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fxus66 kotx 100012 
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Area forecast discussion 
National Weather Service Spokane Washington 
412 PM PST Friday Jan 9 2009 


Synopsis... 
the weather pattern will remain cool through the weekend. A weak 
weather system will bring the threat of light to moderate snow to 
locations near the Canadian border Saturday morning and then shift 
southward through the day. Strong ridging will then bring dry 
conditions to the area through most of next week. 


&& 


Discussion... 
tonight...high pressure is setting up off the California coast 
which is providing a broad ridge over the Pacific northwest. Water vapor 
imagery shows a swath of moisture moving toward the Pacific northwest. The 
flow above 850mb is straight westerly so the moisture and weak 
wave that is moving toward US will skirt along the US border. The 
best chance of showers tonight will be across the US/Canadian 
border. Temperatures will generally be in the 20s. 


Saturday through Sunday...Saturday the ridge axis becomes more 
amplified to the west. This will provide a more northwesterly flow 
across the County Warning Area. A weather disturbance coupled with 
an increase in moisture will move over eastern Washington and north Idaho. 
Snow will move from north to south through the day across mainly 
eastern Washington and north Idaho. Meanwhile at the lower levels southwest 
flow will usher in some warmer air into the basin. 285k isentropic 
analysis shows good upglide into northeast Washington and north Idaho. Have 
decided to issue a Winter Weather Advisory for snow across 
northeast Washington and much of northern Idaho. Snow will start 
Saturday morning across the north...and move south through the 
day. Snowfall will be moderate at times by Saturday evening. 
Valleys will generally see 3-5 inches by Sunday morning and 
mountains 6-8 inches. Light snow will continue into Sunday but 
will mainly be confined to the central Panhandle mountains. 
Spokane will get skipped with this system...generally seeing 2 
inches or less. /Nisbet 


Sunday night through Friday...very few changes to continuity and 
very consistent model solutions lead to fairly high confidence in 
the pattern evolution during the next week or so. The 
GFS...ECMWF...Canadian...and dgex all develop a rather amplified 
ridge off shore and gradually move it on shore by the end of next 
week. In reality...the only difference amongst the global models 
guidance comes on or around mid-week. 


By Tuesday model solutions generally focus on tracking a short 
wave trough down the eastern flank of the off shore ridge. This is 
basically along and east of the Continental Divide with all the 
lift and precipitation generally spreading from the Front Range 
eastward into the Midwest. However...the GFS and dgex have been 
rather insistent on a piece of Canadian air traversing the 
Continental Divide and working into eastern Washington mid-week. 
They have shown this for the past several runs...while the European model (ecmwf) 
has focused all cold advection east of the Continental Divide. In 
examining this further...a decent pressure gradient looks to allow 
extended duration northeasterly flow on the GFS middle-week into 
Thursday night or so. While the European model (ecmwf) generally shows much lower 
pressures along the Front Range that preclude this 
development...that is likely because it drapes the Arctic front up 
against The Rockies. The insistence of the GFS on bringing some 
colder air across The Divide seems reasonable given the depth and 
magnitude of cold air over Alaska at the moment with temperatures 
having fallen as low as -77f over the past day or two. Because of 
the magnitude and depth of the cold air...any flow toward The 
Divide coupled with the short days will likely allow at least a 
portion to cross The Divide. Because of this...the forecast 
temperatures have been adjusted toward the GFS and downward from 
middle-week Onward. 


The influx of possible Canadian air should allow some decent 
northeasterly flow to keep the boundary layer fairly well 
mixed...so again today fog has been left out of the forecast even 
with a ridge building toward the County Warning Area. However...with the ridging 
influence being the largest player in the forecast...the vast 
majority of the County Warning Area save for the central Idaho Panhandle remains 
fairly dry for most of next week. /Fries 


&& 


Aviation... 
VFR conditions should prevail at all taf sites even with thickening 
and lowering overcast through Saturday morning. Snow will gradually 
overspread northeastern Washington and north Idaho during the day 
Saturday...likely affecting the Spokane area and kcoe taf sites by 
late Saturday afternoon. IFR or lower conditions are likely as ceilings 
fall and visible falls with the snow moving in Saturday afternoon. 
/Fries 


&& 


Preliminary point temps/pops... 
Spokane 26 36 27 37 30 37 / 10 30 60 20 30 10 
Coeur D'Alene 27 35 27 36 29 37 / 10 50 80 30 40 20 
Pullman 29 39 33 42 33 42 / 0 10 40 20 30 20 
Lewiston 32 46 35 45 37 45 / 0 0 20 10 10 10 
Colville 26 32 25 34 27 34 / 20 50 60 20 30 10 
Sandpoint 28 31 28 35 30 34 / 30 60 80 30 30 30 
Kellogg 26 33 29 35 30 35 / 10 40 80 60 60 60 
Moses Lake 27 36 27 38 27 38 / 0 0 10 0 0 0 
Wenatchee 27 38 30 41 31 37 / 0 0 10 0 0 0 
Omak 24 33 25 37 27 35 / 10 10 10 10 10 0 


&& 


Otx watches/warnings/advisories... 
Idaho...Flash Flood Watch through Saturday morning for the St Joe and 
St Maries rivers. 


Winter Weather Advisory from 10 am Saturday to 4 am PST Sunday 
for Coeur D'Alene area. 


Winter Weather Advisory from 4 am Saturday to 4 am PST Sunday 
for northern Panhandle. 


Winter Weather Advisory from 10 am Saturday to 10 am PST Sunday 
for central Panhandle mountains. 


Washington...Winter Weather Advisory from 4 am Saturday to 4 am PST Sunday 
for northeast mountains. 


&& 


$$