Wallowa Avalanche Center

Conditions Summary for February 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:

We were graced with about 6 inches of new snow on Friday the 12^th through Saturday early morning but nearly double that in the southern Wallowas. This snow was generally on the heavy side and settled to a denser layer this week. However, since the 12^th there’s been no appreciable new snow and temperatures have surely been above normal. In many places this new layer of snow sits on top of a surface hoar (frost) layer which was deposited during a clear spell Feb. 6 through 8. Refer back to last weeks report. All observers this week report sensitive weak layers in the top one and one half (1½) feet of the snowpack. We have detailed reports this week from Aneroid Basin, Mt. Howard, Fish Lake area via snowmobile, Wing Ridge, McCully Basin, the Ice Lake area and the southern Wallowas.

Photo 1: One of the larger older natural avalanches which released most likely during the 2/5-2/6 storm cycle in the southern reaches of the Wallowas. This one ran on the Pine Creek drainage side to the NW of Simmonds Ridge.

While snowmobiling last Sunday (Fish Lake) and skiing on Monday (Mt. Howard) we found rather stiff feeling, moist, sticky and kinda rubbery snow nearest the surface. Both skis and sleds didn’t really want to turn easily and sometimes you would punch through the upper denser layer into the slightly less dense snow underneath. In the southern Wallowas there is a 2.5 mm rain crust (nearly clear ice) about 65 cm (25 in.) below the surface but from some quick tests generally the instabilities are above that rain crust layer.

Photo 2: Upper Tramway building on Mt. Howard. Looks like you have to cut a hole in the roof to get into the building. photo taken 2-15-10.

Recent activity: As the week wore on and the warm temperatures began to effect the uppermost snow layer(s) the classic evidence of wet activity surfaced. Roller balls, pinwheels and wet loose mash potato snow started slipping down the steeper slopes. This wetness really came to a head in the Southern Wallowas with a fairly large natural wet slab avalanche (WS-N-D2.5-R4-N) on a SE slope. This one released however without any obvious signs of loading (thermal, wind transport or precip.) Crown was up to 150 meters across and ran from tree to tree way above the cliff bands. Many other varieties (SS, WS, WL, L) of avalanches were occurring down there on all aspects and elevations from 6000 to 8500 feet except the largely westerly aspects. The northern and eastern Wallowas have not been near as active. Reports in this region have only recorded a couple isolated wet loose avalanches on southerly aspects of relatively minor size this week.

Photo 3: The professor (Chago) kindly submitted this photo of the amazing surface hoar found on the surface of the snow almost 2 weeks ago in the southern part of the Wallowas. It is now buried underneath from 5 inches to as much as 20 inches of the most recent snow.

Concern #1: As reported last week we continue to see a variety of weak to very weak interfaces and sandwich type layering in the upper 1½ feet of the snowpack. As usual, not everywhere, but in enough places to put this concern in the #1 prime-time slot. These weaknesses are due to recent density changes in the new snow, a buried persistent surface hoar layer(s), and some amount of crusting. This crusting is either a sun crust, melt-freeze crust or a wind crust. From reports, these upper weak layers are being found sufficiently often this week on nearly all aspects and elevations that blanket aspects and elevations can’t be given. What is known is that tests show failures at 3 or 4 interfaces in the upper 1 ½ feet including a poor bond to the much harder homogeneous mid snowpack block.

Concern #2: Wet avalanches. With this constant warmth for mid February we are seeing wet activity quite early. Mostly on the southerly aspects, but due to the greenhouse effect, some of the more northerly lower elevation slopes have been issuing some roller balls.

Concern #3: Borrowing some words from Evelyn Lees (of the UAC); ˜The deep slab weakness/instability is being pushed into the background, but I doubt it’s a thing of the past€˜.

Concern Summary: The upper 1½ feet of the snowpack requires careful evaluation due to numerous sandwiched weaknesses in widespread areas. Wet activity has been noticed a bit in the north but more so in the southern Wallowas with the continued above average temperatures.

Take all these concerns under advisement, perform sufficient evaluative testing and maintain red flag awareness for your safety when traveling in and around avalanche terrain.

Photo 4: Keith and Julian found some of the surface hoar on Mt. Howard, here measuring about 1 cm thick with crystal lengths up to 7mm and under about 5 inches of the new snow (NE aspect, 8140 feet). photo taken 2-15-10. Trouble is, the crystals are standing up and they can collapse like a bunch of dominos and then, guess what..

