Wallowa Avalanche Center

Conditions Summary for December 25, 2009

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.

A Very Merry Christmas to all of you from the Wallowa Avalanche Center

Special Holiday week information:

Those of you lucky enough to receive some new snowshoes, cross-country skiis, sleds (non-motorized) and all others who wish to get out this week to enjoy some of the new snow here is a list of areas safe and Good-to-Go as noted.

Salt Creek Summit designated and marked nordic cross-country trails (loop trails and so forth)

These trails are safe zones and throughout the winter do not enter avalanche terrain.

• The Tenderfoot Wagon Road Trail between Salt Creek Summit and ending in Big Sheep basin at the crossing of North Fork Big Sheep Creek at the 3 way trail intersection. See updated trail conditions on our Forum page - Salt Creek Summit.

This road is generally quite safe from avalanches and particularly so this week.

• New 1.5 mile Nordic trail established at Ferguson Ridge Ski area (Fergi).

No signs put up yet pointing to trailhead but the trail is now fully marked with blue diamonds.

This trail is a safe zone and throughout the winter does not enter avalanche terrain.

• Hurricane Creek trail up to Slick Rock ONLY.

See our Forum page “North Side”  entry for current road and trail conditions. This trail is safe to follow only this week and there aren’t any avalanche hazards. After Friday January 1 and throughout the remainder of the winter this trail crosses many very dangerous avalanche hazards.

The Bottom Line Synopsis:

The snow pack through today (Friday) has had a chance to settle and stiffen but don’t let that fool you in any way, shape or form. What has happened now is that the warmth last weekend has provided us a nice firm upper snow pack layer which generally will feel and appear solid. Above this firm feeling layer is varying amounts of powder received Monday night. However, underneath all this is a booby trap.

The loading (additional weight applied) of the snow pack continued this week from both rain and snow. After some warmth over last weekend and early this week we are now back to colder more seasonable weather with some sun to boot. This warmer weather helped to densify the upper half of the snow pack into a pretty firm slab now. We even got a bit of rain up high on the morning of Monday 12-21 before it changed to snow in the afternoon when through Tuesday morning we received 7 to 10 inches at the 8000 ft. level, and a foot or more in the southern reaches of the Wallowas. This snow was of the medium to high density type. Winds picked up on Monday and then changed direction by Wednesday creating drifting of the new snow and some additional hazards to watch for.

In the southern Wallowas it appears as though the booby trap is near ground level and in the northern Wallowas  it’s in the middle somewhere above the old rock hard crusty snow of early November. Slabs may be harder to trigger but when you find the thinner slab areas, wind loaded areas or places where the loose sugary snow is below the slab the consequences may be sizable. In other words, if you trigger a slide it is likely to be a big one.

Photo 1: Example of growing wind pillows from cross loading snow transport.

Concern 1: Wind slab loading of exposed terrain on N -> E -> SE aspects at mid elevations and upward from winds of Monday from the SW and Wednesday from the NW. Be aware of cracking and movement of new sensitive wind slabs, drifts, pillowing (see photo 1) and the additional load they will apply to the lower layers. Plumes were noticed continually on Wednesday (12-23).

Concern 2: Complex variations in the lower layers of the snow pack. Be especially aware of the weak sugary loose layer located below the newest firmer snow received the past week and a half or so. One pit location likely will not determine adequately the presence of this layer. It is now more prevalent than not, so if your pit doesn’t show it, look for it somewhere else. All aspects are problematic. Southerly aspects weakness is at or nearest the ground, northerly aspects weakness is mid snow pack above the old melt freeze rock hard crusting.

Travel in avalanche terrain this week requires a careful, knowledgeable and experienced evaluation of these concerns and others mentioned below in the more technical section.

Photo 2: Middle Ridge (Wing Ridge) at 7850'. Note the sloped top to the column after testing. This is buried surface hoar causing this very thin weak layer. Very sneaky and hard to detect

Photo 3: Largest natural of 3 spotted (12-23) in Hurricane Creek  released early this week. Start zone at UTM 0475000E 5015500N 7200 feet.

