Wallowa Avalanche Center

Conditions Summary for January 8, 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:

Southern Wallowas: Recent field data shows a sensitive, thin (3 cm) weak layer in the mid snow pack at about 28 inches (80 cm) down from the surface. This appears to be mostly on NW -> N -> E aspects at the mid to upper elevations above 7500 feet. A weather event deposited some Styrofoam ball-like crystals (graupel) on top of  a ”feathery” surface hoar in some areas which are not bonding well to the layers above and below. Tests of this weak layer show moderate strength and the possibility for fracture propagation.

Northern and Eastern Wallowas: Observations last weekend and early this week noted continued weakness and sensitivity at the persistent and long lasting weak layer just above the old rock hard layer down nearest the ground. Although some strengthening has been noticed in the last two weeks, a 3 in. thick layer of crystals (highly faceted, advanced and striated) remain which are sugary and loosely bonded approx. 8 inches above the ground. This weak layer is deeply buried, so even though it may take a fair amount of force to initiate, the consequences would likely be high. Particular caution should be taken in areas where the overlying snow is thinner, as that is a more likely area to trigger these potentially deep avalanches. As always, good habits are bad to break - expose only one person at a time to avalanche terrain, use well-defined zones of safety, and never travel above your partners.

No reports or visual sightings (one was heard) of natural avalanche activity this week. Several human triggered avalanches (ski cutting) were released in the southern Wallowas during the height of the storm cycle last weekend. These were up to 1.5 feet deep, involved the new snow only and were large enough to injure, bury or kill a person.

Whumpfing with little or no cracking at the surface was noted this week in isolated areas and primarily on flatter terrain.

Photo 1: Taken in the Southern Wallowas pointing out the weak layer about 80 cm below the surface.

The Juicy, Techie Stuff:

Concern 1: Storm Snow. In the north, new snow and crusting of early last week. This new snow had many density variations. Heavy wet snow to start, then rain leading to an icy/rain crust layer (¼ inch in many places) and finally a varying amount of light density snow at storms end. This will create a potpourri of upper snow pack weaknesses down to the bond to the previous snow surface. Expect sluffs of the lighter density snow where it may have trouble bonding to the rain crust layer on terrain >35 degrees. All aspects at mid to upper elevations are suspect. Wind slabs may be present on recently wind loaded slopes from the moderate to strong winds all week from the S -> SW, until yesterday when winds shifted to a more northerly direction. Red flags to watch for: pillows, drifts, whumpf noises, cracking, etc.

Concern 2: Deeper hard slab avalanches. With the new snow weight and a trigger an avalanche may release on either deeply buried weak layer noted in the two Wallowa regions above. Particularly be aware of where thinner snowpack areas are likely to be since this is where the deeper slab avalanches typically are triggered. Examples of these places are rock bands, rows of trees/bushes, wind scoured areas, etc. Throughout the range avalanches on this deep weak layer are likely to be large, possibly breaking down to the lowest layers and even the ground. These avalanches can have big consequences. There still exists a large degree of variability to the weak layers so if one area doesn’t show the weakness look elsewhere on the test slope.

Concern 3: Coverage in the northern and eastern Wallowas have not improved since last report due to the low snowfall from the previous storm cycle. See last weeks report. In the southern Wallowas snow pack appears to be sufficient at this point for most activities except possibly at the most exposed ridges and summits.

Figure 1: General conditions after wet snow and rain event of early this week. Test results courtesy of clients of Wing Ridge Ski Tours.

Generally observers have been reporting no change in strength of the snow pack from last week. Shears and fracture propensity is quite variable in both regions.

Evaluate these concerns with due diligence with the existing spatial variabilities in mind when traveling in, below and around avalanche terrain.

Figure 2 : Current and average snowprofile from southern Wallowas near Cornucopia, courtesy Connelly Brown and his team of guides.

Since last Friday the weather started out with what looked like an exciting storm cycle of bountiful snow. Instead it turned quickly into wet heavy stuff and then rain even as high as 8000 ft. throughout Tuesday. Rain crusts from reports in the mid elevations are at least ¼ inch thick on the surface. This rain crust is now covered by a thin coat of snow.Temps have been warm until just yesterday with moderate southerly winds throughout the period. A cold front ushered in more seasonably cold temperatures yesterday (January 6). Total precipitated water in NE Wallowas this week was 1.25 inches WE and 7 in. of quite heavy glop with a crust to finish it off.

Total snow pack depths on average:
Northern and Eastern Wallowas @ 8000 ft.: 36 inches
Southern Wallowas @ 8000 ft.: 77 inches
 

Did you know???

Whenever rain falls on a snow pack it adds weight without adding any strength and sometimes causes a loss of strength by melting the bonds (glue) that keep the snow together. And sometimes you get a rain crust or other nasty feeling crunchiness on the top layer.

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.

