Proceedings, International Snow Science Workshop, Banff, 2014

THE HAWAIIAN SUCKER PUNCH; FORECASTING A WET SLAB CYCLE IN SOUTHCENTRAL JANUARY 2014 John Fitzgerald1

1Chugach National Forest Avalanche Information Center, Girdwood, Alaska

ABSTRACT: Late January 2014 in Alaska brought intense weather that produced an impressive ava- lanche cycle in many areas around the state. A plume of moisture originating in the tropics pumped rain and unseasonably mild temperatures into and on an already tenuous snowpack. Ten days of rain in the mountains resulted in an impressive wet avalanche cycle in the Kenai and . Turna- gain Pass is the main area highlighted in this paper. This paper shows the pre-existing snowpack struc- ture as well as the ensuing weather and avalanche activity during this period. Extensive wet slab activity wiped out the entire snowpack on many slopes. Prior wet snow research is highlighted and shown as a valuable tool for public forecasting.

KEYWORDS: forecasting, wet slabs, rain on snow, Alaska, Turnagain Pass.

1. INTRODUCTION tions that were spared the majority of rain events looked deeper. Unfortunately there is a lack of The winter of 2013-2014 brought extremes in consistent snow depth data derived from weather weather to the mountains around Eastern Turna- stations at the higher elevations around Turnagain gain Arm in Southcentral Alaska. As a result the Pass. From a backcountry snowmachining and snowpack went through several avalanche cycles. skiing standpoint it was considered a generally The most significant cycle of the season came on poor season. January 17th and lasted until January 28th. This paper will highlight the structural make up of the snowpack leading up to this time period as well as the events of the cycle itself. This paper aims to highlight the efficacy of wet snow research as it relates to avalanche forecasting for the public. Figures and data are taken from weather stations near Turnagain Pass, which is the “core advisory area” for the Avalanche

Information Center (CNFAIC). This information is stored at http://www.cnfaic.org/wx/wx_history.php. Fig. 1: Snow depth at Turnagain Pass SNOTEL Variations in weather and snowpack information (573m). 10 years of data is represented based on geographic location will be noted where here. The dark bold line along the bottom applicable. shows snow depth for 2013-2014. Com- piled by Wendy Wagner 2. SEASON HISTORY 2.1 The Snowpack Foundation Develops The 2013-2014 season saw “record” low snow depth based on ten years of data at the Turnagain November and December saw light snowfall and Pass SNOTEL site. (see fig. 1) Despite a lack of Snow Water Equivalent (SWE) gain. a significant data set, one can see from Fig. 1 that November snowfall total equaled 64cm with 6.6cm it was a very low snow year. Rain events contrib- of water. Snowfall came from three storms on No- uted to keeping snow depths low. Higher eleva- vember 10th, 21st, and 26th. 6 out of 10 days lead- ing up to the 21st precipitation and loading event * Corresponding author address: saw surface hoar development and prime condi- John Fitzgerald, Chugach NF Avalanche Center tions for faceting. Several D2 skier triggered ava- lanches were reported following the storm on the PO Box 493, Victor, Idaho 83455 st tel: 307-690-2155 21 . email:[email protected]

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December saw slightly higher amounts, with 104 No known injuries occurred, although there were cm of snowfall and 8.6cm of water. A 15 day many close calls and one dog buried and pre- stretch of almost no precipitation persisted from sumed dead on a popular run in the Turnagain November 27th to December 12th. This period saw Pass area. mild temperatures and one day, December 5th with light drizzle falling up to 610m in elevation. The 2.3 The Hawaiian Sucker Punch formation of what was referred to as the “drizzle crust” occurred with cooler temps following De- A well established ridge of high pressure off the th th th Pacific coast of the helped to push cember 5 . Storms on the 13 -14 (48cm th warm moist air towards Alaska beginning around snow/3.3cm H20) and 18 (15cm snow/1.5cm the 15th of January (see Fig. 3). The brunt of the H20) of the month led into a period of widespread warmth and precipitation hit Turnagain Pass on collapsing and a puzzling lack of avalanche activi- th nd January 17 . 5.5cm of H20 fell within this 24-hour ty. It took until the 22 for skiers to trigger ava- period. Close to double this amount fell in the lanches between D1 and D2 in size. A return to nd Girdwood Valley, roughly 16km to the North and dry and cool conditions continued from the 22 to home to . New Year’s Eve, with the exception being a quick 8cm of snow falling on the 28th. Conditions were again prime for faceting. The slabs that had formed during December were degrading and growing weak.

