Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 191658
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
958 AM MST Fri Jan 19 2018

.DISCUSSION...Showers continue this morning across mainly the
southwest Idaho part of the area as last night`s storm exits the
area. Snow continues in the West-Central mountains, and therefore
the winter weather advisory will be allowed to remain in effect
until its scheduled end time of 11 am MST. Previous forecast is on
track and no changes are anticipated this morning.

&&

.AVIATION...MVFR with isolated IFR in rain and snow east of KMYL-
KTWF line. This should move of the area by 22Z, leaving mostly
VFR, with scattered MVFR showers through the afternoon. Mountain
valley IFR fog possible toward tomorrow morning. Surface winds
becoming west/northwest 10-15 kts with occasional gusts to 25 kts,
especially at KJER/KTWF. Winds aloft near 10 KFT MSL: West 20-25
kts.

&&

.PREV DISCUSSION...
SHORT TERM...Valley rain and mountain snow showers continuing
this morning.  Snow level 3000 feet MSL in Baker County to 5500
feet in Twin Falls County this morning, lowering to 2500 feet
in Baker County to 4200 feet in Twin Falls County this afternoon.
Rain showers may mix with or change to wet snow in the Treasure
and Magic Valleys but no snow accumulation is expected.  However,
a winter weather advisory for snow will continue this morning
in the west central Idaho mountains for a couple more inches of
snow.  Incoming upper trough will split today with the stronger
part going well south of us, and the weaker part continuing a
slight chance of snow showers in our mountains into Saturday.
Today will be quite a bit cooler than yesterday, but only cooling
to normal for mid-January.  Saturday looks about two degrees
cooler than today.  Finally, patchy fog will form in the valleys
tonight and Saturday morning.

LONG TERM...Saturday night through Friday...A typical winter
pattern continues for the forecast area with several systems shown
to move across the region. However, these systems lack significant
cold air limiting snowfall potential for the lower valleys. The next
upper level trough moves quickly across SE Oregon late Sunday night
and into SW Idaho early Monday. This will be the coldest of all the
systems as snow levels sit close to 3k feet MSL for southern portions
of the CWA and below 3k MSL northward. The mountains will see 3 to
6 inches of new snow. Valleys will likely see a mix of rain/snow as
guidance remains consistent keeping surfaces temperatures at or
slightly above freezing Monday morning. The fast moving trough will
also help limit any valley snow accumulations. A brief break in the
precipitation on Tuesday as a ridge develops ahead of the next
trough. The next trough moves in Tuesday night and lasts through
Wednesday. Snow levels ahead of this system climb to near 4500ft MSL
for southern portions of SE Oregon and between 3000-3500 feet MSL
elsewhere. As the cold front with this trough pushes through
Wednesday evening, snow levels plummet back down to valley floors
with most of the precipitation ending by then. Valleys could start
as a mix of rain and snow Tuesday night but quickly change to rain
with passage of a warm front. The mountains still look very good for
snowfall with this system. Snow showers possible on Thursday with
the trough passage. Friday will be dry as another upper level ridge
develops ahead of the next upper level trough for Saturday which
looks to be a wetter and warmer system. Temperatures remain near
normal through the extended period.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Winter Weather Advisory until 11 AM MST this morning IDZ011.
OR...None.

&&

$$

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DISCUSSION...SP
AVIATION.....TB
PREV SHORT TERM...LC
PREV LONG TERM....JDS



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