The Juicy, Techie Stuff:

There has been only one report this week of a possible human triggered avalanche and maybe that’s because folks have been prudent, knowing that the avalanche conditions have been quite questionable and not venturing out into avalanche terrain. See photos 4 & 5 for a possible remotely triggered slide by Jeff and CB when doing their observations for WAC. Outings this week have produced amazement (Keith anyway) at how the weak layers are varying. Some places have an undetectable (except by careful test) buried surface hoar layer (see photo 2), other places have good bonding of the slab to the top of the crusty stuff (much rarer) and other places just 20 feet away from a good bond have very poorly bonded loose sugary sand like grains above the crusty stuff. This is called spatial variability and there appears to be lots of this around. It’s hard to know where this loose sugary snow is and where it isn’t. Much whumpfing was heard in traveling last weekend and is likely to have subsided only a bit as the snow pack has adjusted, but not hearing whumpfing is NOT an indication of stability (the presence of the noise is only an indication of instability).

Figure 1: Middle Ridge,  Location UTM 0491950E 5005100N. Two problematic layers in this pit  but the weak layer in the upper 20 cm range is by far  what is most prevalent in the North & East Wallowas.

Now that I’ve seen some surface hoar nasties between the top of the MF conglomerate and the snow surface I am now paying closer attention to this dragon. It appears, as expected, to be mostly in the northerly shaded aspects. Easy shovel shears brought it out quite definitively but you just can’t see or detect it visually or by hardness on the pit wall. This SH layer described on the diagram below was deposited around December 8^th where I was at the same location and it is very thin. See December 8 Home Page Blog entry photo. Interestingly Julian and I came across a thin dirty layer from some wind event (not a problematic weak layer) which will be useful as a marker for future pits. We have no idea how widespread this dirty layer is.

Please note that the snow profile diagram for Middle Ridge represents what is at that specific location. I bring attention to the layer from 23 - 31 cm. Here the hardness was a bit stronger but in many other places on that outing the layer was approx. F and once you pushed your fist in, it flowed out like sand. This remains the persistent weak layer in my opinion in the Easterly and Northerly Wallowas.

Photo 5: Possible  remotely triggered slide, easterly aspect in McCully Basin Tuesday Dec. 22. Note the two weak interfaces on the far flank. Could the upper one been surface hoar and the lower one the sugary facets?

Photo 6: Debris field of the McCully slide. This slide was a wind loaded slope.

Down south it appears to be next to the ground. This layer is 2.5 mm advanced, striated, facets with some cupping noted. The wind crust located here in the low to mid 30 cm range is not always present. This particular pit represented a bias toward the top of a leeward loaded ridge. No CT’s or ECT’s were done due to the low angle slope. A propagation saw test may have provided some useful info (at least for propagation) for the sugar layer but darkness was just around the corner for us.

Figure 2 : Norway Basin, Jeff, a WAC observer, submitted this snow profile from the southern Wallowas

Average snow pack depths (depths vary wildly):

34" @ 8000 feet in the Northern and Eastern Wallowas

55" @ 8000 feet in the Southern 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.

High pressure will remain entrenched over the Wallowa Mountains through the weekend. Temperatures will slowly get colder but mostly sunny skies will abound. There is an outside chance by Saturday that a temperature  inversion with associated fog  will develop in the Wallowa Valley but the Mountains as usual should stay above it all. Winds will be light from the north throughout the period. Temperatures at 8000 feet; daytime upper 20's and night low teens. Monday is the next chance of some very light snow.

General Announcements:

WAC will have a booth set up at the Winterfest Poker Run in Enterprise on January 9. Stop by and chat with us. See some of the tools an avalanche field practitioner uses to study the snow and some of the safety equipment you should always carry and know how to use when out there.

Place January 12^th (Tuesday) at 6 pm on your calendar. A visiting Avalanche Forecaster from the Payette Avalanche Center will present an Avalanche Awareness Safety Seminar. Cool photos, short wild video clips and a talk  will highlight the dangers out there and then he’ll discuss how to become Avy Savvy to avoid these dangers and be able to more safely enjoy our mountains. He’ll even bring some props that show with a special sand-like material why one snow layer slides on another. Joseph Community Center, AND IT’S FREE!!!!

