451 
fxak67 pajk 211356 
afdajk 


Southeast Alaska forecast discussion 
National Weather Service Juneau Alaska 
456 am akst Sat Nov 21 2009 


Short term...a low over the S-central Gulf will drift east to the 
east-central Gulf by late tonight and slowly weaken through the 
period. Associated weak occluded front will move east to the outer 
coast by early evening...then dissipate as it moves inland 
overnight. A low will develop just SW of the charlottes later 
this morning and move NE to the central British Columbia coast by late evening. 


Main forecast dilemma will be how far inland precipitation will get with 
the front...and what impact the southern low will have on this. Frontal 
band is not very wide at this time...but as it interacts with colder air 
over southeast public...the precipitation with the front will likely expand 
some. The best chances for precipitation will be along the central and 
southern areas today into this evening. The far southeastern corner may see 
precipitation held up some however as that low to the S moves NE...and 
keeps front further west than in areas further north. Flow also becomes 
more Ely there tonight...with some backdoor cold advection 
likely...which will limit precipitation somewhat. Kept highest probability of precipitation along 
the coast...with decreasing probability of precipitation going inland tonight over the S. 


As for ptype/amts...still some shallow Arctic air over the northern 
Inner Channels and that will likely not go anywhere...so the northern 
third of the area will likely be all snow. Should see rain or a 
mix over Central Area with localized exceptions like papg where 
winds will be light enough to maintain a cool enough boundary 
layer for mainly snow. South should be rain although some snow is 
possible around Hyder. With the heaviest precipitation expected along the 
outer coast...places that see snow should remain below advisory level 
snowfall. Generally an inch or two of snow should fall where 
mainly snow is expected today into tonight...with locally 2-4 
inches possible where Ely flow is upslope in places like Hoonah. 


Wind forecast will be tricky for S area tonight. Pressure gradient 
orientation will favor the more east-west Inner Channels...so they 
should see stronger winds than the north-S ones. Looks like winds will 
peak at Small Craft Advisory levels ahead of the front. A band of gales is likely 
on S side of low near second wrap of front...but that will be 
limited to the far southern offshore waters today. The southern area winds 
will depend on how strong that low to the S gets...with a 
potential shift from southeast to NE tonight. This is most likely over 
the more eastern areas. 


Long term...long wave pattern continues to remain consistent 
with the previous package as the long wave trough retrogrades over 
the alaskan peninsula by the middle of next week. This will allow 
the middle level storm track to become less progressive and each of 
the surface lows approaching the Gulf over the next week will have 
a tendency to advect into the Gulf remaining west of 140 in the process. 
With the 00z naefs and European model (ecmwf) ensemble support preferred the 00z 
operational 00z European model (ecmwf) through the long term as it had the most 
consistent western Gulf storm track through next week. With the 963 
mb storm force low advecting into the western Gulf Sunday night 
also preferred the 00z European model (ecmwf) solution keeping the surface low 
further west than the 00z/06z GFS. However...most of the models 
were pretty close with the Sunday night storm force low except the 
00z/06z NAM which was a clear outlier being 10 mb weaker and 12 to 
18 hours slower with the front. Both the 00z European model (ecmwf) and GFS depict 
a developing triple point low at 850 mb that will move into the 
southeastern Gulf and across the Panhandle Sunday night and Monday 
morning. Will have to monitor this triple point feature as it will 
help to bring Wind Advisory gusts along the outer coast. 


Near hand off with short term blended mainly toward the 00z European model (ecmwf) 
to keep a more western Gulf track with the storm force low Sunday 
night and Monday. The associated frontal band will bring locally 
windy conditions along the outer coast with gales in east-west 
oriented channels and gusts to 50 knots in the northern Gulf as 
the barrier flow enhances the 850 mb low level jet. Did decrease winds from 
the previous package slightly across the southeastern Gulf as the 
low level jet will only be around 65 knots there which should only translate 
to gale force winds. Precipitation type will also be of concern for this 
event as overrunning could lead to quantitative precipitation forecast amounts near 0.75 inches in 
the central and northern Panhandle and while warmer air will 
advect northward through the day Monday...could see snow 
accumulations above 6 inches mainly in the Haines area before rain 
mixes Monday afternoon. Will have to continue to monitor the 
overrunning trajectories Sunday night into Monday before the warmer 
air mixes northward. 00z models depict another strong surface low 
moving into the Gulf Tuesday into Wednesday again bringing locally 
windy conditions along the outer coast. 850 mb temperatures will 
have risen above -6 c across most of the Panhandle by Wednesday 
and so the only rain/snow mix will be in the northern Panhandle 
before the southerly surface pressure gradient again advects 
warmer surface air northward. By late next week 00z models 
indicate other storm force low moving into the northeastern 
Pacific and western Gulf but will have to continue to monitor 
model run to run consistency for the best track for this system. 


Forecast confidence is above average through Tuesday afternoon at 
which point 00z models diverge on the timing/movement of the 970 
to 960 mb surface low in the northeastern Pacific and its progress into 
the southern Gulf. Precipitation amounts will be above normal through 
next week with several fronts moving across the Panhandle with 
onshore flow and temperatures will warm through next week with the 
rain/snow line retreating to the northern Panhandle. 


Ajk watches/warnings/advisories... 
public...none. 
Marine...Small Craft Advisory for pkz021-022-032>036-041-043-051-052. 
Small Craft Advisory due to seas for pkz042. 


&& 


$$ 


Rwt/pss 

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