Wallowa Avalanche Center

Conditions Summary for November 27, 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.

The Bottom Line Synopsis:

It’s surprising how similar our Wallowa snow pack is to the Wasatch in Utah so far this season. For a really good early season reminder of the importance of having a really strong background in avalanche snow pack assessment and expert route finding skills check out Brett Koberniks report on 11/25/2009 - 8:22pm . Not all of us would even want to go into terrain such as that depicted in his report but we certainly have it here in the Wallowas. See our pic taken on Wednesday (11/25) looking at Dollar Ridge and part of Tenderfoot Pass, north aspect. Here if you look close, snow was being transported through the pass (R to L) and being deposited on the lee parts of the slopes in cascade fashion just to the left of the sunny parts.

Photo 1: Dollar Ridge and Tenderfoot Pass

Julian and I ascended the south and westerly aspects on our outing to Aneroid Basin where more stable snow or dirt could be traveled upon; much the same as the 2^nd safer alternative route Brett chose. We found some roller balls and pinwheels (see pics) which started on 35+ degree slopes and came to rest on much flatter terrain. These are always really good indicators of impending wet loose or wet slab activity and one should begin thinking about finishing up traveling on slopes such as these fairly soon when these start their downward tumble.

Photo 2: Roller balls, West aspect 7800 ft.

No natural avalanches were noticed on any aspect within the Aneroid Basin this week as of Wednesday the 25th. South through westerly aspects still have very marginal to NO cover and hidden hazards under the snow are present. I’m beginning to see a pattern develop from my notes of 11-8 (McCully), 11-15 (Wing Ridge) and 11-25 (Aneroid). A loosely bonded layer (approx 2 inches thick, see Photo 4 of November 13 summary) is developing directly above the melt/freeze crusts episode of late October/early Nov. and there is now anywhere from a few inches to nearly 2 feet of snow and/or wind slab on top of this weaker layer. This appears to be more general in elevation than originally thought. Continued monitoring and testing of this weak layer should be followed in the future.

Photo 3: Pinwheels, West aspect 7700 ft.

Concern 1: Isolated wind slab areas or any soft slab may have the potential of being triggered and run on this 2� weak layer mentioned above; mostly on the NW -> N -> E aspects. There could be some areas where the rain crust of October 23 may pose problems. This rain crust is below the top of the melt/freeze crust. Be aware that new snow is expected throughout today and adjust your travel accordingly.

Concern 2: Coverage. Southerly and westerly aspects simply have terrible coverage and there are obstacles and booby traps galore. N -> E is better, but by all means not great. Care should be exercised all over for a while yet.

The Juicy, Techie Stuff:

The snow profile below gives a good general average of the snow pack for most uses. The rain crust still needs to be explored further, particularly in Aneroid where I made two attempts to reach it this week to check it’s status since it developed on Oct. 23. , unsuccessfully.

Figure 1: Generalized Snow profile

 Some fabulous examples of surface hoar measuring between ¼”€� and ½” were spotted in localized areas on the trip up Aneroid on Wednesday. Never in trees, spotted Wed. on northerly facing areas and was mixed with diurnal re-crystalization in various places. Some of the SH disappeared where the sun could hit it, even on N, but the diurnal stuff was barely effected.

Photo 4: Surface hoar. North aspect 6700 ft.

Let’s keep this in the back of our mind with the expected light snowfall during the day today (Friday) since this nasty stuff will now be buried. The .5 - 1 mm facets running from 1-3 inches thick above the topmost MF crust has me worried. It’s been around now for almost 3 weeks starting with a diurnal surface on 11-1, then some light 1-2 inch storms 11-6/7 and finishing off with a thin layer of graupel on 11-8 with a cherry on top. Hmmm.

This new snow likely will not pose a threat from the standpoint of additional loading, however as we know, the wind can always play a factor so watch for plumes or transport if the winds pick up and evaluate wind loading variables.

Snowpack depths are around 20" average on northerly upper elevation areas. Depths vary considerably within even 50'.

Evaluate all these concerns and tech discussion before venturing into avalanche terrain.
 

Photo 4: General Snow coverage in the Aneroid Basin 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.

