056 
fxak67 pajk 202109 
afdajk 


Southeast Alaska forecast discussion 
National Weather Service Juneau Alaska 
109 PM akdt Sat Mar 20 2010 


Short term...low pressure about 450 nm west of Seattle will move north-northeast to 
just west of the charlottes sun and slowly weaken. An Arctic front 
over the southern Yukon will move S into far northern Southeast Alaska by late this 
evening...then reach the pajn area late tonight. High pressure will 
move south-southeast into the Yukon tonight and remain there but weaken slowly 
sun. Favored the 00z European model (ecmwf) for tonight and sun due to its better 
handling of the low to the S and the pressure gradient along the Coast 
Mountains 


Main forecast concerns are how much colder it will get when the 
Arctic front moves past and how strong winds will be over the northern 
area later tonight and sun...and how far northwest precipitation with the low will 
get into the southern area sun. The really cold air lags fairly far to 
the north of the Arctic front by about 200 nm so the temperature drop after 
the front moves through will be gradual. Have lowered Sunday maximum 
temperatures over the far north by about 5 degrees...in line with MOS temperatures. 
Would not surprise ME if they were even a bit cooler...but due to 
the somewhat colder air lagging well behind the front did not want 
to jump too hard on the cool down at this time. Airmass will definitely be 
much drier with dewpoints likely dropping into the teens or even 
single digits sun over the northern third of the area. 


As for the winds...pressure gradient does tighten up fairly quickly 
once the front moves past so expect locally breezy to windy 
conditions after frontal passage. Outflow will increase through the NE Gulf 
Coast passes and will issue a Wind Advisory for zone 17 near interior 
passes east paya for late tonight and Sun morning. Will have to watch 
the pagy area also but for now am keeping winds below advisory levels 
there. Will have gales for Lynn Canal and Small Craft Advisory level winds for the 
remainder of the northern Inner Channels later tonight and sun...with 
some decrease in winds Sun afternoon as the high to the north weakens 
slowly. 


Over the southern area...the 00z European model (ecmwf) suggests some precipitation should get 
into the far southern area early Sun morning. Given the weakening trend 
of the low moving north the precipitation area will likely not be widespread 
as it enters the area...so am keeping probability of precipitation in the likely range 
over the pakt and Hyder zones sun. Will have a chance pop for the 
papg/pakw zones sun as it will be questionable whether the precipitation 
gets all the way northwest into those areas. 


Long term...long term forecast starting with low pressure 
system off the Queen Charlottes dissipating as it continues to 
track NE toward British Columbia. Long wave trough moves over the 
Alaska Gulf Tuesday through Thursday with a series of short waves moving over 
the Panhandle. Details on these shortwaves still uncertain as 
model differences were fairly large at this time. Weak ridge 
follows this trough Friday before the next low system moves up from 
the North Pacific by next weekend. Off shore flow keeping the north Panhandle 
dry through Monday before next short waves bring in band of precipitation. 


Arctic air mass tracking S from the Yukon through Monday to about 
Frederick Sound. With tightening press and temperature gradient may see 
advisory level winds to the north and higher gusts in channeled 
terrain. Drop temperatures for Sun night into Monday but may not have gone 
low enough. 


Triple point low on Tuesday still depicted by 12z European model (ecmwf) but not NAM 
or GFS. Did like the look of the ec overall but felt new model 
runs compared to inherited grids were very similar. So few 
changes were made other than some slight changes to pop fields 
and lowering temperatures. Forecast confidence is average for the start 
of the long term then drops due to uncertainty in middle week short 
wave details. 


Ajk watches/warnings/advisories... 
public...Wind Advisory from midnight tonight to noon akdt Sunday for 
akz017. 
Marine...Gale Warning for pkz012-013. 
Small Craft Advisory for pkz011-021-022-031-032-041-043. 
Small Craft Advisory due to seas for pkz042-051-052. 


&& 


$$ 


Rwt/prb 

National Weather Service Glossary of Abbreviations

Non-Expanded Version (with abbreviations)