Freeze Warning 4, NWS Pocatello, ID

Area Forecast Discussion
National Weather Service Pocatello ID
220 PM MDT Sat Sep 30 2017

.SHORT TERM...Saturday night through Monday. The initial
surface front is moving through the Snake River Plain this
afternoon, winds have gusted to near 35 mph in the Arco Desert.
Expect winds will remain breezy over night then increase slightly on
Sunday, but remain below advisory level. Very isolated lightning
activity so far between Richfield and Aberdeen, also a couple of
cells south of Oakley.  Best precipitation the past 6 hours is up to
a third of an inch of rain west slopes of the central mountains,
mostly less than .10 inch elsewhere.  This first round of showers
moves through the Eastern Highlands by around midnight. A second
disturbance drops south into the Central Mountains and Snake Plain
on Sunday. Snow level works lower through the day to around 6000
feet, but still only looking for 1 to 3 inches accumulation in the
mountains through Monday morning. Temperature lapse rates steep
enough for a few thunderstorms again Sunday afternoon. On Monday,
trough develops further into Nevada and Utah in a SW to NE tilted
fashion leaving this area in weak forcing with a few showers around
but not really significant in terms of rain or snow. Northerly
surface winds expected Monday morning should help temperatures in
the Snake Plain drop to around freezing. Freeze Watch remains in
effect. Should be a little colder on Tuesday morning, would not rule
out temperatures cold enough for local hard freeze temperatures,
cloud cover could mean a lot. RS

.LONG TERM...Tue night through next Saturday. Forecast models
beginning to agree on the development of a closed low which is
forecast to develop over SE Idaho Tuesday night into Wednesday,
which may linger across our area through Thursday. This will provide
periods of precipiation along with temperatures near record lows.
Under this low, Snow Levels may drop as low as 6000 feet. The
combination of low Snow Levels and Snow Showers may create slushy
and snow-covered roads for Mountain Passes, and possibly for some
valley areas. Exact timing and amounts are still in question, as
forecast models have struggled with the evolution of this system.
Strong northwest flow forecast to develop across the region for the
end of the week into early next weekend should allow Temperatures to
remain below Seasonal normals and promote rain and snow shower
develop for high terrain areas, northwest-facing slopes in
particular. AD/RS

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.AVIATION...Cold front has generated some -TSRA in the vicinity of
KPIH, otherwise its has been all light rain. Some marginal VFR
conditions developed in the wake of the front, but not expected to
last with moderate wind helping to break up the lower CIGs.
Precipitation will be lighter and more showery than what happened
during the mid-day hours, except for KDIJ, which still has to
contend with the convection this late afternoon and evening. Skies
will partially clear tonight, but more moisture expected Sun
afternoon. Main locations affected by this second wave will be KIDA
and KDIJ. The last forecast problem is wind for the three valley
airdromes. The wind is expected to stay up and elevated through the
night, but there are differences amongst guidance on whether the
wind will be weaker or stronger on Sun. The guidance that is most
correct today is the NAM, which has similar wind as today, with some
weakening in the afternoon. Messick

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.FIRE WEATHER...A cold front will move through today bringing
cooler, wetter and windier conditions. Expect breezy to moderate
winds with gust of 30 to 35 mph, particularly today and Sunday, and
to a lesser degree Monday and Tuesday. Expect precipitation to start
today and continue through next week. Expect around 0.10 of
precipitation in valley locations and 0.10 to 0.40 for mountains.
Snow levels will start around 9000 feet today before dropping to
around 5500 to 6000 feet later Sunday. Expect 1 to 3 inches of snow
mainly for the Central Mountains and Eastern Highlands mainly above
7000 feet. Expect isolated thunderstorms this afternoon as well,
particularly for the Island Park area, and to a lesser degree Sunday
afternoon, which will be mainly for our Eastern areas. Monday
through next week will be even cooler with continued precipitation
chances. However, precipitation looks to be overall light and mostly
in the mountains. Wyatt

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.PIH WATCHES/WARNINGS/ADVISORIES...
Freeze Watch from late Sunday night through Monday morning for
IDZ017-020-021.

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