Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 170334
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
834 PM MST Mon Jan 16 2017

.DISCUSSION...

The only update to the current forecast was to make overnight
temperatures cooler as many locations were quickly approaching
their forecast overnight low temperatures. Remain concerned that
values were not lowered enough, but will continue to monitor and
adjust as needed. No updates or changes made to the Winter Storm
Watch. Models continue to support the notion of the digging trough
with ample moisture beginning late Tuesday and lasting into
Thursday afternoon.

&&

.AVIATION...Below the inversion layer, deteriorating conditions in
low stratus and fog with areas of MVFR/IFR conditions after 07Z.
Above the inversion layer, scattered to broken high level clouds
with VFR conditions. Surface winds light and variable, except near
KJER with northeasterly winds 10-15 knots by morning. Winds aloft
northerly 10-20 knots up through 10K feet MSL.

Outlook for Tuesday night through Thursday...Another pacific storm
system will bring more snow to the region. Widespread IFR and areas
of LIFR conditions in snow along with mountain obscuration will
spread over the region Tuesday night and will remain over the region
through Thursday.


&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Wednesday...Dry tonight and tomorrow
as a ridge axis passes overhead, with continued inversion
conditions in the valleys. As a very moist and strong Pacific
storm approaches Tuesday night, out conditions will deteriorate
rapidly. A Winter Storm Watch has been issued from 11 pm MST /10
pm PST / Tue night through 5 pm MST / 4 pm MST / Thu afternoon.
This system has an impressive moisture tap stretching down to the
tropics. QPF will be high, and models indicating low amounts of
precipitation were discounted. Snow amounts by the end of Wed
afternoon will range from 3 to 6 inches in the Treasure Valley -
highest amounts in the lower Treasure Valley - and between 10 and
20 inches in the highest mountains of Baker and Adams Counties.
Through Wed afternoon, we only see around 1 inch in the western
Magic Valley. There is a chance of freezing rain over portions of
southern Harney and southwest Malheur Counties Tue night and
early Wed. Temperatures will be very cold again tonight, with
stratus possibly expanding in the western Magic and Treasure
Valleys - especially the lower Treasure Valley. Precip type should
remain all snow through the short term in the Treasure Valley,
with snow amounts ranging from 2-3 inches near Mountain Home, 3-5
inches near Boise, and 5-7 inches from Nampa through Ontario and
over most of the lower Treasure Valley. Additional snow will come
Wed night into Thu. Amounts over the northern half of Malheur
County in the short term will range from 5 to 9 inches, while the
southern third of the county will see just 1 to 2 inches.

LONG TERM...Wednesday night through Monday...A Pacific system
with a deep moisture tap will continue to move through the region
Wednesday night into Thursday. Model PWATs are high with percentiles
between the upper 80s and lower 90s. Some forecast uncertainty for
Wednesday evening as the NAM/GFS models show the Treasure valley
mixing sufficiently to switch over to a rain/snow mix, while the
EC/Canadian models keep us much colder. Have opted in favor of the
colder solutions and have kept the precip type as snow for the
Wednesday evening period thinking that the cold temps will hold
on longer than anticipated; will then switch over to a rain/snow
mix Thursday. PWAT percentiles drop off appropriately through the
day Thursday as the moisture/system kicks east and the drier
trough axis pushes in. This will give the region a brief break in
precipitation until Friday when the next system moves in. This
system is a much cooler system, though less moisture laden versus
the previous system, with most of the energy dipping south of the
region. Precipitation is expected to generally fall as snow
through Saturday. Next system to move into the region Sunday for a
continuation of an active weather pattern through the extended.
Temperatures will be about 5-10 degrees below normal through the
period.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Winter Storm Watch from Tuesday evening through Thursday
     afternoon IDZ011>016-028>030-033.
OR...Winter Storm Watch from Tuesday evening through Thursday
     afternoon ORZ061>064.

&&

$$

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DISCUSSION...KB
AVIATION.....JA
PREV SHORT TERM...SP
PREV LONG TERM....AB/WH


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