Southwest flow brought above normal Pacific moisture impacting mainly higher elevations of the Northern Rockies with 5 to 8 inches of snow, and lower elevations with heavy rain. S.
Every event with a place to put it. Tap one for its entry below.
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.
The episode as NWS MSO wrote it up.
Southwest flow brought above normal Pacific moisture impacting mainly higher elevations of the Northern Rockies with 5 to 8 inches of snow, and lower elevations with heavy rain. The heavy rain produced rock slides along U.S. Highway 95 north of Pollock, Idaho.
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 2, 6:28 PM PST, 4 hours 2 minutes earlier.
Area Forecast Discussion...UPDATED
National Weather Service Missoula MT
728 PM MST Sun Dec 2 2012
.UPDATE...Snow advisories have been issued for parts of western
Montana for additional snow tonight and Monday.
&&
.DISCUSSION...A cool and moist airmass has developed over Idaho and
western Montana this evening. Current trends and latest model
guidance agree that snow will enhance this evening and continue
through Monday. Snow levels will also lower overnight that could
allow many valley locations to receive snow. Confidence is not
quite high enough for accumulations in the bigger valleys
(Missoula/Mission/Flathead) so will hold off on advisories and
monitor the situation for additional updates. Mountain passes will
receive another good shot of snow tonight and Monday, so
advisories have been issued through Monday afternoon.
&&
AVIATION...Current radar loops show snow re-enhancing in portions
of Idaho and western Montana. Latest model guidance show this
enhancement and agree that most locations will have high chances
for snow overnight and through Monday. The main focus appears to
be along the ID/MT border and throughout northwest Montana. Expect
obscured mountains and passes due to clouds and snow and lowered
ceilings and periods of reduced visibilities in valley locations
through Monday afternoon. Model soundings for KMSO and KGPI show a
good profile for snow to develop by Monday morning which could
present impacts into Monday afternoon.
&&
.PREV DISCUSSION... /ISSUED 322 PM MST Sun Dec 2 2012/
DISCUSSION...A cold front is currently in western Montana and
will continue to push to the east this evening. Behind the front
the precipitation has become fairly showery in nature, but Lost
Trail, Marias, MacDonald passes and Georgetown lake could still
see significant snowfall this afternoon so have allowed the
warnings and advisories to continue. The snow levels will steadily
fall through out the night allowing the potential for snow to
reach valley floors. Snow accumulations are anticipated to remain
fairly light, but a few locations could see decent amount of snow.
The showers will linger throughout the day on Monday. Then Monday
night a weak ridge of high pressure will move over the Northern
Rockies allowing for a decrease in precipitation. The models
indicate another round of warm subtropical moisture starting to
push into the region on Tuesday. This plume of moisture will cause
snow levels to rise on Tuesday.
A couple of main impacts next week...
1. Another very wet and relatively warm system for central Idaho
and West/Northwest Montana.
2. Colder temperatures Thursday through Sunday. Light Accumulating
valley and mountain snow showers possible Friday or Saturday.
The last in a series of warm subtropical plumes of moisture will
once again move through the Northern Rockies Tuesday and
Wednesday. This very wet moisture source combined with orographic
lift will provide over an inch of precipitation in the mountains.
Snow levels however will remain fairly high and have little impact
at first to mountain passes. A strong cold front will push through
the region sometime Wednesday afternoon. Snow levels will quickly
drop to pass level and the valley floors overnight. Several inches
of snow could fall over the mountain passes through the evening
but confidence in the timing of cold air with available moisture
is somewhat low at this point to nail down snow amount specifics.
Cold air will persist over the Northern Rockies. Models are
hinting at a significant cold outbreak by next weekend. However
there is a lot of uncertainty as to whether the deepest cold air
will make it across the divide. Thus no major impacts from arctic
air are anticipated at this point...but stay tuned for forecast
updates.
AVIATION...The system that bought high amounts of valley rain and
mountain snow today is pushing to the east, and the main bulk of
the precipitation should be out of western Montana by sunset. As
of 02/2200z, the cold front is just off to the west of KBTM.
Southwest Montana can expect to continue to see strong, gusty
south winds until the front passes which should be around
03/0300Z. Low to middle level cloud cover will hang around until
at least Monday morning for much of western Montana and north
central Idaho obscuring mountain tops. Some fog or low stratus
could develop late tonight and early Monday for KMSO and
KGPI, but the amount of cloud cover and drying behind the cold
front is still uncertain and will have a big part on fog
potential tonight.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...WINTER WEATHER ADVISORY until 3 PM MST Monday
Bitterroot/Sapphire Mountains...Lower Clark Fork Region.
WINTER WEATHER ADVISORY until 3 PM MST Monday Potomac/Seeley
Lake Region...West Glacier Region.
ID...None.
&&
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https://www.twitter.com/NWSMissoulaPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MISSOULA MT
551 PM MST SUN DEC 2 2012
...TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
...DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0500 PM SNOW 9 SSW HAPPYS INN 47.97N 115.22W
12/02/2012 M2.8 INCH LINCOLN MT MESONET
REPORTED AT COOP STATION LYBM8 SNOW DURATION
24 HOURS
&&
IRIS SYSTEMPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MISSOULA MT
614 PM MST SUN DEC 02 2012
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0227 PM HEAVY SNOW 5 NNW EAST PORTAL 47.45N 115.69W
12/02/2012 M8.0 INCH MINERAL MT PUBLIC
8 INCHES OF SNOW IN THE LAST 24 HOURS AT LOOKOUT PASS SKI
AREA.
&&
KITSMILLERThe national radar mosaic for the moment the first event began.
1 heavy rain. Local standard time, as filed.
The Idaho Transportation Department reported a large rock slide that completely blocked U.S. Highway 95 at milepost 188 in the Salmon River canyon. Crews were able to open up one lane by the morning of December 3rd. It had been four to five years since there had been any similar problems in that area.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Idaho in 2012Every state in 2012This day in weather historyWarnings in Idaho, December 2012
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: 422472.