595 
fxus65 kboi 231014 
afdboi 


Area forecast discussion 
National Weather Service Boise Idaho 
314 am MST sun Nov 23 2008 


Short term...today through Monday...dense fog is the main 
forecast issue this morning. At 09z...dense fog extended from 
Caldwell through Boise...Mountain Home and into Jerome. Surface 
high building east just north of the forecast area as kept light 
northwest winds in the valley. Thus...fog/stratus has spread southeast 
into the western Magic Valley and remains out of most of the lower 
Treasure valley. Analysis of forecast soundings and surface 
features show good agreement with fog/stratus shifting down the 
valley into lower Treasure valley starting at 18z before lifting 
out by after 21z. This is based on placement of the surface high 
which is forecasts to move into central Idaho by 18z this 
afternoon. This should setup a southeast/northwest pressure gradient for 
southeast winds in the valley. Approaching upper level trough 
towards the West Coast should further tighten the gradient for 
light southeast winds in the boundary layer tonight. Also...model 
soundings indicating quite a bit of drying aloft underneath the 
upper ridge. The RUC and NAM soundings show the dry air descending 
towards the top of the inversion near 800 mb by 18z which is a 
good indication for the dissipation of the stratus deck. Based on 
this...will add the western Magic Valley to the dense fog advisory 
until 18z today. Fog/stratus should begin to lift by 18z moving 
into the lower Treasure. Have forecast stratus to dissipate in the 
lower Treasure valley by 21z this afternoon. Day shift will have 
to monitor surface high location and valley winds to see if dense 
fog advisory may needs some timing adjustments. Have lowered 
temperatures along with guidance as stratus/fog will limit surface 
heating today. Slightly warmer on Monday as light southeast winds 
ahead of the upper trough off the West Coast should increase temperatures 
2 to 3 degrees above todays high. Patchy fog tonight...mainly in 
sheltered mountain valleys and the lower Treasure valley as 
southeast winds should keep the boundary layer mixed enough in the 
upper Treasure and western Magic Valley. 


Long term...Monday night through Sunday...models continue to show a 
split flow pattern evolving over the western United States during 
the upcoming week. But first early in the week...a high amplitude 
ridge will dominate the forecast area Monday through much of Tuesday 
as a deep closed low develops over the eastern United States. This 
upper ridge in our area spells inversion conditions but it is not 
expected to be a long lasting event with the split and new closed 
low moving in later in the week. With such a blocky pattern 
developing across Continental U.S. During the upcoming Holiday week...believe 
features will be both slower to evolve and break down. Even though 
the operational models favor a split flow in the west...there are 
considerable differences in the placement of the parent closed low. 
GFS takes this system much farther south across Southern California 
while the NAM solution has the low farther north in the central 
Great Basin. Implications are significant in that NAM solution 
would bring wet weather and travel implications into our area for 
the Holiday...while the GFS would keep dry weather in the region. A 
quick look at the new European model (ecmwf) would also favor a more southern track 
like the GFS. Have kept climatology probability of precipitation going in this time frame due to 
the uncertainty in this important long range travel period. 


&& 


Aviation...Post frontal moisture and light west winds have produced 
upslope foggy and low cloud conditions over much of the area 
overnight. LIFR conditions expected in southwest Idaho affecting 
kboi...keul and kono terminals...while a more low stratus deck under 
1000 feet affects the higher terrain around kjer and ktwf. Mountain 
locations also expected to see IFR conditions in fog and low clouds 
but mainly centered around the usual early morning times. Strong 
surface high drifting southeast toward eastern Idaho Sunday 
afternoon will bring increasing easterly winds into southern Idaho 
and improve most areas into MVFR conditions or better. Light to 
moderate west winds aloft. 


&& 


Boi watches/warnings/advisories... 
Idaho...dense fog advisory until 11 am MST this morning for idz016. 
Dense fog advisory until 11 am MST this morning for idz012- 
idz014. 
Or...none. 


&& 


$$ 


Weather.Gov/Boise 


Short term...jds 
long term....gs 
aviation.....Gs