Flood Watch 3, NWS Pocatello, ID

Area Forecast Discussion
National Weather Service Pocatello ID
316 AM MST Mon Feb 6 2017

.SHORT TERM...Today through Wednesday. The storm off the coast
will keep trucking east along the US/Canada border today. We are
see a surge of moisture this morning working across eastern Idaho.
Most of this has been falling in the mountains, with little
reaching lowest elevations so far. It looks a bit too dry
initially for some of these areas to get precipitation right off
the bat, but eventually light amounts will fall. Snow levels are
in the 5000-7000ft range as of 2am for most places. They will
change little today this morning, but the potential is there for
them to rise another 500ft ahead of the cold front. That front
arrives late this afternoon and pushes to near the Utah border
overnight. Winds are already howling in some places and will only
get stronger this afternoon and evening. The strongest winds will
be across the Upper Plain and also slopes above 6500ft, peaking at
25-35mph sustained with gusts of 40-50mph. Even with wet snow,
some blowing is expected in the mountains. Down in the valleys,
expect larger vehicles to have issues especially with crosswinds.
A WIND ADVISORY remains in place for the Upper Plain. We are also
expecting a few thunderstorms this afternoon. By this evening and
overnight, most of the precipitation will shift into the southern
and southeast highlands with lingering showers farther north and
west. Snow levels drop, but still remain in the 4500-6000ft range
along/ahead of the boundary. Behind it, any showers will be all
snow. We currently have WINTER STORM WARNINGS for portions of the
central mountains and eastern highlands through this evening.
Those aren't going to be changed at the moment. It's possible (and
yes we realize some people might have warning fatigue) that we may
need to extend it across the southeast corner through sunrise. The
highest snowfall will be above 6500ft with another 5-10" in the
warning areas. Locally higher amounts are possible above 8000ft.
Other ranges will see 1-4 inches and some places below 6500ft may
see similar amounts like in the Upper Snake Highlands and in the
Wood River Valley. Rainfall still looks like although we could
some decent downpours across the Snake Plain, Magic Valley and
southern highlands if we get some good showers or storms going.
See the hydrology section for more on any potential flooding.

We see all of that moisture quickly shift back to the north
tomorrow, as the cold front becomes a warm front and lifts back
across eastern Idaho. Snow levels crash to valley floors briefly
in the morning, but jump back up to between 4500 and 6500ft south
of a Shoshone to Driggs line. Coincidentally, we also expect most
of the precipitation to fall south of that line as well. 1-4
inches of snow is possible in the valleys and 4-8 inches for the
mountains. Rainfall amounts will be light although some pockets of
heavier rain MIGHT fall. Confidence for that remains low as the
models have poorly handled valley rain so far with this event. For
Tuesday night and Wednesday, precipitation becomes more focused in
the mountains. If you are thinking, does that more snow for the
eastern highlands and Sawtooths...you're right. The rest of us
will see some spotty light precipitation. Any cooldown behind this
front is gone by Wednesday.  Keyes

.LONG TERM...Wednesday night through Monday night. Both GFS and ECMWF
build a broad upper ridge over the west Thu night. Pac moisture is
still flowing into the ridge...with precip in the usual westerly
flow upslope regions of the central mtns and eastern highlands. The
GFS is the wettest of the models. By Thu...the ridge axis moves
east. This allows for more Pac moisture to flow into ID on southwest
flow. Thus more widespread precip Thu and Thu night. The southwest
flow means warmer temps so precip is expected to remain liquid at
the lower elevations...with snow upwards of 7000ft or higher. Precip
backs off somewhat on Fri...but the movement of an upper trof into
the west coast maintains the threat of precip across the region. As
the trof moves east on Sat...upper ridging builds into the west.
This results in decreasing precip chances...with dry conditions
expected Sat night thru Mon night. Hedges

&&

.AVIATION...Moist westerly flow will bring another round of precip
to the area today...along with lower cigs. Rain can be expected at
KPIH and KBYI...with a rain/snow mix at KSUN...KIDA and KDGS. Strong
southerly winds at KPIH this morn will become more southwesterly
this aftn and spread into the upper Snake River Plain. Hedges

&&

.HYDROLOGY...We did cancel the Flood Watch for Cassia and Oneida
Counties last night, but we have received a couple of reports of
flooding since then. We might finally see some rainfall down there
late this afternoon and evening as the cold front arrives. For
now, we will NOT issue/re-issue any headlines. Other lower
elevations across the Magic Valley, Lower Plain and valleys near
the Utah border could still see some localized lowland flooding as
well. Keyes

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 11 PM MST this evening for IDZ018-019-
023-025-031.

Wind Advisory from 1 PM this afternoon to 10 PM MST this evening
for IDZ020.

&&