Wallowa Avalanche Center

Conditions Summary for November 20, 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:

Well, boys and girls; This past Sunday I found some really nice POW up on Wing Ridge, but after Tuesday (anybody remember what Tuesday was like?), the snow that once was, is now somewhere on the outskirts of Calgary, Alberta if I have my snow transport equations correct. Yes, 88 mph gust sometime early Tuesday morning recorded by www.josephoregonweather.com and that's in the valley! Fat Ridge (ENE) that I skied Sunday is now rocks and dirt. Presently expect  plenty of wind slab on NNW -> E aspects. Let us hope that the mid week warmth and sun we've had will settle these wind slabs and we'll again be able to enjoy turns up on these northerly and easterly aspects. Any place else; e.g. SE -> S -> W pretty much rocks, dirt, grass, bushes, you get the picture. Our outing; myself (Keith), Julian (WAC Board member & webmaster) and Ted (a good friend) fought our way up Fat Ridge on Tuesday just for all of you, so we would know first hand what damage the winds were doing. Real reason -> we're nuts!!

Photo 1: Tracks from Sunday, before the wind event.

What we found on Tuesday was exposed, very hard melt/freeze (MF) crust that is still slick, bare ground, and wind slab (multiple slab layers) very thick in places with a northerly component above this MF crust. On this outing day we encountered a usual 'red flag' whumpf which was unmistakable but we were taking all the most conservative routes to the top on bare ground or in thick trees away from the heavily wind loaded aspects. A quick look down a few chutes off Salt Crk headwall nearest Middle Ridge yielded much evidence that this is where a lot of snow was captured. My Sunday outing when there was no wind found enough surface hoar from Friday night and especially Saturday night to be of concern on these steep N -> NE aspects under whichever wind slab is now on top of it. You see, there are multiple layers of wind slab (up to 6) generated between Sunday night and Tuesday night. Each one has a different bond to the one below. Some are bonded well, other layers of wind slab not so well bonded.
Wednesday provided us with generally mostly sunny skies and seasonable temperatures but Thursday brought overcast skies and gentle winds in advance of today's storm.
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Concern 1: Wind slab bonding anywhere you see pillows, drifts, or large smooth surfaces mostly NW -> E aspects prior to the beginning of the new snow. Be aware of variable bonding of each of these layers to each other and especially to the MF crust below. After the snow begins additional loading of these fairly recent wind slabs will require careful evaluation. Anticipate earlier cross-loading events from the winds of earlier this week.

Concern 2: There are many slick,  localized and spotty MF crusts due to the micro-wind current variations through trees and around topographical features of previous days. When new snow comes there is likely to be poor bonding in these places. Frequent hand pits in the new snow will tell you whether it's a slick MF crust or wind slab surface in your travels during the first part of the storm but after that hand pits may not be as useful.

Concern 3: Coverage. The new snow will disguise many booby traps anywhere there was no previous snow coverage. For hiking, this is less of a concern, but for skiing - watch out!
Remember, this is early season and there are many blow-downs, branches, etc. just waiting for contact with a tibia or fibula.

Evaluate these concerns with prudence before entering into avalanche terrain.

Photo 2: Top of Fat Ridge, 8,500’. Looking SE. Note the large areas with no snow.

The Juicy, Techie Stuff:

Numerous hand shears in all kinds of places and slope angles proved sensitivity at a variety of interfaces. Pic below shows an overhang at lower elevations which was no different than at upper where F+ hardness snow between 4F+ or even 1F wind slabs were generating very clean, easy, Q2 shears. Snow below the wind slab layering is from early in the wind event where the lighter density snow moved short distances before settling into it's resting place. Other windslab layers likely traveled further and through saltation and rolling are much denser. The interface arrow is representative of different wind events separated by a very thin softer snow. I found up to six of these on the upper elevations. On several occasions I found hand shear slab tests consistently failing about 1-3" above the MF crust leading me to suspect the weak layer being that SH event of last weekend or some small 0.5 mm facets I saw on Sunday (11/15). I really wanted to provide a snow profile at some upper representative elevation but with winds Tuesday 35 mph sustained, gusts to 50+ , well - hope you'll forgive me.
 

Photo 3: Low elevation wind slabs.. This @6500'

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.

