299 
fxus65 kboi 181513 
afdboi 


Area forecast discussion 
National Weather Service Boise Idaho 
913 am MDT Friday Jul 18 2008 


Discussion...12z boi radiosonde observation had temperatures similar to 12z Thursday when maximum 
temperature reached 94f...but today should end up cooler as upper trough 
in western Canada sags south into our County Warning Area...especially northern zones. 
Current forecast and various MOS products agree on several degrees 
cooling today so no update needed for that. The trough will exit 
east across southwestern Canada late tonight/Saturday while another paficic 
trough moves closer to the West Coast. Between the troughs an upper 
ridge will build northward in Oregon tonight then shift to Idaho Saturday 
while continuing to build. This will bring hotter weather Saturday after 
a cool start. Air mass looks too dry for thunderstorms through 
Saturday...although late Saturday some middle-level moisture is prognosticated 
to reach southern Twin Falls County from the south. We will keep haze in 
grids through Saturday due to smoke from calif fires. Fire weather red- 
flag warning in southeastern Idaho today is for wind and low humidity...but 
not as much wind is expected in our zones. 


&& 


Aviation...with SW flow aloft smoke from wildfires in California 
will keep low-VFR to locally MVFR visibilities across the area 
through Saturday. There will be scattered cumulus this afternoon 
over higher terrain of Baker County Oregon and the central mountains 
of Idaho. Surface winds will be light to moderate southwest. Winds 
aloft will be light to moderate westerly. 


&& 


Previous discussion... 
short term...today through Saturday...upper trough dropping into the 
Pacific northwest will bring slightly cooler temperatures to the area today. 
Thunderstorm threat is minimal as best instability and lift is 
focused over east-central Idaho...with best chance of convection 
along far eastern borders of forecast area. Surface winds increase 
this afternoon out of the west and become gusty as momentum aloft 
makes it to the surface. Thinking west-northwest surface winds will improve 
smoke/haze conditions some in the lower valleys today...though not 
scour it out completely. And with middle-level transport winds 
returning to the west-southwest tonight and Saturday expect the 
haze/smoke to worsen into the weekend. Ridge builds on Saturday with 
temperatures warming 4 to 7 degrees from today...putting lower valleys in 
to the middle 90s. 


Long term...Saturday night through Friday...GFS/ec are in good 
agreement through Sunday. Models continue to struggle with track of 
a progressive upper trough over the Aleutians and a slow moving very 
positively tilted trough offshore...and their potential to phase 
towards each other in the GFS. On Monday the 00z European model (ecmwf) has now sped 
up upper height falls vs. The 00z run of the GFS. This reverses the 
timing differences of the 00z runs of the 17th and 16th for Monday 
when the GFS was the fast outlier. So now the European model (ecmwf) is evolving the 
very positively tilted 500 mb low over northern calif and lowering heights 
over southeast Oregon and SW Idaho Monday while in the 00z GFS that trough 
remains from offshore to SW Canada. On Tuesday yet another flipflop 
is noted. The ec minors out that first wave and keeps Gulf of Alaska 
energy to the north whereas the GFS phases the slow offshore trough 
and drops Gulf of Alaska energy...not only into the pacnw but California/Nevada and 
Idaho for another role reversal with the higher heights of the ec. Even 
though 500 mb height differences are only about 30m...for minor/3f 
differences in surface temperature the impact is the pattern. With 
various models at times forecasting troughing across Oregon...the 
impact of concern with falling heights and any attendant moisture bodes 
for an increased dry lightning threat there some time towards 
Tue/Wed. For now am leaning towards the GFS Monday and ec Tuesday/Wednesday 
with little or no phasing. Highs 5-8f warmer than normal across southeast 
Oregon and SW Idaho through Monday...falling back to 1-3 above 
normal Wed-Fri. 


&& 


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


&& 


$$ 


Weather.Gov/Boise 


Discussion...lc 
aviation.....Jt 
previous short term...dg 
previous long term....vm