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fxak67 pajk 212133 
afdajk 


Southeast Alaska forecast discussion 
National Weather Service Juneau Alaska 
133 PM akdt sun Mar 21 2010 


Short term...low just west of the charlottes will weaken to a trough 
and drift north into southern Southeast Alaska this evening...then stall there later 
tonight. Arctic front near pajn-pags line will drift a bit 
further S then stall...likely near pagn late tonight. This front 
will begin to drift northward Monday. Complex frontal system will move NE 
into the Gulf Monday. 


Main forecast concerns are precipitation chances over the S 
tonight...then precipitation chances area wide Monday. At this time...precipitation is 
just entering the far southeastern area with pant reporting some on and 
off light rain. As low/trough drifts northward...expect some light rain 
to get further north into the area but should generally remain in 
zones 28 and 29. Precipitation coverage looks like it will be spotty 
though so likely probability of precipitation will be used for zones 28 and 29. Will go 
with chance or less in zones 26 and 27 for tonight. 


Stage is set then for flow aloft to shift onshore and this may 
lead to a light overrunning precipitation event especially later Monday 
afternoon. There will be lots of dry air over the north in lower 
levels but this may actually increase lift over the top of it due 
to its higher density. There will also be a weak shortwave moving 
NE through the area Monday afternoon. Will show a slow increasing trend 
in probability of precipitation Monday over most of the area...to chance levels...except 
probability of precipitation over the far S drop to chance. These values are a bit higher 
than MOS shows for Monday over northern and central areas but models tend 
to be too slow to develop overrunning precipitation. Ptype should be 
snow over the northern third as airmass will still be fairly cold 
there. 


Otherwise...made little change to winds. The strong north winds over 
the northern Inner Channels should slowly diminish through tonight and 
Monday. Will have Small Craft Advisory as far S as Stephens Passage to start then 
decrease from S to north later tonight and Monday. Ended up tweaking 
temperatures downward a bit especially northern area Monday as airmass coming in 
is a bit colder than MOS shows. 




&& 


Long term...abruft change in the works for Monday night as the 
current nice weather shifts to a wet pattern. The position of an 
Arctic front over the area will make forecasting the precipitation type a 
bit tricky. Think Arctic front will line up along the ice Strait 
corridor Monday evening with snow beginning from along the ice Strait 
corridor and northward Monday night. During the day Tuesday southerly 
flow will begin to push the boundary north with precipitation changing 
back over to rain along ice Strait and snow continuing for Haines 
and Skagway. Snow amounts will be in the realm of 1 to 2 inches 
along ice Strait. The main moisture flow is into the southern 
Panhandle through Wednesday morning but overrunning over the Arctic 
boundary may still induce some heavier snowfalls up to advisory 
for the Haines area. 


Next enhancement to the precipitation will come Wednesday night as a weak short 
wave and jet steak moves over the area. Temperatures should be warm 
enough for rain and the main moisture channel still is focused on 
the central and southern Panhandle. Low level flow turns offshore 
Thursday afternoon and which may give US a break of dry weather for 
Thursday night and Friday morning. After which the next system comes 
for Sat. 


Long range model agreement is not that good today with GFS 
generally portraying a wetter pattern then the ec. The larger scale 
picture is still well represented but the details are still in 
contention. Differences begin to crop up by Monday night into Tuesday 
with the simulation of a triple point low in the north central 
Gulf. Ec is consistently showing a 994 mb low wrapping up toward 
precipitable waters . Meanwhile the NAM has a 993 mb low much farther east and wrapping 
it up toward Yakutat, and the GFS is still showing just an open 
wave. Decided to use mainly the ec for forecast updates due to its 
rather good initialization, consistency, and the fact that it has 
been verifying rather well over the past few days. Forecast 
confidence is about average for the period. 


Ajk watches/warnings/advisories... 
public...none. 
Marine...Small Craft Advisory for pkz011>013-031-051. 


&& 


$$ 


Rwt/eal 

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