Current Regional Weather Synopsis:

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
225 AM PST FRI DEC 25 2009

.SHORT TERM...TODAY THROUGH SUNDAY...HIGH PRESSURE WILL REMAIN IN
CONTROL OF THE WEATHER OVER THE REGION ON THIS CHRISTMAS DAY AND
WILL CONTINUE INTO THE WEEKEND. IT WILL SLOWLY SHIFT EASTWARD WHICH
WILL CAUSE AN INCREASE IN MID LEVEL SUBSIDENCE AND STRENGTHEN THE
SURFACE BASED INVERSIONS...ESPECIALLY OVER THE COLUMBIA BASIN AND
ADJACENT VALLEYS/LOW LANDS. AS SUCH THE STRATUS AND FOG LAYER
CURRENTLY OVER THE FORECAST AREA WILL LIKELY EXPAND OVER THE NEXT
TWO DAYS. DENSE FOG HAS RECENTLY BEEN RECORDED OVER LOCATIONS WHERE
THE STRATUS LAYER MEETS THE TERRAIN IN LOCATIONS SUCH AS REDMOND AND
BEND IN CENTRAL OREGON AND LIKELY IN OTHER LOCATIONS AS WELL. IN THE
LOWEST ELEVATIONS IT WILL BE MAINLY A LOW STRATUS CLOUD LAYER WHILE
ON THE EDGES THERE WILL BE MORE DENSE FOG AS THE STRATUS LAYER MEETS
THE TERRAIN. THIS WILL MOSTLY AFFECT HIGHWAYS AND OTHER ROADWAYS
THAT RISE IN ELEVATION AS THEY CROSS A MOUNTAIN RANGE OR PASSES SUCH
AS INTERSTATE 84 ON CABBAGE HILL AND HIGHWAY 395 AND 97 IN CENTRAL
AND EASTERN OREGON WHICH BOTH CROSS AT LEAST SEVERAL MOUNTAIN RANGES
OR HIGH PLATEAUS. MAY NEED TO ISSUE A DENSE FOG ADVISORY BUT FOR NOW
HAVE COVERED IT WITH NOWCASTS AND IN THE ZONES/GRIDS. IN THE
FOG/STRATUS FREE AREAS CAN EXPECT MOSTLY CLEAR SKIES EXCEPT FOR SOME
HIGH THIN CLOUDS AT TIMES AND SLOWLY MODERATING TEMPERATURES OF A
DEGREE OR TWO EACH DAY THROUGH SATURDAY. ON SUNDAY A WEAK PACIFIC
WEATHER SYSTEM WILL TRY TO PENETRATE THE UPPER RIDGE BUT WILL WEAKEN
AS IT MOVES INLAND. HOWEVER THERE STILL MAY BE A FEW LIGHT RAIN OR
SNOW SHOWERS OVER THE CASCADE EAST SLOPES...MAINLY IN CENTRAL AND
NORTH CENTRAL OREGON. ELSEWHERE WILL REMAIN PRECIPITATION FREE
THROUGH SUNDAY. 88

.LONG TERM...SUNDAY NIGHT THROUGH FRIDAY...VERY FEW CHANGES WERE
MADE TO THE EXTENDED FORECAST BECAUSE GREAT UNCERTAINTY STILL EXISTS
AMONG THE MODELS. HOWEVER...PRECIPITATION CHANCES HAVE BEEN LOWERED
ON SUNDAY NIGHT AND MONDAY SINCE BOTH THE ECMWF AND THE GFS INDICATE
THAT WEAK HIGH PRESSURE WILL REMAIN OVER THE AREA DURING THIS
PERIOD. ALTHOUGH A FEW SHOWERS MAY BE POSSIBLE ALONG THE CASCADE
CREST OR IN CENTRAL OREGON...CONFIDENCE IS LOW THAT THERE WILL BE
MUCH...IF ANY...MEASURABLE PRECIPITATION. THE PRESENCE OF MID-LEVEL
RIDGING WILL ALSO ENSURE THAT THE SURFACE INVERSIONS REMAIN IN PLACE
OVER THE COLUMBIA BASIN...THUS FOG AND LOW STRATUS CAN BE EXPECTED
TO PERSIST THROUGH AT LEAST MONDAY MORNING.

THE GFS BECOMES MORE ZONAL BY TUESDAY...BRINGING A SERIES OF WET
DISTURBANCES THROUGH THE REGION DURING THE LATER HALF OF THE WEEK.
THE ECMWF BRINGS ONE SYSTEM INTO THE AREA ON TUESDAY NIGHT...THEN
BUILDS A STRONG RIDGE OVER THE REGION ON WEDNESDAY BEFORE BRINGING A
MORE POTENT SYSTEM INLAND ON FRIDAY. GIVEN SUCH UNCERTAINTY HAVE
KEPT A CHANCE OF RAIN OR SNOW IN THE FORECAST TUESDAY THROUGH
FRIDAY.  82