Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 280941

Area Forecast Discussion
National Weather Service Pocatello ID
341 AM MDT Sun May 28 2023

.SHORT TERM...Today and Monday. Southeast Idaho remains in overall
troughing. The upper level low that has brought us significant
rainfall the last couple of days has weaken and moved north.
Southeast Idaho is no longer highlighted in the Excessive Rain
Outlook (ERO) or the Extreme Forecast Index (EFI). Lingering
moisture off this northern low will allow for isolated to
scattered showers and thunderstorms, mainly over the northern
Central mountains and the Montana divide this afternoon. Moisture
and instability off a low over California will allow for showers
and thunderstorms over our southern areas along the Utah border
this afternoon. Expect much of the same on Monday. Though showers
and thunderstorms look more likely over the Montana divide than
the Central mountains. Also, slightly more moisture looks to work
into our southern areas. Expected scattered showers and
thunderstorms along the Utah border on Monday afternoon.
Temperatures will run around normal today and slightly above
normal by Monday. Wyatt

.LONG TERM...Tuesday through Sunday. An upper low off the California
Coast will slowly drift inland Tuesday while another trough in the
North Pacific approaches the WA/OR coast. The upper low will begin
to lift through the Great Basin by Thursday, and precip chances
should peak around that time for much of east Idaho. Models show the
upper low will slam into the downstream ridge Thursday and may
actually stall over the Central Rockies. Meanwhile, a shortwave
ejecting from the trough in the Pacific will lift across the PAC NW
on Thursday while the trough deepens of the Pacific Coast. Models
keep the threat of showers and afternoon thunderstorms going through
the week as the Pacific trough offers a steady stream of moisture.


.AVIATION...We transition to a split upper flow this morning with
high-res models keying in on some showers crossing the Utah border.
The 3km NAM shows a more northward projection of the precip, but all
others keep showers south of the terminals. CAMs once again develop
convection this afternoon, but less widespread as previous days.
Forecast soundings show slimmer CAPE profiles today as well, so
thunderstorms should be confined to mountains. VFR conditions are
expected to prevail through the period.


.FIRE WEATHER...Scattered thunderstorms are expected over the
mountains this afternoon with isolated coverage in the Snake Plain.
The pattern of afternoon showers and thunderstorms will continue
through most of the week as an upper low slowly moves into the
southwest US.


Active weather is favored to continue today into this coming week
with at or above normal temperatures and overall light rain
putting slight pressure on high elevation snowpack and already
high flowing rivers. Rainfall from showers and thunderstorms today
and tomorrow look overall light, and rainfall is not expected to
add a lot to flows in rivers today or tomorrow. However,
temperatures, especially through mid-week, look to continue to
gradually increase with southerly flow. These warmer temperatures
will increase high-level snowmelt, increasing flows for most

Below you will find the latest on the basin specific river

Big Wood Region: The Big Wood at Hailey just dropped below
moderate flood stage due to cooler temperatures and lack of
significant rainfall. The Big Wood at Hailey is forecast to rise
back into moderate flood stage, especially by Tuesday into
Wednesday mainly due to warmer temperatures. The amount of rain
continually needs to be monitored and will impact how high this
next river peak is. The HEFS probabilities has now jumped on how
high the maximum peak will be, now showing 29% over yesterday`s
11% chance of hitting record peak this coming weekend. Further
upstream north of Ketchum, the Big Wood has stayed below action
stage but is expected back into action stage by next weekend due
to warmer temperatures and precipitation. Feeder creeks including
the North Fork, Trail Creek, the East Fork, Warm Springs have all
remained mostly in action stage. Expect rises by mid week into the
next weekend due to warmer temperatures and rainfall.

Big Lost Region: Antelope Creek remains in flood stage and will
likely drop slightly due to cooler temperatures the next couple
days. But any additional rainfall will keep Antelope Creek firmly
in flood stage. There is still plenty of snow (35 inches) on
Smiley mountain to keep Antelope Creek in flood stage with warmer
temperatures alone this coming week. Upstream on the Big Lost at
Howell Ranch has dropped into action stage and is forecasted to
stay around action stage all week. The long-range forecast has the
Big Lost at Howell rising back to near minor flood stage by June
nth. The Lost Wood Divide snotel still has 15 inches. In 22 of 33
years the Big Lost river at Howell Ranch peaks when this snotel
melts completely out. If season snow is above 25 inches, which it
was this year, then the river peak occurs around 1 day before melt
out of the Lost Wood Divide snotel.

Henry`s Fork and Teton Region: The Henry`s Fork near Rexburg remains
just in flood stage and the forecast is for the river to drop into
action stage today before rising back to flood stage by next
weekend. The Teton river is dropping slightly and is forecasted to
approach action stage by this weekend due to warmer temperatures
and rainfall.

Blackfoot Region: The Blackfoot river above the reservoir is still
in action stage but is dropping and will likely drop below action
stage today or Monday. We will continue with a flood advisory
here until the river drops below action stage.

Portneuf and Marsh Ck Regions: The Portneuf at Topaz remains in
minor flood and the Portneuf at Pocatello remains above flood stage
in moderate stage and just below major stage.  After today, the
forecast for the Portneuf at Pocatello is for the river to
gradually drop daily and go back to minor flood stage by late next

Bear River Region: The Bear River at the Border remains well into
flood stage and is forecast to stay there over the course of the
coming week.

Raft River Region: The upper portion of the Raft River at One Mile
Ck continues to be in action stage aided by rainfall helping
current snowmelt. However, without significant rainfall, expect
the Raft river to fall below action stage in the next couple of



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