Alrighty, we're getting a ton of phone calls about what we think the weather is going to do this weekend. Here's my best guess:
First: Use this forecast model from the University of Washington. It shows the pressure systems at the 500mb heights (approx 17,000 feet). You can see the upper level low pressure circulating and creeping towards Washington State. The upper level low pressure has been creating unstable air and has been the source of much of our precipitation and clouds over the last couple of weeks. As the low ciculates, grabs moisture from the ocean, it's already cool, and it brings it right to the cascades. As the moisture goes over the mountains, it is cooled as it is forced up, which it will readily do because of the already present unstable low pressure system. That causes the clouds and precipitation.
The next model can be accessed here: University of Washington 4/3km Profile. This model is a x-section of the atmosphere from 0 - approximately 17,000 feet. The red lines are humidities. Here you can see the effect of surface warming each day and the low level instability that creates.
This system is different. There is upper AND lower level low pressure giving high high lapse rates that make clouds and precipitation probable along Mt. Rainier's entire elevational profile.
So do proceed with caution. If you're bent on coming out for a try, please bring some navigational aids like a GPS and a compass and map and know how to use them. Bring extra warm clothes and the sturdier tent. Get a good weather briefing from the CIC before you head up.
With snowfall and precipitation and wind comes avalanche danger. No one issues an avalanche forecast for Mt. Rainier in June. However, there are plenty of anecdotal observations coming in from rangers, climbers, and guides. Yes, there is some observed instability over the last two days. Easy to moderate failures have been observed both yesterday and the day before at and above 11,000. However, climbers did summit yesterday and today on the disappointment cleaver.
I anticipate that through the next 48 hours, climbing above high camps will be limited. It's still too soon to tell about Saturday night and Sunday.