Avalanche Advisory Archive 2016 – 2018
|Date Issued:||2017-04-05 06:42:21|
With the warmest day of the year and no freezing overnight expect to see small wet loose avalanches as trees, rocks, and steep open faces shed their winter coat.
Remember if these small wet loose slabs find the deeper instability they will then fracture out into wet slab avalanches.. these would be much larger with much higher consequence.
Be aware that with these very warm temps and no freezing overnight this adds to the concern.
The deep persistent slab remains. Any place that has not slid remains suspect. Also with new high temps and warming deeper into the snowpack we will start to test every weak layer from the season...
With above freezing temps these could also be viewed as wet slab avalanches... but I am leaving them highlighted as deep persistent weak slabs so you understand these are LARGE slides going a meter plus deep on the deeper weak layers we have been seeing for some time.
Be aware that until temps cool danger will be elevated.
The National Weather Service Forecasts-
Today- Rain in the morning, then widespread rain showers in the afternoon. Highs around 45. Southeast wind 10 mph increasing to 20 to 30 mph with gusts to 40 mph in the afternoon, then diminishing late.
Tonight- Widespread rain showers. Lows around 37. Southeast wind 10 to 15 mph.
Thursday- Widespread rain showers in the morning, then scattered rain showers in the afternoon. Snow level 1400 feet. Highs around 45. Southeast wind 10 mph.
Yesterday saw the warmest temps of the winter/spring thus far... Eaglecrest saw a high of 42 yesterday and is currently at 39f in the base area and 34f on top. Mt Roberts was even warmer yesterday with a high of 45f. Currently its 38f after dipping to a low of only 36f.
Winds are moderate blowing 15-20 but don't have much snow to transport.
With prolonged warming we start to worry about an isothermal snowpack and testing previous weak layers as the upper layers of the snowpack develop a lot of free moisture. This adds a lot of liquid to the snowpack and acts as lubrication. Eroding the bonds in the snow and placing more stress on the weaker deeper layers in the slab.
We have seen a tremendous amount of avalanche activity over the last 6 weeks. Anything that has not slid is suspect at this time... we have a widespread persistent weak layer that is still showing its ugly head.
With prolonged warming even areas that have avalanched and stripped the upper weak layers are suspect. This is the spring meltdown and we will start to see the layers of the onion peeled back. One wet avalanche at a time... Should these loose wet avalanches find weakness in the slab they will cause enough stress to fracture the slab to a bigger deeper avalanche...
Now is a good time to stay away from large historical avalanche paths.
We will see wet loose avalanches on may aspects today with the temps in place. If we see any sun at all expect that weakness to be exaggerated on south to SW faces although the forecast is not calling for much in the way of sun.
The forecast is calling for around .3\" of precip over the next 24 hours. This too adds stress to the snowpack and erodes the bonds even faster also placing additional load on the slab... This will increase weakness.
If you see rain volumes beyond expected please recognize danger is climbing faster than expected.
With natural and human triggered avalanches both possible today avalanche danger is CONSIDERABLE at this time.
Please avoid avalanche zones especially big ones with high consequence.
Release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very destructive.
Avoid terrain where and when you suspect Wet Slab avalanche activity. Give yourself a wide safety buffer to handle the uncertainty.
How they form
Liquid water, from snowmelt or rain-on-snow, moves through the layers of the snowpack at different rates. Wet Slab avalanches happen when a weak layer or interface becomes moist, wet, or saturated. The wet snow loses strength, and the snow above fails and avalanches. Wet Slabs fail because of a decrease in layer strength, compared to dry avalanches that often fail because of an increase in load.
Where they are
Wet Slabs often occur first at lower elevations and areas with a shallower snowpack. Facets and depth hoar layers are especially weak when wetted. After several nights of above-freezing temperatures, wet slabs can occur on many aspects.
In most climates, Wet Slabs are spring-time events. This is when temperatures are warm and snowmelt produces sufficient free water to lubricate the snowpack. Earlier in the spring, the avalanche pattern can be cyclical, occurring in the afternoon or evening hours as melt-water accumulates, and decreasing in the morning as the snowpack cools. Later in the spring, extended periods of above-freezing weather contribute to the problem. The cyclical pattern decreases and it is possible for wet slab activity to occur at any time. In Colorado, one of the indicators of Wet Slab avalanches is two or three nights where temperatures do not drop below freezing.
Snowballing, pinwheels, and small Wet Slabs indicate the potential for larger Wet Slabs. Recent Wet Slab avalanches indicate the type of terrain another cycle will occur on, if similar conditions recur. Temperature data from remote weather stations can be useful to monitor overnight temperatures, watching for the periods of little or no overnight freeze.
Treatment and Avoidance
In many cases, snow conditions are poor when Wet Slabs are a significant problem. Most people leave the mountains or find places with firmer, less slushy snow and away from the slopes where Wet Slabs are a problem. Recognizing the weather factors that lead to Wet Slabs will help you avoid them. When solar radiation is a primary factor, carefully selecting and moving aspects through the day can be effective. Avoid terrain where and when you suspect Wet Slab avalanches. Give yourself a wide safety buffer to handle the uncertainty