Wallowa Avalanche Center
Conditions Summary for February 12, 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:
WAC wants to thank the many observers who contributed data this week giving us a sound database for
this weeks summary. We’ve received data from clients of Wing Ridge Tours, hosts of Wallowa Alpine
Huts, folks skiing in Aneroid, in addition to the normal weekly outings of WAC staff and your director.
Thanks All!
Everyone is reporting good soft snow conditions on northerly facing aspects in the trees or open slopes
generally at or below treeline and away from any exposure to wind. Where the wind gets in, the snow
goes out. That simple. Most experienced observers have been venturing on all terrain and aspects up to
35 degrees in slope angle. Only a couple have dared venture at or above the 40 degree slope angle after
very careful snowpack assessment.
Photo 1: Hidden Peak, McCully Basin on 2-6-10. Sketchy snow cover on this aspect ya think (SE)?
As reported last week we continue to see two near surface weak layers on aspects from W -> N -> SE
and mid to upper elevations. 1. If there is a wind slab, wind crust, or wind board surface it is not
bonding to the softer snow directly underneath. 2. If there is soft snow on the surface (generally
measuring 3 to 8 inches) it is not bonding well to one of the harder snow surfaces below it. SO, in the
upper one foot or so of our snowpack on steep terrain look for sensitivities to loose snow slides, soft
slab type releases and very hard but possibly thinner wind slab releases. Do keep this in mind with the
upcoming storm cycle since these poor bonds will not magically correct themselves before the next
snow loading event. Southerly aspects simply have a miserable melt-freeze or sun crust with similar
sensitivities as the wind slabbed areas. All report the continued sugary type loosely bonded snow way
down at the bottom of the snowpack. Surfaces above treeline and certainly slopes on either side of
ridges have been mercilessly pounded by wind. Some skiable, some you just plain would rather not.
We saw no measurable snowfall this past week in the northeastern Wallowas. The southern wallowas
received nearly 20” of relatively heavy density snow on Friday 2/5 which started out lighter density.
Temperatures have been quite seasonable with many clear days this week. Very little wind was also a
welcome story for this week. With these conditions, surface hoar has been noted on a variety of nonsun effected and non-wind effected surfaces this week, growing up to ½ inch tall primarily late last
weekend into early this week.
Photo 2: Pit studies were performed on either side of this ridge (W and ENE aspects). Whitebark Ridge, LSD section at
8500'. Approx. UTM 0490650E 5005475N NAD 27. 2-9-10
Recent activity: None reported this week from the northern Wallowas. The southern Wallowas, which
received the new snow, had an abundantly active natural avalanche cycle.
Concern #1: Wind crusts, wind slabs, wind board and loosely bonded snow. Constant awareness for
these weaknesses especially with new snow coming that will hide some of the clues. Hand shears were
still working this week to check the upper 12 inches of loose snow bonding and slab bonding. Jump on
any small, low consequence test slope to get a feel if things are going to move before venturing where
the consequences are high.
Concern #2: Deep slab instabilities. Continued signs of lessening reaction to stress, weight and impact
down at the lower level of weakness. It’s just taking more energy to create a failure at this level.
Perhaps a snowmobile might or a skier traveling over just the right trigger point (thinner areas; like
rock outcrops, convexities, rollovers, near a line of trees). This dragon is still there, so don’t let your
guard down.
Concern Summary:
There exists complex variations in the upper one foot of the snowpack. These variations are due to
surface deposits, slabs and crusts. Lowest one third of the snowpack still contains some weaknesses.
Evaluate these sensitive layers of the snowpack carefully before entering avalanche terrain and steep
slopes.
Photo 3: Surprisingly strong bond on this shovel shear test. The exception for sure, not the rule. But strong bonds even
near the rocks, on a steep slope, above a melt-freeze layer? Hmmm.