We'll start out this morning (Friday) with just a bit of sun but skies will be overcast by the end of the day. A storm system is on our doorstep from the Pacific and will begin dropping precipitation in the early morning hours Saturday on a southwest flow. Again this will be similar to last weekends storm where it started with a lighter density snow but will quickly change to a much wetter snow as Saturday wears on. Snow levels anticipated to be at the 6000 foot level early Saturday morning and possibly rising from there. Expect approx. 0.3 inches of water equiv. through Sunday evening. Snow amounts? Who knows! Sunday will likely be dry but overcast. Temperatures again will be a bit above normal with daytime highs about freezing at 8000 feet and nigh time lows in the upper 20's. Winds from the SW in the teens with occasional gusts. Another couple waves of moisture will hit us Monday night and then again on Thursday.
 

General Announcements:

Winterfest Poker Run: We will be setting up a booth at the Chief Joseph Days Rodeo Grounds, Thunder Room, January 9th at 7am. Stop by the booth and see how avalanche practitioners do their work, what tools they carry and most importantly what safety equipment you should carry and know how to use when traveling in avalanche terrain.

FREE Avalanche Awareness Talk on Tuesday January 12^th. It’s at the Joseph Community Center at 6 pm and part of the fabulous Eagle Cap Extreme activities at Race Central. The Payette Avalanche Center is visiting us here to assist us in the talk. Great videos of real avalanches, photos, etc., then some really good info on how to become Avy Savvy, learn the basics and how to learn more. He’ll even bring some props that show with a special sand-like material why one snow layer slides on another. AND IT’S FREE!!!!

January 15 Summary: Next Week look for a bottom line summary on Friday morning on the Home Page Blog. The complete summary will be posted on Sunday. Julian will be in the backcountry providing support for the Eagle Cap Extreme Sled Dog Race!

Current Regional Weather Synopsis:

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
230 AM PST FRI JAN 8 2010

.SHORT TERM...TODAY THROUGH SATURDAY NIGHT...UPPER RIDGE WILL HOLD
ON FOR A WHILE THIS MORNING. SOME MOISTURE WITH A WEAK WEATHER
DISTURBANCE IS TRYING TO MOVE UP AND OVER THE RIDGE AT THIS TIME AND
IT IS GETTING SHEARED APART AS IT DOES SO. THE NEXT SYSTEM WILL BE
STRONGER AND CONTAINS MORE MOISTURE. IT IS EXPECTED TO MOVE INTO THE
CWA BY THIS AFTERNOON AND SPREAD PRECIPITATION ACROSS THE AREA FROM
WEST TO EAST TODAY AND TONIGHT. THERE IS TRAPPED COLD AIR IN THE
LOWER COLUMBIA BASIN AND ADJACENT VALLEYS AND BLUE MOUNTAIN
FOOTHILLS. THIS AIR IS NOT AS COLD NOR AS DEEP AS THE PREVIOUS
WINTER WEATHER EVENT LAST WEEK...BUT ENOUGH TO CAUSE A MIXTURE OF
MAINLY FREEZING RAIN AND SLEET TO START...GRADUALLY CHANGING TO ALL
RAIN FROM SOUTH TO NORTH AS TEMPERATURES WARM UP...AND AS THE
TRAPPED COLD AIR GRADUALLY MIXES OUT. THERE MAY BE A BRIEF PERIOD OF
SNOW IN FAR NORTHERN AREAS OF THE CWA...BUT EVEN THERE THE WINTER
PRECIP TYPE WILL MAINLY BE FREEZING RAIN AND/OR SLEET TO START. ONCE
THIS SYSTEM MOVES ON TO THE EAST ON SATURDAY AFTERNOON AND SATURDAY
NIGHT LINGERING RAIN AND HIGHER MOUNTAIN SNOW SHOWERS WILL
PERSIST...THOUGH DECREASE WITH TIME. WILL KEEP PATCHY FREEZING FOG
MENTIONED THROUGH THIS MORNING AS THERE ARE STILL AREAS WITH REDUCED
VISIBILITY AND LOW STRATUS THAT IS CONTACTING HIGHER TERRAIN WITHIN
THE LOWER COLUMBIA BASIN AND ADJACENT VALLEYS. AT THIS TIME THE
AREAS WITH THE LOWEST VISIBILITY IS CENTRAL OREGON WITH REDMOND AND
BEND BOTH REPORTING LESS THAN A MILE AT TIMES. 88

.LONG TERM...SUNDAY THROUGH THURSDAY. HIGH PRESSURE WILL KEEP MOSTLY
DRY CONDITIONS ACROSS THE AREA SUNDAY. A STORM SYSTEM WILL APPROACH
THE TWO STATE AREA MONDAY SPREADING SOME SHOWERS TO THE OR/WA
CASCADES MONDAY. AS THE HIGH PRESSURE SLIPS EAST...THE SHOWERS WILL
MOVE INTO THE REMAINDER OF THE AREA TUESDAY AND WEDNESDAY. HOWEVER A
BRIEF PERIOD OF FROZEN PCPN IS POSSIBLE MONDAY NIGHT AND TUESDAY
NIGHT ACROSS PORTIONS OF THE AREA. AS THE STORM SYSTEM DRIFTS EAST
HOWEVER MOISTURE LINGERS AND THE UNSETTLED WEATHER IS EXPECTED TO
PERSIST INTO THURSDAY.