Winter Storm in Idaho, December 31, 2019

Name: Winter Storm in Idaho, December 31, 2019
Start: 2019-12-31T19:30
End: 2019-12-31T23:59
Location: Idaho

December 31, 2019 · NWS MSO · 1 event in 1 county or zone

A warm and moist air mass overran valley cold air trapped across eastern Lemhi County, leading to a prolonged period of heavy snowfall the evening December 31st into the morning of January 1st.

Where it happened

Every event with a place to put it; 1 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.

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The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 1

Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.

What happened

The episode as NWS MSO wrote it up.

A warm and moist air mass overran valley cold air trapped across eastern Lemhi County, leading to a prolonged period of heavy snowfall the evening December 31st into the morning of January 1st.

What forecasters said that day

The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Missoula, MT wrote its last area forecast discussion before the first event at Dec 31, 2:20 PM MST, 5 hours 10 minutes earlier.

Area forecast discussion, Dec 31, 2:20 PM MST, 5 hours 10 minutes before

Area Forecast Discussion
National Weather Service Missoula MT
220 PM MST Tue Dec 31 2019

...HEAVY MOUNTAIN SNOW AND MIXED VALLEY PRECIP THROUGH
WEDNESDAY...

.DISCUSSION...
Winter weather advisories remain in place over much of the
Northern Rockies through Thursday morning. We are holding off on
issuing warnings for now. Our reluctance is due to continued
uncertainty on precipitation type as valley high temperatures look
to approach 40 degrees today and lows only dip to the low 30s
Wednesday morning in the Bitterroot, Mission, and Lower Clark Fork
valleys. Do not get us wrong, the mountain passes and high
terrain above about 4500 feet will see a formidable and much
needed snow storm. Major impacts in the form of snowfall, however,
will be limited to these areas in the near term. Valley impacts
will include the potential for periods of freezing rain. A weak
cold front moves through on Wednesday night. Temperatures will
decrease slightly and snow levels will drop back down below 3500
feet. All of this said, mountain snow totals will be counted in
feet by Wednesday night as 1-2 feet accumulate in the higher
terrain of the Cabinet, Bitterroot, Mission, Flathead, and
Clearwater ranges. Lookout, Lost Trail, and Lolo Passes will pick
up about a foot.

The scenario on Thursday is shaping up to be one that is very
conducive to produce snow bands across the region. As we know with
banded snowfall, nailing down exact locations can be tricky as
they are prone to moving, but can produce moderate to heavy
snowfall in a short amount of time. This will be the case,
particularly across north central Idaho mountains into west
central Montana, where snow bands will have the best chance at
forming. Anywhere that bands form, expect highly changeable travel
conditions.

As we head into Friday, winds will begin to increase dramatically
in terrain 5000 feet and higher, lasting through Saturday morning
before dissipating later in the day. Valleys will see wind gusts
kicking up late Friday into early Saturday. As for precipitation
on Friday, valleys will begin as all snow, with a transition to a
mix of rain and snow in the afternoon and evening hours. It will
then change back over to snow overnight into Saturday. During the
day Saturday, snow bands will once again be likely under a highly
convective environment. Additional snow accumulations will be
possible across western Montana and north central Idaho (all
elevations).

Winds will finally dissipate Sunday, with only lingering light
snowfall expected in the mountains along the Continental Divide
and along the Idaho/Montana border. The weather will once again
become active as we head into the first half of next week.

&&

.AVIATION...
Precipitation, heavy at times, will affect all terminals for the
next 24 hours and beyond, especially KMSO and KGPI. Expect flight
rules to drop to IFR and below during periods of heavier precip.
Precipitation types have been a forecast challenge during this
event as temperatures linger around freezing. Bouts of freezing
rain are not out of the question, especially overnight at KGPI.
Expect terrain obscurations over the entire Northern Rockies
airspace.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...     Winter Weather Advisory until 5 AM MST Thursday Lower Clark Fork
     Region.

     Winter Weather Advisory until 6 PM MST this evening
     Flathead/Mission Valleys.

     Winter Weather Advisory until 5 AM MST Thursday West Glacier
     Region.

