Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 180958

Area Forecast Discussion
National Weather Service Pocatello ID
258 AM MST Mon Dec 18 2017

.SHORT TERM...Today through Wednesday night.
Some moisture riding over upper level ridge will bring only light
snow showers to the central mountains and upper snake highlands
today and Tuesday. Elsewhere just expect extensive cloud cover. Do
not expect much accumulation in the mountains the next two days
with most areas under an inch. Big event will be strong cold front
which will move through the state on Wednesday with snow starting
in the central mountains late Tuesday night and spreading east
through the day Wednesday. Event will begin around midnight
Tuesday night in the Central mountains and end Thursday morning in
the eastern highlands. Expect widespread difficult driving in the
snow during the Tuesday night through Wednesday night time frame
with 4 to 8 inches possible in the mountains and 1 to 3 inches in
the Snake River Plain as early estimates on this storm system.
Breezy conditions behind the cold front with some blowing snow
possible as well. Good potential Winter Weather Advisories may be
issued for this system in the next 24 hours. Temperatures Monday
and Tuesday are expected to be above normal with temperatures
turning sharply colder Wednesday behind the cold front.

.LONG TERM...Thursday through Christmas Day. Current trends show
drier conditions along with the beginnings of much colder weather
especially if the ECMWF pattern pans out. Look for lingering light
snow across the southern and eastern highlands Thursday as the storm
presses south toward the Four Corners. It will be breezy in some
spots with local pockets of blowing/drifting snow possible. This is
where the various forecast ideas quickly grow apart. The GFS wants
to keep the storm for Friday farther east than before and certainly
the ECMWF. The latest forecast is a blend of the 2 ideas with a
decent chance of powdery snow (especially in the mountains) and
gusty winds.  That means some blowing/drifting snow possible for
anyone that might begin holiday travel. By Saturday, both the GFS
and ECMWF dry things out, but keep the winds going for continued
blowing/drifting in spots even where it stops snowing. After that
the GFS stays dry and quickly shifts a ridge over Idaho. The ECMWF
maintains more of a blocking/stagnant pattern, which is also the
colder of the two ideas. It keeps some light snow/flurries going at
times today
along the Divide as well. We kept with a rather dry forecast but
went colder. We`re talking by Christmas Eve and Day, highs in the
single digits and teens. Lows could range between 5 to -15 degrees.


.AVIATION...Quite a bit of mid and high level clouds overhead this
morning. Moisture will continue to stream over the state today,
keeping some clouds around. We are also looking for some light snow
to fall over portions of the central mountains and eastern
highlands. That aspect should just be a possible impact for KDIJ,
dropping conditions to MVFR/IFR if it indeed happens. So far, any
fog has been very spotty and with the current should
remain that way. While it`s possible, the potential fog affecting
our TAF sites today looks to be low. Most ceilings are VFR, but a
few locations are dropping close or actually to MVFR due to lower
mid clouds. That trend will continue through the day, so be aware of
that for any of the TAF sites in eastern Idaho. Southerly winds of
10-25kts (including gusts) are expected at KBYI, KPIH and KIDA
today. A little lighter overall for KDIJ.  Keyes


.AIR QUALITY...Thanks to the latest storm moving through and an
overall pattern change, air quality and inversions conditions are
improving. We might see a brief dip in that improvement in the next
24-36 hours as weak high pressure returns, ahead of a stronger storm
arriving midweek.  Keyes



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