Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 162005 CCA

Area Forecast Discussion
National Weather Service Pocatello ID
205 PM MDT SUN OCT 16 2016

.SHORT TERM...Tonight through Tuesday Night. The latest satellite
imagery was showing a low pressure trough advancing into the NW
coastal waters with a fairly stiff WSW flow aloft across SRN Idaho.
Numerical models continue to show a decent S/WV ejecting from the
trough across Oregon and into Idaho late tonight/Monday morning with
an accompanying upper jet of 170kts and a surface front pushing into
SE Idaho in the morning. Thus have issued a wind advisory for the
Snake River Plain and eastern portion of the Eastern Magic Valley
for Monday. An increasing threat of Precipitation is expected across
the region overnight, shifting into the ERN highlands Monday morning
as the front and upper wave traverse the region. Snow accumulations
in the mountains above 7500 MSL are expected to remain at and below
advisory levels and thus will adjust wording in going special
weather statement and allow it to continue through Monday morning.

A second weaker Pacific disturbance traverses the region late Monday
night/Tuesday with elevated chances of precipitation across the
region but with less wind and precipitation anticipated. Thus no
highlights are warranted with this second system at this time.

.LONG TERM...Wednesday through next Sunday. After the storms of the
near term, an impulse in the zonal flow moves through for Wed and
Wed night, mainly bringing the northern half of the forecast area a
threat of light showers, including a rain-snow mixture possible at
the floor of the Snake River plain, should precipitation
materialize. After this impulse, and extended period of dry zonal
flow keeps precipitation mainly to the northwest and out of the
region except for the extreme western and northern parts of Custer
County. And even this area has a threat only because of the ECMWF
solution. If the GFS proves correct, then the only day that
threatens precipitation, and this is the same on the ECMWF, is next
Sun/Sun night--the last day of the forecast. Temperatures in each
guidance product are very similar, with temperatures warming in the
Snake River plain to above normal, with some 60s possible for Thu
through Sat. With the zonal flow, there is some possibility of
breezy to windy conditions in the afternoon when any morning
inversion breaks, but there is no significant feature to bring wind
strong enough for an advisory. Messick

.AVIATION...The expected surge of moisture has already returned to
the ID-UT border region and should spread northward overnight,
affecting all airdromes. Marginal VFR should develop for all the
valley airports, but the southerly wind at KBYI and KPIH make this a
tricky call as far as when that occurs, as this will counteract the
high low level moisture content with the downslope conditions. So
have delayed the onset at those two airdromes until the wind shifts
during the early morning. But would not be surprised if it developed
earlier this evening. The most impacted airfields will be KSUN,
which should be near minimums for CIG at closing time tonight. Also,
KDIJ should be shrouded in low CIG and low VSBY to IFR. Neither one
will clear up much until late morning. Messick

.FIRE WEATHER...Very moisture rich westerlies off the Pacific
continue across Southeast Idaho today. The second in a series of
embedded waves is crossing the Snake Plain, Southern Sawtooth Forest
and Caribou-Targhee Forest today. There is one twist, that band of
precipitation moves back north early this evening, possibly as far
north as Kimama and Aberdeen through about midnight before being
shunted off to the east, just as the third wave in the series off
the Pacific approaches from the west. Overnight snow levels dip to
near 6500 feet in the central mountains where 1 to 5 inches
accumulation is possible in the upper elevations. Looks like some of
the very moist air is being diverted along the southern border
Sunday Evening, taking some away from the Galena Summit area. This
afternoon will be windy in the Snake Plain with the passage of a
cold front, an advisory has been issued. A second and stronger front
is expected Monday afternoon. Southwest winds in the Upper snake
Plain Monday will be 30 to 4o mph with gusts closer to 50 mph. The
fourth and what should be the last wave in the series is still on
track to come through on Tuesday. After that, a ridge of high
pressure builds in and will bring warmer temperatures and drier
conditions the last half of the week. RS

.PIH Watches/Warnings/Advisories...
Wind Advisory from 7 AM through 6 PM MDT Monday for IDZ017-020-021.

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