Avalanche Forecast

New snowfall received Saturday night and Sunday may bond poorly to thin melt-freeze/sun crusts found at lower elevations and solar aspects. Heavier showers Sunday will promote storm instabilities within the new snow.  More snowfall is expected near and south of Mt. Rainier Sunday during the daylight hours. A Puget Sound Convergence Zone may produce locally heavy snowfall Sunday evening between Stevens and Snoqualmie Passes. Pay attention to quickly changing surface snow characteristics; April avalanches involving new snow often catch those expecting a more predictable spring regime. Last year, we had 2 avalanche fatalities in mid-April. 

New snowfall will still be susceptible to strong spring solar effects and daytime warming Sunday despite the cool snow levels and mostly cloudy skies forecast. Watch for wet surface snow deeper than a few inches, natural or triggered snowballing, and small natural wet loose avalanches which usually precede larger avalanches on solar slopes.

New wind slab should build on Sunday on lee slopes mainly above treeline. Watch for signs of firmer wind transported snow or cracking snow. 

Despite the cool temperatures recent loading and daytime warming will continue to stress cornices.  Give them a wide berth and avoid travel below them...especially in the afternoon. 

The last full week of April has felt more like winter than spring; the Forks, WA freezing level has averaged 4300 feet over the last week which is almost a 1000 feet lower than the average for the entire month of March. Upper NWAC stations at Green Valley, Crystal Mt, Paradise, MRNP, top of Alpental (measured by ski area), Snoq Pass, Pigtail Peak, White Pass, and Timberline, Mt. Hood all experienced a second snowdepth maximum with snowdepths equaling snowdepths from late March or the first week of April. While your favorite ski area or trailhead parking lot might be looking a bit sad this time of year...keep in mind there's still plenty of snow the higher you go.

Water equivalents at NWAC stations near and west of the crest for the 4 days ending Friday morning are 1.5-3.5 inch range with the most at Paradise and Mt. Baker. Snowfall received during the span in the near treeline zone is in the 1-2 foot range with the most at Paradise and the top of Alpental, and with more snow at higher elevations.  East of the crest stations received about 0.5-1 inch of water during this 4 day stretch. 

Generally cold temperatures, light winds and light snow showers with sunbreaks were seen on Friday and Saturday...allowing for gradual settlement of this week's snow but also potentially preserving any recent wind or storm slab instabilities in the near and above treeline zone especially on non-solar aspects.  Breakable melt-freeze crusts have been reported at lower elevations and on slopes receiving sunbreaks.  

Avalanche observations (note that we receive far less observations than during winter):

Mt. Baker:  On Friday near Church Mtn, Brian Kennedy reported small wet loose slides on solar aspects becoming more reactive in the afternoon with sunbreaks and warming with a few point releases stepping down and entraining soft slabs about 20" (50 cm) down, but not propagating. 

Alpental: The Alpental ski patrol reported a widespread natural avalanche cycle Wednesday night followed by easy ski triggering in the above and near treeline zone Thursday producing 8-12" storm slabs. Large wet loose avalanches were easily ski triggered below treeline Thursday.  With explosives Friday, Alpental patrol produced loose slides that entrained and ran further than the Wed night natural cycle. Ski cuts Friday produced isolated soft slabs. 

Chinook Pass: On Thursday morning the DOT crew reported a large wet loose avalanche that reached the road entraining 12-16" of new storm snow and sliding on top of a thin crust formed Wed PM (see photo by John Stimberis, DOT). After an extended period of sunshine Thursday, a very large wet loose involved moist or wet snow from below the thin crust and also reached the road. Ski cutting produced easy results.    

Tatoosh Range, MRNP: On Saturday, NWAC Observer Dallas Glass found shallow but hard wind slab that was easily ski triggered on a N aspect above treeline (see below). Dallas also found widespread evidence of point releases from earlier in the week that had stepped down to lingering slab instabilities. Highlighting the power of late April insolation during this cool week, check out this picture from Dallas of a glide avalanche on a SW aspect at 5000'; the new snow from this week released on a lubricated smooth rock surface. 

Eastside: At lower elevations and further east of the crest there has been less recent precipitation and a few recent reports on Turns-All-Year that describe more stable and spring like corn snow in the afternoons.

D1-R1-HS-ASi-N, Tatoosh Range, Dallas Glass 4-26-14