Wallowa Avalanche Center

Conditions Summary for March 12, 2010

Disclaimer: Wallowa Avalanche Center assumes no liability for the accuracy of the information contained in this summary. Information provided does not constitute or imply any type of forecast, advisory, or recommendation. Users are warned to use this information at their own risk.

The Bottom Line Synopsis:

During the snow event of midweek and soon afterwards, the new snow was sliding off the older snow surface. Mostly it was sliding easily on some type of crust most noted in the Wing Ridge area. This is very likely to continue as the strong winds of yesterday (Thursday) have placed even more snow onto these slippery crusty surfaces. Under this newest snow there are numerous crust layers. Sometimes only one, other times up to 4. Some are very sensitive to failure and others are not. Almost all the ones of concern are in the uppermost 18” of the snowpack. It is still a good idea to be looking down the full meter for weaknesses if you plan to bet your life on the slope. That buried surface hoar is still down there and in some places it’s lower down than 18”. Just for the record, Julian and Keith made a mission of looking for the buried surface hoar on South Ridge last Saturday. It took some looking and was not present in one place and clearly obvious in another spot no more than 100 feet away on the same slope, same elevation and aspect. At this particular spot the surface hoar was bonded to the snow layer both above and below.

Photo 1:  Julian on his normal walk-about doing Obs for the Center. Here on a southerly aspect with very soft corn snow on Saturday last in the Big Sheep drainage.

Latest Conditions:

A welcome addition it was; 6 to 10 inches of light density snow fell between Tuesday and Wednesday this week. In a few places it had trouble sticking to the slippery crust surfaces, particularly on the more southerly or easterly aspects. It freshened up the northerly aspects just splendidly. In certain areas you could feel the crunchy crusts under the light density snow. No sooner did the new snow blanket the area and the wind picked up to take it away. By Thursday afternoon the winds from the south were redistributing it in leaps and bounds; Gusts up to 35mph. The southern and southwestern Wallowas didn’t fair quite as well for snowfall this time around with at most a couple new inches.

Recent Activity:

Most of the recent activity was during or just after the new snow event of mid-week. Whumpfing on SE aspect off Wing Ridge sometime during the new snow event. An intentionally triggered avalanche was initiated on a NE aspect off Wing Ridge; 41 degree slope, in a large open area. This was all new snow with the bed surface the old shiny crust layer. Another observer was able to release some sluffs with ski cuts in the Wing Ridge area. These also ran on the uppermost old crust surface.

Additional activity was spotted on March 9-10 in Wing Ridge. Three skier triggered slides measuring 8” deep running on old surface crusts in eastwardly facing terrain. These were on slopes from 30 – 45 degrees. Two other slides from a distance were noted: one in 3rd Bowl on W aspect and another on W aspect in 1st Bowl. These were about 30 feet wide and 150 feet long and either sluffs or soft slabs.

Photo 2: Chago sent this photo from an outing last week in the southern Wallowas. Great lookin' POW but he said slope choice required very careful analysis before jumping in.

Southern Wallowas: (from Chago)

The southern Wallowas are still riddled with dangerous slabs. We backed-off several places due to ECTP and Q1 scores. Compression scores were moderate, but again, clean sudden planar and sudden collapses 35-50 cm below the snow surface, and the energetic propagation put a break on us to jump in more ambitious lines.

Also during the last week of the warm temps in the valleys didn’t effect the snowpack above the 7000 foot level, even on slopes with south aspects. Yes, very dislikeable crusts developed on all aspects below 8000 feet, but the snowpack under the top 10 cm remained very much a winter snowpack. And temp gradients 3-4x above the critical level present above 7000 feet & below the top 20 cms of snow (faceting continues!).

However, some of the slopes had slabs/pillows that got our attention, and test results clearly indicated dangerous instabilities. There exists concern that some might get attracted to such slopes (seen in Chagos’ pic) and be tricked into thinking that the instabilities have gone away. That is NOT the case. As I boot into some lines, I had whumpfs (collapses) on isolated slabs sitting between rocky outcrops.

Photo 3:  Both Keith in the north and Chago in the south came across radiation recrystalization (RR) this past weekend. This phenomenon doesn't occur all that often. It requires just the right ingredients. See a very good tutorial by a fellow researcher, Brett Kobernik at

http://utahavalanchecenter.org/photos_videos_radiational_recrystalization_conspiracy_12312009
 

Concern #1: Wind blown snow creating drifts, wind slabs and wind crusts. This newly transported snow will generate additional loading on the variety of crusts just below the new snow addition. Winds of Tuesday and Wednesday during the storm were from the north creating drifts on more southerly aspects.  The winds of yesterday (Thursday) were from the south and today (Friday) are also expected from the south at strong gusty levels. Much wind loading should be expected on a variety of aspects including a very watchful eye for cross-loaded slopes. New snow this afternoon into Saturday will continue to load the already fragile crust layering.

Concern #2: The potpourri of crust layering and the inherent weaknesses so involved. In places the crusts will be at the surface where the wind has blown off all the new snow. In certain other places the wind will have generated a new wind slab/crust and the windblown snow will have covered a variety of crusts deep down. Either way, these crusts and the weaknesses between them are still there. These crusts now can now be found in the top 12” to the top 36” of the snowpack. The buried surface hoar is not to be forgotten. It is still down there in isolated places, mostly on northerly and easterly aspects.

