Debris Flows in Idaho, April 11 to 12, 2023

Area Forecast Discussion
National Weather Service Pocatello ID
406 PM MDT Tue Apr 11 2023

.SHORT TERM...Tonight and Wednesday.  A quick update late this
afternoon to cancel the Wind Advisory across the central mountains.
Current observations were showing peak wind gusts well below the 45
mph lower threshold required for an advisory. See the previous
discussion below. Huston

 Today will be the last day we experience above normal
temperatures for awhile as a high pressure ridge will give way to a
digging trough across the Pacific NW. We're already feeling the
impacts from the aforementioned trough as the tightening pressure
gradient is causing winds to ramp up across much of the area. The
Wind Advisory continues across portions of the central mountains and
along the Continental Divide and this is certainly where the
strongest winds thus far have been observed but it remains breezy
into the Snake Plain and Magic Valley. Similar to yesterday, seeing
a wide range of temps across the CWA but most of us are in the 50s
to lower 70s, with the highest values in the lower Snake and into
the Magic Valley. Continued snowmelt remains problematic across
portions of the area. See the hydrology section below.

As the trough continues to dig across the Pac NW, we'll see PoPs
begin to slowly tick up across the central mountains and into the
eastern highlands later this evening although chances aren't overly
high. Better chances look to occur later in the day on Wednesday and
become a bit more widespread during the overnight hours into
Thursday morning. Temps will support rain at the onset gradually
becoming rain/snow mix and then all snow as temps and snow levels
begin to drop. McKaughan

.LONG TERM...Thursday through next Tuesday.
By Thursday, a closed low will pass directly over Idaho before
continuing to track northeastward into Montana and eventually
Canada. The National Blend is carrying the highest PoPs of the
period during the earlier part of Thursday and QPF will be
greatest across the east and southeast highlands during this
timeframe. By late week, temperatures will support mostly snow
region-wide, with snow levels generally remaining 4,000 feet or
below on Thursday. The NBM shows around a 30-70% probability that
the Central Mountains will receive 2" or more of snow during the
24 hours leading up to Friday morning. For this same period, there
is a 40-70% probability that the Centennials and Island Park
region will receive 4" of snow. Current snow totals for the
Centennial, Big Hole, Beaverhead and Lost River Ranges are around
3-6 inches. Locations above 6,000 feet elevation across the
southeast highlands will likely see a couple inches, as well.
Thursday will be the coolest day of the long-term, with area-wide
high temperatures generally in the 30s and 40s. Winds will become
elevated again Thursday as the low passes and the gradient
tightens, especially across the Magic Valley, with sustained winds
of 20-30 mph and gusts potentially reaching 40 mph. A Wind
Advisory may be warranted, but at this time it looks as though
winds may fall short and so we will continue to see how models
trend. A transient ridge will begin to build in Friday, however
models still show some light precipitation breaking through across
the highest elevations of the Central Mtns. and E/SE Highlands
prior to Saturday. Dry conditions will last throughout the weekend
before the next PNW low brings impacts to southeast Idaho again
by early Tuesday. Cropp
&&

.AVIATION...
Hi-res models show showery precipitation in the vicinity of KDIJ by
early this evening, with light rain showers lasting through
tomorrow. High clouds will increase area-wide throughout the period,
but CIGs are expected to remain VFR. Southwesterly winds around 15
KTS with gusts pushing 30 KTS will begin to subside late this
evening, although winds will remain breezy Wednesday. Cropp
&&

.HYDROLOGY...
This is the last day of well above normal temps which will support
continued melting snow and localized flooding before a trough of low
pressure brings a cooling trend for the rest of the week that
should stabilize the snowpack. River responses will lag the
warmest temps and will remain quite modest for most areas with
this first warmup of the season...the Portneuf River at Topaz and
Pocatello, and the Bear River at the ID/UT border, are forecast to
approach bankful Thu and Friday. Continue to refer to our
Hydrologic Outlook (ESF) for additional details and suggested
preparedness actions.
&&

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