Avalanche Forecast

Sunny, warm weather is expected on Thursday.

Loose wet avalanches, mainly involving any recent storm snow from Monday and Monday night, will be possible on any steep slope, especially during the warmest part of the day Thursday afternoon. Pay attention to the integrity of surface crusts formed overnight. Backcountry travel early in the day is recommended since conditions can change rapidly due to daytime warming. Watch for wet snow deeper than your boot tops especially on steep solar slopes during the midday and afternoon hours.

The likelihood of cornice releases will continue on Thursday from intense solar radiation and warming temperatures. Cornice releases can be unpredictable during the spring so avoid areas below cornices and remember that cornices can break much further back than expected along ridges.

Any wind slab deposits caused from the snow received Monday, in combination with moderate westerly winds should have mostly stabilized by Thursday and wind slab won't be listed as an avalanche problem on Thursday. However, continue to watch for signs of wind slab mainly on north to east facing slopes above treeline where extra caution is warranted.  Firm wind transported snow and snowpack cracking can be good signs of wind slab layers.

Although not listed as an avalanche problem, large, powerful glide avalanches can release unexpectedly so avoid areas below steep unsupported slopes or rock faces.

Avalanche activity on Thursday is not expected to be as extensive as during the warm weather last week which more closely followed a period of heavier snowfall and already caused consolidation and some stabilizing. Hence the moderate avalanche rating in all areas. But heat related small to large loose wet avalanches, cornice releases and glide avalanches will be possible on Thursday. You will need to be able to evaluate avalanche conditions on specific terrain features and change your plans if snow conditions are more dangerous than expected.

Weather and Snowpack

A large upper ridge dominated the weather last week through early Sunday, resulting in very warm and dry weather. A spring avalanche cycle occurred in most areas over this stretch, likely peaking Thursday or Friday during the warmest temperatures and lightest winds. After a stormy March, the snowpack has undergone significant settlement and multiple melt-freeze cycles over the last week.

A front moved across the Cascades early Monday morning, resulting in a period of mostly light to moderate precipitation, cooling and moderate westerly crest level winds.  Precipitation transitioned from rain to snow as cooling occurred, forming a generally good bond to the old melt freeze crust. Showers at cooling temperatures occurred overnight Monday through Tuesday. NWAC stations along the west slopes received storm snow amounts ranging from 3-9 inches as of Tuesday. A convergence zone helped the Stevens Pass area Monday night, depositing the most snow with about a foot of new by Tuesday morning.

Another upper ridge is currently over the Northwest causing sunny weather and warm temperatures.

Frequent March storms have built unusually large cornices along many ridges.

The mid and lower snowpack along the west slopes should generally be a stable mix of crusts and layers of moist and rounded snow crystals.

Recent Observations

Numerous professional and recreational observations focused on the spring avalanche cycle that occurred last week throughout the west slopes of the Cascades.  

On Saturday 4/2, a cornice failure and wet snow avalanches were observed above treeline on the Worms Flow route on Mt. St. Helens reported via the NWAC observation page. A large wet snow avalanche was also reported from Chair Peak that ran to Source Lake at Snoqualmie Pass via Turns All Year.

A brief transition back to winter like weather was reported by Dallas Glass in the Paradise area on Monday 4/4. Dallas observed the new storm snow was scoured down to the melt-freeze crust on wind exposed, westerly facing slopes, while some leeward, easterly facing slopes, received as much as 6-12 inches of wind loaded new snow as of Monday afternoon. However, a good bond was reported to the old crust layer with evidence of rain near treeline. No signs of recent avalanches were noted with no evidence of new storm slab development.

NWAC observer Lee Lazzara was in the Mt Baker backcountry Tuesday 4/5 and reported about 4 inches of storm snow, well bonded to the moist old melt-freeze layer. There were some specific features that had up to a foot of wind loaded snow, but good bonding and settlement kept that snow from moving. He was out again in Swamp Creek drainage on Wednesday 3/6 and found similar conditions. Debris from a large heat related avalanche was seen from a steep, complex northwest facing slope. The main take away currently in this area is to continue to be aware of the potential for low probability/high consequence encounters, such as cornice failures and glide avalanches from steep unsupported slopes and smooth rock faces.