Wallowa Avalanche Center

Conditions Summary for March 19, 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:

Stability this week has shown some improvement in the Wing Ridge areas, at least after the natural activity ceased from last weekend. During early last weekend with the heavy snow and very strong winds, some natural avalanches released. Generally things have quieted down since then and bonding has been occurring this past week with the warm temperatures. In fact in places (SW -> S -> SE aspects) the snow warmed so much by mid afternoon that wet loose or even wet slab activity became a concern to be mindful of as parties returned from their daily backcountry outings.

New postings on the forum contain recent information from Aneroid Basin.

Photo 1: Ken on the way to an Observation day on Pyramid Peak. Test pit performed on the north aspect slope of Pyramid behind the two tallest trees in the foreground. Photo taken 3-17-10.

Generally when timed correctly the 1 – 2” of creamy corn snow over an occasional crust was very pleasant skiing. On shadier upper elevation terrain there was widespread wind crust and occasional wind board. This wind crusting was typically unpleasant for skiing as one would break through every so often and get tripped up. However, the crusts at or nearest the surface appeared to be bonded sufficiently to not cause stability concerns. Most of the stability concerns were a bit lower in the snowpack in the range of 6” to perhaps about 18” below the surface. Even within this range, results were showing relatively good bonding of the weak layers found down there. A few isolated places exhibited a surface crust or layer bond that warranted a bit further investigation for stability.

Latest Conditions:

Warmth and plenty of it has been the story this week. During last Friday night into very early Saturday morning, we received nearly a foot of rather dense snow. It has been pretty much mostly sunny and warm since. Temperatures even at the 8000 foot level have maxed out at or above 40 degrees every day. Winds which were nearly calm directly after the snowstorm reached a crazy strong peak on Tuesday/Wednesday from the south then returned to near calm for the latter part of the week. These types of conditions sure go a long way in assisting bonding of layers within the snowpack closest to the surface. The new snow from early last weekend is a very evident layer when you do a simple hand pit. Very distinguishable from a sometimes thin crust above it or below it with mostly a consistent feel (cohesion) and color.

Photo 2: Large avalanche to lookers right of Pyramid Peak from 2nd Basin viewpoint. Note that the slide initiated from just below the cornice at ridgeline and likely sympathetically triggered a lower slide after the snow above fell over the cliff band. This slide may have occurred during the strong wind loading events of last Friday and Saturday during the most recent storm cycle.

Recent activity:

Two fairly major avalanches were documented in the easternmost region of the Wallowas. The NNE aspect of Mt. Nebo slid as well as the N aspect of Pyramid. You can judge for yourself the relative size and destructive power of each from the photos. It is quite likely these released during the same wind loading event of late last week as the storm was eminent and producing. No other reports of slide activity have been received.

Southern Wallowas:

We received a snowpilot diagram from a WAC observer venturing around on Simmons Ridge which was dug adjacent to (but not on the flank) of an intentionally triggered slide last week. The intentionally triggered avalanche released and rode on the uppermost surface hoar layer shown in the diagram and did not step down to the lower surface hoar layer.

Photo 3: This photo courtesy Ken Bronec who spotted this avalanche off the NNE aspect of Nebo while on an outing last weekend all the way from Wing Ridge. He said his strong telephoto lens was maxed out and that the slide likely occurred due to the strong winds of last Friday just prior to or at the beginning of the storm.

Concern #1:   General awareness for isolated weak layers in pockets on all aspects and mid to upper elevations particularly in the uppermost 18” of the snowpack. In both the northern and southern Wallowas continue to be mindful of the buried surface hoar layer; now down 1 ½ to 3 feet from the surface.

Concern #2: Wet activity. This week has seen the top surface of the snowpack just on the cusp of wanting to do something in the wet department. Some wet loose mud slumping was even noted along the roadside half way up the road to Salt Creek Summit. In one place on a WAC obs outing the upper snowpack became so weak from heating that it simply collapsed during a turn and the skis sunk in more than a foot on an open slope of 20 degrees. These are red flag signals that it’s time to get off steep sun heated slopes.

Average snowpack depths at 8000 feet:

Northern and Eastern Wallowas: 10-12 inches new, 55 inch total (what was gained last weekend in new has since been lost due to settlement and melting). Depths remain essentially the same.

Southern Wallowas: 6 inches new, greater than 100 inches total

The Juicy Techie Stuff:

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 still seeing a slight increase in propagation potential. Results from Wednesday (3/17) in the Wing Ridge area are:

E aspect, 8000’, 32 deg slope: CT21Q2 down 23cm within a small facet layer

N aspect, 8250’, 41 deg slope: CT21Q2 down 18cm at a hardness change

     ECTN25Q3 down 43cm in Fist hardness facets

     STM down 43cm in Fist hardness facets

     UTM: 0491218E 5005157N NAD27

S aspect, 7900’, 20 deg slope: Moderate hand shear down 25cm just above a very     moist  crust layer. This layer was class 6cl (S.       Colbeck, 1990).