Average snowpack depths at 8000 feet this week:

Northern and Eastern Wallowas: 6 inches new, 50 inch total depth
Southern Wallowas: 12 inches new, more recent and accurate data indicate high 90 inch total depths
With the warmth and so few storms, it’s a bit tough to build a deeper snowpack.
 

Photo 5: After Matt chopped an entrance through the cornice and dropped some big blocks down this couloir with no signs of instability he dropped in on 2-15-10 (N aspect, 7700 feet). On the way up the Falls Creek trail he continually checked for instability on similar aspects. See many entries by Mprimomo on the forum this week.

The Juicy, Techie Stuff:

Pics and snow profile diagrams pretty much sum it up. Hand shears this week have still been working to get a quick handle on some of the layer bonding nearest the surface. Interestingly, in some places shovel shear and CT’s weren’t consistent on the surface hoar (SH) layer. Shovel shear tests would generally shear on the SH but the compression test or ECT would fail (not propagate) on some weakness about an inch or so above the SH. This interface failure was at a very subtle hardness difference. Also noted in some drainages was a minor wind crust (½ in. thk) about 12 to 20 cm below the surface while in others this was nonexistent. Where this crust is present we’ve recorded quite sensitive compression test failures just above it or below it. It’s important to note that all observers this week who employed an ECT found no propagation results in the top meter of the snowpack. The buried surface hoar could be problematic as the snow stiffens and becomes slab like and could pull back onto lower angle slopes.

Figure 1: Mt Howard pit data

Besides the snowpilot test results here is a list of other reports: (all measured down from surface)
North-West aspect, 6880 feet, 28 degree slope
CTMQ2 25 cm - same results two times
CTHQ3 45 cm - same results two times
East aspect, 7200 feet, 30 degree slope
CTMQ3 25 cm - same results two times
ECTN11N 25 cm
CTHQ2 45 cm - same results two times
ECTN23 45 cm
East aspect, 8000 feet, 35 degree slope
CTMQ1 80 cm (DH) - same results two times
Lemon count @ 80 cm = 4
RB test at 8400 feet east aspect and resulting test was a 4 (we used our heaviest person for this test). 50cm down on a 25 degree slope.
Other test scores: CT 6 quality 2, and ECTN 8 15cm down on the new/old interface. CT26 quality 2, and ECTN 22 90cm down at a hardness change from 1F to Pencil. (unclear what aspect and elevation for these other scores)

Figure 2: Redmont Ridge pit data

Figure 3: Idealized profile - Northern and Eastern Wallowas

General Announcements
Here is one final reminder that the Wallowa Avalanche Center is hosting a free transceiver practice day at Salt Creek Summit on Sunday, Feb 21. We will meet at 8:30 and carpool from the parking lot in Joseph, which is on the right side of the Imnaha highway a block east of Main Street. We plan to be done up there by 3:00 PM. The day will include some indoor discussion about search techniques and some hands-on transceiver drills. We will also set up practice scenarios for both beginner and more advanced transceiver users. We will be using our probes too, since they are a very important part of pinpointing the location of a buried individual.

So bring your transceivers and probes, along with lunch and water, and be ready for a day out on the snow. We will have extra transceivers and probes to loan out to those who do not yet have them.

It is important for us to know how many people are coming so we can prepare an efficient and educational day using the proper number of instructors. Please let Ken Bronec know (kbronec@eoni.com, 541-432-3281) by 7pm Friday evening 2/19 if you plan to attend and whether you need any loaner equipment.
 

Next weeks summary report will be written by Ken Bronec giving Keith a break to visit the Wasatch in Utah to play of course, but also to work with research partners in the wonderful world of snow science. Thanks Ken!
 

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.

A large omega block is now entrenched as of yesterday (Thursday) with a high pressure ridge simply parked over the coast of Oregon. There are low pressure systems to either side of this ridge but we will not benefit. Expect dry conditions with mostly sunny skies through the weekend and into early Monday. There is an outside chance for spotty valley inversion. Sometime during Monday through mid week we 'might' see an active weather pattern develop with possible snow.

Upper level winds will be on the lighter side generally from the north. Temperatures will be slightly above normal but cooling ever so little as the weekend progresses. Generally temps at 8000 feet will be upper teens at night and upper 20's to low 30's for daytime highs.

