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fxak67 pajk 201346 
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Southeast Alaska forecast discussion 
National Weather Service Juneau Alaska 
546 am akdt Sat Mar 20 2010 


Short term... at 1200 UTC Biorka radar shows scattered showers 
have diminished and their motion is shifting from onshore to 
southeasterly which is parallel to the outer coast. Isolated 
showers lingering over portions of the interior Southeast Alaska 
are expected to dissipate by late morning. The latest satellite 
image shows high clouds over the southern Panhandle that are 
associated with the old front that has stalled there. Klawock is 
reporting intermittent rain associated with this weakening band. 


Pressure rises in the Yukon confirm that a weak low is being 
replaced by high pressure there. A 998 mb low 900 nm south of 
Ketchikan is moving northward and is expected to be just west of 
the Queen Charlottes by 1800 UTC Sunday. Model agreement with this 
low is good through Sunday but then differences begin to grow as 
the low continues northward and weakens to a trough. 


Winds will shift to northerly over most of Southeast Alaska early 
today as pressures rise in northwest Canada and the Pacific low 
moves approaches the Panhandle. Skies will become partly cloudy 
over northern Southeast Alaska and the northeast Gulf later today 
and tonight. Rain from the Pacific low will spread over the 
northern b.C. Coast tonight and reach southern Southeast Alaska by 
Sunday morning. 


Long term...long term pattern is a little bit clearer this 
morning with better 00z operational model compromise through the 
middle of next week. Will see a brief dry period across the 
Panhandle at the beginning of the long term before a long wave 
trough digs into the western Gulf helping to steer the storm track 
and associated frontal boundaries more toward the Panhandle. 
However...there remains large variability with the strength and 
timing of each individual frontal boundary to move across the 
Panhandle from Tuesday through Thursday. In coordination with pafc 
used a blend of the 00z GFS/European model (ecmwf) through Thursday as both these 
models were in fairly good agreement with the individual frontal 
boundaries and gave better definition to the wind structure in the 
eastern Gulf than the HPC solution. Day 7 Onward a GFS/HPC 
solution was preferred with the increased offshore flow component 
and the 00z ensembles and operational models were trending that 
direction. 


Will see strong offshore flow across the majority of the Panhandle 
on Sunday and Sunday night and that will keep the central 
Panhandle northward precipitation free. A weak surface low will advect 
over the charlottes from the northeastern Pacific by Sunday 
afternoon and the increased onshore flow from this system will 
bring a good chance of precipitation to the southern Panhandle. The main 
forecast problem through Monday morning will be the strong 
northerly surface pressure gradient and the locally windy 
conditions across the northern Panhandle and near interior passes. 
At this time...do believe winds will remain below advisory near Skagway Sunday 
and Monday as the surface pressure gradient will remain just weak 
enough with the filling surface low near Dixon Entrance. Will see 
northerly smcr winds across the northern inner channel waters with 
gusts to 40 knots near interior passes. 


The onshore flow through 500 mb will increase on Monday through 
Monday night with a middle level shortwave advecting into the western 
Gulf and its associated frontal boundary moving into the eastern 
Gulf spreading precipitation northward across the Panhandle. 850 mb 
temperatures will initially remain cold enough for snow from the 
Icy Strait corridor northward...however as warm air advection increases into 
Tuesday the rain/snow line will retreat to near Haines and 
Skagway. The 00z European model (ecmwf) develops a strong triple point low that 
moves into the northern Gulf Monday night and with the 00z/06z GFS 
being less aggressive with this feature did not increase winds to 
gale force across the outer coastal waters however the feature 
does bear watching for locally windy conditions Monday night and 
Tuesday. 


From Tuesday through Thursday a middle level baroclinic boundary will 
remain across the southern and central Panhandle and with 850 mb 
winds out of the south and above 30 knots will see locally heavy 
rainfall at times...especially near Ketchikan. Northeasterly 
surface flow from Juneau northward will limit the precipitation amounts 
across the northern Panhandle. 850 mb temperatures will remain 
above -4 c across the Panhandle during the middle of the week and 
this will keep the rain/snow line across the far northern 
Panhandle. By the end of next week 00z ensemble guidance is 
suggesting the return to stronger offshore conditions and 
increased northerly flow as a middle level trough undercuts the 
Panhandle. Will have to monitor model trends toward next weekend 
for drier weather conditions and a more showery precipitation 
pattern. 


Forecast confidence is above average with the overall weather 
pattern through next Thursday but forecast confidence remains 
below average after Tuesday for individual wind events and frontal 
boundary passages as 00z/06z models are flip-flopping on which 
triple point features will strengthen. After the dry conditions 
this weekend expect temperatures and precipitation amounts above normal 
toward the middle of next week. 


Ajk watches/warnings/advisories... 
public...none. 
Marine...Small Craft Advisory for pkz011>013-031-036-041. 
Small Craft Advisory due to seas for pkz042-043-051-052. 


&& 


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Cfd/pss 

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