Tornado and Hail in Idaho, May 26, 2023

Area Forecast Discussion
National Weather Service Pocatello ID
117 PM MDT Fri May 26 2023

.SHORT TERM...Tonight through Saturday night.
The main impact of the short term period will be the continued
showers and thunderstorms as an upper level trof remains to the
west today with southerly flow aloft continuing to pump moisture
into Idaho. A short wave will rotate through Saturday keeping the
threat for showers and thunderstorms going. Rain amounts through
tonight expected in the 0.10 top 0.30 range, however, where local
heavy rain sets up could see over an inch. Similar amounts
expected Saturday where again heavy amounts will be highly
localized. Low temperatures tonight and Saturday night mainly in
the 40s with highs Saturday in the 60s to lower 70s. Mainly light
winds other than very gusty near the thunderstorms. Re-iterating
the big impacts through Saturday will be localized heavy rainfall
under thunderstorms and a low chance to see some flash flooding.
GK

.LONG TERM...Sunday through next Friday. The forecast indeed sounds
like a broken record...showers and thunderstorms expected each day.
There are some subtle changes though for at least for the end of the
holiday weekend. As the first low lifts northeast, we are seeing the
pattern reload to our south and west. The forecast is trending
toward that while we see a daily risk of rain and thunder, that
coverage may be less and that the threat of more widespread heavier
rain drops off somewhat. Given the amount of recent rainfall in some
areas and already high river/stream flows...the flooding threat
(flash or spikes in flow levels) will be non-zero. It does look like
by the middle and the end of next week, we will see something
similar to what has been happening the past few days. The low
deepens and eventually lifts northeast, meaning a gradual increase
in coverage and threat for heavier rainfall could return. These are
trends we will need to watch in the coming days.  With southerly
flow picking back and up and potentially more sunshine, highs should
again push back into the 80s early on in the week.  Keyes

&&

.AVIATION...Another round of showers and thunderstorms is already
underway and will impact our area into tonight. We are forecasting
VFR weather overall, but gusts over 35kts with storms are possible
along with small hail and heavy rain. We may see quick drops to IFR
when we see heavier rainfall impacting a particular airport. We do
have -SHRA VCTS or -TSRA through this evening, with VCSH overnight
and Saturday morning. However, it wouldn't be a shock to see a few
lightning bolts overnight. Keyes

&&

.HYDROLOGY...Active weather is favored to continue through the
holiday weekend with at or above normal temperatures and rain
putting pressure on high elevation snowpack and already high
flowing rivers. Thunderstorms over the coming days will be
conducive for moderate to heavy rain in slow moving and or
training thunderstorms leading to a slightly increased, urban,
lowland and river flooding potential. Temperatures, especially
early next week, look to continue to gradually rise with
increased southerly flow. See short term discussion above on how
much precipitation is expected today and Saturday.

Below you will find the latest on the basin specific river
information:

Big Wood Region: The Big Wood at Hailey remains in moderate flood
stage and is forecast to stay there through the coming week. The
amount of rain needs to be monitored. The forecast has the river
rising slightly higher. How much higher will depend on rain
amounts every day through next week and warmer temperatures next
week. The HEFS probabilities continue to show a downward trend,
now just showing a 14% chance of hitting record peak later next
weekend. The Big Wood at Hailey is staying fairly steady just
above Moderate stage. Further upstream north of Ketchum, the Big
Wood has stayed below flood stage but is expected back above flood
stage later in the week with rainfall. Feeder creeks including
the North Fork, Trail Creek, and the East Fork have all remain
just below flood stage and any future peaks the next couple of
days will be mainly rainfall driven. In addition, Warm Springs
Creek which feeds into the Big Wood at Ketchum decreased some
yesterday and just dropped below minor flood stage. The Magic
reservoir forecast now shows Magic reservoir filling Sunday into
Monday, spilling for the first time in several years. The flow
downstream of the reservoir should come close to action stage, but
little impacts, if any, are expected in our area.

Little Wood Region: The Little Wood River above High Five Creek was
running near bankfull with its diurnal peak decreasing slightly
from the day before and likely to remain near this level for the
next few days.

Salmon Region: Valley Creek (feeding into the Salmon in Custer
County) has dropped slightly more but is still near bankful. The
rest of the streams as well as the Salmon river remain below
action stage. We will have to continue monitoring these sites as
we work into the moderating temperatures next week. But for now
each site is expected to remain below warning stage with no
highlights warranted at this time.

Big Lost Region: Antelope Creek has dropped slightly below flood
stage and is expected to remain oscillating between action and
flood stage dependent on rainfall and warmer temperatures. Thus,
the Flood Warning will continue there. Upstream on the Big Lost at
Howell Ranch we expect readings to oscillate around flood stage
for the next few days and will continue to keep the flood warning
out. The long range forecast has the Big Lost at Howell rising
well into minor flood stage next weekend responding to warmer
temperatures and rainfall that are expected next week.

Henry's Fork, Camas Ck, and Teton Region: The Henry's
Fork near Rexburg has just climbed back above flood stage this
afternoon. The Teton river continues to rise ever so slightly but
remain out of flood stage, for now. Reaching flood stage this
weekend will be very dependent of rainfall this weekend and
hitting flood stage next weekend will be very dependent of warmer
temperatures and rainfall next week.

Blackfoot Region: The Blackfoot river above the reservoir has
leveled out in action stage and will likely stay at this level as
long as there is daily precipitation. Thus, we will continue with
an Advisory here as it continues to run at bankfull.

Portneuf and Marsh Ck Regions: The Portneuf at Topaz and Pocatello
remain above flood stage in moderate stage and just below major
stage. With significant rain today, the river may hit major flood
stage. From here the forecast is to gradually drop daily and go
back to minor flood stage by mid next week.

Bear River Region (including Bear Lake, Franklin, and Oneida Co):
The Bear River at the Border remains in 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 oscillate ever so slightly at bankfull while no
water was observed flowing downstream at the interstate suggesting
irrigation demand is high. No problems anticipated here.
Wyatt

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
None.
&&