479
FXUS65 KPIH 042021
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
221 PM MDT Sat May 4 2024

.SHORT TERM...Tonight through Sunday night.
A powerful storm system will move in from the Pacific tonight and
quickly move east with a strong cold front moving through eastern
Idaho Sunday morning. Precipitation will overspread all of
southeast Idaho overnight. Snow levels will start out at over 9
thousand feet and quickly drop to 5 to 6 thousand feet in the
southern hills and raft river region and winter weather advisories
have been issued there Sunday morning through Sunday night as some
accumulations are expected with up to a foot over 8 thousand feet
but snow levels dropping to 4 to 5 thousand feet overnight could
cause some travel issues in interstate 84 south of Burley to Utah.
The winter storm watch has been upgraded to a warning from noon
Sunday through Monday night in the Bear River Range where again a
foot or more may fall at the highest elevations. Winter weather
advisories have been issued for the eastern mountains beginning
Sunday night through Monday night. Again overnight Sunday into
Monday morning could see travel problems in the eastern highlands
as low elevations seeing 3 to 5 inches through Monday with much
higher amounts above 6000 feet. Rain amounts over a half inch are
likely in the Snake River Plain Sunday into Monday with over an
inch possible in the southern and eastern mountains liquid amounts.
Snow levels will be threatening to drop to valley floors late
Sunday night and Monday morning so again there is a low
probability of light accumulations from American Falls through
Pocatello to Idaho Falls late Sunday night into Monday for now
have it limited to around a half inch. So it will be a very high
impact short term period with wind, rain and snow affecting
everyone. It will be much colder Sunday with highs in the 40s and
50s and lows Sunday night into the 20s and 30s. Lows overnight
tonight will be in the 30s and 40s.
GK

.LONG TERM...Monday through next Saturday.
Scattered rain and snow showers will continue into Monday and
Tuesday as a H5 low and negatively tilted trough shift eastward onto
the Great Plains. Seasonably cold, well below normal temperatures
will be the going trend for early next week with highs in the
30s/40s/50s each day with overnight lows around or below freezing.
Given the placement of the low now to our east to start next week,
better chances for accumulating snow will shift to being confined to
ERN Idaho where snow levels support a mix of rain/snow in the
valleys and predominant snow in the mountains. Light snow will also
continue to be possible across the CNTRL Mountains as more moderate
accumulation potential remains in ERN Idaho. While there continues
to be uncertainty regarding snow levels, roadway surface
temperatures will be the main focus of transportation impacts and
with colder air settling in for early next week, this could present
hazardous travel conditions at times.

In addition to precipitation, winds will also remain elevated Monday
and Tuesday aided by 30-45 kt 700 mb winds aloft and an enhanced PGF
which will support gusts around 30-50 mph with locally stronger
gusts across the Snake Plain and Magic Valley to around 50-65 mph.
Additional WIND ADVISORIES will likely be needed to capture these
strong winds as lighter winds return midweek.

The passage of a shortwave trough Tuesday will keep precipitation
chances going into Wednesday and also aid in keeping temperatures
well below normal given its track from WRN Canada. By Wednesday with
the bulk of moisture now confined east of the Continental Divide,
showers will see a decrease in areal coverage as drier conditions
progressively return later in the work week.

This drier progression will be aided by a well defined H5 ridge
building into the NE Pacific and WRN CONUS which will begin to force
moisture east. As a result, 70% of ensemble clusters show a well
defined ridge building into our region late next week with around
60% of clusters also favoring a Rex Block to establish which would
mean a H5 low over the SW CONUS, splitting off of the main H5 low
circulation on the Plains. The other 30% of ensemble clusters show
this low further north across the NRN Great Basin which would mean
continued isolated showers. This is split nicely amongst the ECMWF
favoring the 70% solution while the GFS favors the 30% solution with
latest guidance. The NBM continues to favor more closely to the
ECMWF which means gradually warming temperatures through the weekend
as conditions remain dry but does keep some elements of the GFS with
very isolated mountain showers. The NBM 50th percentile high
temperatures starting Friday through the weekend show highs returns
to the 60s/70s with the potential for even some low 80s across our
lowest elevations which could mean the warmest airmass we have seen
so far this year. MacKay

&&

.AVIATION...For the 18Z TAFS through 18Z Sunday.
Predominant VFR and dry conditions will continue through this
evening as mid/upper-level clouds increase out of the west
associated with our next incoming system. Ahead of the arrival of
precipitation, winds will increase out of the south as a mix of
rain/snow builds in tonight through Sunday morning. MVFR CIGS/VIS
will be possible as moisture builds into the region with a slight
chance for IFR CIGS/VIS associated with moderate to heavy
precipitation at times. The HREF model probability of thunder also
shows a 10-20% chance of thunderstorms at KBYI and KSUN through 12Z
Sunday morning. Those thunderstorm chances will increase and shift
east for Sunday afternoon into Monday morning where a 20-50% chance
will exist at KPIH, KIDA, KBYI, and KDIJ with less than a 10% chance
at KSUN. Confidence remains low on Sunday regarding precipitation
type at times giving varying snow levels but confidence remains high
on breezy winds continuing into Sunday across the Magic Valley and
Snake Plain before stronger winds move in for Monday/Tuesday. MacKay

&&

.HYDROLOGY...
Flooding has dropped to minor at the Portneuf River at Pocatello
with rising levels back to moderate on Sunday and forecast to
continue to be at moderate stage through next weekend. Peak is
forecast to reach 10.8 inches very near major flood stage on
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 Sunday and Monday, rivers will need to be monitored
closely.
GK

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 4 AM MDT Sunday for IDZ056-057.

Winter Weather Advisory from 6 AM Sunday to 6 AM MDT Monday for
IDZ056-057.

Winter Storm Warning from noon Sunday to 6 AM MDT Tuesday for
IDZ060.

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

&&

$$