Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 160343

Area Forecast Discussion
National Weather Service Boise ID
843 PM MST Fri Dec 15 2017

.DISCUSSION...Leading band of snow moving through Ada County as of
830 pm MST, with snow occurring for several hours after frontal
passage. As of 8 pm MST, snow was reported at McCall, Burns,
Ontario, and Caldwell. Snow is expected to get to Mountain Home
between 930 and 10 pm, and Twin Falls and Jerome around midnight.
Burns has received 0.09 liquid equivalent, all in the form of
snow, and should have around an inch on the ground. Amounts in
lower elevations of Idaho are still expected to average around an
inch, while 1 to 2 inches fall below 5000 feet in southeast
Oregon, and 1 to 3 inches in the mountains. No changes are
planned at this time.


.AVIATION...Areas of IFR conditions in -SN through 12Z as a cold
front tracks eastward across the area. At 0330Z, the SW-to-NE
oriented front was just east of the Oregon/Idaho border, nearing
KBOI, and expected to reach KTWF and KJER around 07Z. Surface
Winds: Generally west 5-10 kt, becoming gusty after sunrise.
Winds Aloft: Northwest averaging 25 kt through 10K ft MSL. Expect
significant clearing and predominantly VFR conditions by 19Z


SHORT TERM...Latest models support previous forecast of snow to
occur with tonight`s cold front. That is, 1-3 inches in mountain
areas, 1-2 inches in Oregon valleys and the lower Treasure Valley
in Idaho, about 1 inch in the Upper Treasure Valley, and less than
1 inch in the western Magic Valley and Camas Prairie. The front
and snow should pass through eastern Oregon 5 PM-10 PM PST, and
western Idaho 7 PM-3 AM MST. Snowfall duration should average 3 to
5 hours. For the Boise area we estimate one inch between 8 PM and
midnight MST. Front will also bring a wind shift to the west or
northwest, briefly 15-30 mph in open areas, then easing after the
front passes. West/northwest winds will increase again Saturday to
20 to 30 mph in the Snake Basin, with gusts to 40 mph east of
Mountain Home. Elsewhere expect 10 to 20 mph, mainly in the
afternoon hours. These winds will completely scour the inversion,
so expect good visibility Saturday. Clearing and colder Saturday
night, with diminishing winds. Any of tonight`s snow cover that
remains Saturday night will make those areas colder. We therefore
lowered min temps for Saturday night a few degrees below model
forecasts, and added patchy fog to the valleys. Sunday morning
looks cold and dry except for the patchy morning fog. Warm-frontal
clouds will spread in from the west Sunday, leading to a slight
chance of snow in Baker County and the west central Idaho
mountains Sunday afternoon.

LONG TERM...Sunday night through Wednesday...The upper level jet
will sag south for the beginning of the extended period, bringing a
warm front and moisture to the region Sunday night into Monday.
Temperatures will warm a few degrees to about normal and
precipitation will spread across the region, mostly north of a Burns-
Boise-Fairfield line. Precipitation will fall first as snow, but as
the day warms, will transition to a mixture of rain and snow. By
Tuesday, a northwesterly flow aloft will turn westerly for a brief
break in precip as the warm front glides north. Temperatures will
warm again Tuesday by a few degrees to about 5 degrees above normal.
Models are in agreement that a trough off the Pacific coastline will
dig southeast Wednesday, bringing widespread precipitation to the
region by daybreak. As snow levels fall with an associated cold
front and temperature return to normal, rain will transition to a
wintry mix along the Snake River Plain.

Wednesday night through Friday...The upper level trough continues to
dig southeastward and out of the area Thursday. Snow levels plummet
to valley floors as the cold boundary passes through. Precipitation
begins to move out just as the snow levels take this dip, but
chances of snow for valley locations remain for Thursday. Drying
conditions for Friday with just some passing showers in the central
Idaho mountains. Temperatures will remain below normal through the
period with highs right around freezing and lows in the teens to low
20`s for valleys and single digits for higher elevations.





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