2.2 New Year’s Avalanche Cycles While much focus has come to the late January cycle that impacted most of Alaska, New Years Eve and January 4th saw rapid loading from snow, rain and wind. The December 31st storm total was 28cm snow/2.8cm H20. The January 4th storm total was 30cm snow/2.8cm H20. These storms resulted in widespread natural and human trig- gered activity ranging in size from D1-D3. Remote Fig. 3: A screen shot of a NOAA image taken on triggers were very common during this period. January 23rd. A stubborn ridge of high Common weak interfaces were facets above and pressure parked on the US Pacific coast below the “drizzle crust”, as pictured in Fig. 2. diverted moisture away from the lower 48 and pushed it from the tropics directly to- wards Alaska.

Freezing levels at the outset of this event fluctuat- ed between 300m-550m ASL. Winds averaged 80kph with a 170 kph gust recorded. An exciting avalanche day ensued, as Alaska DOT & Alaska Railroad performed extensive artillery work along their respective corridors with results. CNFAIC forecasters went into the field and were able to observe some of the action, including a natural D3 spewing wet debris down to sea level in the Por- tage valley. One pertinent field observation that day was noting small drainages between sea level and 300m pumping water by midday.

The next day, January 18th, brought enough visi- th bility to see some of the damage. Wide propagat- Fig. 2: Pit profile from January 9 2014 shows the ing avalanches in the lower elevations were pulling generally poor structure of the snowpack. out at the ground. The highest elevation starting Multiple periods of dry and cool weather zones for observed avalanches on this day was contributed to a weak foundation. around 1130m (Sunburst) – 1220m (Moose Mt).

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Between January 19th and 23rd, mostly rain fell at The water factory refers to the presence of free the Turnagain Pass SNOTEL site at 573m. Each water somewhere in the snowpack, caused by day had at least 1.2cm of H2O and three of those radiation or precipitation (or both). The funny days had 1.5cm. Temperatures and freezing lev- business refers to a (persistent and/or mix of grain els were on a gradual rise during this period as types) weak layer below the slab. well. Our sources for snow and water come from a On January 23, when skies cleared, we were able SNOTEL site that is difficult to access, especially to see extensive avalanche activity. The average when the snow is isothermal. SWE readings dur- destructive force/size on this day was D3; the ing this cycle were sometimes hard to follow or most obvious one was the West Face of Pyramid believe, but still provided some insight into water Peak, which ran full track to sea level & mostly to gain and loss. Our ridgetop stations on Turnagain the ground (starting zone 945m). Although activity Pass are reliable and accurate and helped us get seemed to be climbing in elevation in concert with a better idea of freezing levels, as well as wind freezing levels, we were still observing new activity data. on Seattle ridge as low as 600m on this day. 4. FORECASTING CONSIDERATIONS January 25 brought the first day since the 16th with abundant sunshine. As one might expect, Listed below are some factors that can be useful natural wet avalanches occurred on this day, with to focus on when confronted with the coming of a Ragged Top and Goat mountain, in the Girdwood warm storm where rain falling on a tenuous snow- Valley, shedding size D3-4 avalanches to the pack seems like a real possibility. ground. 4.1 Understand Underlying Snow Structure The next three days brought another 2cm of H2O and the Sunburst Station at 1162m reaching a It is critical to know your snow structure prior to an high temp of 7.2 C. During and beyond this period event like this. Extensive field observations in the several more avalanches were observed, including form of pit data, surface observations, and weath- a piece of hangfire on Pyramid approximately er effects help us to develop a region-wide under- 120x120m. At this point people were kayaking, standing of structure (McCammon & Schweizer kite surfing, and not playing on snow. Alyeska 2002), and how it might vary from slope to slope Resort was forced to close for several days to pre- across a large geographic area. (What is the dis- serve its snowpack. tribution of the slab and the funny business?)

