000
FXUS65 KPIH 280850
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
250 AM MDT Sun Apr 28 2024

.SHORT TERM...Today through Monday Night.
Following yesterdays widespread light to moderate rain and high
elevation mountain snow, conditions will turn predominantly dry
today as zonal flow builds in from the west out of Oregon. What
precipitation we do see today will be courtesy of lingering
moisture behind our exiting system now situated on the CNTRL
Plains. This will support isolated showers throughout the day and
a 10-20% chance of thunderstorms this afternoon across the ERN/SRN
Highlands and Upper Snake Plain as conditions remain dry elsewhere.
Winds will also be on the breezy side today courtesy of 25-35 kt
700 mb winds aloft which will support sustained winds up to 15-25
mph with gusts to around 25-40 mph, primarily across the Snake
Plain and Magic Valley.

Dry conditions will return regionwide tonight into Monday morning
as attention turns to a series of H5 lows moving onshore from the
NE Pacific to the PacNW. The first system will move onshore
overnight tonight to Washington and WRN Canada and work east
through NRN Idaho and WRN Montana as increasingly strong 40-50 kt
700 mb winds build in overhead. As a result of these elevated
winds aloft courtesy of a cold front, strong winds will begin to
mix down to the surface late Monday morning into the early
afternoon hours and continue through the end of the day. Winds
will peak with sustained winds of 30-40 mph and gusts up to 55
mph leading to much of our region seeing solid, high-end WIND
ADVISORY level criteria. While we may see gusts locally stronger
in that 55-65 mph range, we have gone ahead with at least a WIND
ADVISORY on this shift with the potential need to upgrade to a
HIGH WIND WARNING especially for the Arco/Mud Lake Desert and
Upper Snake Plain over the coming days. This uncertainty is
evident when taking a look at the NBM probability of wind gusts
greater than 60 mph which is around 25-60% across the Magic Valley
and Snake Plain region. That decreases to around a 5-10% chance
of getting above 70 mph but still supports the underlying
potential for a need to upgrade on future shifts.

In addition to strong winds on Monday, we will see increasing
precipitation chances throughout the day bringing isolated to
scattered showers and a 15-30% chance of thunderstorms. Best
chances for convection will remain confined to the higher terrain
and across the Upper Snake Plain with the driest conditions
favored in and around the Magic Valley. As colder air builds in
for Monday into Monday associated with this cold front, snow
levels will fall to valley floors by the end of the day with
widespread below freezing temperatures expected for Tuesday
morning. This will support light snowfall accumulations across our
higher elevation mountain valleys in places such as Stanley,
Island Park, and the Teton Valley with Stanley seeing chances for
snow throughout the entire day.

As quickly as this system exits to our east Monday night, the
second in a series of Pacific lows will move onshore Monday night
into Tuesday following a similar track to our Monday system which
is expected to bring another round of precipitation and strong
winds. With respect to temperatures, look for highs in the
40s/50s/60s in the valleys and 30s/40s in the mountains today
before cooler conditions settle in midweek. MacKay

.LONG TERM...Tuesday through next Sunday.
Tuesday will be mainly dry but still breezy to windy but not
nearly as windy as Monday but widespread 20 to 30 mph sustained
winds still possible. Another wave will begin to approach from
Canada and showers will return to the mountains with low snow
levels at 4 to 5 thousand feet. It will be very cold with highs in
the 30s and 40s mountains and 50s valleys. The upper level trof
will form a closed low over southern Idaho Wednesday. Cold
conditions will continue with lows Wednesday morning in the teens
and 20s mountains and 20s to lower 30s valleys so the entire
region will likely be below freezing. Highs will be mainly in the
30s and 40s Wednesday with lows Wednesday night again very cold
and teens and 20s mountains and upper 20s to lower 30s valleys
again below freezing. Snow levels again very low 4 to 5 thousand
feet and snow levels will approach valley floors. The system is
dry so significant snows not expected and minimal impact if any
from the snow. Will see a warming trend Thursday through Sunday
with temperatures warming significantly and highs in low
elevations reaching the upper 60s to lower 70s Saturday and
Sunday. Will be mainly dry in the Thursday through Sunday period
with only some isolated showers. Not expecting significant winds
after Tuesday. GK

&&

.AVIATION...For the 12Z TAFS through 12Z Monday.
Showers have ended at all TAF sites this morning and expect dry
conditions with the only chance of showers at DIJ today. Should be
VFR other than at DIJ which occasionally may see a MVFR ceiling
in showers. Expect 10 to 15 knot sustained winds at BYI, PIH and
IDA with some gusts 20 to 25 knots. Main impact aviation wise will
be strong winds on Monday with 25 to 35 knot sustained winds
expected at BYI, PIH and IDA by afternoon with gusts possible 40
to 50 knots at times. SUN and DIJ more in the 15 to 25 knot range
Monday afternoon with gusts 30 to 35 knots. GK

&&

.HYDROLOGY...
Water levels remain elevated on the Portneuf River from Pocatello
to Chesterfield Reservoir where River Flood Warnings remain in
effect until further notice. Minor to moderate flooding is ongoing
in this area with both the Pocatello and Topaz river gauges
forecast to crest this weekend into early next week before
dropping slightly heading into midweek next week.

Further north and west along the Snake River, water managers have
increased releases from upstream reservoirs leading to high flows
in excess of 10,000 cfs downstream from Palisades to Milner. The
Snake River near Heise and Snake River at Lorenzo gauges have
reached action stage as a result and are expected to be at that
stage until further notice. Water managers have also increased
releases from Blackfoot Reservoir which is leading to increased
flows across the Blackfoot River with the river gauge up
Wolverine Canyon having reached action stage this weekend but is
still about half a foot below minor flood stage.

Willow Creek below Tex Creek above Ririe Reservoir and the
Blackfoot River above Blackfoot Reservoir both also continue to be
in action stage since earlier in the week with no other major
impacts seen elsewhere in our CWA as of Sunday morning. MacKay

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Wind Advisory from noon Monday to midnight MDT Monday night for
IDZ051>057-067-068-075.

&&

$$