This is not an Avalanche Advisory. This information is a Conditions Update. The next avalanche advisory is scheduled for Saturday December 22, 2018.
MIDWEEK SNOW AND AVALANCHE CONDITIONS SUMMARY
Dangerous avalanche conditions continue at Hatcher Pass. Numerous large avalanches, including some widely propagating natural avalanches up to size D2, have been reported by observers over the last few days. Moderate winds gusting into the 20s mph have picked up some of the 2+ feet of snow available for transport and deposited it into leeward terrain above 3500’. This new stress on the snowpack has overloaded buried persistent weak layers, resulting in natural avalanches in Lower Microdot (NW aspect), Marmot W to SW aspects, Hatch Peak NE aspect, and Martin Mine NE aspect. These avalanches have all occurred in steeper, 35 degree + terrain. Observers have also reported whumphing.
Careful snowpack evaluation, cautious route-finding, and conservative decision making will be essential if you venture into the mountains in Hatcher Pass, especially above 3000’. Be on the lookout for wind-loaded slopes where a thicker slab exists sitting over buried persistent weak layers. Although most of the recent natural avalanches appear to have occurred in 35 degree + terrain, because of the widespread, poor structure, and unpredictable problem, avoid traveling on, under, or in the runout of terrain steeper than 30 degrees. Be conservative and give this problem a wide berth. Avoid slopes that have terrain traps including creeks, gullys, cliffs, and large bowls that funnel into narrow gullies. Hatcher Pass is loaded with terrain traps. If you choose to travel in avalanche terrain, choose slopes with gentle, fanning runouts. Be on the lookout for recent avalanches, whumphing/collapsing, and shooting cracks. These are all red flags for dangerous avalanche conditions.
This report is a mid-week conditions update, so please be sure to check hpavalanche.org for advisories on Saturdays and follow the HPAC Facebook for updates. Help us keep tabs on the Hatcher Pass area! If you see any avalanche activity send us an observation HERE. Thank you to everyone who has already submitted observations this season - you can see those HERE!
Problem 1: Persistent Slab
2” of new snow has fallen since Saturday 12/15 and easterly winds have transported snow in upper elevations (>3500’). With 2+ feet of available snow for transport, slabs are believed to be 1-4’ thick. These slabs are sitting on top of a thin, weak snowpack containing several persistent weak layers including a layer of buried near surface facets in the midpack, buried surface hoar, facets above a decomposing melt freeze crust, facets below the melt freeze crust, and basal facets at the ground. Large and some widely propagating natural slab avalanches were reported Monday, Tuesday and Wednesday by observers.
Observers have found a variety of persistent weak layers in our snowpack
Problem 2: Wind Slab
Fresh wind slabs have formed over the last few days from Easterly winds. Little is known about the thickness of these wind slabs, but we do know that they sit on top of low density settled snow and near surface facets. Expect these winds slabs to be reactive to touchy in leeward terrain. Be on the lookout for evidence of wind loading such as pillowed snow, cross-loaded gullies, and stiff feeling and hollow sounding snow underfoot. Wind slabs may allow you to travel out onto them and then break above you.
Cross-loading on the Sunnyside of Hatch Peak
Natural avalanches have been reported in the past several days on Lower Microdot (NW aspect), Marmot SW aspect, Hatch Peak NE aspect, and Martin Mine Gully NE aspect. See photographs below.
Above: Natural avalanches on Lower Microdot NW aspect on Wednesday 12/19
Above: Natural avalanches observed on Marmot W to SW aspects on Wednesday 12/19
Widely propagating natural avalanche on NE aspect of Martin Mine Gully on Monday 12/17
Winds picked up this week, with Easterly winds at ridge tops gusting light to moderate Saturday 12/15 and Sunday 12/16 and moderate winds Tuesday night 12/18. At Independence Mine, winds have been calm to light from the N/NW since Saturday 12/15. Independence Mine received 2” of snow (0.2” SWE) Saturday 12/15 into Sunday 12/16 night. Temperatures have been in the teens to 20s F since Saturday 12/15.
Today (Thursday 12/20) the weather is expected to be partly sunny, with temperatures in the single digits F and calm winds. Friday 12/21 temperatures are expected to warm into the teens F; however, there is disagreement in the weather models regarding the potential for scattered snow showers in the afternoon and evening.
Stay tuned to the NOAA point forecast for an updated weather forecast each day. The best way to see if it's snowing in Hatcher Pass is to look at the webcam snow stake HERE and the Independence Mine SNOTEL site HERE
Dangerous avalanche conditions continue at Hatcher Pass. Moderate winds gusting into the 20s mph have picked up some of the 2+ feet of snow available for transport and deposited it into leeward terrain above 3500’. This new stress on the snowpack has overloaded buried persistent weak layers, resulting in numerous large avalanches over the last few days.
Join us tonight at Hatcher Pass Polaris for a FREE avalanche awareness program with Alaska Avalanche School!
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