This avalanche advisory is provided through a partnership between the Tahoe National Forest and the Sierra Avalanche Center. This advisory covers the Central Sierra Nevada Mountains between Yuba Pass on the north and Ebbetts Pass on the south. Click here for a map of the forecast area. This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires 24 hours after the posted time unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.

This advisory was posted on February 18, 2008 7:00 AM
Click here for a detailed map of the SAC forecast area

1_low
Today's Advisory:

This morning, avalanche danger is LOW for all elevations and aspects. Isolated areas of MODERATE avalanche danger will develop on SE-S-SW aspects steeper than 37 degrees that experience significant sun exposure today.

The high pressure ridge remains over the area keeping temperatures warm today. A weak low pressure system should start to impact the forecast area later today and tomorrow bringing slightly cooler temperatures, cloudy skies, more wind, and slight chance of snow showers. Temperatures climbed into the mid to upper 40's above 8000' across the forecast area again yesterday before dropping back below freezing overnight. Remote sensors show that they have already started warming back up at the higher elevations with some sensors reading in the mid 30's by 6am.

Increased cloud cover forecasted for this afternoon should limit the amount of solar radiation that can melt the upper layers in the snowpack. Yesterday only the top 3 to 5 inches of snow on sun exposed southerly aspects softened. These snow surfaces refroze overnight due to radiational cooling and below freezing air temperatures. Melt water that forms due to daytime warming should dissolve some of the bonds between the refrozen snow grains and areas of wet surface snow instability may form on steep SE-S-SW aspects. Low sun angles and forecasted cloud cover should lead to less melting and less melt water infiltrating the snowpack. Melt water pathways that drain this water through the snowpack have formed during this prolonged melt/freeze cycle. These things should help keep wet snow instability from becoming widespread today. If the forecasted cloud cover does not occur expect more wet snow instability to form. Below this surface layer of melt/freeze snow, observations continue to show a strong, well bonded snowpack. On the northerly aspects snow surfaces remain cold and observations show a strengthening snowpack below the surface. Today snow surface conditions will continue to be a mix of wind affected surfaces on northerly aspects above treeline; pockets of soft snow on shaded, wind sheltered northerly aspects below treeline; some melt/freeze crusts below 7500' on all aspects; and corn/crust snow conditions on the southerly aspects.

Isolated areas where human triggerable wet snow avalanche activity is possible could form today on steep SE-S-SW sun exposed aspects due to daytime warming. Most of this activity should be in the form of wet surface instabilities like pinwheels and point release avalanches. Wet slab avalanche activity is unlikely but it is not impossible today. Simple clues and tests like pinwheels, roller balls, and how deep boots penetrate into wet snow (ankle deep or deeper is a bad sign) are good indicators of when it is time to find more frozen slopes.

The bottom line: This morning, avalanche danger is LOW for all elevations and aspects. Isolated areas of MODERATE avalanche danger will develop on SE-S-SW aspects steeper than 37 degrees that experience significant sun exposure today.

Please send us your snow, weather, and avalanche observations by clicking the submit observations link on our contact page.

Andy Anderson, Avalanche Forecaster

Today's Central Sierra Weather Observations:
0600 temperature at Sierra Crest (8,700 feet): 32 deg. F
Max. temperature at Sierra Crest past 24 hours: 46 deg. F.
Average wind direction at Sierra Crest past 24 hours: Northeast shifting to the southwest
Average wind speed at Sierra Crest past 24 hours: 15 mph
Maximum wind gust at Sierra Crest past 24 hours: 35 mph
New snow fall at 8,200 feet past 24 hours: 0 inches
Total snow depth at 8,200 feet: 79 inches
Mountain Weather Forecast For Today:
Partly cloudy this morning becoming mostly cloudy this afternoon.
Temperature forecast for 8,000 to 9,000 feet: 40 to 46 deg. F
Ridgetop winds forecast for the Sierra Crest: South at 10 to 15 mph
Snowfall expected in the next 24 hours: 0 inches
2 Day Mountain Weather Forecast:

7000 to 8000 Feet:
Today, partly cloudy this morning becoming mostly cloudy this afternoon with daytime highs 47 to 53 deg. F. Winds out of the southeast at 10 mph.

Tonight, mostly cloudy skies with overnight lows 22 to 28 deg. F. Winds out of the south at 10 mph.

For Tuesday, mostly cloudy with a slight chance of snow showers in the afternoon. Daytime highs 43 to 49 deg. F. Winds out of the southwest at 10 to 15 mph with gusts to 25 mph.

Above 8000 Feet:
Today, partly cloudy this morning becoming mostly cloudy this afternoon with daytime highs 40 to 46 deg. F. Winds out of the south at 10 to 15 mph.

Tonight, mostly cloudy skies with overnight lows around 24 deg. F. Winds out of the southwest at 10 to 15 mph with gusts to 25 mph.

For Tuesday, mostly cloudy with a slight chance of snow showers in the afternoon. Daytime highs 36 to 42 deg. F. Winds out of the southwest at 10 to 15 mph with gusts to 30 mph increasing to 15 to 25 mph with gusts to 40 in the afternoon.

The bottom line:

Andy Anderson - Avalanche Forecaster, Tahoe National Forest

Weather Observations from along the Sierra Crest between 8200 ft and 8800 ft:

0600 temperature:	deg. F.
Max. temperature in the last 24 hours:	deg. F.
Average wind direction during the last 24 hours:
Average wind speed during the last 24 hours:	mph
Maximum wind gust in the last 24 hours:	mph
New snowfall in the last 24 hours:	O inches
Total snow depth:	inches

Two-Day Mountain Weather Forecast - Produced in partnership with the Reno NWS

For 7000-8000 ft:
	Monday:	Monday Night:	Tuesday:
Weather:
Temperatures:	deg. F.	deg. F.	deg. F.
Wind direction:
Wind speed:
Expected snowfall:	O in.	O in.	O in.
For 8000-9000 ft:
	Monday:	Monday Night:	Tuesday:
Weather:
Temperatures:	deg. F.	deg. F.	deg. F.
Wind direction:
Wind speed:
Expected snowfall:	O in.	O in.	O in.