Wallowa Avalanche Center

Conditions Summary for January 22, 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:

Continued warm weather is slowly improving the lower snowpack strengths. Winds over this past week have been relentless, cooking right along generally in the teens to 20s mph continuously (photo 1). This has caused much wind transported snow generally from the southerly direction. Expect a wide variety of wind slab layering and crusts, with some weak sensitivities, any place the wind can get through. We’ve seen drifts through rows of trees this week unless they are mighty dense and extend a decent distance to the leeward. New snow this week has given us about 8 inches in several separate impulses. Therefore, in wind sheltered terrain the turning experience is quite pleasant. Also, the old rain crust of almost 2 weeks ago now is far enough down that it's no longer interfering with our fun but has become one of our concerns when in avalanche terrain.

Photo 1: Relentless winds on the upper reaches of Fat Ridge, 8000 feet, Wednesday 1-20-10.

There have been no reports this last week of natural or human triggered avalanche activity. Red flags such as collapsing, whumpfing, cracking have become much less prevalent and isolated this week from reports.

Concern #1: Wind Slabs, crusts and drifts in the upper portion of the snowpack. With strong SSE -> SW winds this whole week, there are a variety of wind slabs (varying thickness) on north through easterly aspects in wind exposed terrain. We have been able to get a thin crust (about 1 inch) to crack and break apart on all aspects. This thin crust didn’t cause us major concern but it could trip you up. About 30cm down (a foot) we saw the first sensitive weak layer directly above the old rain crust of January 5. In tests, this weakness shows stability, but my gut feel is to be wary of it for a bit longer until perhaps continued warmer weather breaks down the (now decomposing) rain crust. In certain other areas of the NE Wallowas at a similar distance down, a weak layer may be comprised of an old surface hoar layer.

Concern #2: New snow. Starting  tonight (Friday) into Saturday some new snow is expected. Watch for bonding to the wind slabs/crusts noted above and further wind transport as usual. The new snow may bond to the old snow surface but it is quite likely the weakness (failure plane) will be under the thin (1 inch) crusts developed this last week on all aspects. Quick hand shears work really well for checking this bonding or use ski cuts. On your hand shear, be sure to cut down below the thin crust layer.

Concern #3: Deep slab instabilities. Continued strengthening of the lowest sugary (facet) weak layer is evident. However, we still have a relatively thin snowpack for this time of year. And, of course, there are areas that are much thinner still. Compare the two photos (NE aspect photo 2 vs. SE aspect photo 3). There still remains some risk to triggering an avalanche at a trigger point involving a thinner snowpack spot where the weight of a person or snowmachine can reach down to this layer. If this were to occur, tests are still showing a likelihood that this failure and subsequent fracture will propagate down to this weakness and across the slope, possibly resulting in a very large and destructive avalanche.

Photo 2: Ken Bronec modeling a beautiful pit to ground on NE aspect Fat Ridge at 8000 feet (taken 1-20-10). Snowpilot diagram below is of this pit.

Concern Summary:

The wide variety of wind slab thicknesses and bonding to each other is the primary area of concern. Secondary layer of concern is new snow instabilities and the bond to the old snow surface. Third concern is the possibility of a triggering a deep slab avalanche running on the still somewhat sensitive deeply buried weak granular snow. Evaluate these concerns carefully when traveling in, around or below slopes exceeding 30 degrees.

Photo 3 caption: Keith couldn't model for this SE aspect pit at 7900 feet on Middle Ridge since no photographer available (taken 1-20-10)

Southern Wallowas: No new reports this week.

Snowpack depths: (Depths are still varying wildly)

Northern and Eastern Wallowas: 8 inches new, 44 inches average depth @ 8000 feet

Southern Wallowas: A few inches new, 80 inches average depth @ 8000 feet

The Juicy, Techie Stuff:

This warmth combined with overburden is continuing to increase hardness of the faceted depth hoar layer (either directly above the MF crust or at the ground) from what was originally almost F hardness to 4F+. Additionally, the striated crystals originally measuring nearly 3 mm are now down to about 2 mm, having lost most, if not all of their striations. They are beginning to show some rounding, and with it, increased sintering among grains.

Photo 4: Ken Bronec performing an Extended Column Test,  after test failed at the first significant weak layer (12 inches down, paint brush in photo 2)

Surfaces just prior to this upcoming storm cycle is a collection of ‘you name it’. Soft stellars and needles from yesterday morning’s light snow in wind protected areas, sastrugi on the most wind affected terrain and wind crust (northerly) or sun crust (southerly). The sun crust (southerly aspects) seen on Wednesday has gone through two or three cycles of melting and refreezing and so measures around an inch and in places the layers are quite distinct.

Figure 1: This diagram is of the upper extent of Fat Ridge at 8000 feet, NE aspect, 34 degree slope at approx. UTM 0492200E 5004550N.

General Announcements

This Friday evening, 1-22-10, WAC will have an information booth at the Frostbite film festival at the Joseph Community Center, 5:30 pm. We’ll have educational literature, tools of the avalanche practitioner on display as well as the all important safety gear you should always carry with you. We’ll be selling raffle tickets for a complete safety package of equipment which includes a shovel, probe, backpack and beacon. This is a value worth $700.

Don’t forget our Wallowa Avalanche Center biggest fun event of the year on February 11 (Thursday) 6pm at the OK Theater in Enterprise!!  Cool movies!! The event will feature pizza from Embers in Joseph and beer from Terminal Gravity, as well as a raffle and a drawing for items that include a backcountry safety package consisting of a backpack, shovel, probe and electronic beacon. Proceeds from the event will purchase additional educational materials to be offered free to the public; instrumentation for better wind data from the top of Mt. Howard; additional Web site enhancements; and support for WAC’s Observers Network.

