Area Forecast Discussion
Issued by NWS Pocatello, ID

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000
FXUS65 KPIH 201945
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
145 PM MDT Fri Oct 20 2017

.SHORT TERM...Tonight through Monday. A strong low pressure trough
was advancing east across SRN Idaho early this afternoon resulting
in a broad area of advisory level winds throughout the ERN Magic
Valley and Snake River Plain and a smaller area of stronger winds
across CNTRL INL. Areas of blowing dust and reduced visibility were
noted on several ITD web-cams due to the strong winds. Thus the wind
advisory will continue for the aforementioned area through 9PM MDT
this evening. Radar was showing scattered snow showers across the
CNTRL mountains where a colder and drier airmass was advancing into
the region from the west. Across the SE Highlands where temperatures
were warmer, light rain showers were noted. The trough axis is
expected to work into the Wyoming border area early this evening as
a secondary trailing wave digs into WRN Idaho. The resulting WNW
flow aloft will be supportive of upslope showers favoring the CNTRL
and NE mountains overnight and little or now precipitation
elsewhere. The next upstream storm system begins to setup over the
Gulf of Alaska Saturday resulting in a warm moist overrunning
pattern which edges into the CNTRL and NE mountains Saturday night
and continues through Sunday evening as an ejecting short-wave
shears east through Canada. Thus we should see ongoing snowfall and
periods of lower valley rain mainly north of the Snake River Plain
Saturday night and Sunday. Wind speeds will nose up towards advisory
levels once again Sunday as the short-wave shears north and east of
the region. Drier and warmer conditions follow Sunday night into
Monday as a ridge of high pressure builds along the west coast
driving the storm track north into Alaska and Canada. Huston

.LONG TERM...Monday night through Friday. Expect dry and warm
conditions Tuesday. A Canadian wave circles around upper ridge in
Pacific Wednesday and both the GFS and European operational models
have it affecting southeast Idaho to varying degrees Wednesday into
Thursday.   GFS stronger and much colder with system.  Introduced
some precipitation chances Wednesday night mainly in high elevations
and dropped high temperatures considerably Thursday with warming
again Friday as system pushes east. Tuesday and Wednesday should be
very warm with highs well above normal. GK
&&

.AVIATION...Strong winds will continue through sunset at BYi, PIH
and IDA with speeds in the 20 to 35 knot sustained range and gusts
40 to 50 knots at times.   Some MVFR ceilings will continue at those
sites as well as DIJ where rain will likely change to snow showers
and could lead to some reduction in visibility as well.  Lower
ceilings expected to linger at DIJ the longest through sunset or
slightly beyond.   Precipitation has moved out of SUN and expect VFR
conditions through Saturday.  Sustained winds of 15 to 25 mph
expected again Saturday afternoon at the Snake Plain sites BYI, PIH
and IDA. GK
&&

.FIRE WEATHER...A surface cold front associated with the low
pressure disturbance moving inland will cross the Snake Plain early
this morning. Southwesterly winds 25 to 35 mph with gusts to near 50
mph will develop this morning and continue through early evening. A
Wind Advisory is in effect. Southwesterly winds will increase over
the exposed upper elevations of the mountains in all areas, gusts to
30 mph pretty common, 35 for the Southern Sawtooth and Caribou
Forests. The disturbance is tracking a little more south which
helped easy the winds on the Lemhi Range down some. Showers will
spread to the Wyoming border by noon today. Through about midnight
Friday night, the west slopes of the Central Mountains, including
Stanley and Galena Summit area could see .10 to .40 inches liquid
equivalent of precipitation, a few west facing slopes possibly a
half inch. Temperatures drop back to the 40s in the mountains and
around 50F valleys Friday. Snow levels after rising to near 10000
feet elevation on Thursday, come back down to around 5500-6000 feet
Friday afternoon and continue to fall to the valley floors by
Saturday morning. Scattered showers will diminish Friday night and
early Saturday before the next round of moisture advances across the
Central mountains and Eastern Highlands Saturday night and Sunday.
This second round may target the west slopes of the Central
Mountains Saturday evening through Sunday evening, thus the wet
facing slopes could see an additional .1 to .3 inches of
precipitation. Banner and Galena Summits may see 1 to 4 inches of
snow from this second round. Then a gradual return to dry high
pressure ridge follows Monday and Tuesday. Models are more in
agreement by Wednesday of next week and bring a chance of showers in
north-northwest flow through the Salmon-Challis and Targhee Forest
area. This is followed by another two day period under a ridge of
high pressure. RS
&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Wind Advisory continues through 9 PM MDT this evening for IDZ017-020-
021.
&&

$$


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