Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 212115
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
215 PM MST Sat Jan 21 2017

.SHORT TERM...Tonight through Monday night. The forecast continues
to be full of twists and turns. As expected, pockets of light
snow continue across eastern Idaho. Accumulations aren`t much at
all and roads are in good shape due to warm air and road
temperatures. The issue is that snow continues across the south-
central highlands and Magic Valley where all indications were it
was going to stop or already stopped earlier. We are still looking
for snow to gradually wind down tonight although some will linger
through the night across the eastern highlands and the Sawtooths.
We are expecting stratus and fog to form in some valleys
especially the Snake Plain AWAY from the I-15-84-86 corridor. As
gusty winds develop, that should keep the fog from forming.

We turn our attention to the next storm that brings the initial
wave of moisture in around lunchtime Sunday, with the storm
continuing to affect us through Monday night (if not into
Tuesday). The ONLY timeframe we are certain on for precipitation
is tomorrow afternoon. We should see a pretty good shot of snow
for the Arco Desert and northern Magic Valley, Wood River Valley
and Sawtooths, the southern and eastern highlands. We should see
snow in most areas. The exception will be from Pocatello through
Burley and adjacent valleys south of I-84/86. We are looking from
temperatures to push to around 36-42 degrees and stronger
downslope flow. This will likely produce light rain vs snow AND
limit amounts. We will generally see warmer temperatures in the
valleys but even where it warms up (outside of those areas), it
should be snow. For tomorrow evening and night, this is where
twists and turns (figuratively and literally) throws confidence
out the door except for the southeast and eastern highlands.
We expect snow to continue in earnest and be locally heavy at
times. Breezy conditions will no doubt create some blowing and
drifting especially at higher elevations. At the moment, we had to
discard the NAM forecast data because it is the outlier due to
having a much slower/west placement of the low by Monday night.
Even going with only the GFS and ECMWF, they are not in sync by
midnight. Both bring another surge of moisture with the GFS
pushing some decent moisture into mountains from Hailey to Monida.
The ECMWF isn`t quite as aggressive with the moisture or northerly
push into the mountains. We leaned more toward the GFS pattern but
with amounts in between the ECMWF and GFS across the north and
also areas west of I-15. It will still be windy so
blowing/drifting in the mountains. This also continues the
downslope from around Pocatello to Burley, so expect light
precipitation and warm lows. Things are still out of sorts for
Monday and Monday night. The GFS brings the low right over us
Monday, which greatly dries out the the Snake Plain and southern
highlands. This also pushes more snow into the central mountains
and eastern highlands. The low moves southeast that night allowing
snow to push back south. The ECMWF does something similar but not
as much across the south, but at least is similar with the main
band across the north. It also holds off until Tuesday with the
southward shift. With all of that said, we are expecting a wet
period for most areas. It`s just the details in most places need
to be worked out. Like we mentioned several sentences ago, we are
more confident across the southeast where 6-12 inches is possible
with higher amounts above 7500ft. We left the Winter Storm Watch
going there. We expanded it to the south-central highlands where
Up to 6 inches below 5500ft and up to 12 inches above that is
possible. Stronger winds and blowing/drifting led us to do that.
We also left the Watch up for the Sawtooths and Wood River Valley
due to uncertainty in the storm track. Later shifts will likely
make changes to those headlines, plus add any others if necessary.
Keyes


.LONG TERM...Tuesday through next Saturday. Lingering effects from a
broad open trough expected Tuesday through Thursday of next week.
The question will be how quickly and easily the high pressure ridge
from the west will build into our area through Saturday. It does not
appear to be in a hurry based on these forecast models. Therefore,
we are forecasting a chance for snow showers in most locations
through Thursday, especially in the Upper Highlands, Caribou
Highlands and Southern Highlands. Snake Plain areas are likely to
see snow accumulations here and there as well. Expect temperatures
to hardly change at all throughout this period, which will be in the
20s or teens for highs. NP/Keyes

&&

.AVIATION...Light snow showers will pop in and out of Driggs
otherwise TAF locations should be done with any more precip in the
near term. Ceilings are the concern. We expect BYI and DIJ to have
VFR ceilings, despite any possible snow showers at DIJ as they are
light and intermittent. Ceilings at PIH are improving and will
achieve VFR status early this afternoon. IDA and SUN are expected to
be at IFR or MVFR status for a few more hours afternoon with only
SUN breaking out mid afternoon then becoming VFR. IDA is forecast to
improve, but not into VFR status. By tomorrow morning, ceilings are
likely to go down again for PIH, IDA and SUN with areas of mist/low
stratus. Occasional periods of gusty winds are forecast this
afternoon as well at IDA and PIH. NP/Keyes

&&

.HYDROLOGY...We still have ice jams occurring in places across
eastern Idaho. We re-issued the Flood Advisory for the Challis
Recreation Site at the 93 Bridge per request of BLM officials.
Flooding continues in/around Darlington along Antelope Creek and
the river, but that appears to be an isolated and long term
problem.  Keyes

&&

.AIR STAGNATION...Air quality has improved a bit in Franklin
County, but still rather poor. It`s enough to continue with the
Air Quality Alert at least for another day. We may see conditions
improving by tomorrow and Monday. Precipitation and stronger winds
should begin scouring out the bad air.  Keyes


&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Sunday morning through late Monday night
for IDZ018-019-022-023-025-031.

&&

$$



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