Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 201651
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
951 AM MST Fri Jan 20 2017

.DISCUSSION...Snow is increasing across southeast Oregon this
morning. Cooling cloud tops evident in IR imagery combined with
obvious diffluence on the north side of an incoming jet max
indicate moderate to heavy snow in store for northern Harney and
Malheur counties through mid-afternoon. This band of moderate to
heavy snow will weaken only slightly as it moves through the
western Lower Treasure Valley and then north into the mountains
late this afternoon and evening. Winter weather advisories for
snow still appear on track with no changes in expected amounts.
There is a dense fog advisory in effect for the Lower Treasure
Valley and Upper Weiser River Basin until 18Z, and this will
remain in effect as well. Webcams and the KONO observation show
dense fog has not lifted yet. As today`s storm lifts northeast, it
will spread snow over much of the area. Amounts outside the
advisory area will be generally an inch or less, except in the
mountains, of course. We still see more snow showers tomorrow,
then a system bringing additional snow Sunday, and one final
system beginning early Monday and lifting rapidly north across the
region. No changes at this time.

&&

.AVIATION...Generally VFR this morning. Snow spreading across SE
Oregon this morning and into SW Idaho this afternoon with
widespread MVFR-IFR conditions as the snow passes through.
Mountains becoming obscured. Winds aloft at 10kft MSL: southerly
20-30kt becoming WSW 10-20kt by 09z/Sat. Surface winds: generally
E-SE 10-20kt, strongest in Baker and upper Treasure Valley.

Weekend Outlook...Mountains will be obscured. Scattered to isolated
snow showers will remain over the area Saturday and Saturday night
with MVFR conditions and areas of IFR conditions. Next round of
heavier snow will move over the area Sunday into Monday for
widespread MVFR and areas of IFR conditions.

&&

.PREV DISCUSSION...
SHORT TERM...Today through Saturday...Areas of dense fog (with
visibilities of a quarter mile or less) will continue this
morning from west of Boise to Ontario and northeast into the
Upper Weiser Basin. The fog is expected to dissipate by late
morning. An upper trough near the coast will direct precipitation
into SE Oregon this morning and SW Idaho late this afternoon and
evening. Latest models continue with the trend of slightly warmer
temperatures and slightly higher snow levels through Saturday.
Therefore, will adjust both of these weather parameters
accordingly. The net result, however, doesn`t change the Winter
Weather Advisories for portions of SE Oregon. Northern Harney and
northern Malhuer Counties are still on track to receive 2-5 inches
of snowfall today through this evening, and the Lower Treasure
Valley around Ontario is also on track for 1-3 inches late this
morning through this evening. The slightly warmer temps and higher
snow levels will lead to the possibility of rain with the snow in
Upper Treasure Valley, where snow levels will average 2500-3000
feet tonight through Sunday. Snow accumulations are possible in
the Upper Treasure and Western Magic Valleys, but total amounts
are expected to be less than an inch.

LONG TERM...Saturday night through Thursday...Active weather
pattern still on track through Tuesday. An upper level low off the
Pacific Northwest coast Saturday night will slowly shift east
through Monday night. Best chance of precipitation will be Sunday
as a moist southwesterly flow develops over the area ahead of the
approaching upper level low. As with the previous weather systems,
snow level will be tricky, but still looking like most locations
will see snow, but there could be a change to at least a rain/snow
mix in the lower valleys by Sunday afternoon. As the upper level
low gets closer to the region, snow levels will once again fall to
valley floors. Models do not seem to have a good handle on how
much precipitation we will see with this latest storm but still
thinking 2-4" in the valleys and 4-6" in the mountains. Upper
level low will move over the forecast area Tuesday with decreasing
precipitation. Wednesday and Thursday an upper level ridge
develops over the area with a cold northerly flow and increasing
chance of valley inversion developing.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Dense Fog Advisory until 11 AM MST this morning IDZ012-033.
OR...Dense Fog Advisory until 11 AM MST this morning ORZ064.
     Winter Weather Advisory until 11 PM MST /10 PM PST/ this evening
     ORZ061-063.
     Winter Weather Advisory until 11 PM MST this evening ORZ064.

&&

$$

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DISCUSSION...SP
AVIATION.....KA
PREV SHORT TERM...BW
PREV LONG TERM....JA


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