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Area forecast discussion 
National Weather Service Boise Idaho
941 PM MDT Tuesday Aug 4 2015

Discussion...shower and thunderstorm activity which initiated
over far southeast Oregon and the in/Nevada border is decreasing in coverage
with sunset. Watching a second area of lighter shower activity
over northern Nevada which is associated with an upper low circulation
in northern California. Showers will develop across southeast Oregon and SW Idaho
as the low center tracks to the NE overnight. Evening weather
balloon from kboi showing elevated instability which would support
potential for nocturnal thunderstorms given forcing from the upper
low. However...confidence on coverage and strength of deeper
convection that develops remains low. Newest model guidance hasn/T
changed much with overnight forecast so will not update at this


Aviation...VFR with increasing middle and high level clouds. Isolated
showers and thunderstorms this evening mainly north of a kboi-ktwf
line. After 05z scattered showers and isolated thunderstorms will
spread over the entire forecast area and remain over the region
through the night. Surface winds generally 10 knots or less...with
gusty winds to near 30 knots near thunderstorms. Winds aloft
westerly 10-15 knots up through 10k feet mean sea level.


Previous discussion...
short term...tonight through upper level wave that
was moving northeast across northern California this afternoon will continue
into southeast Oregon and SW Idaho overnight and Wednesday. This will bring a
chance for showers and thunderstorms to the area overnight...which
is relatively unusual...and which would make two nights in a row
for many folks in the Boise area. These showers and storms will
move east tomorrow...resulting in decreasing probability of precipitation in southeast Oregon
through the day. As the system exits SW Idaho in the evening...
probability of precipitation will rapidly decrease Wednesday night across the remainder of the
area. Relatively dry zonal flow will come in Thursday...bringing a dry
and mostly clear day. Temperatures will be 5 to 10 degrees below normal
both Wednesday and Thursday...with overnight lows dropping considerably from
tonight to Wednesday night. Tonight...with clouds around...lows will be
around 5 degrees above normal. Wednesday night...with dry air and clear
skies...expect lows around 5 degrees below normal.

Winds near showers and storms today and tomorrow could gust 35 to
45 miles per hour...and brief heavy downpours will accompany the stronger
storms. Lightning is always a hazard with thunderstorms...
regardless of the intensity of rain...hail...or wind.

Long term...Thursday night through Tuesday...upper low off of
the California coast will begin moving inland Thursday night into
Friday morning. By Friday afternoon...showers and thunderstorms
are expected to develop along the Idaho/Nevada border...and spread
through the rest of the County Warning Area by Saturday morning. By Saturday
afternoon...the low will have weakened and been partial absorbed
into the westerly flow associated with a larger upper low off of
the British Columbia coast. Nonetheless...the trough axis will
have shifted east by this time so most convection is expected to
be confined to the eastern most portions of the County Warning Area...especially
the Idaho central mountains. Convective parameters do not look
impressive Saturday surface heating and orographic
lifting will be the main forcing mechanism. By Sunday...upper low
off of the British Columbia coast will slowly drift southward and the area will
transition into a southwest flow with some moisture transport to
support some thunderstorms Sunday afternoon in the northern
mountains. Southwesterly flow Monday and Tuesday will lead to an
upper level low moving in from off the Washington coast by
Wednesday. Disagreement in timing of the next system leading to
low confidence in timing of any precipitation. Left probability of precipitation to model
consensus and climatology for now. Temperatures linger right around normal.


Boi watches/warnings/advisories... flag warning from 6 am to 7 PM MDT Wednesday
Red flag warning until 7 PM MDT Wednesday idz423-426. flag warning from 6 am to 7 PM MDT Wednesday orz637.




previous short term...snow pellets
previous long term....ep/jc

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