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000
FXUS65 KPIH 062127
AFDPIH
Area Forecast Discussion
National Weather Service Pocatello ID
227 PM MST Fri Dec 6 2019
.DISCUSSION...
A storm system remains on track to impact SE Idaho this weekend but
impacts will vary greatly based on location and elevation. For
tonight, expecting the low stratus that has plagued much of the
region for the past few days to return although perhaps not quite as
widespread. This low stratus, combined with incoming clouds from the
aforementioned storm system approaching the region, may enable a
seeder-feeder process to develop across southeastern portions of the
CWA so have introduced low PoP snow potential into the forecast
tonight to account for this although confidence in this is quite
low. It's entirely possible that this does not occur and may just
persist as low clouds or patchy fog in spots but felt it wise to at
least mention the potential. Any accumulations would be low but with
temps below freezing this could create some icy surfaces on area
roads if it does pan out.
Shifting gears into the weekend, the much advertised storm system
remains on track as an area of low pressure pushes into the Pacific
Coast later tonight with the associated moisture reaching our area,
namely the Central Mountains, around daybreak Saturday with the rest
of our area getting in on the precip during the afternoon and
evening hours. Similar to our last event, 850 mb flow will be out of
the south so this will support a downslope flow off the mntns along
the Snake Plain from Oakley, to American Falls, to Pocatello, to
Blackfoot, to Idaho Falls, and perhaps into the Teton Valley.
Additionally, temperatures will be marginal for this event in the
valleys as highs are expected to top out in the upper 30s and lower
40s with snow levels in the 5300-5900 ft range for much of the day.
So for much of the day in the lower elevations precip will be mostly
rain or perhaps a rain/snow mix with a potential changeover
overnight to more snow but even then temps/snow levels look
marginal. Evaporative cooling processes may play a role in precip
type as well so needless to say it's a very tricky forecast across
the Snake Plain.
All that being said, have seen a trend in hi-res model guidance
delaying the onset of precip across the Snake River Plain until very
late in the evening or perhaps into early Sunday morning. Haven't
gone this extreme with the forecast yet but something to keep an eye
on. Multiple hi-res model solutions have been showing the first wave
of precip progressing through the Central Mountains and into the
Lemhi Highlands and Island Park area keeping much of the Plain dry
through the day Saturday. Something to monitor.
Across the mountains no major changes to the ongoing forecast as we
still expect 4-10 inches of snow across the Central Mntns west of
Challis and Mackay (including the Wood River Valley due to upslope
enhancement), and similar values across the Upper Snake Highlands,
Teton Valley, Caribou Highlands, and Bear River Range. Valley
locations can expect anywhere from a dusting to around 2 inches
through this event but again it's a very tricky call with so many
factors in play.
Overnight Saturday into Sunday as temps cool and snow levels drop
may see a bit more snow than rain across valley locales but again it
is marginal but this would be the mostly likely time for any
accumulating snows. During the day Sunday, temps again look to warm
into the upper 30s and lower 40s so similar forecast challenges
exist there. Later in the day, seeing the potential for an enhanced
convergence band to set up as cooler NW flow filters into the region
late Sunday so this may provide more potential for accumulating snow
across the Snake Plain.
As we move into the start of next week, the remnants of the upper
trough stick around Mon over higher elevations east of I-15. There
is low confidence chance of a few showers lingering Monday night
into Tuesday as well, but if so these are expected to be light and
fairly isolated. Cooler temperatures will be in place under
influence of colder northerly flow behind trough axis as well with
limited precip potential until late in the forecast period when
models are showing the potential for the next weather maker to reach
our area. McKaughan
&&
.AVIATION...
Fog and stratus has thinned out with slightly drier air at PIH and
BYI this afternoon. That "dry punch" is trying to work north toward
IDA as well as SUN, but confidence is not high it will actually make
it to either airport. We did show some slight improvement to
MVFR/low end VFR weather. DIJ is barely VFR right now but should
stay that way even if clouds remained socked into the Teton Valley.
Tonight and Saturday morning will be interesting as the models try
to redevelop fog and stratus where things have cleared or could
clear across the Snake Plain. Persistence would say YES, but it
depends on how much we cool with the drier air working into that
area. We went with persistence and dropped conditions slowly back
through MVFR to IFR overnight at BYI, PIH, and IDA. We did the same
for DIJ as well. With the potential return of stratus, we did add
VCSH for IDA and DIJ due to possible light snow developing ahead of
the main storm. We are expecting the a bigger wave of light snow to
impact the central mountains late tonight and Saturday. We kept with
the trend of snow with MVFR/IFR conditions at SUN because of this
through the day. We COULD see at least VCSH for the other sites
during the afternoon, but that likely will hold off until tomorrow
evening/night. Keyes
&&
.PIH WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 4 PM Saturday to 5 AM MST Monday
for IDZ060-062>066.
Winter Weather Advisory from 8 AM Saturday to 11 PM MST Sunday
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