Tickets are available for only $5.00, while children under 6 are free. Purchase tickets at the Bookloft, Central Copy and Shipping, and The Sports Corral. More information is available by calling Penny at 541-263-1454 or emailing info@wallowaavalanchecenter.org

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.

Finally we can expect a real snowstorm. I’m crossing my fingers for a real pounding. However, NWS models indicate most of the deepest amounts will be to our south and west. The southern Wallowas will likely benefit greatly from this storm. We will see increasing clouds today with snow beginning overnight tonight (Friday) and continuing through Saturday. Snow levels will start at about 5500 feet but drop to around 4500 feet overnight and stay there throughout the storm cycle. Expected accum. 6 to 10 inches at 8000 feet before the trough leaves the area Sunday morning. Another wave of moisture possible Sunday night into Monday but less intense. SW winds until Saturday night then changing to NW for Sunday ushering in the next upper level low pressure. Daytime highs = mid 20’s, nighttime low’s = upper teens.

Current Regional Weather Synopsis:

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
510 AM PST FRI JAN 22 2010

UPDATED AVIATION DISCUSSION

.SHORT TERM...TODAY THROUGH SATURDAY NIGHT...ACTIVE SHORT TERM
PERIOD IN STORE AS COMPLEX UPPER LOW OVER NORTHERN NV LIFTS
NORTHEAST INTO IDAHO AND WRAPS MOISTURE AROUND ITS WEST SIDE INTO
PORTIONS OF EASTERN OREGON AND EXTREME SOUTHEAST WASHINGTON. LIFT
WILL BE ENHANCED BY UPSLOPE FLOW INTO THE EASTERN MOUNTAINS
RESULTING IN A SNOW EVENT...ESPECIALLY AT ELEVATIONS ABOVE 4000
FEET. HAVE DECIDED TO ISSUE WINTER WEATHER ADVISORIES FOR SNOW FOR
THE EASTERN THIRD OF THE FORECAST AREA WITH THE EXCEPTION OF THE
GRANDE RONDE VALLEY WHERE IT MAY STAY A LITTLE WARM FOR ADVISORY
LEVEL SNOW AMOUNTS. COULD VERY WELL BE PUSHING 24-HR WARNING
CRITERIA ACROSS THE NORTHERN BLUES AND OCHOCO-JOHN DAY HIGHLANDS
WITH THIS EVENT SO THE SITUATION WILL NEED TO BE MONITORED DURING
THE 12 HOURS FOR THE NEED FOR AN UPGRADE. IT HAS BEEN SNOWING IN
BEND FOR THE PAST FEW HOURS AND FROM THE WEB CAMS IT APPEARS THAT
1-2 INCHES OF SNOW HAS FALLEN. LATEST IR IMAGERY INDICATES THAT THE
AREA OF ENHANCED CLOUDINESS ASSOCIATED WITH THE SNOW IS MOVING OFF
TO THE WEST SO HAVE DECIDED TO HOLD OFF ON AN ADVISORY FOR DESCHUTES
COUNTY. SNOW WILL CHANGE TO RAIN THERE DURING THE DAY AS
TEMPERATURES WARM UP INTO THE LOWER 40S. BY LATE SATURDAY NIGHT THE
EFFECTS OF THIS STORM WILL BE OVER WITH BRIEF RIDGING BEFORE THE
NEXT SYSTEM MOVES IN.  78


.LONG TERM...SUNDAY THROUGH FRIDAY...BRIEF RIDGING OVER THE AREA ON
SUNDAY WILL GIVE WAY TO A STRONG FRONT SUNDAY NIGHT AND MONDAY. SNOW
WITH SOME RAIN BELOW 3000 FEET WILL MOVE OVER THE CASCADES AND
AFFECT MAINLY CENTRAL AND NORTH CENTRAL OREGON IN THE AFTERNOON.
OVERNIGHT IT WILL CROSS THE AREA WITH SNOW LEVELS LOWERING TO BRING
SNOW EVEN TO PORTIONS OF THE COLUMBIA BASIN. THE MOUNTAINS MAY SEE
ADVISORY OR WARNING AMOUNTS BUT WILL WAIT UNTIL AFTER NEXT SYSTEM TO
SEE IF ANY WATCHES...ADVISORIES OR WARNINGS WILL BE NEEDED. THIS
STORM WILL WEAKEN QUICKLY AND MOST OF THE PRECIPITATION WILL
DECREASE AND/OR TURN TO RAIN DURING THE DAY ON MONDAY. AFTER THAT A
TROUGH SETS UP OFF THE COAST WITH A RIDGE TO OUR EAST. A WEAK SYSTEM
MOVES THROUGH TUESDAY BUT WILL SPLIT WITH MOST OF THE ENERGY GOING
TO THE NORTH AND SOUTH OF US. WE SHOULD STILL SEE A CHANCE OF RAIN
AND SNOW TUESDAY AND TUESDAY NIGHT. AFTER THAT CURRENT MODEL RUNS
ARE SHOWING A RIDGE OVER THE AREA THAT WILL KEEP THE AREA MOSTLY DRY
AND WARMER. WOULD LIKE TO SEE THAT FOR MORE THAN ONE RUN BEFORE
GOING WITH THAT SCENARIO SO HAVE KEPT CURRENT FORECAST OF A CHANCE
OF RAIN AND SNOW WEDNESDAY THROUGH FRIDAY. TEMPERATURES WILL
GENERALLY BE NEAR SEASONAL NORMALS WITH HIGHS IN THE MID 30S TO MID
40S AND LOWS IN THE 20S TO LOWER 30S. PERRY