Area Forecast Discussion
Issued by NWS Boise, ID

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645
FXUS65 KBOI 292103 CCA
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
303 PM MDT Wed Mar 29 2017

.SHORT TERM...Powerful North Pacific storm will affect our
area tonight through Friday.  Moderate to heavy rain will begin late
tonight and continue through Thursday morning with the storm`s cold
front expected to move across southeast Oregon around 4-5 AM PDT,
southwest Idaho 7-8 AM MDT, and the Magic Valley 10-11 AM MDT. The
front will be unusually strong due to steep thermal gradient across
it and its forward speed.  Behind the front, sustained west and
northwest winds will increase to 30 to 40 mph with gusts to 55 mph.
The sustained winds are strong enough for a high wind warning in the
Upper Treasure Valley east of Boise, through the western Magic
Valley and south to the Nevada border.  Elsewhere, will meet
advisory criteria.  These winds will begin right after the cold
front passes and continue through the day, diminishing only
gradually Thursday night.  Snow level will start out between 7000
and 8000 feet MSL ahead of the front but fall rapidly behind it, all
the way to 3500-4000 feet MSL Thursday afternoon which is low enough
for a rain/snow mix even in the lower valleys.  The front`s speed
and lifting ability may even produce thunderstorms at the time of
frontal passage.  The upper low supporting the storm will move
south-southeast right through our CWA Thursday morning into Nevada
later Thursday.  Wrap-around moisture will produce snow near the
Idaho/Nevada border and 3 to 6 inches, locally 8 inches, are
expected to accumulate Thursday afternoon and night.  Strong winds
will also be blowing at the same time.  Friday will be milder and
generally dry, but still windy especially in southern Idaho.

.LONG TERM...Friday through Wednesday... An upper level ridge will
build over the area Friday night and into Saturday. By Saturday
night, models are showing a shortwave out ahead of the next
upper level trough starting to push into the area. There are
differences in precipitation placement with this shortwave, but
chances remain for showers with it. Sunday night the upper level
trough begins to press southeastward increasing chances of
precipitation for the area. Snow levels drop Monday to under
4000 feet MSL. As this upper level trough presses further
eastward, snow levels begin to climb once again to above 5000 feet
MSL. By Tuesday morning another upper level ridge begins to build in
ahead of the next Pacific trough. There are some timing differences
between the models with this next system. The GFS brings it into
SE Oregon Wednesday afternoon while the ECMWF waits until Thursday
night. Temperatures will be above normal through Monday, then drop
a few degrees below normal before climbing back up above normal by
Tuesday.

&&

.AVIATION...Mostly VFR. Rain will continue to increase in coverage
as the evening goes on. Areas of heavy rain will cause MVFR/IFR
conditions. Surface winds, variable 10-25 kts through 06z Thursday
then 20-35 kts with higher gusts within showers. Winds aloft to
10k feet MSL, westerly 25-40 kts through 12z Thursday then
north-northwesterly 35-45 kts.

&&

.HYDROLOGY...Hydrologic outlook (ESF) was re-issued for increased
river flows tonight through the weekend, mainly due to heavy rain
tonight and Thursday.  Colder air later Thursday through Friday
morning will decrease snowmelt, however.  Flood watches have also
been issued for the malheur River and Vale, OR, and the Payette
River at Emmett.  A flood watch is also being issued for the Big
Wood River in Gooding County, ID, due to outflow from Magic Dam
on Magic reservoir.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...High Wind warning from 9 AM Thursday to midnight MDT Thursday
     night IDZ014>016-030.
     Winter Weather Advisory from noon Thursday to 6 AM MDT Friday
     IDZ015-030.
     Wind Advisory from 9 AM Thursday to midnight MDT Thursday night
     IDZ012-029.
OR...Wind Advisory from 9 AM MDT /8 AM PDT/ Thursday to midnight MDT
     /11 PM PDT/ Thursday night ORZ061>064.

&&

$$

www.weather.gov/Boise
www.facebook.com/NWSBoise
www.twitter.com/NWSBoise

SHORT TERM...LC
LONG TERM....JC/WH
AVIATION.....JC
HYDROLOGY....LC



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