USGS officials are holding a news conference right now, and have just announced an explosive event on Mt St Helens is possible, and the alert level has just been raised by the USGS for the mountain. The lava dome in the crater has apparently moved a measurable amount, and seismic activity has taken a noticible upturn.

They are now seeing quakes at the rate of 4 a minute. They are larger quakes, 2 to 2.5 in magnitude. Describing the seismic activity, they say it is definitely ramping up and plateauing in phases, not falling back down. Explosion and ash are the risks. This behavior is similar to what was observed on the mountain in 1986: Big increases in seismic energy over past 8 hours.

I'm at the airport flying out to Reno at 12:45, mobile posting from my handheld device. I hope it keeps its top on.

Update: USGS Advisories and information about the mountain activity available here.