Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 200848

Area Forecast Discussion
National Weather Service Pocatello ID
248 AM MDT Fri Apr 20 2018

.SHORT TERM...Today through Sun night. Spring snowstorm continues
to move through Utah and continues to bring a threat of rain to
the Bear Lake basin and the southern half of the ID-WY border
region. This should end tonight as the low continues its slow
eastward progression. Sat, Sat night, and Sun should be dry under
the influence of strong upper level high pressure. There is strong
westerly wind aloft, and so breezy to windy conditions can be
expected, mainly for the eastern Magic Valley and the lower Snake
River plain. However, at this time do not see sustained wind
exceeding 30 mph and thus do not believe a Wind Advisory will be
necessary. Sun night becomes more problematic. The NAM of 20/00Z
has an absolutely dry trough moving across southern Idaho, while
the GFS has a much wetter scenario. Have attempted to back off on
the likely PoPs for the central Idaho mountains as much as
surrounding office forecasts allow, as there is some uncertainty
growing on what happens on Sun night. Temperatures will soar well
above normal starting today, and continuing Sat where temperatures
plateau. The incoming cloudiness takes the edge off of Sun highs,
while overnight lows Sun night should be very mild. Messick

.LONG TERM...Monday through next Friday night. A trough of Low
Pressure remains slated to slide Eastward across SE Idaho on Monday
with an associated shield of Precipitation expected to be ongoing
across much of SE Idaho Monday morning. Precipitation amounts and
coverage will be greatest North tapering to a chance along the Utah
border. It appears Temperatures will be cold enough for a changeover
to Snow across the Central Mountains stretching Eastward along the
Montana border. This may result in some Winter Driving Conditions
for Galena, Willow Creek, Monida and Targhee Passes Monday morning.
By Monday Afternoon, Precipitation is expected to linger along the
Montana and Wyoming borders and gradually come to end end before
Sunrise Tuesday Morning. Breezy conditions will follow in this
trough`s wake Monday into Tuesday, along with a cooldown to below
average Temperatures. A Ridge of High Pressure is then slated to
build into the region beginning on Tuesday, and this will usher in a
warming and drying trend. Latest guidance is much warmer than
previous runs. Tempered this a bit -- but even so Temperatures
should easy achieve 70 degrees for highs by Thursday across much of
the Snake Plain and Cache Valley. Precipitation chances begin to
increase Friday, but coverage should remain limited to isolated
Showers. AD/Messick


.AVIATION...Expect VFR conditions through the period. Forecast issue
will be with winds. Stout down-valley flow in place across the Snake
Plain. Model forecast soundings and observed data from Big Southern
Butte confirm the presence of NE winds in the 30-35 kt range
developing around 2000ft AGL just prior to 12Z this morning at PIH
and IDA, with these winds slackening by mid-morning (15Z or so).
Will add WS to TAFs at PIH and IDA to account for this. SFC winds
then expected to veer to up-valley for BYI and PIH around the above-
mentioned time, so expect a resultant WSHFT to W/SW from the sfc-
1000 ft AGL for the Southern Snake plain along/south of a developing
surface boundary. AD/Messick


.HYDROLOGY...The Snake River at Lorenzo and Menan continue to be
above flood stage, although barely. This is mainly driven by
optimizing releases from Palisades Dam for the oncoming snow melt.
High flows continue all along the Snake until it reaches American
Falls Reservoir. This is creating a hazard for recreational
interests for this stretch of the river with the strong and high
flows. Messick



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