Area Forecast Discussion
Issued by NWS Pocatello, ID

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591
FXUS65 KPIH 202132
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
232 PM MST Tue Feb 20 2018

.UPDATE...Have received reports of hazardous drifting and blowing
snow in the upper Snake River plain and the upper Snake highlands.
Have issued a Winter Weather Advisory for this.  Messick

&&

.PREV DISCUSSION... /issued 131 PM MST Tue Feb 20 2018/

SHORT TERM...Tonight through Fri afternoon. After a brief break
from a snow event due to an area of convergence, another trough
will begin its approach from the northwest tonight, arriving over
the forecast area by Wed afternoon. This is a very weak trough,
with little surface development, so no repeat of last weekend`s
storm. Some light snow should develop mainly for the mountains and
highlands. One to six inches are expected for Wed/Wed Night in the
central Idaho mountains, with amounts above 3 inches expected
above 7500ft elevation. Lesser amounts, 1 to 3 inches, are
expected at the highest elevations along the border with Montana,
and very little expected south of Palisades Reservoir. A deeper
trough develops during the day over the Pacific northwest, digging
southward and into Nevada allowing the forecast area to get caught
on the north side of the low. This will mean more snow, 1 to 3
inches in the Snake River plain/eastern Magic Valley. Elevations
above 7500ft to 8000ft could also receive Advisory-level snowfall
on Thu/Thu night/Fri. Temperatures will continue cold for another
two nights, but with the Thu night storm there is a shift from
cold northerly flow to more westerly and even southwest flow. This
will warm things up, although still staying below climatic
normals. After the breezy conditions today, expect wind to
decrease and stay somewhat light until the Thu storm exits Fri
afternoon. Messick

LONG TERM...Saturday through next Tuesday. Or next weather maker
arrives later Saturday into Sunday. The models are showing some
subtle differences of opinion, enough to be off on timing that by
about 12 hours. If the faster version (the GFS) pans out, it could
end up being a rain/snow mix across the Snake Plain with some decent
snow in the high country. If the EC ends up right, it would be snow
and persist longer along I-84 & 86 Saturday night. The GFS is
pushing it out already Sunday morning, while the EC isn`t done until
afternoon. There will be wind with this one, so expect some more
blowing and drifting snow especially on some of the passes and in
the backcountry.  After that, it looks yet another storm drops in
over the west. That means more needed precipitation and cool
temperatures.  Keyes

AVIATION...The main forecast question for pilots is there going to
be any snow around and how much stratus will there be especially
tonight and Wednesday morning. The more widespread threat of light
snow is winding down. It does look like though there might be a risk
of persistent showers in nearby terrain for VCSH at KDIJ tonight. We
also have lower ceilings (IFR). The rest of the TAF sites should see
scattered to broken ceilings between 2000-5000ft or fairly close to
that. Whether or not there is enough coverage to actually go to
MVFR/IFR is a remaining question. We don`t indicate that but it`s
certainly possible. We are NOT expecting fog since the air is drying
out and not much melting is expected due to cold temperatures and
lack of better sunshine. We should not see any showers across the
Snake Plain tomorrow but a repeat of showers over the mountains will
keep VCSH for KDIJ and a return to that in the afternoon at KSUN.
The wind will also drop off quite a bit in the next 24 hours so any
risk of blowing snow will also disappear.  Keyes

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 8 PM MST this evening for IDZ019-
020.

&&

$$



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