Concern summary:

1. Wind effected surfaces -> wind slabs, drifts, crusts and new storm snow. 

2. Numerous, possibly quite sensitive, crusts buried generally in the uppermost 18” or so of the snowpack.

Evaluate these concerns with sufficient testing before deciding to travel and recreate in avalanche terrain. Maintain red flag awareness this weekend with the new snowstorm on our doorstep. Case in note: Your director was traveling in McCully Basin on Wednesday (while snowing) and came to a steep northeasterly wind sheltered slope. After tests and knowing what’s underneath I decided not to test the strength of the crusts and most importantly the isolated chance of running into the buried surface hoar. It meant about a half mile skin traverse to a lower angle SE aspect to ski. Hated to bypass nearly 10” of northerly freshies.

Average snowpack depths at 8000 feet:

Northern and Eastern Wallowas: 8 inches new, 55 inch total

Southern Wallowas: 2 inches new, no recent total snowpack depth data

The Juicy Techie Stuff:

It’s quite possible that in certain places these inter-crust layering weaknesses may be due to radiation re-crystalization (RR). Or perhaps just simply near surface facets (same thing right? just different mechanism of manufacture). Something to ponder. Last weekend the RR was found on flatter slope angles (not to say it wasn’t on somewhat steeper angles) at the 6500 foot elevation. See picture and great tutorial at the UAC link shown.

Photo 4: Crusting such as this is more prevalent on W -> S -> E aspects. Northerly aspects have some crusting. This photo @UTM 0487000E 5007228N NAD27 @8600 feet, E aspect,  taken on  3-10-10.

Generally most observers are not getting propagation in the ECT’s they are performing in the northerly reaches of the Wallowas. The southern Wallowas are seeing a slight increase in propagation potential.

Figure 1: Snowpack diagram showing the crusts generally more prevalent on southerly aspects and the buried surface hoar generally more prevalent on northerly aspects.

Figure 2: Pit diagram from South Ridge in the Wing Ridge Area

Wallowa Mountain Weather Briefing:

We are working directly with the National Weather Service in Pendleton through special briefings to provide you with applicable local mountain weather information. You should always obtain a weather forecast from National Weather Service before undertaking any winter outdoor activities.

Snow is coming once again with a steady increase in the chance of precipitation as the day today (Friday) wears on. By nightfall the snow will intensify markedly. Snow will be heavy Friday night and be done by Saturday afternoon. Snow levels will start around 6000 feet but quickly drop to about 4000 feet overnight Friday. Winds will continue strong and very gusty from the south and southwest until the storm clears Saturday evening. Temps will be just under 20 at night and near 30 during the day at 8000 feet. Snow accumulations are difficult at this early hour but somewhere in the 6” to 10” range in the Mtns. Expect a total of ¾” of water weight to be applied to the snowpack.

Clearing, drying and some sun expected Sunday and Monday with the next storm system to impact the Wallowas during Tuesday.

General Announcements:

We are nearing the end of the season if you can believe it. We are considering offering up our last weekly summary on April 9. We would appreciate comments this next month on how we can improve for next year. Over the summer we will be working to incorporate ideas and suggestions on what works better for you as we prepare for next year. Write us an email on info@wallowaavalanchecenter.org.

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Current Regional Weather Synopsis:

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
331 AM PST FRI MAR 12 2010

UPDATED AVIATION DISCUSSION

.SHORT TERM...TODAY THROUGH SATURDAY. A STRONG UPPER LEVEL LOW
PRESSURE SYSTEM WILL MOVE ACROSS THE PACIFIC NORTHWEST TODAY AND
EARLY SATURDAY. A COLD FRONT ASSOCIATED WITH THIS LOW WAS LOCATED
ALONG THE COAST EARLY THIS MORNING. THE FRONT WILL MOVE THROUGH THE
FORECAST AREA LATE THIS AFTERNOON INTO TONIGHT. EXPECT A PERIOD OF
RAIN AND MOUNTAIN SNOW. A SNOW ADVISORY IS IN EFFECT FOR THE BLUES
AND WALLOWA COUNTY. SURFACE PRESSURE GRADIENTS ALONG WITH STRONGER
SOUTHWEST WINDS ALOFT WILL CONTINUE TO PRODUCE BREEZY TO WINDY
CONDITIONS AT SOME LOCATIONS. A WIND ADVISORY REMAINS IN EFFECT FOR
THE GRANDE RONDE VALLEY TODAY. WINDS WILL SHIFT TO THE WEST
OVERNIGHT BEHIND THE FRONTAL PASSAGE. DECENT COLD ADVECTION WITH
THIS FRONT SO WILL SEE A GOOD TEMPERATURE DROP TONIGHT WITH MOST
PRECIPITATION CHANGING OVER TO SNOW. THE COLD UPPER LEVEL TROUGH
WILL BE OVER THE REGION SATURDAY MORNING AND EXPECT SCATTERED
SHOWERS TO CONTINUE. BY AFTERNOON THE TROUGH IS MOVING EAST AND AN
UPPER RIDGE IS STARTING TO BUILD IN WHICH SHOULD BRING IMPROVING
CONDITIONS.  94

.LONG TERM...SATURDAY NIGHT THROUGH THURSDAY...A WEATHER SYSTEM WILL
BE DEPARTING ALLOWING A RIDGE OF HIGH PRESSURE TO BUILD OVER THE
REGION. THIS RIDGE WILL KEEP CONDITIONS WARM AND DRY THROUGH
TUESDAY. THEN THE NEXT WEATHER SYSTEM WILL PUSH A COLD FRONT INTO
THE REGION LATE TUESDAY AND WEDNESDAY FOR COOLER AND SHOWERY
CONDITIONS. A NORTHWEST FLOW WILL THEN PERSIST OVER THE REGION
THURSDAY AND FRIDAY WITH SOME LINGERING SHOWERS OVER THE EASTERN
MOUNTAINS.