An unknown number of back-country skiers are missing after an avalanche hit Tuesday morning in the Castle Peak area near Donner Pass, as some parts of the Sierra experience their harshest winter conditions in three years.

The Bay Area obviously remains pretty stormy today, and as it does every winter, that means very treacherous winter storm conditions up near Donner Pass. So treacherous, in fact, that KTVU is reporting that the UC Berkeley Central Sierra Snow Lab said parts of the Sierras are “being hit with the worst winter conditions in three years, with more than five feet of snow expected in a matter of days.” So that’s alarming enough, but much more seriously, that same KTVU report informs us that an unknown number of back country skiers are missing after an avalanche that hit at about 11:30 am Tuesday morning.

At this point, we don’t know much more than what was communicated above by the Nevada County (California) sheriff’s department. “The Nevada County Sheriff's Office along with our Nevada County Sheriff's Search & Rescue team and allied agencies, are responding to a report of an avalanche in the Castle Peak area that occurred at approximately 11:30 am today,” that department posted to Facebook just after noon Tuesday. “It has been reported that a group of back country skiers was involved in the incident, with several members of the party missing at this time.”

Search and rescue teams from the Nevada County Sheriff's Office have been deployed. The problem is, they don't know how many potential injured or affected victims they are looking for, and they’ve a pretty wide area to cover. To reiterate, the only information they have is that "a group of back country skiers” was potentially caught up in the avalanche,” and that “several members” of that ski party are currently missing.

If you’re not familiar, Castle Peak is on the California side of the California-Nevada border along I-80 near the Donner Summit and Truckee. It’s about two miles north of the popular resort Boreal, and one of the more popular back-country ski spots in the region.  

That area was already under an avalanche warning when the suspected avalanche hit Tuesday morning, and that avalanche warning is expected to remain in effect through Wednesday morning at 4 am.

Related: Storm Impacting Bay Area Roads; Chain Controls In Effect on I-80 In Tahoe Area [SFist]

Image: Nevada County Sheriff's Search & Rescue via Facebook