The Juicy, Techie Stuff:
It’s taking more and more stress to get any results way down deep on the sugary facet layer. We’re
seeing CT22-25Q2/Q3 and RB6 consistently, failing anywhere from 10 to 40 cm above ground on
snowpacks greater than 1 meter. Where the snowpack depth is appreciably less than 1 meter, the deep
basal facets are a bit more sensitive. In particular WAC recorded a CT13Q3 and STM in the 0 to 10 cm
above ground range. This was surely the exception on an ENE aspect on 36 degrees @8500 feet.
Propagation propensity results using extended column tests are showing less likelihood of propagating
a fracture. I am still leary since natural activity in the northern reaches was not that long ago. With the
stoutly bonded mid pack strength I can’t help but wonder when the next major snow load or wind event
will tip the balance on the still somewhat weak facets near the ground and cause big crown/flank
fracture heights. Likely our biggest issue will be the uppermost foot of existing weak variability that
will ride downhill along with the new snow yet to come.
Photo 4: Keith performing an Extended Column Test in McCully Basin on 2-6-10. See discussion for this weeks results
of fracture propagation propensity. Location: 0487212E 5006733N NAD27, N aspect, 8500 feet.
Southern Wallowas: As mentioned, much natural activity occurred with the new snow of 2-5-10. In
particular there was a SS-N-R2-D2.5 near Blue Creek. Heavy wind loading on NE -> E aspects from
7000 feet upward. Stay tuned next week for a detail loaded report on the southern reaches when one of
WAC’s Professor of Snow-ology exits the outback.
Figure 1: Generalized snow profile
Average snowpack depths this week:
Northern/Eastern Wallowas: no new, 47 inches total
Southern Wallowas: Up to 20 inches new, 108 inches total
Figure 2: Snow pit profile which is quite representative and a composite of all profiles sent in to WACÂ from Aneroid,
McCully and Wing Ridge on N to NE aspects at 7800 to 8800 feet
General Announcements
February 21st (Sunday) is our beacon practice day up on the Salt Creek Summit. Please sign up at
[email protected] and also let us know if you need a loaner beacon.
Quiz!
Photo: QUIZ......Surface hoar downtown Joseph on a propane tank none-the-less and nearly no surface hoar on the
ground below. Why? (photo 2-7-10).
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.
National Weather Service models indicate a shift in the upper atmosphere to a more pronounced
westerly flow aloft bringing with it a possibility for some stronger weather systems. The first of two
weather systems moved through the Wallowas last night bringing with it a couple of inches in the
northern Wallowas and about 6 inches in the Southern areas. The second systems should reach us by
late tonight and carries with it a slightly higher probability of precipitation, however amounts will
generally by in the 2-6 inch range, with possibly more in southern reaches of the range. Snow levels
should run 3500-4500 feet. Saturday will show a drying trend but watch out for those strong winds at
the higher elevations. Sunday should continue with generally unsettled weather, with the bulk of the
next system deflected to the north by a ridge that builds up on Saturday.
Current Regional Weather Synopsis:
000
FXUS66 KPDT 121132 AAA
AFDPDT
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
330 AM PST FRI FEB 12 2010
UPDATED AVIATION DISCUSSION
.SHORT TERM...TODAY THROUGH SUNDAY...A SERIES OF WEATHER SYSTEMS
WILL KEEP THE SHORT TERM ACTIVE...WITH PERIODS OF LIGHT RAIN AND
MOUNTAIN SNOW. SATELLITE IMAGERY SHOWS EASTERN OREGON AND
WASHINGTON CURRENTLY IN A BREAK BETWEEN SYSTEMS. BY LATE MORNING
PRECIPITATION WITH THE NEXT SYSTEM WILL HAVE CROSSED INTO THE EAST
SLOPES OF THE WASHINGTON CASCADES...THEN SPREADING ACROSS THE REST
OF THE INTERIOR PACIFIC NORTHWEST THIS AFTERNOON AND EVENING. THE
LATEST OBSERVATION AT STAMPEDE PASS INDICATES A SNOW FLURRY...AND
LIGHT SNOW OR RAIN-SNOW MIX IS EXPECTED TODAY ALONG THE EAST
SLOPES...MAINLY NEAR THE CREST...ABOVE ABOUT 3500 FEET.
