Avalanche in Idaho, February 19, 2021

Area Forecast Discussion
National Weather Service Pocatello ID
117 PM MST Fri Feb 19 2021

.SHORT TERM...Tonight through Sunday night.

We're sitting in the warm sector this afternoon with a
few isolated snow showers still drifting through the region. A cold
front will arrive Saturday morning. In advance of that front, expect
to see showers increase tonight. The eastern highlands still looks
like they receive the best snowfall amounts tonight into tomorrow
morning. But, the model qpf has picked up on the showery nature of
tonight's event and as a result the forecast snowfall amounts have
gone down in the valleys but remain reasonably high near pass level.
As mentioned in yesterday's discussion, expect snowfall tonight to
be feast or famine. Where the heavier bands/showers set up will see
the more impressive amounts but some areas will see very little.
With that said plan on expanding the advisory in the eastern
highlands to include the Ashton Hill to Island Park stretch. Expect
winds to increase late tonight into tomorrow morning which may
produce some blowing and drifting issues across the eastern highland
areas. Snow amounts look less in the Snake Plain south of Rexburg
where too much warm air will work in resulting in an inch or less of
snow. The central mountains from Bellevue up to Stanley should see 1
to 3 inches with an inch or less expected for the remainder of the
central mountains.

Light snow showers may persist across the high country through the
weekend as we remain in the moist northwest flow. But amounts look
fairly light. Temperatures in the forecast may be too warm for
Sunday as the models may not be fully accounting for current
snowpack.

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.LONG TERM...Monday through next Friday night. Deterministic and
ensemble guidance remain in solid agreement through Friday before
some differences emerge. Overall, the forecast has changed little
through this time. Moist northwest flow is expected to remain in
place through Monday evening, maintaining high-elevation snow
showers, with local enhancement on northwest-facing slopes. Winds
will increase through the day, with a modest warm-up favored for the
downslope corridor across the southern Snake Plain from Burley to
Blackfoot, where highs in the 40s may be achieved. A strong cold
front will then swing through the area Tuesday morning, bringing a
chance for snow showers to the Snake Plain and eastern Magic Valley.
Combined with gusty winds and falling temperatures, this remains a
period where travel could get a bit dicey. Moist northwest flow will
once again become re-established by late Tuesday/early Wednesday
across the region in the face of low-level cold advection. Snow
showers will once again be favored for mainly high-terrain areas
with some local northwest-facing slope enhancement. Breezy
conditions will likely remain, especially across the southern Snake
Plain. High elevation snow showers should gradually taper off
through the day Wednesday as shortwave ridging gradually builds in.
Pattern recognition and WPC clusters indicate there is some
potential for temperatures to be a bit colder than currently
forecast in the Tuesday night-Wednesday night period -- especially
for typical cold spots where cold air drains/pools. By Thursday,
another low pressure system is seen approaching from the west, and
current indications suggest precipitation will develop from west to
east across the region by late Thursday. This system bears some
resemblance to our Tuesday system, with cold, moist northwest flow
expected to re-develop in its wake by Friday-Saturday. There remain
some differences in the strength and timing of trailing troughing
that is expected to develop across the Great Basin in this system's
wake, so future adjustments to precipitation timing, coverage and
temperatures are possible during this period.

AD

&&

.AVIATION...The aviation forecast through the period will be
challenging. To start things off this afternoon, freezing drizzle
and associated IFR CIGs has developed where mid-level moisture has
stripped away across the northern Snake Plain. This has impacted the
KIDA terminal this afternoon. High-resolution guidance suggests this
may continue through the 22-00Z timeframe. MVFR stratus remains in
place at KPIH and KDIJ -- and this may linger through a similar
timeframe, and possibly beyond. A shortwave trough will zip east
across the region tonight, bringing a round of showers to area
terminals tonight. Due to the spotty nature of this activity, have
timed the start and end of this activity using a high-resolution
ensemble blend, which places the most likely timeframe for showers
generally between 02-09Z across the area. It is possible for showers
to begin earlier than this (especially KBYI) and end later than this
(especially KDIJ). Went with a blanket MVFR predominant group, but
given the expected spotty/convective nature of the activity, there
will be times with VFR conditions overnight interspersed with
periods of IFR conditions, with briefly worse conditions possible
under the heavier showers. Will need to address this with TEMPOs and
amendments as necessary tonight. IFR or MVFR stratus is then
expected to build across the Snake Plain after the passage of the
shortwave disturbance, mainly after 09Z. A weak Snake Plain
convergence band is then expected to spread a renewed round of SNSH
activity across KIDA, KDIJ and possibly as far south as KPIH during
the mid-morning hours. Gusty W/SW winds will develop after the
passage of the shortwave trough as well, with winds expected to
increase into the 15-25kt range with occasionally higher gusts
through the day.

AD

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 6 PM this evening to noon MST
Saturday for IDZ060-063>066.

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE POCATELLO ID
814 AM MST FRI FEB 19 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0813 AM     SNOW             BELLEVUE                43.47N 114.26W
02/19/2021  M1.5 INCH        BLAINE             ID   CO-OP OBSERVER

            STORM TOTAL SNOWFALL.

0800 AM     SNOW             4 NNE MENAN             43.77N 111.96W
02/19/2021  M1.3 INCH        MADISON            ID   CO-OP OBSERVER

            CO-OP OBSERVER STATION MEAI1 MENAN 4 NNE.

0744 AM     SNOW             1 ESE IONA              43.53N 111.92W
02/19/2021  M0.5 INCH        BONNEVILLE         ID   AMATEUR RADIO

            MORNING TOTAL SNOW SO FAR. STILL SNOWING AT
            OBSERVATION TIME.

0715 AM     SNOW             3 NNE DRIGGS            43.77N 111.08W
02/19/2021  M1.9 INCH        TETON              ID   COCORAHS

            COCORAHS STATION ID-TT-1 3 NNE DRIGGS.

0700 AM     SNOW             4 ENE UCON              43.62N 111.88W
02/19/2021  M0.6 INCH        BONNEVILLE         ID   COCORAHS

            COCORAHS STATION ID-BV-6 4 ENE UCON.

0700 AM     SNOW             SODA SPRINGS            42.66N 111.59W
02/19/2021  M1.0 INCH        CARIBOU            ID   COCORAHS

            COCORAHS STATION ID-CR-1 SODA SPRINGS.

0540 AM     SNOW             PAUL                    42.61N 113.79W
02/19/2021  M0.5 INCH        MINIDOKA           ID   COCORAHS

            COCORAHS STATION ID-MN-3 PAUL 0.4 WNW.

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE POCATELLO ID
857 AM MST FRI FEB 19 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0738 AM     SNOW             ASHTON                  44.07N 111.44W
02/19/2021  E6.0 INCH        FREMONT            ID   PUBLIC

            RECEIVED VIA SOCIAL MEDIA. STILL SNOWING AT
            OBSERVATION TIME.

&&

AD

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE POCATELLO ID
914 AM MST FRI FEB 19 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0904 AM     SNOW             1 WSW ST. ANTHONY       43.96N 111.70W
02/19/2021  M7.0 INCH        FREMONT            ID   EMERGENCY MNGR

            SNOWFALL FROM OVERNIGHT THROUGH OBSERVATION
            TIME. STILL SNOWING AT TIME OF OBSERVATION.

&&

AD

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE POCATELLO ID
1132 AM MST FRI FEB 19 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1130 AM     HEAVY SNOW       1 E ASHTON              44.07N 111.42W
02/19/2021  E6.5 INCH        FREMONT            ID   TRAINED SPOTTER

&&

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