Backcountry Avalanche Forecast Sawtooth & Western Smoky Mtns This Avalanche Forecast is expired Issued Sunday, March 12, 2023 - 7:00AM Expires Monday, March 13, 2023 - 4:00AM Author: Ben VandenBos THE BOTTOM LINE Dangerous avalanche conditions exist. Human-triggered avalanches involving dense, 1-4 foot thick slabs of snow are likely. Avalanches may be very large and destructive and can be triggered from long distances away from steeper slopes. Conservative terrain selection is encouraged today. Avalanche Danger Monday, March 13, 2023 (Apparent error? - March 12 not 13) All Elevations: 3 - Considerable Avalanche Problem #1 Wind Slab All Aspects Above 7500' Elevation Likely Large (D2) Friday's storm brought 20-28" of snow (1.8-2.3" of SWE) to this zone. Snowfall was accompanied by strong winds blowing out of the SE-S-SW. This combination built very large, dense, 1-3 foot thick wind slabs on many slopes. Triggering a wind slab avalanche large enough to bury you remains likely today. Wind slabs will be largest and most broadly distributed in upper and middle elevation terrain. Wind slabs commonly form along ridgelines and near mid-slope terrain features like ribs and gullies. Large slabs also build at the base of large cliffs and on aprons below couloirs during storms, a common occurrence in the Sawtooths. Wind slabs and cornices that fail can be very effective triggers for the enormous, destructive persistent slab avalanches described below in Problem 2. Avalanche Problem #2 Persistent Slab All Aspects All Elevations Likely Large (D2) to Very Large (D3) Weak layers are buried underneath dense, 2-4 foot thick slabs of snow in this zone. This combination can produce very large avalanches capable of destroying a house. If you dig down, you'll find facet+crust combinations on slopes that face the sun and thicker stacks of weak facets on shaded slopes. Yesterday, an observer near Smiley Creek reported seeing multiple avalanches that had failed naturally on Eureka Peak in the Western Smokys. These slides broke hundreds of feet wide on E-NE facing slopes. Avalanches that fail on these layers can break very wide, wrapping around multiple aspects and connecting multiple avalanche paths. These slides can run the length of an avalanche path, impacting flat terrain long distances away from steeper slopes. Managing persistent slab problems is difficult. If you want to completely eliminate the risk of triggering one of these beasts you'll have to avoid avalanche terrain. You can reduce (but not eliminate) your risk by choosing gentler slopes that are sheltered from the effects of the wind. And don't forget to pay attention to what is above you, these avalanches can be triggered from long distances away from steeper slopes. Forecast Discussion Friday's storm produced a truly impressive cycle of natural avalanches. Avalanche activity was much most pronounced in our Galena Summit and Eastern Mtns and Soldier and Wood River Valley Mtns forecast zones. Head over to our Avalanche Database to browse through some of these, we've entered about 200 avalanches large enough to bury you that occurred since Friday. Notable avalanches include slides on Della and Carbonate Mountains west of Hailey that dammed the Big Wood River and hit several houses. We observed a number of very large natural avalanches in the Boulder and Smoky Mountains that broke thousands of feet wide. Natural avalanche activity was most widespread on Friday, though Scott observed 5 large natural avalanches that released in the Wood River Valley yesterday as well. The Avalanche Warnings have expired, but conditions remain dangerous. Avalanche accidents commonly occur during the period of decreasing danger following major loading events. This is exactly where we find ourselves today. The mountains may not be crashing down like they did on Friday, but that doesn't mean it's time to let your guard down. Human-triggered avalanches remain likely, and the slides you trigger will not be small. I recommend you head into the mountains with a conservative mindset today. If you are dead set on entering avalanche terrain, choose terrain where the consequences of being caught in an avalanche are lower. Your likelihood of surviving an encounter with an avalanche is greater in terrain free of terrain traps (creek bottoms, trees, rocks). If you just want to be outside in the mountains and come home safely tonight there are lots of great options; the skiing and riding are excellent in low angle terrain right now. Weather Forecast Yesterday was a wild day in the mountains and the valleys of our area. An intense storm tapped into moisture from an atmospheric river, bringing heavy snow and strong to extreme winds blowing out of the SE-S-SW. The Soldiers were the big winner on wind, recording a gust of 121 MPH yesterday afternoon. Heavy snowfall began Thursday evening and continued through most of the day Friday. Temperatures climbed through the first half of the storm, and some precipitation fell as rain on the floor of the Wood River Valley yesterday afternoon. Snowfall favored the mountains on the western and southern edges of our forecast area, where 14-20 inches of dense snow fell during the day. Less favored areas still managed to tally 10-16 inches of snow during this time frame. A cold front arrived in the afternoon, causing wind direction to shift to blowing out of the W-NW and briefly clearing the skies. Cloud cover increased late in the day, and an additional 1-5 inches of low density snow accumulated in the mountains overnight as temperatures dropped into the single digits to low teens F. Moderate to strong W-NW winds continued to blow overnight, though wind speeds are finally easing off this morning. Today will dawn with clear skies above the Wood River Valley, with cloud cover increasing slightly as you travel north. Expect to see plenty of sunshine across the forecast area today, with brief shady breaks provided by passing bands of clouds. Light winds blow out of the SW-W-NW as mountain temperatures climb into the upper teens to upper 20s F. Our northern mountains may see a few brief flurries of snow in the afternoon hours, but these will be short-lived and no accumulating snow is expected. Overnight, temperatures drop into the single digits to low teens F and pockets of clouds continue to pass over the region. Winds remain light and continue to blow out of the SW-W. Tomorrow will be similar to today, with a weak storm moving into the area late in the day. Snow totals look to be in the 1-5 inch range on this one, with snowfall favoring our western mountains. A double-hitter of warm, wet storms arrives on Monday and Tuesday. It's too early to have much confidence, but I'm seeing the possibility for another 1-2 feet of snow accumulating in the mountains by Wednesday.