160
FXUS65 KPIH 031930
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
130 PM MDT Fri May 3 2024

.SHORT TERM...Tonight through Saturday night.
Main impacts in the short term will again be Freeze warnings and
Frost advisories in effect once again as skies should clear
overnight with below freezing or near freezing temperatures
expected to be widespread in the Snake River Plain, Magic Valley
and Arco desert. On Saturday flow aloft turns southerly ahead of
the next upper level trof approaching Idaho and southerly winds at
the surface will increase ahead of the approaching cold front. It
will be very mild compared to recent days with highs in the 60s
mountains and 70s low elevations. A wind advisory has been issued
beginning at noon Saturday in the Southern Hills, Albion Mountains
and Raft River Region as speeds are expected to reach 25 to 35 mph
with gusts expected to reach 45 to 55 mph at times. Rain and very
high elevation snow will spread rapidly east Saturday night with
rain covering all of southeastern Idaho by Sunday morning. Snow
levels start out very elevated in the 8500 to 9500 foot level and
dropping snow levels is more a concern in the long term period.
The central mountains will see precipitation amounts in the 0.25
to 0.50 inch range overnight Saturday. Lows Saturday night will be
mild ranging from the 30s mountains to 40s valleys.
GK

.LONG TERM...Sunday through next Friday.
Under the influence of an organized H5 low directly overhead for
Sunday and Monday, widespread precipitation, strong winds, and
colder temperatures will return to begin the extended period.
Confidence continues to increase regarding this system moving
onshore for Saturday around Oregon before shifting east over SRN
Idaho and the NRN Great Basin for Sunday and Monday. The latest
QPF/rainfall forecast has gone up slightly over this morning now
showing more solid 0.50-1.25" across the region with locally lighter
totals across portions of the NRN Magic Valley and Arco/Mud Lake
Desert. Locally higher totals in the mountains will be in that 1-2"
range.

Given colder air associated with this system, a mix of rain and snow
in the valleys and predominant snow in the mountains continues to
remain favored. There also exists moderate to heavy snow potential
in the backcountry above 7000-8000` where up to around 1-2` of snow
will be possible. As we get colder air in place Sunday night into
Monday as the H5 low works NE into Wyoming and Montana, this will be
the best timeframe for widespread valley snow potential especially
south and east of the Snake Plain as snow levels fall to valley
floors. WINTER WEATHER ADVISORIES will likely be needed to capture
this event in the mountains with only light accumulations expected
at this time across the Snake Plain and Magic Valley. Taking a look
at winds, strong winds out of the W/SW are favored to continue into
Sunday and Monday aided by an enhanced PGF and 30-45 kt 700 mb winds
aloft. This will support additional WIND ADVISORY potential across
the Snake Plain and Magic Valley where wind gusts up to 40-60 mph
will exist. With respect to temperatures, highs on Saturday in the
60s/70s will quickly fall heading into Sunday and Monday with a
return to the 30s/40s/50s of which will continue through midweek
under the continued influence of a broad H5 trough overhead.

As this system ultimately exits to our east onto the NRN Great
Plains for Tuesday and Wednesday, temperatures will remain
seasonably cool with isolated to scattered rain/snow showers.
Starting Thursday, around 75% of ensemble cluster solutions show a
return to a broad H% ridge over the PacNW and NRN Rockies which will
begin to shift east heading into the weekend. This will support
warmer and drier weather to round out the work week into the weekend
with highs back in the 50s/60s/70s as soon as Friday. The latest NBM
50th percentile high temperatures also show the potential for mid to
upper 70s across our lowest elevations by the weekend which could
mark the warmest airmass we have seen so far this year. Stay tuned
as we track the latest and plan ahead for wet and windy weather
Sunday and Monday with lingering showers through midweek. MacKay

&&

.AVIATION...For the 18Z TAFS through 18Z Saturday.
Predominant VFR conditions have returned at all terminals late this
morning as lingering low-level CIGS continue through this afternoon
and evening behind an exiting shortwave trough into Wyoming. These
clouds will support isolated showers today with brief rain/snow
possible on station. Further to our west, a large low pressure
system will begin to move onshore tonight into Saturday as
conditions remain dry with increasing mid/upper level CIGS. As a
warm front lifts north out of Utah for Saturday, look for increasing
winds out of the south up to 15-25 kts with gusts to 20-35 kts.
Widespread precipitation will progressively return west to east
starting Saturday afternoon and continue through the overnight hours
into Sunday. Both strong winds and precipitation will then continue
into early next week as a colder airmass returns. MacKay

&&

.HYDROLOGY...
Moderate flooding remains ongoing at the Portneuf River at
Pocatello with rising levels late this weekend into early next
week with the latest river forecast reaching 10.8 inches very near
major flood stage next Tuesday. Minor flooding continues for the
Portneuf River at Topaz where the gauge remains above flood stage
and will remain so for several days with only a slight rise
expected late this weekend into early next week. 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 the
potential for significant precipitation this weekend rivers will
need to be monitored closely.
GK

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Frost Advisory from 2 AM to 9 AM MDT Saturday for IDZ051-055.

Freeze Warning from 2 AM to 9 AM MDT Saturday for IDZ052>054.

Wind Advisory from noon to 11 PM MDT Saturday for IDZ056-057.

&&

$$