045 
fxak67 pajk 191328 
afdajk 


Southeast Alaska forecast discussion 
National Weather Service Juneau Alaska 
528 am akdt Friday Mar 19 2010 


Short term...at 1200 UTC surface observations and satellite 
imagery indicate that a low in the Gulf of Alaska is about 250 Michigan 
south of Valdez moving slowly northeastward. An occluded front 
bulges from the low to within 150 Michigan of the Southeast Alaska 
coast while clouds ahead of the front cover most of the 
Panhandle. Radar shows precipitation close to the outer coast 
that should start moving onshore in the next few hours. The 
advance has been slowed by frontal waves and downslope drying 
from strong easterly winds in interior sections. Gale force winds 
in the outer coastal waters should diminish once the front 
passes. 


Models are in good agreement with the evolution of 
this system...moving the main low to Prince William Sound while 
pushing the front through the northern Panhandle early tonight. 
The front is then expected to stall over southern Southeast 
Alaska and winds diminish significantly overnight as an upper 
ridge rebuilds in the eastern Gulf. 


Long term...long wave pattern into the middle of next week shows 
high variability and run to run inconsistency between models 
mainly with the progression of a large amplitude middle level ridge 
building into the Bering at the end of the weekend and a middle level 
ridge building over western Canada by the middle of next week. In 
between these two middle level ridges 00z models indicate a long wave 
trough will develop and strengthen along the alaskan peninsula 
which will send several surface lows and associated frontal 
boundaries across the Panhandle and eastern Gulf from Monday 
through the end of next week. Timing and strength of these frontal 
boundaries is difficult to determine at this time with all the model run 
to run variability. For this reason made only minor changes to the 
extended grids. Did blend toward the 00z ec/GFS through Sunday 
afternoon to capture the northerly winds and drier weather over 
the weekend. The 00z NAM was the main outlier with the surface low 
moving toward the charlottes Sunday afternoon...as its solution 
was 12 hours slower than all other models. The main forecast 
problem into the long term period was the development of a surface 
low in the northern Gulf Monday as a middle level shortwave advects 
through the Gulf in the 00z models. However 06z models are much 
weaker with the surface low and onshore flow Monday afternoon and 
so will wait for better model consistency before increasing the 
chance of precipitation for early next week. 


After handoff with short term...expect clearing skies throughout 
the Panhandle Saturday with offshore flow increasing. Patchy fog 
will develop in wind sheltered areas Saturday night...but the 
northerly surface and middle level flow will remain strong enough to 
not allow widespread fog formation. With a 1032 mb surface high 
building into northwest Canada by Saturday night will see locally 
breezy conditions develop near Skagway with smcr northerlies in 
Lynn Canal as the northerly surface pressure gradient strengthens. 
Will see clouds advect from south to north across the Panhandle on 
Sunday as a surface low moves to just west of the charlottes but 
with the increased northerly flow and a strong downslope wind 
component only the southern Panhandle will see a chance of precipitation. 
Expect locally breezy conditions near interior passes on Sunday 
with the increase surface pressure gradient. 


On Monday onshore flow increases through 500 mb and so will see 
an increasing chance of precipitation and with 850 mb temperatures -6 c and 
warmer...the rain/snow line will remain along and north of Icy 
Strait. The next strong frontal boundary approaches the Panhandle 
by Tuesday night but models are still having difficultly on the 
exact timing. 850 mb low level jet winds are near 60 knots and so will see 
gale force winds in the eastern Gulf Tuesday with possible Wind 
Advisory gusts in exposed locations along the outer coast and locally 
windy conditions across the Inner Channels. Wednesday to the end 
of next week 00z models are flip flopping on whether offshore 
flow develops again drying out the Panhandle or whether a middle 
level baroclinic boundary stays over the Panhandle bringing a 
good chance of precipitation and this all depends of the location of the 
middle level ridge in western Canada. Will wait for more model 
consistency but long term package from Wednesday Onward reflects 
a more climatological and seasonal pattern. 


Forecast confidence is below average after Sunday afternoon as 
model run to run consistency is very poor in the operational 
models and there is a large spread in the 00z European model (ecmwf) and naefs 
ensemble solutions as well. Expect temperatures at or above normal 
through next week with precipitation amounts near normal and windy 
conditions toward the middle of next week. 


Ajk watches/warnings/advisories... 
public...none. 
Marine...Gale Warning for pkz042-043-051-052. 
Small Craft Advisory for pkz011-013-021-022-032>035-041. 


&& 


$$ 


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