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Area forecast discussion 
National Weather Service Boise Idaho
902 PM MST sun Jan 25 2015

Discussion...dense fog already seen on webcams and also indicated
on satellite images across the upper Weiser basin. Expect the
fog and low stratus to expand in the Treasure valley /especially
west of Boise/ through Monday morning. A dense fog advisory will
be issued for the upper Weiser basin for the remainder of tonight
through Monday morning...and the Treasure valley for late tonight
through Monday morning. Conditions are expected to improve Monday
afternoon...although the inversion will remain as high pressure
aloft continues over the region.


Aviation...MVFR stratus and IFR/LIFR fog in the lower Treasure
valley and upper Weiser basin this evening which is expected to
expand eastward overnight. Kboi will likely see stratus and fog by
09z. Expected stratus to fill in across the Long Valley and the
western Magic Valley early Monday morning. VFR elsewhere. Surface
winds will be light and variable. Winds aloft at 10
kft...northwest around 20 kts.


Air stagnation...continued inversion conditions through Tuesday
as a strong high pressure moves across the area. A weak system
currently near Baja California California will move northward across the area
Tuesday night into Wednesday. This system may temporarily clean
the air especially in the Magic Valley...but inversion conditions
will return as another upper ridge is expected to build over the
west by the end of the week.


Previous discussion...
short term...tonight through Tuesday...a ridge of high pressure
is transitioning across the Great Basin through Monday morning.
Low clouds and fog persist in the lower Treasure valley as
expected. Expect stratus and patchy fog to expand during the
night and slowly dissipate during the day in the upper Treasure
and Magic Valleys while persisting through the period in the lower
Treasure valley. A weak system currently near Baja California California will
move northward across the area Tuesday night into Wednesday.

Long term...Tuesday night through Sunday...widespread inversion
pattern will return late next week. Inversion will probably not
break for the Oregon lower Treasure and Baker valleys as a moist
upper low crosses SW Idaho Tuesday afternoon through Wednesday
evening. Split flow over the west Thursday will be followed by
another upper level ridge over the pacnw/Idaho Friday through
Sunday. Split flow will have weak winds which will allow low layer
stratus to form or spread. Uncertainty in the strength of the ridge
will determine if upper troughs in the northwest flow can influence
northern tier zones but model trend is for a strong enough ridge to
bring a strong inversion back. The second Baja California low Sunday looks to
remain in a southern stream storm track. Dry weather with very mild
mountain highs are expected Thursday through Sunday. Below around
3500 feet mean sea level /including Boise/ an inversion pattern with slightly
above normal temperatures is expected Thursday through Sunday.
Normal high temperatures at Boise get up to 40 degrees by middle


Boi watches/warnings/advisories...
Idaho...dense fog advisory until 11 am MST Monday idz033.
Dense fog advisory from 2 am to 11 am MST Monday idz012-014.
Or...dense fog advisory from 2 am to 11 am MST Monday orz064.



air stagnation...ka
previous short term...ka
previous long term....vm/wh

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