Expect cloudy skies today (Friday) with precipitation moving in by afternoon. Snow levels will be dropping from above 7000' to under 5000' through the night Friday period and into Saturday. Heaviest snowfall amounts likely to be very early Saturday morning and tapering off in the afternoon. Another wave of moisture expected beginning sometime on Sunday with lesser amounts expected. Storm totals snow through Sunday night (QPF of 0.5" water) just over  a half foot @ the 8000' level. Clearing overnight Sunday and cold with a ridge of high pressure moving in for the first part of next week.

General Announcements:

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

Current Regional Weather Synopsis:

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
300 AM PST FRI NOV 20 2009

.SHORT TERM...TODAY THROUGH SATURDAY...A DEEP...NARROW UPPER TROUGH
CONTINUES TO MOVE TOWARDS THE WEST COAST. THE SOUTH END OF THE
TROUGH IS STILL DIGGING SOUTH SOME...THUS WILL SEE SOME SPLITTING OF
THE ENERGY WITH THIS SYSTEM. THIS SPLIT DOES APPEAR TO BE TAKING A
SIGNIFICANT AMOUNT OF THE SYSTEMS MOISTURE SOUTH INTO CALIFORNIA...
THUS LIMITING THE TOTAL PRECIP AMOUNTS WE SEE OVER OREGON AND
SOUTHERN WASHINGTON. WILL SEE SOME PRECIP SPILL EAST OF THE CASCADES
INTO CENTRAL OREGON AND WASHINGTON THIS MORNING...THEN THE PRECIP
WILL SPREAD EAST THIS AFTERNOON AS THE COLD JUMPS ACROSS THE CREST.
THE AMOUNT OF TIME THAT THE CENTRAL WASHINGTON CASCADE EAST SLOPES
EXPERIENCE UPSLOPE FLOW SHOULD BE LIMITED TO THIS MORNING. THE FLOW
THEN TURNS WESTERLY THIS AFTERNOON. THUS COMBINING LIMITED UPSLOPE
FLOW TIME AND SNOW LEVELS GENERALLY AROUND 2500 TO 3000 FEET
TODAY...ONLY EXPECT 2 TO 5 INCHES OF SNOW ABOVE 2500 FEET WITH UP TO
2 INCHES BELOW 2500 FEET. THEREFORE WILL DROP THE CURRENT WATCH AND
GO WITH BELOW ADVISORY AMOUNTS. ELSEWHERE SNOW ACCUMULATIONS ABOVE
2500 FEET THROUGH TONIGHT WILL ALSO STAY BELOW ADVISORY LEVELS.
CURRENT WIND ADVISORIES ARE GENERALLY FINE AS WINDS KEEP FLUCTUATING
UP AND DOWN OVER UNION AND WALLOWA COUNTIES AND ALONG THE BLUE
MOUNTAIN FOOTHILLS. FOR NOW WILL CONTINUE THE ADVISORIES DUE TO
THESE PERIODIC WIND SURGES. PRECIP WILL DECREASE AFTER MIDNIGHT AND
THROUGH SATURDAY OVER OUR EASTERN ZONES. THE WESTERN ZONES WILL SEE
AN INCREASE IN PRECIP CHANCES SATURDAY AFTERNOON AS YET ANOTHER
SYSTEM APPROACHES THE PACNW. 90

.LONG TERM...SATURDAY NIGHT THROUGH NEXT FRIDAY...IN THE NEAR TERM A
WEATHER SYSTEM WILL CROSS THE REGION SATURDAY NIGHT AND THE QUICKLY
EXIT THE REGION ON SUNDAY. THIS SYSTEM WILL BRING MAINLY RAIN WITH
SNOW IN THE MOUNTAINS. RIDGING WITH DRIER CONDITIONS WILL MOVE IN
AND PREVAIL ON MONDAY. A PROGRESSIVE FLOW PATTERN WILL THEN DEVELOP
AND PERSIST THROUGH MUCH OF THE REMAINDER OF THE EXTENDED PERIOD
WITH ONE PACIFIC WEATHER SYSTEM AFTER ANOTHER MOVING ACROSS THE
REGION. EACH ONE WILL BRING A ROUND OF PRECIPITATION...MAINLY RAIN
WITH SNOW CONFINED TO THE MOUNTAINS. SNOW LEVELS WILL BE MODERATE SO
THE HIGHER MOUNTAIN PASSES AND RIDGES WILL BE AFFECTED THE MOST. 88