Photo 4:  Ken performing a quick pit for layering and stability info on an east aspect off Middle Ridge. Elevation 8200'. Photo taken 3-17-10.

Figure 1: Snowpit diagram from Simmons Ridge, Southern Wallowas

Video 1: Ken Bronec performing an Extended Column Test on the same aspect and similar elevation to the starting zone of the Pyramid Peak avalanche. The track of this avalanche can be seen in the background. UTM for this test pit location: 0491218E 5005157N NAD27 @8200 feet.  Result: ECTN25.

Figure 2: Composite diagram for Northern and Eastern Wallowas.

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.

The warmth and sun continues, at least for the next 2+ days. Expect sun and light winds daily through Sunday morning when a weak cold front moves into the area bringing increasing clouds. Highs today (Friday) near 40 and on Saturday in the mid forties at 8000’. As Sunday progresses the clouds will thicken with light precipitation beginning sometime early on Monday. Winds will increase Sunday from the south.

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.

Now you have every reason to send in a donation to WAC. This week we received official notification from the IRS that we are now a 501(c)(3) tax exempt / tax deductible organization. You may deduct any charitable donation to us since our inception on July 27, 2009 to the extent allowed by law on your 2009 and future tax year forms. So please step up and support our cause. Many of you have been very generous. We appreciate it very much. For those of you who regularly use our site for information please send in an amount you feel comfortable with. Send a check made out to Wallowa Avalanche Center to the PO Box on our home page or use the handy PayPal button.

Current Regional Weather Synopsis:

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
346 AM PDT FRI MAR 19 2010

UPDATED AVIATION DISCUSSION

.SHORT TERM...TODAY THROUGH SATURDAY NIGHT. HIGH PRESSURE ALONG THE
WA/OR COAST WILL DOMINATE THE AREAS WEATHER WITH DRY CONDITIONS
TODAY. AFTERNOON HIGH TEMPERATURES WILL REMAIN AT OR SLIGHTLY BELOW
NORMAL BEFORE A WARMING TREND IS EXPECTED INTO THE WEEKEND. THE HIGH
PRESSURE DRIFTS INTO WA/OR TOMORROW AND TEMPERATURES SHOULD CLIMB
INTO THE 60S ACROSS PORTIONS OF THE REGION SATURDAY. AS THE HIGH
PRESSURE DRIFTS EAST...A DISTURBANCE APPROACHES OUR WASHINGTON AND
OREGON CASCADES THAT MAY PRODUCE A FEW SHOWERS ACROSS THIS AREA
SATURDAY NIGHT.

.LONG TERM...SUNDAY THROUGH THURSDAY AFTERNOON...A COLD FRONT WILL
APPROACH THE COAST ON SUNDAY SPREADING INCREASING MOISTURE AND
CLOUDS ACROSS THE FORECAST AREA FOR A CHANCE OF RAIN WITH THE SNOW
LEVEL AROUND 5000-6000 FEET MSL DURING THE DAY. THE FRONT WILL MOVE
THROUGH THE INTERIOR PACIFIC NORTHWEST SUNDAY NIGHT WITH SNOW LEVELS
LOWERING TO 3500-4500 FEET MSL OVERNIGHT AS THE ATTENDANT MID/UPPER
LEVEL TROUGH MOVES THROUGH THE REGION. A SECOND MID/UPPER LEVEL
TROUGH WILL THEN MOVE ACROSS THE REGION ON MONDAY KEEPING A CHANCE
FOR A CHANCE OF RAIN SHOWERS AT LOWER ELEVATIONS AND RAIN AND SNOW
SHOWERS LIKELY IN THE MOUNTAINS. THE TROUGH EXITS THE FORECAST AREA
MONDAY EVENING FOR DECREASING POPS AND MAINLY DRY CONDITIONS IN THE
LOWER COLUMBIA BASIN MONDAY NIGHT. ON TUESDAY A SLIGHT CHANCE OF
OROGRAPHIC RAIN/SNOW SHOWERS IN THE NORTHERN BLUE MOUNTAINS AS WELL
AS THE ELKHORN AND WALLOWA MOUNTAINS. OTHERWISE...TUESDAY LOOKS TO
BE DRY AS A MID/UPPER LEVEL RIDGE OF HIGH PRESSURE BUILDS OVER THE
PACIFIC NORTHWEST. THE RIDGE MOVES INTO IDAHO/MONTANA ON WEDNESDAY
THUS ALLOWING A MID/UPPER LEVEL PACIFIC TROUGH TO MAKE LANDFALL
ALONG THE COAST BY WEDNESDAY AFTERNOON. THE GFS AND ECMWF MODELS
SHOW THE TROUGH MOVING THROUGH THE EASTERN SECTIONS OF WA/OR
WEDNESDAY NIGHT AND SPREADING INCREASING MOISTURE AND CLOUDS ACROSS
THE FORECAST AREA FOR A CHANCE OF PRECIPITATION...MAINLY IN THE
MOUNTAINS WEDNESDAY NIGHT AND THURSDAY.  POLAN