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Daily Winter Weather Report

Date: Saturday - December 17, 2011

Station Max Temp Min Temp Pres Temp New Snow Depth Sky Present Conditions

East Entrance 25 3 4 0 16 BC Calm
Grant Village 21 12 12 0 22 SC Calm
Lake 22 9 9 T 15 BC Lt Snow

Madison 21 8 10 0 12 OC Calm
Mammoth 31 19 24 0 5 OC S@2-4mph
Old Faithful 22 2 2 T 13 SC Calm

Snake River

Soda Butte

Thumb Divide

West Entrance              
T=Trace / BC=Broken Clouds / OC=Overcast / SC=Scattered Clouds
All Temperatures are in °F ~ All Snow Depths are in Inches

* * * Road Conditions * * *
Road Section Status Conditions Public Access / Info
Gardiner to Mammoth YR Good STA
Mammoth to Tower YR Good STA
Tower to NE Entrance YR Good STA
Beartooth Highway CLOSED * CLOSED * CLOSED *
Firehole Canyon Drive CLOSED CLOSED CLOSED
Grant to South Entrance Open   Rubber tracked oversnow concession vehicles
Junction to Chief Joseph Hwy CLOSED * CLOSED * CLOSED *
Lake to East Entrance CLOSED CLOSED CLOSED
Madison to Old Faithful Open   Rubber tracked oversnow concession vehicles
Madison to West Yellowstone Open   Rubber tracked oversnow concession vehicles
Mammoth to Norris Open   Rubber tracked oversnow concession vehicles
Norris to Canyon Open   Rubber tracked oversnow concession vehicles
Norris to Madison Open   Rubber tracked oversnow concession vehicles
Old Faithful to Grant Open   Rubber tracked oversnow concession vehicles
Tower to Canyon CLOSED * CLOSED * CLOSED *

YR=Year Round / NR=No Restrictions / STA=Snow Tires Advised / STR=Snow Tires Required


# Poor road conditions - bare spots and melting snow - Restricted to Snowcoaches Only.

The park service plowing schedule for roads for the spring season.

******** FOR CURRENT ROAD INFORMATION PLEASE CALL 307-344-2117 ********


Yellowstone Forecast on December 17, 2011
by the National Weather Service Riverton, WY

Saturday: Sunny, with a high near 29°F and a low around 5°F. Wind chill values as low as -5°F. West southwest wind around 6 mph.

Sunday: Partly sunny, with a high near 28°F and a low around 3°F. Southwest wind around 8 mph.

Monday: Mostly sunny, with a high near 24°F and a low around -3°F. North northeast wind between 3 and 5 mph.

Tuesday: Mostly sunny, with a high near 23°F and a low around 4°F.

Wednesday: A slight chance of snow. Partly sunny, with a high near 20°F and a low around 1°F.

Thursday: A slight chance of snow. Partly sunny, with a high near 15°F and a low around -8°F.

Snowflake Hazardous Weather Snowflake Gibbon Falls Forecast Snowflake Mammoth Forecast Snowflake Midway Forecast Snowflake Norris Forecast Snowflake Old Faithful Forecast Snowflake

* * * Snow Depth Totals as reported at SNOTELs * * *
Station Depth (inches) Station Depth (inches)
Black Bear 35 Parker Peak 33
Blackwater 36 Snake River Station 19
Canyon 18 Sylvan Lake 27
Evening Star 35 Sylvan Road 17
Fisher Creek 43 Thumb Divide 20
Grassy Lake 27 Two Ocean Plateau 42
Lewis Lake Divide 29 West Yellowstone 14
Madison Plateau 24 Whiskey Creek 19
Northeast Entrance 11 Wolverine 14

Avalanche Information
from the Gallatin National Forest Avalanche Center - December 17, 2011 - this report is by Mark Staples. This advisory does not apply to operating ski areas.

Mountain Weather

This morning temperatures were near 20 degrees Fahrenheit except near Cooke City and West Yellowstone where temperatures were near 10 degrees Fahrenheit. Winds this morning varied across the region blowing from all directions on the western half of the compass. At ridgetops near Bridger and Hyalite Canyon winds were blowing 20-40 mph, near Big Sky 5-15 mph, and further south near West Yellowstone and Cooke City 5-10 mph. No snow fell overnight and none is expected today which will have mostly sunny skies and temperatures approaching 32 degrees Fahrenheit. Westerly winds will blow 10-20 mph.

Curious why La Nina hasn't brought more snow to Southwest Montana? Read a brief explanation from the National Weather Service office in Missoula here.

Snowpack and Avalanche Discussion:

The Bridger, Gallatin and Madison Ranges, the Lionhead area near West Yellowstone and mountains around Cooke City:

The snowpack is weak in most places especially where it is less than 2 feet deep. Near West Yellowstone yesterday during an avalanche class, Eric found a snowpack that is one big weak layer containing depth hoar, near-surface facets, and surface hoar. Similar conditions can be found in many other areas. The missing ingredient for an avalanche in these areas is a slab.

Some places have a slab on top of the snowpack. Near Beehive Basin yesterday, skiers found a recent human triggered avalanche about 8 inches deep and 10 feet wide. This avalanche slid on weak faceted crystals that formed on the snow surface prior to Wednesday's snowfall. While most areas only received a few inches from that storm, upper parts of Lone Mountain received 8-12 inches. Watch for isolated areas with this much new snow OR places with wind deposited snow. These areas have a slab that can produce human triggered avalanches.

Other places have a slab in the middle of the snowpack. The mountains near Cooke City and Hyalite Canyon have a snowpack with depth hoar crystals near the ground, a slab in the middle, and more facets on top. In these places the snowpack has not been stressed with significant snowfall. (What is significant snowfall? See note below.) In areas like these, the snowpack has all the ingredients for an avalanche. While human triggered avalanches are not likely, they remain possible.

Today, slopes with a snowpack deeper than 2 feet have a slab and a weak layer present making human triggered avalanche possible. These slopes or any with wind deposited snow have a MODERATE Avalanche Danger. Slopes without wind deposited snow and a shallow snowpack less than 2 feet do not have a slab to make an avalanche. These slopes have a LOW Avalanche Danger.

What is significant snowfall? When assessing stability we care how much weight was added to the snowpack. Because some snow is wet and heavy and other snow is light and fluffy, we focus on the amount of water contained in this snow. The measurement is called snow water equivalent (SWE). It is how much water you would have if you melted the snow. Luckily an extensive network of remote SNOTEL sites measures SWE. During winter in Montana 1 inch of SWE usually means about 1 foot of snow, and this is a significant amount if it falls in less than 24 hours. With such a weak snowpack right now, even a .5 inch of SWE falling overnight would be concerning.

The next advisory tomorrow morning at 7:30 a.m. If you have any snowpack or avalanche observations, drop us a line at or call us at: 406-587-6984.


1. We've recently uploaded more photos and snowpits to our web site, more than what are linked in the advisory.

2. We're creating a series of "How To…" stability test videos. So far we've got clips on performing a CT and ECT. There are located under Stability Tests on the Resources page.

Information provided by Doug Chabot, Mark Staples, and Eric Knoff from the Gallatin National Forest Avalanche Center. For Photos and Videos, please visit the Avalanche Centers Website!

If you have any snowpack or avalanche observations, drop them a line at or call: 406-587-6984.

For detailed Avalanche Terms utilized here, please see the Avalanche Glossary.

Avalanche Danger Scale

Back to the Yellowstone Daily Winter Reports or the Yellowstone Weather Page

Information provided by Yellowstone National Park, National Weather Service and Gallatin National Forest Avalanche Center

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