Weather; Expect snow to continue to move into the area today with snow levels below 6000 ft. Expected accumulation a few inches at 8000 ft. Winds moderate from the south today then changing gradually to the NW on Saturday, ushering in a mild cold front. Clearing skies a bit Saturday late and partly sunny Sunday. Temps generally seasonable through the weekend.
 

General Announcements:

To our Observers: There was an error in the meeting date originally given as Dec. 12. It is Monday, December 14.

Be careful out there and keep looking at our Home Page Blog for updates during the week.

Current Regional Weather Synopsis:

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
332 AM PST FRI NOV 27 2009

UPDATED AVIATION DISCUSSION

.SHORT TERM...TODAY THROUGH SATURDAY NIGHT...A SLOW MOVING COLD
FRONT CONTINUES TO MOVE ACROSS THE FORECAST AREA THIS MORNING. MAIN
FRONTAL PRECIPITATION BAND STRETCHES FROM NORTHERN CALIFORNIA ACROSS
EASTERN OREGON TO FAR EASTERN WASHINGTON AND THE IDAHO PANHANDLE.
PRECIPITATION ALONG THE EAST SLOPES OF THE CASCADES HAS DECREASED TO
SHOWERS AT THIS TIME. AS THE FRONT CONTINUES TO SLOWLY MOVE EAST WE
WILL SEE THIS TRANSITION FROM A STEADY PRECIPITATION TO SHOWERS ON A
WEST TO EAST PROGRESSION. THE FRONT WON`T EXIT THE FORECAST AREA
UNTIL LATE THIS AFTERNOON SO AREAS EAST OF JOHN DAY AND MEACHAM WILL
SEE A STEADY PRECIPITATION UNTIL THIS AFTERNOON BEFORE TURNING OVER
TO SHOWERS. OTHER THAN A FEW LINGERING SHOWERS NEAR THE IDAHO
BORDER EARLY TONIGHT THE OVERNIGHT PERIOD LOOKS TO BE DRY AS HIGH
PRESSURE BUILDS BACK OVER THE REGION FROM OFF THE PACIFIC OCEAN.
THIS HIGH PRESSURE WILL DOMINATE THE WEATHER ON SATURDAY FOR MOST OF
THE FORECAST AREA. HOWEVER...A WARM FRONT WILL BE CLIPPING WESTERN
WASHINGTON SO COULD SEE SOME LIGHT RAIN AND SNOW NEAR THE SNOQUALMIE
PASS AREA OTHERWISE JUST SOME MID AND HIGH LEVEL CLOUDS ON
SATURDAY.

.LONG TERM...SUNDAY THROUGH THURSDAY. AN UPPER LEVEL RIDGE WILL
BUILD OVER THE PACIFIC NORTHWEST SUNDAY. AN UPPER LEVEL TROUGH WILL
APPROACH THE PACIFIC NORTHWEST MONDAY..AND FLATTEN THE RIDGE AS IT
MOVES THROUGH MONDAY NIGHT WITH A CHANCE OF RAIN AND MOUNTAIN SNOW.
THE UPPER RIDGE WILL REBUILD OFFSHORE AREA TUESDAY AND MOVE SLOWLY
EAST OVER WASHINGTON AND OREGON WEDNESDAY AND THURSDAY. NORTHWEST
FLOW MAY KEEP A FEW SHOWERS IN THE NORTHEAST OREGON MOUNTAINS
TUESDAY. THE GFS AND ECMWF HAVE VERY DIFFERENT TIMING AND TRACK OF A
CUTOFF LOW UNDERCUTTING THE RIDGE...WITH THE GFS MOVING THE CUTOFF
OVER OREGON AND THE ECMWF MOVING IT THROUGH CALIFORNIA. WITH WIDELY
DIFFERENT SOLUTIONS MADE NO CHANGES TO CURRENT EXTENDED FORECAST
BASED ON THE RIDGE MAINTAINING ITSELF. KEPT PARTLY CLOUDY SKIES WITH
PATCHY FOG DEVELOPING IN THE COLUMBIA BASIN AND ADJACENT VALLEYS
WEDNESDAY AND THURSDAY.