087
FXUS65 KPIH 052056
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
256 PM MDT Sun May 5 2024

.SHORT TERM...Tonight through Monday night.
Upper level low moves from southwest corner of state to southeast
corner after midnight. Will see rain and snow showers continuing
tonight and expect some precipitation to increase as wrap around
moisture moves into the eastern areas after midnight and snow
levels will likely drop to valley floors once again overnight into
Monday morning. Winter weather advisories remain in effect in the
eastern highlands and winter storm warning in the Bear River
Range. Amounts generally 2 to 4 inches through Monday in the
valley locations in the eastern mountains with much higher amounts
at pass levels. Expect the potential of 1 to 2 inches of snow in
the Snake River Plain overnight into Monday morning. There is less
than a 20 percent chance more than that will fall. High
probability of no impacts with the snow in the snake plain. Winds
will increase in the southern hills, raft river region, Magic
Valley and Snake River Plain on Monday and wind advisories have
been issued starting Monday morning through Monday early evening.
Speed up to 30 mph and gusts up to 50 mph possible. Lows tonight
mainly 20s mountains to mid 30s low elevations and highs in the
upper 30s mountains to around 50 valleys on Monday. Lows in the
20s and 30s. Monday night and Tuesday morning.
GK

.LONG TERM...Tuesday through next Sunday.
Unsettled and seasonably cool weather will continue into Tuesday as
a H5 shortwave trough works through SRN Idaho. This will keep
chances for snow going in addition to supporting strong winds as a
cold front moves through the region. 30-40 kt 700 mb winds and an
enhanced PGF will bring strong winds throughout the day on Tuesday
around 20-40 mph with gusts up to 30-60 mph. The strongest winds
will be favored around the Magic Valley and Lower Snake Plain region
south into Utah and Nevada where locally stronger gusts around that
60-70 mph range will be possible. While additional snowfall amounts
Tuesday will be around that T-2" range, locally higher totals will
be possible along the Wyoming border region up to around 2-4".

As Tuesday`s shortwave trough is absorbed into a much larger H5 low
centered over the NRN Plains, isolated to scattered snow showers
will continue further north and east as drier conditions return
further west. Those precipitation will further decrease for
Wednesday as the H5 low over the Plains splits, sending the bulk of
its energy east as a secondary H5 low tracks SW over the Great
Basin. This will be further aided by a well defined H5 ridge over
the ERN Pacific with increased confidence on a Rex Block setting up
late next week over the WRN CONUS. As a result, highs in the
30s/40s/50s midweek will increase to the 60s/70s as soon as Friday
with the NBM 50th percentile high temperature forecast supporting
the potential for some upper 70s and low 80s across our lowest
elevations on Sunday. This would likely mean the warmest airmass in
place over SRN Idaho that we have seen so far this year with normal
highs for mid-May around the upper 50s to upper 60s.

This ridge feature over the West shows little signs of breaking down
when taking a look at the EPS as the polar jet shifts further
north/west leading to a broad SW/zonal flow over the western CONUS.
The GEFS in contrast takes more of a broad NW/zonal flow route which
returns for early the following week leading to the EPS being the
warmer model by around 10-15 degrees. This will ultimately come down
to the strength and placement of the polar jet which will come into
focus over the coming week but at this time, the NBM continues to
follow more closely to the ECMWF. Stay tuned and enjoy the warmer
weather on the way to round out next week! MacKay

&&

.AVIATION...For the 18Z TAFS through 18Z Monday.
Scattered rain/snow showers and isolated thunderstorms along the
Wyoming border will continue through this evening as a dry slot
shifts overhead. This will lead to more isolated precipitation
chances ahead of a cold frontal passage Monday morning. This front
will support an uptick in winds and areal coverage of precipitation
with predominant snow favored as even colder air builds into the
region. MVFR/IFR CIGS/VIS will be continue to be possible at times
as bands of moderate to heavy snow move on station.

As a secondary trough begins to move through the PacNW on Monday,
lingering instability behind the exiting cold front will support
isolated to scattered thunderstorm development for Monday afternoon
and evening. The HREF model probability of thunder 12Z Monday to 12Z
Tuesday shows a 40-60% chance at KBYI and KSUN with a 20-40% chance
at KPIH, KIDA, and KDIJ. In addition to the strong synoptic winds
tomorrow, primary hazards around stronger storms will center around
heavy precipitation, small hail, and gusty outflows. MacKay

&&

.HYDROLOGY...
Flooding has dropped to minor flood stage at the Portneuf River
at Pocatello with rising levels back to moderate on Monday after
all the precipitation and forecast to continue to be at moderate
stage through next weekend. Peak is forecast to reach very near
major flood stage on Tuesday. Minor flooding expected to continue
for the Portneuf River at Topaz where the gauge remains just below
flood stage and will rise above Monday and remain so for several
days. Flood warnings also remain in effect for the Blackfoot
River near Shelley at Wolverine Canyon with the river remaining at
flood stage and also near Blackfoot where the river remains in
flood stage. With more precipitation tonight and Monday, rivers
will need to be monitored closely.
GK


&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Wind Advisory from 6 AM to 8 PM MDT Monday for IDZ051-052-
054>057.

Winter Weather Advisory until 6 AM MDT Monday for IDZ056-057.

Winter Storm Warning until 6 AM MDT Tuesday for IDZ060.

Winter Weather Advisory from 9 PM this evening to 6 AM MDT
Tuesday for IDZ062>066.

&&

$$