Winter Storm Watch 9, NWS Pocatello, ID

Area Forecast Discussion
National Weather Service Pocatello ID
207 PM MST Sun Feb 19 2017

.SHORT TERM...Tonight through Tuesday night. Broad area of weak
convection moving into western portions of forecast area this
afternoon. Have seen lightning and pea size hail reports on west
side of state. Believe that strongest convection across E ID will
probably fit that criteria as well. Flow aloft remains unsettled
tonight with broad area of weak precip mainly over higher
elevations. Weak precipitation could remain focused over central
mountains and along WY border, but enough of a break in widespread
heavy precipitation to drop current headlines early. Next round
pushes in by early Monday, and this round another significant
precipitation producer into Tuesday. Snow levels rise to between
6500-7000 ft with this system, with continued rain at lower
elevations. Above snow line, snow looks to be heavy at times
particularly in central mountains. Total accumulations through
Tuesday could reach to 2 ft at the highest elevations. Pass level
likely in the 12-18" range but wouldn't be surprised to see
locally higher numbers. Sharp cut off below 6500 ft with mainly
rain or a very wet slushy mix to valley floors. Have issued a
winter storm watch for areas above 6500 ft. Other concern with
this system will be winds. Models have been consistent in showing
strong 700mb jet of 65+ kts push into the region mainly Tuesday
with strong sfc low deepening over central MT. Guidance continues
to increase winds Monday night and both NAM/GFS numbers hitting
well into advisory criteria during the day Tuesday. Jet is
strongest overnight and weakens during the day but could still be
sufficient to support strong winds across the region. Cold front
drops through during the afternoon. Snow levels do drop toward
valley floors Tuesday night, but heavy precipitation threat
already over by this time. DMH

.LONG TERM...Wednesday through next Sunday. Mean upper trough
remains resident over the West throughout the course of next week,
but models differ on the distribution of moisture. Most of the
dynamics ride well to the south as the jet carves out the trough, so
no significant change in PoPs. Continuing with broad-brushed chance
to likely PoPs through Friday, then slight chance to chance
thereafter. Temperatures will drop starting Tuesday night after a
cold front pushes through. Highs Wednesday may be in the 40s, but
only in the 30s thereafter. GFS/ECMWF drop a cutoff low off the
WA/OR coast Friday into Saturday and drive a weak upper ridge across
the forecast area. Hinsberger

&&

.AVIATION...Generally fair weather as upper trough exits the
forecast area this morning, but models are keying in on some latent
instability this afternoon which may mean some isolated
thunderstorms until around sunset. KIDA ceiling is below 1000 ft,
but should lift to VFR as the low-levels destabilize. Conditions
will begin to deteriorate again late in the TAF period as the nose
of an advancing atmospheric river edges into the area. Hinsberger

&&

.HYDROLOGY...Precipitation amounts and mild low elevation
temperatures past several days have maintained and potentially
worsened low land flooding threat across the region. Some rises
have been seen in area creeks, and beginning to see small
responses on the rivers as well. Will continue all low land flood
headlines. Have also issued a flood watch for Portneuf River at
Pocatello with river forecasted to rise to flood stage Monday
night or very early Tuesday morning. Trend has been to increase
crest and lengthen time the gage spends above flood stage.
Anticipate moving to flood warning no later than Monday if trend
continues, especially with continued threat of precipitation
across the region and temperatures remaining near or above
freezing at night in upstream basins. DMH

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Monday morning through Tuesday afternoon
for IDZ018-031.

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