A “persistent weak layer” is just that: a weak layer beneath the snow that sticks around and causes avalanche problems. That’s because newer snow on top slides off of the weak layer, rather than bonding to it.
PWLs are often caused by facets: shiny and crystalline bits of snow that don’t sinter. Faceted snow is sometimes mistaken for powder.
Northern Utah formed a faceted PWL in December, and it has been dogging backcountry skiers and riders ever since.
But now the Utah Avalanche Center reports that layer, which is 4 to 8 feet deep, is healing. UAC forecaster Trent Meisenheimer said the problem is currently isolated to steep, rocky and unsupported terrain.
“It’s becoming more and more unlikely to trigger that layer,” Meisenheimer told KPCW.
But he also said a brand new weak layer just formed last week.
“On Valentine's Day, we had the sun warm up the southerly-facing slopes just a little bit, and then it snowed on top of that,” Meisenheimer said. “We've actually seen some avalanches break to that crust.”
The new PWL is mostly between the west and southeast sides of the compass, according to Meisenheimer. It’s just 1 to 3 feet below the surface, meaning it may be easier to trigger.
On top of that, there’s considerable new snow from the latest storm, which brought more than a foot to most northern Utah resorts over 48 hours.
Meisenheimer quoted his colleague Drew Hardesty, who likes to say “the glue is yet to dry.” Patience is recommended.
The top avalanche problem as of Feb. 21 is wind-drifted snow. Click here for the latest forecast.