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Southeast Alaska forecast discussion 
National Weather Service Juneau Alaska 
232 PM akst Sat Nov 21 2009 


Short term...satellite images this morning show a 983 mb low 
spinning in the central Gulf. The associated front is currently 
making land fall along the southern and central outer coast. The 
precipitation band, that was seen on pacg radar this morning, with the 
front is relatively narrow. The precipitation has just reached Juneau 
and Gustavus, but the back edge of the band has already reached 
Sitka. More convective precipitation is in the cards for Sitka for the 
rest of today. Precipitation type so far has been all snow north of a 
line from Kake to perl Strait with a mix to all rain south. 
Except for Hyder where it has been switching back and forth from 
snow to rain and back again most of the morning. 


Highest winds today have been mainly confined to the east-west Inner 
Channels, Clarence Strait and the coastal waters. Mostly in the 
realm of Small Craft Advisory winds with some localized higher gusts. 


Winds and precipitation will dissipate through the night tonight as the 
low and the front weaken and break apart. The low will not even 
make it to shore before it weakens away to nothing just off the 
central outer coast. Expect that the front will dissipate rather 
quickly as it moves through the Panhandle tonight so no advisory 
level snow amounts are expected where snow does fall. 


For tomorrow, northern areas are expected to be dry. Still keep 
a chance of precipitation for southern areas as a weak trough is still 
present over the south and extends into the NE Gulf. It will 
gradually weaken through Sunday afternoon when the frontal bands 
from our next system start making their way across the Gulf. 


Forecast today was updated with the GFS with a bit of the ec 
blended in for Sunday afternoon. GFS looked to have the best 
placement of the low in the Gulf while the other models placed it 
a bit too far south and west. It also seemed to have a good grasp 
of upper level features as well. However, the ec appeared to have 
a better grasp on the system for Sunday night, so elected to 
start blending in more ec toward the handoff with the long term 
desk. Forecast confidence is a little above average today since 
model consensus is good for the current system, but most of the 
models do not quite completely capture what is currently going 
on. As such some differences in the model solutions start 
appearing Sunday afternoon. 


Long term...the forecast models this afternoon are in fair 
agreement with a series of low pressure systems moving into the 
Gulf with associated weather from lifting over the Panhandle. The 
subtropical jet will slowly lift north and drift developing lows 
into the Gulf and send in warmer temperatures through the week. Where 
changes were made used the 12z ec through Tuesday night then blended 
the current forecast with HPC. The reason for this was that the ec 
has been consistent the past few model runs and the the 12z run 
kept a low over the southern Gulf in Wednesday and this fit well with 
the ensembles. The GFS was lifting this system north into the northwest 
Gulf much faster and was not preferred. Other wise the there was 
much better agreement with the operational ec/nafes and the ec 
ensemble so with that said forecaster confidence is fair to good. 


At the start of the long range period a low pressure system with 
good upper level support will lift out of the North Pacific Sun 
night and into the west/central Gulf by Monday afternoon. The 
associated weather front will begin to affect Southeast Alaska Sun night with 
snow over the northern portions due to overrunning while the 
coastal and southern inside areas will see rain and windy 
conditions. The forecast problem with this system is when the 
precipitation will start and the snow change to rain. As there will be strong 
easterly winds at the surface but aloft the flow will be from the 
southeast. At this time the north-central inside areas will see possible Snow 
Advisory amounts late Sun night into Monday morning before the front 
moves through and the precipitation turns to rain. Further north near 
pahn amounts may be much larger with amounts above Heavy Snow 
Warning criteria and possible 2 feet near the border along the 
Haines Highway and near White Pass. Later shifts will need to keep 
an eye on this situation. 


As for winds with the front...gales force winds will develop over 
east/west channels with min small craft from the north as the front 
approaches but change to the south through Monday. Over the Gulf 
storm force winds will develop over the northern Gulf as a barrier 
jet will form Sun night and persist into Monday afternoon. The rest 
of the Gulf will see maximum gale force winds before diminishing to SW 
25kt Monday afternoon. Over land the coastal areas will see the winds 
increase to Wind Advisory levels through Sun night as a 70kt low level jet 
associated with the front will move over the area but the winds 
will quickly decrease by Monday afternoon but the winds over the far 
northern areas will increase as a ridge will build behind the 
front. 


There will be 3/4 more low pressure systems that will move over 
the Panhandle the week bring in slightly warmer temperatures so most of 
the precipitation will fall as rain but there may be times of some snow 
mixed in as freezing levels will not get above 3500 feet. A very 
strong front will move over the Panhandle from the south as the 
associated in the North Pacific slowly lifts north through Wednesday. 
This will bring in large amounts of rain to the area and raise the 
freezing level to about 3500 feet. As that low lifts into Canada 
Thursday another front will be right behind it and move into the 
eastern Gulf late Thursday and over the Panhandle Friday. 






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. 


&& 


$$ 


Eal/abj 

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