     Winter Weather Advisory until 11 AM MST Wednesday
     Kootenai/Cabinet Region.

     Winter Weather Advisory until 5 AM MST Thursday
     Bitterroot/Sapphire Mountains.

     Winter Weather Advisory from 6 PM this evening to 5 AM MST
     Thursday Potomac/Seeley Lake Region.

     Winter Weather Advisory from 6 PM this evening to 5 AM MST
     Thursday Butte/Blackfoot Region.

ID...     Winter Weather Advisory until 5 PM PST this afternoon
     Orofino/Grangeville Region.

     Winter Weather Advisory until 4 AM PST Thursday Southern
     Clearwater Mountains.

     Winter Weather Advisory until 4 AM PST Thursday Northern
     Clearwater Mountains.

&&

In the hours before

Local storm report, Dec 31, 2:05 PM MST, 5 hours 25 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MISSOULA MT
205 PM MST TUE DEC 31 2019

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

1000 AM     SNOW             1 S ELK RIVER           46.77N 116.18W
12/31/2019  M2.5 INCH        CLEARWATER         ID   CO-OP OBSERVER

            CO-OP OBSERVER STATION EKRI1 0.7 S ELK
            RIVER.

0700 AM     SNOW             4 ESE PABLO             47.57N 114.04W
12/31/2019  M1.1 INCH        LAKE               MT   COCORAHS

            COCORAHS STATION MT-LK-10 3 ESE PABLO.

&&

Local storm report, Dec 31, 5:03 PM MST, 2 hours 27 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MISSOULA MT
503 PM MST TUE DEC 31 2019

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

0455 PM     SNOW             4 S WHITEFISH           48.36N 114.35W
12/31/2019  M4.0 INCH        FLATHEAD           MT   TRAINED SPOTTER

            SNOW FELL OVER ABOUT THE PAST 3 HOURS.

&&

IV

Local storm report, Dec 31, 5:21 PM MST, 2 hours 9 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MISSOULA MT
521 PM MST TUE DEC 31 2019

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

0510 PM     SNOW             3 WNW KALISPELL         48.21N 114.36W
12/31/2019  E2.1 INCH        FLATHEAD           MT   PUBLIC

            SNOWFALL FROM 11PM LAST NIGHT THROUGH THIS
            AFTERNOON. STILL SNOWING AS OF THIS REPORT.

&&

Local storm report, Dec 31, 5:48 PM MST, 1 hour 42 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MISSOULA MT
548 PM MST TUE DEC 31 2019

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

0548 PM     SNOW             BIGFORK                 48.07N 114.07W
12/31/2019  M3.2 INCH        FLATHEAD           MT   TRAINED SPOTTER

&&

IV

Local storm report, Dec 31, 7:21 PM MST, 9 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MISSOULA MT
721 PM MST TUE DEC 31 2019

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

0600 PM     SNOW             3 NW HERON              48.08N 116.00W
12/31/2019  M6.4 INCH        SANDERS            MT   CO-OP OBSERVER

            CO-OP OBSERVER STATION HERM8 2.5 NW HERON.

&&

The radar

The national radar mosaic for the moment the first event began.

Open the radar archive at this moment

Event by event

1 winter storm. Local standard time, as filed.

Winter Storm, Eastern Lemhi County

When: December 31, 7:30 PM MST to 11:59 PM MST
Where: Eastern Lemhi County forecast zone
Reported by: Department of Highways
Coordinates: 44.943, -113.933 (the zone’s center; the record gives no point)

Heavy snowfall was reported across northern areas of eastern Lemhi County. Salmon was impacted by 8 inches of snowfall while areas along US 93 between Gibbonsville to Lost Trail Pass saw 12 inches. Blowing snow also caused significantly reduced visibility on Idaho Highway 28 between Leadore and Gilmore Summit.

What these are

Winter Storm: A storm that brought snow, sleet or freezing rain at warning levels, usually over several hours or days.

After NWS Directive 10-1605, the rules offices file Storm Data by.

The same day elsewhere

Every storm in Idaho in 2019 Every state in 2019 This day in weather history Warnings in Idaho, December 2019

Sources

NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 865616.