FXUS65 KBOI 181034

Area Forecast Discussion
National Weather Service Boise ID
334 AM MST Fri Jan 18 2019

.SHORT TERM...Today through Sunday...A few light rain and snow
showers will continue in our CWA early this morning but end
later this morning. A very moist Pacific warm front will begin
snow and rain in Harney County this afternoon. The leading
edge of pcpn will reach western Idaho around sunset, then
central Idaho this evening. Widespread pcpn, locally heavy,
will fall in our CWA tonight, then concentrate on western Idaho
Saturday morning, and central Idaho Saturday afternoon. Pcpn
will decrease in southern Harney and Malheur Counties Saturday
afternoon. The main Pacific moisture fetch will arch northward
across Baker County and western Idaho Saturday night, then sag
southward again directly over our CWA Sunday. Quite a bit of
pcpn will therefore fall on our CWA through Sunday. Snow levels
will be 3000 to 4000 feet MSL tonight as pcpn spreads in. Several
inches of snow will fall in Baker County and west Central Idaho,
and a winter weather advisory will be issued for these areas
tonight through Saturday morning. After that the Pacific warm
front will raise snow levels sharply. By Saturday evening snow
levels will range from 5500 feet MSL in Baker County and Valley
County, to 7500 feet MSL in southeast Oregon and southwest Idaho.
Snow levels will remain above 5500 feet in all areas through
Sunday as pcpn, locally heavy, continues. Free-flowing creeks
and streams will run higher. Temperatures will be about ten
degrees above normal today, then 10 to 15 degrees above normal
Saturday and Sunday.

.LONG TERM...Sunday night through Thursday...A cold front will move
through the region Sunday night into Monday morning. The core of
this system will track across SW Oregon into NW Nevada on Monday
morning. Thus, the bulk of the precipitation associated with this
system will be along the NV border. Snow levels will initially be
4500-5500ft along the front, but lower to the valley floors behind
it. Precipitation should quickly shut off behind the front. Upper
level ridging will build off the West Coast on Tuesday with
northwest flow over our area. Moisture will spill over the ridge
into the region on Tuesday afternoon as a system tracks across
British Columbia into Wyoming by Wednesday. Temperatures will be
cold enough to support snow at all locations with this system.
Tuesday will likely be the coldest day of the period, with
temperatures near normal. The upper level ridge will amplify on
Thursday and Friday with dry conditions and north-northwesterly
flow aloft. Temperatures, with the exception of Tuesday, will
remain around 5 degrees above normal for the period.


.AVIATION...Generally VFR. Scattered showers through 15z/Fri. Snow
levels 3500-4000ft MSL. Mountains obscured. Then, deteriorating
conditions again from widespread precipitation after 22z/Fri in ern
OR and 00z/Sat in sw ID. LIFR to IFR visibilities in snow, MVFR
ceilings in rain. Snow levels at 4000-4500ft MSL at the onset of
precipitation, rising to 6500-7500ft west of BNO-ONO-TWF with 4000-
5000ft east. Surface winds: NW winds 5-15kt, shifting to the SW-SE
5-15kt after 00z/Sat. Winds aloft at 10kft MSL: westerly 15-25kt
increasing to westerly 35-60kt (strongest in OR) by 09z/Sat.

Weekend outlook...Mountains obscured. Widespread precipitation
expected on Saturday with snow levels 5500-7500ft. A lull in
precipitation expected Sunday morning ahead of cold front. Cold
front will move through late Sunday night, with snow levels lowering
to valley floors by Monday morning. Winds aloft at 10kft MSL: West-
southwesterly 40-50kt. Surface winds SW-SE 10-20kt.


ID...Winter Weather Advisory from 11 PM this evening to 11 AM MST
Saturday IDZ011-013-033.
OR...Winter Weather Advisory from 4 PM this afternoon to 10 AM PST
Saturday ORZ062.



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