608 
fxus65 kboi 292045 
afdboi 


Area forecast discussion 
National Weather Service Boise Idaho 
245 PM MDT Friday Aug 29 2008 


Short term...very tricky forecast this weekend as a major weather 
system evolves along the Pacific northwest coast. This scenario is 
expected to basically slow everything down...hence the forecast for 
Saturday is the most difficult time frame. Temperature solutions 
are wide ranging and could end up anywhere from the lower 90s to 
around 80 depending which model you choose. I have chose a 
compromise/blend in this situation but still feel Saturday will be 
a warm day ahead of the cold front which will crawl eastward toward 
the Idaho border Saturday night. A good strong southeast gradient 
will also set up again Saturday enhancing temperature potential. 
Models do point to frontal passage Saturday night or early Sunday then 
essentially stall the front as it gets caught up in strong south to 
north flow ahead of long wave trough. Thus...even slower systems by 
Sunday and maybe even stationary. 


Probability of precipitation and convective instability are expected to be minimal ahead of 
frontal passage but there is some noted over southeast Oregon where lifted/S 
may get down to minus 1 right along frontal zone. Have included a 
small area of thunder in southeast Oregon to capture this convective 
potential. Not anticipating a big wind event from this feature as 
system slows to a near grinding halt. Strongest winds expected Post 
frontal Sunday morning in the very cool and moistening air mass. 
Speaking of which...Sunday is appearing very unsettled and cool 
compared to Saturday with a sharp drop in temperature...increase in 
clouds and showers and gustiness. Models lean to higher probability of precipitation over 
north and central Idaho along baroclinic zone with limited probability of precipitation 
south of the Snake River Valley. This period starts the process of 
even cooler weather for Monday as entire forecast area gets to the 
west of the long wave trough and settles into a very cool Labor Day. 


Special Weather Statement issued for the big change to cool and unsettled weather 
conditions for the Holiday weekend. 


Long term...Sunday night through Friday...active weather to 
continue through the extended period with a shift to a fall type 
pattern. Models remain in decent agreement in closing off the deep 
trough over the area on Sunday night. There is some differences in 
placement of the upper level low center. The operational GFS places 
the center south over northestern Nevada the past three runs and the European model (ecmwf) 
and GFS ensemble remain consistent in placing the closed low over 
the County Warning Area. Based on consistency...will keep forecast trends in line 
with the European model (ecmwf) solution. Upper low taps into monsoonal moisture 
flowing up from the south late on Sunday. The deepest moisture looks 
to remain over eastern Idaho...Montana...and Wyoming however...with 
the low center over the area...the models have shifted some of this 
moisture into the central Idaho portion of the County Warning Area. The low center 
shifts east Monday keeping the moisture across much of Idaho and the 
northern rockies. This system will be cold enough to bring a few 
inches of snow to the higher elevations /above 7000 feet mean sea level/ of the 
west central and Boise Mountains mainly on Monday. Temperatures will 
remain well below normal Monday and Tuesday with the coldest 
temperatures on Monday as plenty of cold air advection will be in place. Region 
will stay in broad cyclonic flow Tuesday through Thursday with both 
the European model (ecmwf) and the GFS suggesting another deep trough or possibly 
even closed off low will drop down from Canada Thursday night into 
Friday. This will keep temperatures at or below normal and probability of precipitation at 
or above normal Wednesday through Friday. 


&& 


Aviation...VFR conditions under mostly clear skies through 
tomorrow. Local MVFR visibility due to smoke in the vicinity of 
wildfires will continue through Sunday. This includes near 
Featherville Idaho...Picabo Idaho...and Jackpot Nevada. Weak trough 
moves trough overnight tonight with winds shifting from the 
southeast to northwest. However...surface winds will be light with 
moderate westerly flow aloft. Cold upper trough moves into the 
region late on Saturday with cold frontal passage expected early 
Sunday morning. 


&& 


Boi watches/warnings/advisories... 
Idaho...none. 
Or...none. 
&& 


$$ 


Weather.Gov/Boise 


Short term...gs 
long term....js/LH 
aviation.....Js