Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 092050

Area Forecast Discussion
National Weather Service Pocatello ID
150 PM MST Sat Dec 9 2017

.SHORT TERM...Tonight through Tuesday. Water vapor satellite
imagery was showing an amplified upper ridge over the WRN states
early this afternoon while the latest observations and visible
satellite imagery continued to highlight the broad area of low
clouds and fog trapped within the Snake River Plain and Eastern
Magic Valley. I see no real change to this pattern in the numerical
progs nor any relief from the resulting inversions until Friday at
the earliest (see long term discussion below). Thus I have made a
purposeful effort to maintain the stratus and fog in the valleys
along with cooler temperatures until things break. Huston

.LONG TERM...Tuesday night through Saturday. An area of high
pressure continue early this forecast period, supporting inversions
through next Thursday night. The ridge is expected to break toward
the end of next week, as early as Friday and continue into the
weekend as a trough of low pressure and likely a surface cold front
push southeastward through Idaho. This will bring the next chance
for snow showers, though it is not a significant or widespread
chance. Right now, it is looking to be a quick line of showers
passing through Friday into Saturday for higher elevation areas.

.AVIATION...Observations and satellite imagery continue to show fog
and low stratus decks across the majority of the Snake River Plain
late this morning. We are currently forecasting a brief period of
clearing this afternoon, with a moderate confidence in this, based
on reports of some clearing, and forecasts of some stronger
northerly winds. Ceiling will so back down to IFR or LIFR status by
early evening though, so any relief will be short lived, should any
break out. SUN has cleared out though and is expected to remain
outside of the fog directly at the terminal. DIJ will remain outside
of any lower ceilings or visibility as well. NP/MH

AIR STAGNATION...Inversions continue to hold and reduce air quality,
particularly for Franklin County where and Air Stagnation Advisory
remains in effect. Saturday night and Sunday morning, looking for
development of more persistent easterly winds at the surface and
near the top of the low level stratus in the Snake Plain. Both the
NAM and GFS models have supported this idea the past two days. It
probably will not get rid of the inversion completely, but it can
transport some of the low stratus out of the Snake Plain and
towards the west side of the state. RS


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