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Southeast Alaska forecast discussion 
National Weather Service Juneau Alaska 
551 am akdt sun Mar 21 2010 


Short term...high pressure remains strong in the Yukon as a 
997 mb low just west of the Queen Charlottes moves northward. 
This has tightened the pressure gradient across Southeast Alaska 
producing increased northerly winds...especially in the northern 
interior and northeast Gulf Coast. Gales are occuring over 
northern Lynn Canal but gusty winds near Skagway...downtown 
Juneau...and portions of the northeast Gulf are not quite strong 
enough for wind advisories in the public zones. 


The low is expected to weaken to a trough over the southern 
Panhandle Sun night and then creep northward. There are minor 
disagreements between models over how far north the trough will 
make it before it stalls somewhere near central Southeast Alaska. 


As the low to the south weakens...the high in northwest Canada 
shifts slowly eastward later today and tonight. This relaxes the 
gradient across the Panhandle allowing the strong northerly winds 
in the northern interior and northeast Gulf Coast to gradually 
decrease through tonight. 


Little precipitation is expected through tonight except for a 
slight chance of rain in extreme southern portions of Panhandle as 
the low drifts northward. Skies will remain clear to partly cloudy 
over northern sections. && 


Long term...long term pattern is a little less clear this 
morning than yesterday as model variability by Tuesday morning 
becomes significant. 00z/06z operational models continue to 
struggle on which triple point surface lows will develop with the 
individual frontal boundaries moving through the eastern Gulf from 
Tuesday through Friday. All models except for the 00z GFS develop 
a triple point low in the north central Gulf Monday night. Due to 
this the 00z European model (ecmwf)/NAM were used through day 3 then used inherited 
grids with the 00z European model (ecmwf) afterwards. The 00z European model (ecmwf)/NAM provided a 
nice compromise on the strength of the triple point low Monday 
night near 996 mb. The 00z European model (ecmwf) continues to be the most 
aggressive with developing this low and so will have to monitor 
how much cold air advection is ingested into the developing wave by Monday 
morning. Will have to raise winds to gale force along the outer 
coast Monday night and Tuesday morning if the triple point low 
develops stronger than 00z models indicate. From Wednesday through 
Friday most of the middle and upper level energy undercuts the 
Panhandle...however a middle level baroclinic boundary will remain 
along the southern Panhandle and with onshore flow will continue 
to see a good chance of precipitation each day from Juneau southward. 
Next weekend 00z ensembles are trending toward keeping the 
longwave trough in the western Gulf more progressive which will 
continue to allow frontal boundaries to move across the Panhandle 
next weekend...unlike yesterdays more blocked middle level pattern. 


Near hand off with short term will continue to see a 1030 mb 
surface high in the Yukon supplying cold northerly surface flow 
across most of the Panhandle. By Monday night a developing triple 
point low and increasing onshore flow through 500 mb will spread 
precipitation over the majority of the Panhandle. At this time...with the cold 
surface flow expect the precipitation to start out as snow along and 
north of Icy Strait before warmer surface air advects northward by 
midday Tuesday. The strong easterly surface flow should keep 
precipitation and snow amounts down along the Icy Strait corridor. Could 
see snow accumulation near advisory levels near pahn as the warm air 
over runs the Arctic boundary. Will see locally windy conditions 
along Lynn Canal Tuesday with the strong northerly surface 
pressure gradient. Elsewhere will see locally breezy conditions 
across the rest of the Panhandle with 850 mb southerlies near 40 
knots. The heaviest precipitation will remain across the southern 
Panhandle and outer coast Tuesday and Wednesday as the strongest 
middle level dynamics remain near Prince of Wales Island with the 
upper level jet left exit region over Baranof Island. Could see 
higher rainfall amounts across the eastern Inner Channels if the 
850 mb winds do become more southwesterly. 


With the upper level jet energy undercutting the Panhandle toward 
Thursday and Friday the 00z models bring a weak surface low over 
the charlottes on Thursday and develop weak offshore across the 
central and northern Panhandle bringing drier weather. 
However...models have been flip-flopping with this solution over 
the past few days so forecast confidence is low beyond Wednesday. 
Expect temperatures and precipitation above normal toward the middle of 
the week...with temperatures returning to more normal values by 
next weekend. The rain/snow line will be along the Icy Strait 
corridor until Tuesday before retreating into the far northern 
Panhandle for the remainder of the week. 


Ajk watches/warnings/advisories... 
public...none. 
Marine...Gale Warning for pkz012-013. 
Small Craft Advisory for pkz011-022-031-032-051. 


&& 


$$ 


Cfd/pss 

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