155 
fxak67 pajk 151337 
afdajk 


Southeast Alaska forecast discussion 
National Weather Service Juneau Alaska 
537 am akdt Monday Mar 15 2010 


Short term...only small changes to stort range forecast pkg. MDT 
rainfall rates in showers have been reported at several stations 
overnight, and should periodically occur today, but the cells 
will weaken this evening as vorticity maxima become weaker. 


The large scale context for our forecast domain is still the 
cyclonic flow around a complex of low centers with 
vertically-stacked center about 300 nm S of pawd. This complex 
of lows and the associated cold tongue are being modified away from 
the west however this modification is too far west to be significant to our 
forecast domain through tonight. The polar front zone has moved east beyond 
our domain until Tuesday night due to a low approaching the charlottes from 
the S, and is discussed in the long range section below. What matters 
from this approaching low is that a ridge aloft on the north side will 
suppress the showers in the Panhandle in a S to north sequence tonight. 


One convective mass does have an organized circulation. At this time it 
is tracking north over cde and has been moving at 35 knots over the past 
10 hours. This low has slowed little and has upper level support 
that should reach southern Yukon trrty about 02z. The GOES infrared shows the 
cloud mass as having a smoothness of the cloud tops consistent 
with only modest convection and much of the cape should already 
be used up. Fmh1 heavy rainfall should not occur, albeit MDT should 
occur. Sleet has been mentioned for zones in the southern Panhandle but 
again the use of the cape should prevent such precipitation further north. 


Model consensus has improved for the waves tracking north along the 
Panhandle. Most important, the NAM has joined the GFS with the 
trough aloft extending east-northeast across the central Panhandle 18z Monday. 


&& 


.Long term...More precipitation coming to the southern Panhandle for 
the middle of the week and a ridge building over the area for 
next weekend are the main highlights of the long term forecast 
today. Middle Range forecast features a 999 mb low moving north over 
the Queen Charlottes islands and into the southern Panhandle Tuesday 
night. Frontal band rapping around and ahead of the low will 
bring more precipitation to the area for Tuesday night into Wednesday night. 
Easterly downsloping winds to the north of the low will limit 
precipitation amounts particularly for the northern and central 
Panhandle. Feature rapidly decays as it moves into British Columbia by Wednesday 
morning. Models are still having a hard time pinning this feature 
down. GFS is the fastest this morning and the most consistent on 
timing compared to yesterdays runs. Meanwhile the ec and the NAM 
have gone with a slower progression compared to yesterday. 
Preferred the GFS with this feature given its consistency on 
timing over the past few runs. 


Once the system middle week moves out, a upper ridge will settle 
over the area for the weekend. Long range models are rather set 
on this scenario as even most of the members of the GFS ensemble 
are leaning toward that solution. What remains to be seen is how 
long it will last. The ec and various ensemble members are 
keeping it through Sun night while other members and the 
operational GFS are undercutting the base of the ridge as early 
as Sat night. 


Forecast this morning was updated with the 0z GFS through Thursday 
as it provided the best consistent forecast for the southern 
Panhandle low. After thurs, went with the HPC guidance for any 
changes that needed to be done. Forecast confidence is a little 
above average out to Thursday night and about average for the 
position of the southern Panhandle low Tuesday night. After Thursday 
night confidence drops as model agreement begins to break down in 
regards to the staying power of the ridge. 




Ajk watches/warnings/advisories... 
public...none. 
Marine...Small Craft Advisory for pkz021-033>036-041>043-051-052. 


&& 


$$ 


Jbt/eal 

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