Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 190322

Area Forecast Discussion
National Weather Service Boise ID
822 PM MST Thu Jan 18 2018

.DISCUSSION...Radar remains filled in this evening with valley
rains and mountain snows. Significant moisture remains across
eastern Oregon this evening and radar appears to be showing the
back edge of the heavier precipitation moving closer to the Lower
Treasure Valley. Overall, forecast is in good shape, with the
advisory persisting across the West Central Mountains. Webcams
around McCall, Idaho have demonstrated around an inch of snow
accumulation, with more expected tonight. Models continue to
indicate showers weakening across the area by Friday morning,
though residual moisture will keep some rain and snow around
through Friday evening. No changes made to the forecast so far,
though timing of the heavier activity will continue to be
monitored for needed updates.


.AVIATION...Widespread MFR and IFR with rain and snow continuing
through Saturday morning. Surface winds becoming west/northwest with
occasional gusts to 20 kts. Winds aloft near 10 KFT MSL: Southwest
40-50 kts becoming west 20-25 kts.


SHORT TERM...Tonight through Sunday...A winter storm is moving
through the area at this time. So far, it has been raining below
about 5000 feet elevation, but as a cold front moves through this
afternoon and tonight, snow levels will fall quickly. By Friday
midday, snow levels will range from around 2500 feet in Baker
County to near 3000 feet in the McCall and Boise areas, to 4000
feet in Twin Falls and Jerome. For most areas, by the time the
cold air arrives, the precipitation will be over or nearly so.
However, it still appears the West Central Mountains will see
around 4 inches of snow in the valleys, with 5 to 9 inches above
7000 feet. Therefore, the Winter Weather Advisory will stay in
place. Rain is expected to change to snow in McCall, for example,
by 8 pm this evening. An outflow boundary from showers has
recently moved through the Lower Treasure Valley and was headed
through Ada County into Elmore County as of 230 pm MST. This will
switch winds from southeast to northwest, but is not the front.
The front will move through this evening and overnight.
Precipitation will be moderate overnight and early Friday, with
amounts from 5 pm MST today through 11 am MST tomorrow ranging
from 0.15 to 0.25 in the valleys, and from 0.75 to 1.00 inches in
the mountains. Of course, in the mountains, much of that
precipitation will fall in the form of snow at higher elevations.
Temps the next few days will be much cooler than in recent days,
but will actually just get back down to a couple degrees above
normal. Highs in the valleys will average 40-45, with the
mountains headed into the 20s and lower 30s. Overnight lows will
range from the 20s in the valleys to the teens in the mountains.

After this initial system moves through tonight and tomorrow, we
will see isolated to scattered snow showers, mainly in the
mountains of the north, through Sunday. A weak ridge aloft will
move through Saturday night into Sunday. Late Sunday, another
system approaches from the west. Light snow may spread into mainly
Harney and Baker counties Sunday afternoon, but the main impact
will be felt from Sunday night onward.

LONG TERM...Sunday night through Thursday...An active and wet
long term forecast remains in place. The next upper level trough
begins to press into SE Oregon Sunday night into early Monday. The
northern portions of the CWA look to be the hardest hit with this
trough passage. Snow levels sit close to 3k feet MSL for southern
portions of the CWA with below 3k MSL northward. The mountains
will have a promising forecast for the long term with snow likely
as each system makes its way through. Valleys, on the other hand,
will see some fluctuation between a wintry mix/snow to straight
rain as we get into the warm sectors of some of these systems.
Tuesday, precipitation lingers in the northern mountains. The next
trough hits Tuesday night into Wednesday. Snow levels out ahead
of this one climb to near 4500ft MSL for southern portions of SE
Oregon and between 3000-3500 feet MSL elsewhere. As the cold
boundary with this trough pushes through Wednesday evening, snow
levels plummet back down to valley floors. The mountains still
look very good on snowfall with this system, but valleys will
depend on where the precipitation falls. Models keep most in the
northern zones or central Idaho mountains at this time.


ID...Winter Weather Advisory until 11 AM MST Friday IDZ011.



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