Current Regional Weather Synopsis:

FXUS66 KPDT 191045
AFDPDT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
245 AM PST FRI FEB 19 2010

.SHORT TERM...TODAY THROUGH SUNDAY. A SIMILAR SITUATION IS TAKING
PLACE IN TERMS OF THE EXPANSION OF STRATUS CLOUDS THAT OCCURRED
YESTERDAY MORNING.  A NORTHERLY FLOW ALOFT IS PROVIDING SOME LOW
LEVEL UPSLOPE ALONG THE PAULINA AND OCHOCO MOUNTAINS ALLOWING
STRATUS TO EXPAND ACROSS CENTRAL OREGON.  ALTHOUGH DRIER AIR HAS
SPREAD OVER THE REMAINDER OF THE FORECAST AREA...FOG CONTINUES TO
REMAIN A PROBLEM AT THE LOWEST ELEVATIONS IN THE LOWER COLUMBIA
BASIN...PARTICULARLY ALONG THE COLUMBIA AND SNAKE RIVERS.  THIS
INCLUDES THE TRI-CITIES AREA WHERE DENSE FOG AND FREEZING FOG HAVE
BEEN OBSERVED.  WILL ISSUE A DENSE FOG ADVISORY FOR THIS AREA AS
EARLY MORNING COMMUTERS MAY EXPERIENCE TRAVEL PROBLEMS. BELIEVE A
NORTHERLY GRADIENT AT THE SURFACE WILL TIGHTEN LATER TODAY...WHICH
WILL ERODE THE FOG OR POSSIBLY PUSH IT TOWARDS THE BLUE MTN
FOOTHILLS.

VERY LITTLE CHANGE IN THE WEATHER PATTERN IS EXPECTED TONIGHT.  WILL
KEEP PATCHY FOG IN THE SAME AREAS AS THIS MORNING...I.E. AT THE
LOWEST ELEVATIONS OF THE COLUMBIA BASIN AND TOWARDS THE BLUE MTN
FOOTHILLS.  A POSITIVE TILT TROUGH AND A BACKDOOR COLD FRONT MOVING
SOUTH ALONG THE ROCKIES TODAY AND TONIGHT WILL HAVE LITTLE MOISTURE
IN OUR FORECAST AREA...BUT COLDER AIR WILL SPREAD OVER THE REGION.
TEMPS TONIGHT WILL BE IN THE UPPER TEENS TO UPPER 20S. A STRONGER
PIECE OF ENERGY ON SATURDAY AND SATURDAY NIGHT MAY PROVIDE ISOLATED
SNOW SHOWERS OVER THE CENTRAL MOUNTAINS OF OREGON WITH LITTLE OR NO
ACCUMULATION.  THE MAIN EFFECT WILL BE ADDITIONAL COOLING.  ON
SUNDAY...HIGH TEMPS WILL BE IN THE MID 30S TO UPPER 40S WHICH IS
NEAR TO SLIGHTLY BELOW SEASONAL AVERAGES.  MODELS CONTINUE TO
DIVERGE IN THEIR SOLUTIONS...BUT THE PROBLEMS MAINLY ARE IN THE
EXTENDED PERIOD.  JOHNSON


.LONG TERM...SUNDAY NIGHT THROUGH FRIDAY...VERY FEW CHANGES HAVE
BEEN MADE TO THE EXTENDED FORECAST. HIGH PRESSURE SHOULD REMAIN OVER
THE AREA THROUGH MONDAY FOR DRY CONDITIONS UNDER MOSTLY CLEAR SKIES.
TROUGHING IN THE EASTERN PACIFIC WILL THEN SEND A SERIES OF WET
DISTURBANCES THROUGH THE REGION TUESDAY THROUGH FRIDAY. WHILE THERE
ARE STILL NUMEROUS DETAIL DIFFERENCES BETWEEN THE GFS AND THE
ECMWF..THE GENERAL CONSENSUS IS THAT THERE WILL BE A CONTINUOUS
CHANCE FOR RAIN AND HIGH MOUNTAIN SNOW DURING THIS PERIOD. OVERNIGHT
LOWS HAVE BEEN RAISED SOMEWHAT WHILE DAYTIME HIGHS HAVE BEEN CUT
DOWN BY A FEW DEGREES TO ACCOUNT FOR THE PERSISTENT CLOUD COVER
ASSOCIATED WITH THIS PATTERN. HOWEVER...TEMPERATURES ARE STILL
EXPECTED TO BE NEAR TO SLIGHTLY ABOVE NORMAL.  82