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Area forecast discussion...updated 
National Weather Service Spokane Washington 
432 am PDT Sat Aug 30 2008 


Synopsis... 
another deep low pressure system will linger over the forecast 
area through the weekend. This will bring cooler air to the 
region...with showers mainly over mountain locations. Rather dry 
conditions for the valleys will prevail through next week...with 
temperatures remaining mainly below average well into next week. 








&& 


Updated aviation discussion 


Previous discussion... /issued 226 am PDT Sat Aug 30 2008/ 


Synopsis... 
another deep low pressure system will linger over the forecast 
area through the weekend. This will bring cooler air to the 
region...with showers mainly over mountain locations. Rather dry 
conditions for the valleys will prevail through next week...with 
temperatures remaining mainly below average well into next week. 


Discussion... 
today and tonight...the progressive pattern that has been over the 
Pacific northwest...seemingly the entire Summer will continue 
through the weekend. Water vapor loops show another deep (for the 
season) cold trough moving into the forecast area at the time. The 
associated cold front is stretched from about Mullan Pass 
southwest to near Walla Walla. Both the NAM/GFS indicate the front 
slowly continuing the eastward progression through the 
day finally clearing the forecast area between 18-21z. The 
focusing point for precipitation has been with the lift provided 
by the front tapping into some middle level instability. As such the 
highest probability of precipitation will remain along the front through the morning 
hours. A few lightning strikes have been observed over night and 
went ahead and added isolates thunder to the forecast through the 
early morning hours. As the trough moves into the region today it 
will issue in much cooler air for the next couple of days. With 
the cold pool moving in there is some weak instability...mainly 
across the north Cascades and northern mountains. However the 
water vapor loop also shows some pretty dry air moving in with the 
trough. Lastly any short wave disturbances should drop south of 
the forecast area around the bottom of the trough. All of this 
spells out some weak and isolated convective showers across the 
the Cascades crest and northern mountains through sunset. Next we 
look at temperatures and snow levels. Temperatures are expected to 
be 10 to 15 degrees cooler today than on Friday. By Sunday morning 
all forecast areas will see some pretty chilly over night 
temperatures. Snow levels along the Cascade crest drop to 
5500-6000 feet...and with some lingering showers near the crest 
the highest elevations have the possibility of picking up a 
dusting of snow. With air mass changes of the nature gusty 
afternoon winds can be expected...especially across the basin and 
Palouse. /Tobin 


Sunday through Monday night...the upper level trough digging across 
the region will keep the threat of showers in the forecast but 
confined to the mountain zones as deep moisture is still lacking. 
As the trough continues to dig south some wrap around moisture 
works its way into the Panhandle of Idaho. The latest European model (ecmwf) 
guidance shows the moisture encroaching a bit farther west into 
the Panhandle while the GFS barely clips the eastern edge of the 
forecast area. Will keep a chance of showers in the central 
Panhandle mountains through Monday as the trough slowly moves to 
the east. The western portion of the forecast area will dry out as 
the Cascades transition to dry northerly flow. Temperatures will 
remain cool on Sunday with valley readings in the upper 60s to middle 
70s then warm a couple of degrees on Monday. 
Tuesday through Friday...the region will be under northwest flow 
aloft with a string of weak impulses riding along the flow. This 
will keep the threat of showers across the northern mountains 
through midweek. By the end of the work week a middle level ridge 
will build over the region with dry conditions prevailing. 
Temperatures will be on an upward trend as the ridge builds with 
readings near seasonal normals by Friday. /Kelch 


Aviation... 
a middle level cloud deck with isolated showers and thunderstorms can 
be expected across the extreme southeast zones through 
15z...including keat. Otherwise expect some lingering high clouds 
with VFR conditions the remainder of the forecast area through 12z 
Sunday. Gusty westerly winds from the basin eastward can be 
expected through the day. /Tobin 




&& 


Preliminary point temps/pops... 
Spokane 71 47 68 47 70 47 / 10 10 10 10 0 10 
Coeur D'Alene 71 45 67 45 68 44 / 10 10 20 20 20 10 
Pullman 71 43 66 43 69 46 / 10 10 10 20 20 10 
Lewiston 78 51 71 52 74 53 / 10 10 10 20 30 0 
Colville 73 41 70 44 73 38 / 10 0 10 20 0 0 
Sandpoint 69 39 65 43 66 39 / 10 10 20 20 20 10 
Kellogg 68 44 61 44 64 46 / 20 20 20 30 30 20 
Moses Lake 77 48 75 51 77 50 / 0 0 10 10 0 0 
Wenatchee 74 52 73 53 77 54 / 0 0 10 10 0 0 
Omak 76 45 75 48 78 49 / 0 0 10 10 0 0 


&& 


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


$$