Avalanche Forecast Snoqualmie Pass

Thursday 24th January 2019

Avalanche Danger Ratings Thu 24th Jan 6:00PM Danger Ratings Alpine: Moderate Danger Ratings Treeline: Moderate Danger Ratings Below Treeline: Low Storm Slabs Storm Slabs Loose Wet Loose Wet

Forecaster: Dallas Glass

Date Issued:

Valid Until:

The Bottom Line: The snowpack in the Snoqualmie Pass area seems to be gaining strength. That doesn’t mean we are out of the woods yet. You may still find pockets of unstable storm snow at higher elevations, and in wind prone areas. When the sun comes out, snow conditions can change quickly, and may produce loose wet avalanches.

Snow and Avalanche Discussion

Thursday was pretty quiet in the Snoqualmie Pass area. We did not receive reports of any new, notable avalanches. However, evidence of Wednesday’s avalanche cycle was easy to find. Debris from several large and very large avalanches was observed on Denny Mountain and around Source Lake.

Very large natural avalanches on Chair Peak from Wednesday’s avalanche cycle: Photo: Jeremy Allyn

The layer of buried surface hoar from January 17 is not as prevalent near Snoqualmie Pass, as it is in the nearby Stevens Pass and East-Central zones. That doesn’t mean it is absent. You would be most likely to find this persistent weak layer 1-2 ft below the snow surface in areas near Stampede Pass, or valleys outside of the main Pass locations.

The lower elevation snowpack continues to creep and glide under the weight of recent rains. While no glide avalanches have been reported, they are on our mind. If you see crevasse like features on a slope, limit you exposure by avoiding traveling on or below these areas.

Expect difficult travel conditions at lower elevations including breakable crust, wet heavy snow, and open creeks.

Weather Forecast

Fri 25th Jan 16:19 - Robert Hahn

Weather Synopsis for Friday night through Sunday

The high-amplitude upper-level ridge offshore pushes slightly further into the region with temperatures aloft warming further tonight into tomorrow, giving us the warmest temperatures we've experienced since November over our mountains by late Saturday into Sunday. Weak systems are spilling over the top of the ridge into SE Alaska and are dropping south through the Rocky Mountains, leaving our region largely unimpacted. Low-level moisture is generally decreasing, so clouds should be mostly clearing out on Saturday. Low-level inversions and fog or freezing fog are likely in some locations. Saturday will be the warmest day for our mountains since November 19th, with freezing levels pushing 11000 ft. On Sunday, a trough moving east along the Rockies will knock back temperatures slightly in our region, but it will remain unseasonably mild.

Regional Synopsis

Sun 20th Jan 09:00

January 20, 2019

The recent weather pattern of lower accumulation storms (by NW standards) and longer stretches of calm weather should continue as we move into late January. Since January 17th, incremental snow accumulations punctuated with rising freezing levels favored the south and eastern parts of the region. Storm instabilities have risen with storms and gradually subsided.

A storm slab at Mt Baker.

New Snow Problems

Storms over the past week have brought a range of layers from rain crusts, to heavy moist snow, to stiff drifts, to light dry powder. Some storm days, like the 18-19th, saw reactive, but very short-lived avalanches caused by heavy precipitation and wind. Even the longer-lasting avalanche problems, wind slabs, haven't persisted for more than a few days. Where the recent snow is stressing underlying weak layers, more dangerous avalanche conditions have prevailed.

Surface hoar in the East Central zone

Old Snow Problems

Persistent weak layers (PWLs) have been a constant in the eastern zones of the Cascades this winter. As usual, they have been much less problematic at the Passes and west of the Cascade Crest. The latest PWL is a layer of surface hoar, buried around January 17th and found generally east of the Cascade Crest. Buried surface hoar is an active weak layer in the eastern zones and can be found to a limited extent on the eastern edge of the Stevens and Snoqualmie Pass zones. There few, if any, avalanches have been reported on the buried surface hoar. It may be most problematic in open, wind-sheltered terrain, especially well above the valley floor.

You are most likely to find other layers of old weak snow the further you move east from the Cascade crest. Here snowpacks are shallower, more variable, and generally weaker. In some locations, weak snow near the ground can still be found. These basal facets have hung around all season. Digging profiles and using snowpack tests is the best way to gain information about these old persistent weak layers. However, snowpack tests are just one piece of the puzzle. Your terrain decisions shouldn't hinge on any given test result. Because of the size of our forecast zones and the variability in the snowpack, it's important to make snow observations as you travel. We’ll keep watching these old layers, but let us know what you see while you are in the mountains.

Storm Slabs Storm Slabs



Expected Size

2 - 2

Recent storm snow should be gaining strength. However, we have a high degree of uncertainty at higher elevations. You may still trigger lingering storm slabs on very steep slopes, near convex rollovers, or in unsupported terrain. If you see evidence of wind drifted snow, storm slabs in these areas may be deeper and easier to trigger. A little patience and caution will go a long way if you are traveling into alpine areas or more remote locations.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Loose Wet Loose Wet



Expected Size

1 - 2

Warm air temperatures and sunshine will continue to create wet snow surface conditions on steep southerly slopes. Be leery of sun-exposed terrain, particularly after a few hours of direct sun. If you see rollerballs or experience wet surface snow deeper than you ankle, loose wet avalanches are becoming more likely on similar slopes. Even small loose wet avalanche can be harmful if you are in confining terrain features, such as gullies or chutes.

Aspects: South East, South, South West.

Elevations: All elevations.

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