Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 221013

Area Forecast Discussion
National Weather Service Boise ID
313 AM MST Wed Feb 22 2017

.SHORT TERM...Today through Thursday...A strong Pacific storm will
move east across northern CA today, helping to spread light to
moderate snow into southeast Oregon and southwest Idaho. As the
storm moves east along the Idaho/Nevada border tonight and
tomorrow, snow will become moderate to heavy at times in the
Southwest Highlands, Southern Twin Falls county, and southeast
portions of the Western Magic Valley. A Winter Weather Advisory
has been issued for these areas. Snowfall will generally range
from 3 to 6 inches, but amounts at elevations above 5000 feet,
expect 4 to 12 inches.

Temperatures will be considerably cooler today compared to recent
days, with highs in the mid 30s to lower 40s at lower elevations,
and in the 20s in the mountains. Thursday will see another several
degrees of cooling in most locations, especially in the south
where snowfall will occur. NW to W winds will increase in the
Treasure and Magic Valleys and southward to the Nevada border
tonight and Thursday. Speeds will average 10-15 mph tonight, and
15-25 mph tomorrow. These winds will result in snowfall that
appears to be almost horizontal from late tonight through
tomorrow in and near the advisory area mentioned above. Finally,
with very cold air moving in aloft, snow will be enhanced by
convection throughout this event. This will result in periods of
heavy snow that move rapidly, lasting only a short while in most
locations. Higher terrain will see extended periods of moderate to
heavy snow due to the added upslope that will accompany the
snow showers.

Two rivers, the Malheur near Vale and the Weiser near Weiser, are
in flood. Please see the hydrology section below for details.

.LONG TERM...Thursday night through Tuesday...Weak ridging over
the region Thursday night through Saturday as a weak upper level
low pressure system moves south along the Pacific Northwest
coast. This will bring west-southwesterly flow over the region and
limit cold air advection. Limited moisture remains over the area
but there could be enough for showers across the higher elevations
Friday and Saturday afternoons. Models continue to differ on
their handling of another stronger upper level low pressure
system forecast to move south along the coast Friday night through
Saturday. Confidence remains low as each new model run continues
to shift this low pressure system farther south along the
California coast before it weakens as it shifts inland
Sunday/Monday. At the moment, the best chance for precipitation
looks to be Monday with a warm frontal passage. Precipitation type
will be tricky, but it would appear the valleys would see a mix
of wet snow and rain below 4000 feet with the mountains seeing all
snow. Above-freezing ground temperatures will likely limit
snowfall as well. A warming trend follows with an upper level
ridge building over the west coast through the middle of next
week. Moist northwesterly flow could bring showers to the higher
terrain Tuesday and Wednesday. Below normal temperatures Friday
will slowly increase, reaching near normal by Wednesday.


.AVIATION...Mainly VFR. Numerous MVFR/IFR snow showers will
develop this afternoon along the Nevada border and Western Magic
Valley and continue through Thursday morning. Remaining areas will
see isolated showers diminishing after sunset. Surface winds west
to northwest 5- 15 kts increasing to 15-25 kts late tonight.
Winds aloft at 10k ft msl west 10-20 kts, becoming north and
decreasing to 5-15 kts after 18z.


.HYDROLOGY...Two rivers, the Malheur near Vale and the Weiser
near Weiser, are in flood. The forecast for the Malheur was
recently increased and is now expected to just cross over into the
moderate category late this morning. The new forecast for the
crest is 21.1 feet. It is forecast to fall below flood stage
around 4 am MST Thursday morning. The Weiser River near Weiser has
crested and is on the way back down. It is forecast to fall below
flood stage around 5 pm MST today.


ID...Winter Weather Advisory from 5 PM this afternoon to 11 AM MST
     Thursday IDZ016-030.
     Winter Weather Advisory from 11 AM this morning to 11 PM MST
     this evening IDZ015.



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