Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 221710

Area Forecast Discussion
National Weather Service Boise ID
1010 AM MST Wed Feb 22 2017

.DISCUSSION...Incoming shortwave from the south and west beginning
to build strength this morning as it pushes into the region. This
system is set to bring precipitation to most of the region, with
its main focus along the Idaho-Nevada border and north into the
western Magic Valley as it slides to the east. These areas are
under a Winter Weather Advisory beginning late this morning
through tomorrow morning for now. The Lower Treasure Valley is
expected to remain dry today, as will portions of the western
Canyon and Ada Counties. Most precipitation will fall as snow with
a mix of rain and snow at the lower elevations. Have updated the
QPF and snow amounts to reflect an increase in amounts from
multiple model solutions this morning. A few solutions are
hinting that the shortwave may bring wrap-around moisture into the
western Magic Valley and Boise Mountains tomorrow evening and
early Friday morning. Will need to address this in the afternoon
package. Otherwise, expecting an increase in clouds today as this
shortwave moves through the region. Cooler temperatures today
will begin to bring hydrology related concerns down a notch. Still
have Flood Warnings out for both Weiser River at Weiser and
Malheur River at Vale, but both river have either crested or are
near crest and will be receding with cooling temperatures.


.AVIATION...Mainly VFR with periods of MVFR/IFR. Shower activity
present across the southern third of the forecast area through the
day, most likely to impact KBNO through around 00z. This moisture
will move northeast through the evening, with periods of shower
activity anticipated across the western Magic Valley and impacting
KJER and KTWF through the overnight hours. Surface winds Northwest 5-
15 kts becoming north to northeast by 03z. Winds aloft at 10k ft msl
west to southwest 10-20 kts, becoming north to northeast 10-20 kts
after 03z.


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.

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.


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



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