of Sunday. 


The temperature trend in the extended range for both daytime 
highs and night time lows is down by a degree or two and is 
several degrees below normal for this time of year. 




&& 


Ajk watches/warnings/advisories... 
public...none. 
Marine...Small Craft Advisory for pkz021-022-032>036-041>043-051. 


&& 


$$ 


Sja/fritsch 

National Weather Service Glossary of Abbreviations

Non-Expanded Version (with abbreviations)