Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 012057

Area Forecast Discussion
National Weather Service Pocatello ID
157 PM MST Thu Dec 1 2016

.SHORT TERM...Tonight through Saturday...Drier air is now evident
on water vapor imagery this morning behind the cold front that
passed through SE Idaho overnight. The band of snow showers from
this front have all but left our region early this afternoon but
lingering showers may develop across the Caribou and Wasatch
areas. As a result of this activity exiting the Snake Plain
regions, the Winter Weather Advisory has been allowed to expire.

Looking at the backside of the low pressure area located further
to our north, a new plume of moisture will be surging southward
rather quickly this evening across the Central Mountains and Upper
Snake Highlands. New snow showers are expected through the
overnight hours as a result and should improve by early morning
Friday. Additional snowfall amounts will be light, and not exceed
2 inches. As a result of this new activity, we will keep the
Winter Weather Advisory for the Upper Snake Highlands in effect.
There is less confidence in new showers developing in the
Caribou/Wasatch region, however, latest short term models are
indicting at least scattered re-development this evening. The
placement of these showers are so widespread it is nearly
impossible to say who will get more snow and who won`t, the
majority are perhaps likely to not see any additional snow
tonight. Nonetheless, since our Winter Weather Advisory is in
effect there is not enough reason to cancel it early quite yet.

High pressure will come to the region by Friday and we will see a
quiet, but cooler, day. New low pressure troughs filter southward
after sunset and may bring new snow to the Central Mountains into
Saturday morning. NP/Messick

.LONG TERM...Sun through next Thu night. Differences in timing on
the major winter storm for the weekend appear to result in large
solution differences afterwards. The trends are similar to last
night; The lower amplitude pattern of the GFS allows much wetter
and more frequent storms to enter southern Idaho, especially next
Thu/Thu night. The ECMWF is much drier with a higher amplitude
ridge. I will say that the ECMWF did come around to the magnitude
of precipitation forecasted by the GFS, but its timing is
unchanged (still 12 hours slower than the GFS). There are such
huge differences by Wed night that a very broad-brush of slight
chance to low chance PoPs were used. With either storms or an
arctic outbreak, temperatures are expected to be below normal
either way, but even the timing of the arrival of any cold air has
strong differences in the solutions. Have taken compromise
solutions for the temperature without using bias-correction, since
there is likely to be a huge air mass change and the biases are
likely incorrect. If the storm follows the ECMWF timing, then a
wind event will be underway on Sun night. Wind appears
insignificant for the rest of the time, unless a GFS-forecasted
storm arrives on Thu, which the ECMWF does not have. Overall, low
confidence for anything beyond Mon night. Messick


.AVIATION...After measurable snow this morning in the three eastern
airports, upper level skies clear enough to lead to a fog and
stratus event for those locations. Time-height cross sections don`t
do much for aiding the forecast, so have tried to do a compromise
solution to the onset, duration, and magnitude of the stratus or
fog. Needless to say, KIDA with the most snow will have the hardest
time, but KDIJ and KPIH not far behind. Expect at least IFR
conditions by airdrome operational openings for all three. KSUN
should not have much in the way of problems, as long as the
northwest flow down the Wood River valley keeps pushing any stratus
back into the Snake River plain. KBYI has not had much snow, but is
expected to receive at least some stratus tonight that will impede
approaches. Not much is expected in the wind department with light
wind all locations. Messick


Winter Weather Advisory until 5 AM MST Friday for IDZ019-023-025.


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