Monday April 8, 2019

Wednesday April 10, 2019
Tuesday April 9, 2019
Monday April 8, 2019
Confidence: High - Weather models in agreement and good field data.

Main Concerns

Loose Wet, Storm Slab - view Avalanche Problems for detailed information.

Travel & Terrain Advice

Give storm and wind slabs a couple days to bond to old surfaces before hitting those big slopes (especially those NW-NE treeline and alpine ones).

Avoid big solar slopes if the sun peaks out as the moist snow pack will loose stability quickly. Keep an eye on temps during the day and play it cautious if rain is falling on the snow. Avoid exposing yourself to terrain traps during these times as well.

Avalanche Summary

-Few wind slab avalanches from size 1 to 2 reported with the storm Saturday in the alpine and treeline . Mt Washington Patrol got a few loose avalanches with explosive control and ski cutting on treeline west aspects Saturday. -No new reported Sunday. -One size 3 wind avalanche came through my back yard and sent my tarp style wood shed flying against the fence. Structural damage was witnessed (numerous broken poles and rips) thus bumping the avalanche size up to 3.

Avalanche Problems

Loose Wet

Our moist spring snow pack will be quick to weaken if temps rise, rain falls and/or the sun bakes the slopes. Avoid all big slopes and features if things warm up or if rain falls on the snow as we could very well see loose wet avalanches up to size 2 on all aspects in the below treeline zone. With strong sun input we could also see avalanches up to size two on solar aspects in the below treeline, treeline and lower alpine. These loose wet avalanches will trigger in the possible to likely range with human activity (skiing, sledding, snow shoeing etc..) and are possible with natural triggering (for example solar warming of steep rocky outcrops or tree bombs).

Storm Slab

All that new snow (especially on the lee NE to NW zones where the high winds loaded slopes even more) means we should give the big faces and features some time to settle. There are storm slabs on all aspects in the treeline and alpine elevation bands that may trigger in the possible to likely range with human activity and possible by natural triggers up to size 3. Day time warming on Tuesday will potentially increase their sensitivity to triggering as well.

Snowpack Summary

Holly smokes!!! up high 35 to 85 cm of snow has fallen over the past three days!! We also had winds from strong to extreme during the Saturday blizzard. On lee slopes one can expect to find 100 to 150+ cm of new, due to significant wind transportation…..

New precip from storm

45-50 mm in Washington/East

80-85 mm in Strathcona/West

35-40 mm in Cain/North

note: amounts above 1500 m where all the precip was snow 1 mm precip is equivalent to around 1 cm of snow. 1500-800 m saw a mix of snow and rain. below 800 m was mostly all rain.

Snowpack Details

SurfaceMoist snow on solar aspects, preserved snow on shaded non solar with open zones highly wind effected
Upper35 to 85 cm of new up high (with more in lee zones) bonding well to old surfaces below
Midmultiple crust and well settled snow layers
Lowerwell settled

Past Weather

Significant new snow fell Friday into Saturday with more again Saturday into Sunday. Strong SE to SW winds and even some extreme winds Saturday at the height of the blizzard with temps hovering around -2 to -5. Sunday during the day, things slowed and eased up as the storm ended and temps climbed back above zero once again in the below treeline elevation bands.

Weather Forecast

Small amounts of precip (type elevation dependent) will fall Monday, very little to none Tuesday, and a small to moderate system arriving Wednesday. Temps will hover around -2 to plus 2 Monday and Tuesday with a good looking cooling trend for Wednesday.

Monday - 1 to 6 mm of precip, temps -1 to +2, winds light to moderate SE switching to light to moderate NE-NW, freezing levels 1000 to 1450 m.

Tuesday - 0 to 2 mm of precip, temps -2 to +2, winds light to moderate NW switching to light to moderate SW, freezing levels 1200 to 1800 m (good time to watch for those loose wet avalanches)

Wednesday - 6 to 12 mm of precip, temps drop -1 to -4 (coolest zone up north), winds moderate to strong SW to NW (up north Strong SE also), freezing level 1000 to 1350 m.

Posted on Monday April 8, 2019 by Bill Phipps

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