3. PRIOR RESEARCH 4.2 Have Reliable Weather Stations & Ground Truth Them As this weather pattern was forming, I did my best to brush up on wet snow theory and research. Having reliable weather stations combined with There are great resources available, primarily ground-truthing allows us to anticipate wet slab found by using the ISSW database (Clark et al. avalanche release. We don’t have the ability to 2012) The most useful paper for me (as a practi- measure outflow with lysimeters, or to dig hun- tioner) is Forecasting For Natural Avalanches Dur- dreds of pits to see if drainage channels have ing Spring Opening of the Going To The Sun been established. Some days we were simply Road, Glacier National Park, USA (Reardon & unable to travel on snow. Other days we were Lundy 2004). This work breaks things down in a able to get out and see things progressing. With way that is usable for public forecasting for a large these limitations in mind, it was helpful to simply area with minimal instrumentation related to wet keep track of freezing levels and SWE gain and snow. loss. We use a total of three stations for our core advisory area. Because of this, there is a need to In their research Lundy and Reardon suggest a infer/deduce information when we are unable to simple conceptual model for anticipating wet slab get in the field. (Is the water factory working avalanche release. The main questions to ask around the clock?) based on this model are: • Is there a slab? 4.3 Drainage-More Complex Than You Might • Is there a “water factory” present? Think Is there “funny business” below the slab? • I’ve always thought that once drainage channels are established the pack can absorb more stress.

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Multiple studies have concluded this to some de- been put through the wringer by the weather, it still gree. What I’ve come to realize is that this is a maintained enough of a slab and a reactive weak very difficult parameter to measure. Without more layer to correlate with activity 400m higher. These precise instrumentation and the ability to forecast results were a surprise to me. on the slope scale, this concept does not help an- ticipate avalanche activity over a large area such as our forecast zone. I thought that maybe by looking at creeks, streams, and waterfalls I would gain a sense of outflow. While these casual and rough observations point to some level of drain- age, they don’t help me know if water is pooling at a given layer or on a particular piece of terrain that might absorb water for over a week before ava- lanching. Another attempt to measure outflow by using data did not correlate with avalanche activity (see Fig 4). The nearest USGS stream gauge to Turnagain Pass is at Six Mile Creek. Lag time between water being delivered from avalanche terrain into creeks is certainly too long in this case. Perhaps there Fig. 5: WS-N-R2-D3-G Butcher Peak in the are other areas where this could be a helpful tool Summit Lake region south of Turnagain in lieu of lysimeters or field observations on slope. Pass on January 24. This was one of 8 observed natural avalanches that occurred towards the end of this avalanche cycle.

5. CONCLUSION Rather than try to discuss climate change or start some political debate on global warming, I think it is important for us as a community to be ready to anticipate cycles such as this. More extremes in weather, including rain-on-snow and seemingly summer-like temperatures in mid-winter, necessi- tate a better understanding of how to use our re- sources to forecast more accurately and arm our audience with information that is useful and will Fig. 4: A screen shot of USGS Stream Gauge keep people and property out of harms way. Station at Six Mile Creek near Hope, AK. ACKNOWLEDGEMENTS Station is approximately 10 km from Turn- again Pass. Distance combined with lag I would like to thank my co-workers at the time make it difficult for this data to be CNFAIC, Wendy Wagner, Graham Predeger and useful for anticipating avalanche activity in Kevin Wright and intern Katie Johnston for gather- the future for Turnagain Pass. ing and sharing much of this information and being great field partners. Thanks to Don Sharaf for 4.4 Be Prepared for Surprises helping me to ask the right questions when storms like this are on the doorstep. One pit stood out to me during this cycle. On Jan 24th I traveled to Summit Lake to look at approxi- References mately eight D3 avalanches (Fig. 5) that had oc- Clark, J., Marriot R., Custer S., Adams E., Bonnand S., Miller curred overnight. We dug in the lower elevations, T., Young S., Hendrixx J. 2012: A Searchable Digital Ar- around 670m, in an area that had seen rain and chive Of ISSW Proceedings Is Available Online. Proceed- ings of the 2012 International Snow Science Workshop, warm temps since the 17th (half the amount of Anchorage, Alaska rain as Turnagain). I was able to get impressive McCammon I., Schweizer J. 2002: A Field Method For Identify- ECT results on low angle terrain (ECTP 11 SP on ing Structural Weakness In The Snowpack. Proceedings of a 23 degree slope). Even though this snow had the 2002 International Snow Science Workshop, Penticton, BC

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Reardon B., Lundy C., 2004: Forecasting For Natural Ava- lanches During Spring Opening Of The Going-To-The-Sun Road, Glacier National Park, USA. Proceedings of the 2004 International Snow Science Workshop, Jackson, Wy- oming

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