Warm, summer-like temperatures are coming to Mount Rainier this week. And with this rapid change in temperature will come rapid changes to the snowpack as it transitions from cold, wintery snow into consolidated spring snow. This isn't terribly surprising since the freezing level is climbing from roughly 2500' last week to well over 10,000' this week!
The Northwest Avalanche Center (NWAC) has issued a special avalanche bulletin due to these warm temperatures. Read their forecast and discussion here.
If you're planning to visit the park this week, be especially cognizant of overhead hazards like cornices and hanging snowfields that will weaken and may collapse as the mercury rises. Other hazards may include rapidly opening creeks, difficult travel conditions, and possibly very large, deep slab avalanches. Be on the lookout for signs of avalanche activity including pinwheel-shaped avalanche debris, and deep, sloppy postholing. Select conservative terrain and remember that conditions will change rapidly as temperatures climb throughout the day.