Area Forecast Discussion
Issued by NWS Pocatello, ID

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000
FXUS65 KPIH 131000
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
300 AM MST Wed Dec 13 2017

.SHORT TERM...Through Friday. Influx of mid and high-level cloud
cover allowed for brief improvements to visibility early this
morning and some contracting/lifting of Fog, but clearing skies
at the mid/high levels has allowed for radiational cooling to re-
develop at the top of the Fog layer, and thus Fog has resumed its
thickening and expanding trend. Widespread Fog exists along the
I-15/86/84 corridor from Blackfoot to Boise, as well as the Idaho
portion of the Cache Valley (Preston/Franklin). Dense Fog Advisory
currently in effect will be allowed to continue through 11 AM MST.
Attention then turns to a weak trough of Low Pressure currently
moving ashore across NW Washington State. This will drive a weak
cold front through the area, bringing a round of Snow Showers
across the Pashimeroi region eastward across Monida to Island
Park, and southward along the Eastern Highlands including Pine
Creek Pass. Snow Showers are expected to develop around Noon
across the Pashimeroi east to Monida, and by 2-3 PM for Island
Park to Pine Creek Pass/Palisades area. Snow Showers are forecast
to end shortly after Sunset. Snow accumulations are expected to
range from a Trace to upwards of 2", with mainly Passes impacted
in terms of Driving Conditions. The Front is expected to
temporarily eliminate the Inversions that have been in place since
last Monday. This should do two things: 1) Eliminate the majority
of the Fog, and 2) Restore more typical atmospheric lapse rates
(higher elevation areas cooler than valleys.) This, however, will
be temporary as Inversions are expected to once again build into
the region late Thursday into Friday, with Inversion strength
peaking on Friday. This may mean a return to Stratus/Fog Thursday
night and Friday. AD/Valle

.LONG TERM...Friday night through Wednesday. A cold front will
arrive from the northwest Friday night. This will bring some light
snow to the region for Friday night into Saturday. Amounts look
light at this point with an inch possible for the valleys and up to
3 or 4 inches for the high country. Rest of the extended forecast
looks dry as the ridge is expected to deflect most of the systems
north and east of the area. Have retained some slight chances during
this time based on previous model solutions.

Valle


&&

.AVIATION...Areas of fog and low stratus continue to cause problems
in some locations. Expect most of this to break up by the afternoon
as a cold front will arrive. Could see some snow showers around
Idaho Falls and Driggs this afternoon.

Valle


&&

.AIR STAGNATION...Inversions continue to hold and reduce air quality,
particularly for Franklin County where an Air Quality Alter remains
in effect. Temporary improvements possible behind a weak Cold
Front beginning this afternoon. However, inversions are expected
to re-develop late Thursday into Friday which may bring a return
to degraded Air Quality. AD/Valle/RS


&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 11 AM MST this morning for IDZ017-021-
022.

&&

$$



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