Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 082211

Area Forecast Discussion
National Weather Service Pocatello ID
311 PM MST Fri Dec 8 2017


Updated sky forecast into Saturday based on satellite imagery that
is showing the stratus over the Snake Plain, Magic Valley, and
adjacent valleys making little progress in dissipating. With the
deathridge parked overhead, am not at all optimistic that it will
budge much anytime soon.



.PREV DISCUSSION... /issued 207 PM MST Fri Dec 8 2017/

SHORT TERM...Tonight through Sunday night. Satellite imagery
shows stratus entrenched across the region. Areas affected
primarily include Snake Plain and connected valley fingers, but
Marsh Valley, Cache Valley and areas along Salmon River also
affected today. Surface observations and area web cams show much
improved visibilities over this time yesterday. Believe stratus
back to being the primary driver but have left patchy freezing fog
across low elevation regions. Will forego another headline at this
time, though still can`t rule out a few locations seeing
restricted visibilities overnight. As far as temperatures, still
playing catch up with observations. Trended mountains warmer, and
limited daytime highs for valley locations under influence of
inversions. DMH

LONG TERM...Mon through next Fri night. The upper level ridge that
is blocking all the storms northward into Canada continues through
this period. There was a Tue night/Wed trough riding down the east
side of the ridge, but this morning the indications are that it will
be so far east of Idaho that it will have little to no impact on the
stratus and fog situation in our valleys and basins. The last day or
so looks like the ridge does get beaten down a little and some upper
level cloudiness may infiltrate the ridge, but it just may be that
the GFS and ECMWF move it around because it has to. However, the 5-
wave pattern does indicate the upper level ridge axis shifting
westward, which could open the door so shortwaves getting closer to
eastern Idaho, from the Wyoming side. Afternoon highs were made
colder since the MOS guidance believes in clear skies, and morning
lows were made slightly warmer to compensate for higher cloud cover.
Humidity was also adjusted for higher afternoon and lower
morning, but not by as much. Messick

AVIATION...Moisture in a very thin boundary layer is producing all
the operational aviation problems at every airdrome. The NAM
guidance is indicating at least a partial lifting during this
afternoon, as does conditional climatology. With little else to go
on, have gone along with this, but there is also the indication that
it will return most places, except for KSUN and KBYI. While that
scenario is plausible for KSUN, believe KBYI should have problems as
they did this morning. While there is high confidence in the
airports being threatened with closure, the timing has very low
confidence, at with no clouds aloft, it will be either unlimited or
closed, with little in between. Messick

AIR STAGNATION...Air quality statement continues for Franklin
country at request of Idaho DEQ. High pressure remains firmly in
control with inversions in place. No significant change in the
pattern is expected into early next week. There are some signals
that a feature will rotate around the top of the ridge into the
region Tuesday night or Wednesday. However, the system is
extremely small and there is a lot of uncertainty as to the track
it will take if not the validity of the feature at all. If it
makes it over the ridge into East Idaho, there is further question
as to how much influence it will have on the strong surface-based
inversions. For now, persistence is the safe bet. DMH



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