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Area forecast discussion 
National Weather Service Boise Idaho
845 PM MST Thursday Feb 11 2016

Discussion...showers have exited to the east and dissipated as
cloud tops warmed. Visibility has dropped to around 7 miles
across the lower Treasure valley where humidities were in the 80s
percents. Patchy middle clouds were present across Oregon to central
Idaho. Dry forecast on tap tonight with patchy dense fog across
the lower T.V. And Weiser basin...and patch fog elsewhere
generally below 5k feet mean sea level. Upper ridge breaks down with a cold
frontal passage Saturday morning but dirty ridge rises Sunday through
Tuesday. 18z GFS is in general agreement with above climatology probability of precipitation and
SW flow/troughing Thursday with snow in the mountains.


Aviation...generally VFR with scattered-broken middle level clouds.
Patchy fog developing overnight with local LIFR conditions. Surface
winds variable 10kt or less. Winds aloft at 10kft mean sea level...west-southwest 20-30kt.


Air stagnation...pattern will weaken Friday and break down
Saturday due to cooling aloft.


Previous discussion...
short term...tonight through Saturday...updated for this evening
to increase probability of precipitation north-northwest-east of Boise. Showers brought sprinkles across
the Treasure valley and radar echoes were stronger and cloud tops
colder across the west central and Boise Mountains. So increased
probability of precipitation this evening across central Idaho to Boise. Gem/consall blend
preferred. End update. Friday and Saturday...the large upper
level ridge that has brought inversion conditions to the area for
days will finally move off to the east and be replaced by a
trough. This trough will move in Friday night and out again
quickly by Saturday afternoon. An associated cold front should be
enough to clear out the inversion as it moves through during the
same time period. Until then...however...we are still dealing with
what is left of the inversion for one more day. Highs on Friday
will be similar to recent days for most of the area...although
higher elevations will cool slightly while the inverted areas warm
a little. There was a significantly smaller amount of low clouds
and fog this morning over the area...with even more having burned
off in the early afternoon hours. As of 2 PM MST...only the lower
Treasure valley was still dealing with clouds below 2500 feet. We
expect about the same thing tomorrow clouds overnight
again work against fog and stratus formation. Temperatures Saturday will
be warmer in lower elevations even though we will see a so-called
cold front move through from Friday night through the first half of
Sat. This is because the inversion will be removed. Upper levels
will cool significantly compared to Friday...however. Precipitation will
largely be confined to the northern sections of the County Warning Area...mainly Baker
County and the west-central mountains but we have left low probability of precipitation
further south as a few stray showers could develop as far south as
the Treasure valley Saturday with the frontal passage.

Long term...Saturday night through Thursday...models remain in
relatively good agreement with a more active weather pattern in
the extended period. A series of upper level troughs will move
through the Pacific northwest for periods of precipitation over
the forecast area. The first upper level trough will move
southeast of the region Saturday night...but the northwest flow
that will develop behind this exiting system is moist with the
best chance of precipitation over the area Sunday. Snow level
Saturday night will be between 4000-5500 feet and rise to
5000-7000 feet by Sunday evening. Flat upper level ridge will be
over the region Sunday through Tuesday for warming temperatures
and snow levels around 7000 feet. Due to the ridge being flat
moisture will be moving through the flow for at least slight
chance probability of precipitation over northern zones while southern zones will remain
dry. High temperatures for Monday and Tuesday will be in the 40s
in the mountains and in the 50s in the lower valleys with some
isolated locations possibly reaching 60 degrees. Tuesday night
into Wednesday models begin to diverge on the timing of the next
upper level trough that will move into the West Coast...but will
see increasing chance of precipitation over the area Tuesday night
with precipitation lingering over the region through Thursday.
High temperatures will cool to near normal by Thursday with highs
in the 30s in the mountains and in the 40s to low 50s in the lower


Boi watches/warnings/advisories...




air stagnation...vm
previous short term...snow pellets long term....ja/wh

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