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fxus66 kotx 210643 
afdotx 


Area forecast discussion 
National Weather Service Spokane Washington 
1043 PM PST Friday Nov 20 2009 


Synopsis... 
after a short break in the weather on Saturday...a stronger and 
colder storm system will bring the potential for moderate to heavy 
snowfall mainly in the high valleys and mountains. A series of storm 
systems will continue to pass through the inland northwest every 
24 to 36 hours well into next week. 


&& 


Discussion... 
a strong Pacific system is expected to impact the inland northwest 
Saturday night into Sunday morning and winter storm watches have 
been posted for parts of the area. There continues to be 
disagreement from model to model regarding the track and strength 
of a surface low as it passes across Washington. The 00z GFS model is 
the strongest and tracks the low along the Washington/British Columbia border...while 
the NAM is slower and tracks the low from Portland towards 
Pullman. The new 00z Canadian supports the GFS...while the 00z 
European model (ecmwf) has not yet come in but previous European model (ecmwf) supported the NAM. 
Doing a model initialization of this system...the GFS initialized 
a little bit deeper compared to the 12 hour forecast from the 12z European model (ecmwf) 
which was supported by ship observations. Water vapor also shows 
some darkening with this system with the left exit portion of a 
jet streak aiding in intensification. Based on satellite trends 
and that the Canadian backs up the GFS and with the GFS appearing 
to have a good initialization...leaned towards the GFS. The GFS 
shows deep moisture and lift as a 992-995mb surface low tracks 
through the area with quantitative precipitation forecast amounts over an inch along the Cascade 
crest and over a half inch over the northern half of eastern Washington/north 
Idaho. This looks to fall mostly in a 12 hour period with the bulk 
of the precipitation falling Saturday night in the Cascades and 
overnight Saturday into Sunday morning over eastern Washington/north Idaho. 
Tricky part is snow levels with 1000-850mb thicknesses 1305-1310 
dm...and 850mb temperatures of -2 to -3 snow levels look to be near 2000 
feet. Thus the winter storm watches have been issued above this 
elevation. Snow levels could end up a little higher at times over 
the Spokane/Coeur D'Alene area as well as the Palouse with 
southerly low level winds developing as the low tracks north of 
the area. Thus with lower confidence in these areas held off on 
any potential watches. 


For tonight drier air will continue to move into eastern 
Washington behind the earlier cold front passage...while upslope 
Post frontal snow showers fall in the mountains of north Idaho. 
Accumulations in the mountains however will only range from 1 to 3 
inches. Jw 


&& 


Aviation... 
areas of MVFR and IFR ceilings will occur through 18z due to abundant 
low level moisture across eastern Washington/north Idaho. In the Lee of the 
Cascades VFR conditions will persist at keat/kmwh as downslope 
flow has dried out the lower levels. Jw 


&& 


Preliminary point temps/pops... 
Spokane 33 39 32 37 27 39 / 20 20 90 80 10 40 
Coeur D'Alene 33 39 31 37 28 40 / 40 20 80 70 20 50 
Pullman 32 39 32 36 28 42 / 50 20 70 80 20 40 
Lewiston 36 47 36 41 30 48 / 40 10 40 90 20 30 
Colville 32 40 33 40 28 38 / 10 30 80 70 10 60 
Sandpoint 32 36 32 37 28 36 / 90 40 80 80 20 60 
Kellogg 32 33 30 34 27 35 / 90 70 90 90 40 60 
Moses Lake 31 45 32 43 26 43 / 0 10 80 60 0 40 
Wenatchee 32 43 32 43 29 41 / 0 30 90 50 10 50 
Omak 28 43 31 42 25 40 / 10 60 90 60 0 60 


&& 


Otx watches/warnings/advisories... 
Idaho...Winter Storm Watch from Saturday evening through Sunday 
afternoon above 2500 feet for central Panhandle mountains. 


Winter Storm Watch from Saturday evening through Sunday morning 
for northern Panhandle. 


Washington...Winter Storm Watch from Saturday evening through Sunday morning 
for east slopes northern Cascades. 


Winter Storm Watch from Saturday evening through Sunday morning 
above 2000 feet for northeast mountains...Okanogan 
Highlands. 


Winter Storm Watch from Saturday evening through Sunday morning 
above 2000 feet for Okanogan Valley...Waterville Plateau. 


&& 


$$