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Area forecast discussion...updated 
National Weather Service Spokane Washington 
343 PM PST Friday Nov 21 2008 


Synopsis... 
another cold front will move through the inland northwest 
tonight. Precipitation amounts will generally be light with this 
quick moving frontal system. Strong high pressure will bring dry 
and seasonably cool weather Sunday through Tuesday. Later in the 
week a series of very weak disturbances will trigger mainly 
mountain snow showers. 




&& 


Discussion... 
updated aviation discussion. 


Tonight and tomorrow...weak low pressure system with tap into 
subtropical moisture weakening with its approach as the moisture 
tap elongates and shears the more it progresses through the mean 
longwave ridge over the area...additionally with essentially no 
cold air to overrun at the lower levels and the surface low 
associated with the passing frontal zone so far to the north with 
its passage the rain/snow shadow produced off the Washington 
Cascades will inhibit the chance of any significant rainfall over 
the basin...thus probability of precipitation are not as high in comparison to yesterdays 
weather system passage which brought a decent amount of 
precipitation to the area yesterday. Improvement shown by 
decreasing cloud cover and probability of precipitation in a west to east manner in the 
wake of the system exit remains depicted in a robust manner 
tomorrow. /Pelatti 


Saturday night through Monday...there is good model agreement between the 
GFS...NAM...and European model (ecmwf) latest runs in depicting a sharp short wave 
ridge popping up over the region Saturday night and Sunday on the 
backside of saturday's wave passage. A relatively strong surface 
high pressure will become established over the Idaho Panhandle by 
Sunday morning. Thus...after lingering orographic snow showers 
Saturday night as the weather system exits the region...in general 
a dry and quiet forecast is expected through the remainder of the 
short term forecast. The main weather element impacting this quiet 
period will be the return of a moderate subsidence inversion to 
the basin which...like last week...will decouple the low level air 
mass allowing a general stagnation period to set in. Whether or 
not a new air stagnation advisory will be needed for this 
situation is not known yet...with longer range models suggesting 
the next weather disturbance due in around late Tuesday or 
Wednesday which will weaken this inversion pattern and provide 
some ventilation to the region before air quality can deteriorate 
too much. This Prospect will need to be monitored during upcoming 
shifts. Otherwise...sensible weather for the Sunday through Monday 
time frame will consist mainly of patchy late night and early 
morning valley fog and stratus fields...which may have trouble 
burning off during the afternoons in the deep basin and Cascades 
valleys since the Idaho high pressure will provide an easterly 
gradient forcing cooler air to dam against the Cascades. 
Temperatures will probably cool to seasonal normals at night and 
rise to 3 to 5 degrees above normal during the day time. /Fugazzi 


Monday night through Friday...the upper level ridge axis will be 
nudged east by an approaching Pacific trough during the first half 
of the workweek. Models disagree in the timing and strength of this 
trough. Will lean towards the 12z European model (ecmwf) as it has been a bit more 
consistent handling the closed low off the California coast. The latest GFS 
guidance brings a shortwave trough through the region on Tuesday but 
keeps most of the energy either to our north or wrapped into the 
closed low off California. Stagnant conditions will likely persist 
until Tuesday night/Wednesday when the European model (ecmwf) brings a stronger 
frontal system through the inland northwest with greater mixing 
potential. The threat of precipitation will shift from west to east 
Tuesday and Wednesday. Snow levels will fall to around 3500 feet mean sea level 
Wednesday morning. This system does not maintain a good moisture tap 
so quantitative precipitation forecast is expected to be light. Model solutions continue to diverge 
through the end of the workweek. There is some indication of a ridge 
of some sort returning so probability of precipitation trend below climatology with low end values 
in the mountains. Temperatures will continue to trend a bit above 
seasonal normals. /Kelch 


&& 


Aviation... 
a weak frontal system will bring scattered showers to the 
region...with the best chance of low VFR ceilings in rain showers 
over the eastern taf sites. The mountains of the Idaho Panhandle 
may experience areas of obscuration in clouds and precipitation from 08z 
to 16z Saturday from this storm system. Skies will clear from west 
to east behind the front on Saturday. /Ek 










&& 


Preliminary point temps/pops... 
Spokane 31 43 26 43 26 44 / 40 10 0 0 0 10 
Coeur D'Alene 33 43 29 43 27 46 / 50 40 10 0 0 10 
Pullman 36 45 31 46 29 50 / 30 30 10 0 0 10 
Lewiston 38 50 31 51 31 52 / 10 20 10 0 0 10 
Colville 31 41 24 39 25 40 / 40 10 10 0 0 10 
Sandpoint 32 41 28 42 25 43 / 50 30 10 0 0 10 
Kellogg 34 39 30 40 28 43 / 40 50 20 0 0 10 
Moses Lake 31 48 26 45 27 42 / 20 0 0 0 0 10 
Wenatchee 35 46 29 42 28 42 / 20 0 0 0 0 10 
Omak 32 44 24 42 25 44 / 30 0 10 0 0 10 


&& 


Otx watches/warnings/advisories... 
Idaho...none. 
Washington...none. 
&& 


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