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Area forecast discussion 
National Weather Service Boise Idaho
953 am MDT Wednesday Sep 17 2014

Discussion...a lightning strike occurred in the Owyhee Mountains
around sunrise indicative of instability there. Models however
have only weak instability. High clouds have overspread most of
our County Warning Area and kept nighttime temperatures mild again...and may take a couple
degrees off maximum temperatures today but not enough to update for that. We did
update sky grids but left temperature grids alone. Models also
still entrain smoe of Odile/S tropical moisture and draw it into
our eastern-most Idaho zones tonight and Thursday morning. Highest
probability of precipitation are located there. Meanwhile...Pacific upper trough now
moving toward the coast. Trough will close off a low when it
reaches the southern Oregon coast Thursday. From there the low is forecast
to move due south along the coast and eventually turn back toward
our area late Sunday...quite different from earlier solutions
which had a big upper ridge and hot weather over our area at that time.

&&

Aviation...
through 09z...Oregon VFR high clouds with surface winds SW 15-25kts
up to 35 kts at 10k feet through 09z. Idaho...mostly VFR with broken-overcast
middle clodus at or above 15k feet mean sea level and isolated showers and thunderstorms.
After 09z throughout broken-overcast 12-15k feet mean sea level with scattered showers
and isolated thunderstorms...areas of mountains obscured and local
MVFR in precipitation. Surface winds south to west 10-15kts shifting
to west and northwest 10-20kts Thursday. Winds aloft SW to west 25-35kts.

$$

Previous discussion...
short term...today through Friday...southwest flow aloft increases
today as an upper trough approaches the coast. Moisture and marginal
instability will support isolated showers and thunderstorms over the
eastern Boise Mountains today. Airmass remains warm and high temperatures
are similar to yesterday. Elevated terrain across southeast Oregon and mountains
of SW Idaho will tap into the stronger winds aloft and see gusts
around 30 miles per hour by afternoon. The chance of showers and thunderstorms
increases tonight as the upper low reaches the norther calif coast
and a jet maximum tracks across the intermountain northwest. The chance of
showers and thunderstorms continues on Thursday as the upper low
weakens and slowly drops south along the California coast. Drier conditions
Friday as a ridge builds into the Pacific northwest. Temperatures pull back from
near record highs after today...but remain above normal throughfriday.

Long term...Friday night through Wednesday...upper level trough
will split and cut off from the jet stream late Friday night. As
this happens the cutoff low will become situated in the center of
the upper level ridge centered over the western United States. The
cut off low will center itself over central California and pull in
monsoonal moisture from the southeast. This cutoff low will slowly
move northeastward over the Great Basin into our southern zones by
Sunday for a chance of showers and slight chance of thunderstorms
during the afternoon in our southern zones. The cutoff low will
exit our region by Tuesday and a shortwave ridge will build into
the region for drier conditions. Forecast confidence beyond
Tuesday is low as the European model (ecmwf) brings in a trough from the Gulf of
Alaska and the GFS builds a ridge over the area.

&&

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

&&

$$

Weather.Gov/Boise

Discussion...lc
aviation.....Vm
previous short term...dg
previous long term....ka

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