ONE FORECAST PROBLEM IS THE EXTENT OF FOG TONIGHT IN THE LOWER
COLUMBIA BASIN AND YAKIMA AND KITTITAS VALLEYS. THIS
MORNING...DESPITE MODERATELY STRONG RIDGE TOP WINDS...SURFACE
MOISTURE DID NOT DECREASE MUCH IF AT ALL. VISIBILITIES DUE TO FOG SO
FAR HAVE VARIED BETWEEN 3 MILES AND ONE QUARTER MILE AT THE
DALLES...YAKIMA AND PASCO. TONIGHT...AFTER A FRONTAL PASSAGE...
ONLY A SLIGHTLY DRIER AIR MASS IS EXPECTED. SURFACE MOISTURE WILL
LINGER AND AS SUCH OVERNIGHT TEMPERATURES HAVE BEEN RAISED A FEW
DEGREES AND PATCHY FOG WAS INTRODUCED INTO THE COLUMBIA BASIN AND
GORGE BELOW 1000 FEET. DEWPOINT TEMPERATURES WILL NEED TO BE
MONITORED THIS AFTERNOON TO BETTER ASSESS THE MOISTURE TREND AT THE
SURFACE.
IN GENERAL LIGHT PRECIPITATION AMOUNTS ARE EXPECTED. HOWEVER..THIS
AFTERNOON AS THE FRONT PASSES MODELS HINT AT WEAK ELEVATED
INSTABILITY. LIFT IS NOT STRONG AND THUNDERSTORMS ARE NOT
EXPECTED. HOWEVER...THE ELEVATED INSTABILITY...IF RELEASED...COULD
LEAD TO SHALLOW CONVECTION AND BRIEF MODERATE RAIN...WITH AMOUNTS
PERHAPS AROUND 0.5 INCHES...FOR SOME LOCATIONS THIS AFTERNOON. THE
BEST FORCING FOR LIFT...WHICH COULD RELEASE THE INSTABILITY THIS
AFTERNOON...APPEARS TO BE ACROSS UMATILLA AND GRANT COUNTIES IN THE
AFTERNOON...THEN IN THE EARLY EVENING MOVING EAST ACROSS OREGON TO
THE IDAHO BORDER. THIS REGION WILL BE IN THE LEFT-EXIT REGION OF
THE UPPER-LEVEL JET. 80
LONG TERM...SUNDAY NIGHT THROUGH THURSDAY...AN UPPER LEVEL TROUGH
AND ASSOCIATED FRONT WILL MOVE THROUGH SUNDAY EVENING. A QUICK
CHANGE TO WESTERLY FLOW WILL LIMIT PRECIPITATION IN TYPICALLY RAIN
SHADOWED AREAS OF THE COLUMBIA BASIN. A FEW SHOWERS MAY LINGER
MONDAY IN THE MOUNTAINS...THEN ANOTHER TROUGH AND FRONT WILL MOVE
THROUGH MONDAY NIGHT AND TUESDAY. TUESDAY NIGHT THROUGH THURSDAY AN
UPPER LEVEL RIDGE WILL BUILD NEAR THE COAST. THIS WILL KEEP EASTERN
WASHINGTON AND OREGON MAINLY DRY. HOWEVER...A WAVE MOVING DOWN THE
BACKSIDE OF THE RIDGE INTO MONTANA TUESDAY NIGHT AND WEDNESDAY MAY
TRIGGER A FEW SHOWERS IN THE NORTHERN BLUE MOUNTAINS AND WALLOWA
COUNTY. WITH DECREASING CLOUD COVER DUE TO THE BUILDING RIDGE
WEDNESDAY AND THURSDAY DIURNAL RANGES WILL INCREASE WITH SOME
RADIATIONAL COOLING AT NIGHT...PARTICULARLY IN THE HIGH VALLEY
LOCATIONS LIKE BEAR VALLEY AND MEACHAM. COONFIELD