Wallowa Avalanche Center

Conditions Summary for October 30, 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.

Current Wallowa Mountains Summary:

Only a few hours passed since last weeks summary hit the wires on  morning (10/23) and the rains began in earnest with up to 0.5" (1.3 cm) of water (not equiv.) at the SNOTELs. Temps were in the 30's(f) (0 C)  early on Friday but began dropping in the afternoon with winds changing to NW; not soon enough however to change the precip to snow before the storm ended. Little did most of us suspect what might be going on up there. A rain crust was forming which your director took a look at on Sunday the 25th.

Saturday (10/24) was mostly sunny with seasonable temperatures and moderate NW winds.

Sunday morning lows were nearly the coldest yet with 18F (-8 C)  at 8000' (2400 m), sunny, hardly a cloud in the sky and calm wind all day. Beautiful day to take a jaunt up to the Aneroid Basins' Dollar Ridge area to find a barely noticeable rain crust (rc) at the 7600' (2300 m) level whose thickness continued to build to nearly 3mm at 8350'  (2550 m) the highest I dared travel without crampons on the steeper slopes. Temps warmed into the 30's (0 C) while up there.

The rc was independent of aspect which is almost always the case. However the rc was very elevation dependent with a previously water soaked upper 3"-4" (7 - 10 cm) (of the snowpack at 7400' (2250 m), 1mm rc @ 8000' (2450 m), & 3mm rc @8350'(2550m). I would confidently suspect the rc to extend all the way to the ridgetops. This rc was bonded on it's underside to the old snowpack surface (will that bonding last?) but the top of the rc was slick, polished and shiny. No anchors of consequence on the steeper slopes in this Basin will assist any new snow layer.

Snowpack depths:  7.5" @ 7400'  (19 cm @ 2250m)   11.5" @ 8350'  (29 cm @ 2550)  on Sunday 10-25

A snowpack profile @ 7400' (2250 m) on level open meadow yielded the following: Upper half or so of pit is rain soaked supportable crust (1-2mm rounds, class 6mf, P hardness), lower half is bonded (1F hardness, class 3mx, 1mm) but less so and is moving from faceted rounds to facets from 10x observations and temperature gradient measurements.  

Monday brought mostly overcast skies with winds SSW @22 gusting to 50 mph (10 - 22 m/s) but changing to NW by mid afternoon and slowing a bit to the teens. Daytime temps around 40F @8000'. (5 C @ 2450m)

By Tuesday the snow that fell overnight Monday and through the daylight hours Tuesday likely didn't stick well and has been transported from the windward aspects to the E -> S leeward aspects from winds averaging about 20mph (9 m/s)  from the NW. Anybodys guess where the transported snow came to rest since the rain crust is quite slick. My guess is that numerous isolated areas or slopes will trap snow and disguise the slippery dragon below.  Temps were hovering around 20F (-6 C) all day.

Wednesday brought occluded skies, temps in the teens at 8000' (-7 - -12C @ 2450m), flurries, winds , and a chance to make another observation. A trip up McCully Basin to elevation 8400' (2550 m) at UTM 0487310E 5006265N.

The rc layer is clearly evident about 8 inches from the surface. SnowPilot data for this pit is shown below. Unfortunately we are experiencing some software glitches and the data is shown on 2 frames.

On the way up I observed wind drifts 2'+ (60 cm) deep, scouring to nearly ground level in other spots, and a rain crust (now under a new 8" (20 cm) snowfall) that alternated between slick (not bonding) and bonding to the new snow layer over very short distances (2 feet (60 cm)).

I suspect that the warm temperatures and warm winds of Monday morning may have softened the previously hard slick crust. Wind drifts at this location were deposited on the east -> S aspects, south appearing to be the deepest.

Three small natural avalanches (L-NL-R2-D1) released on a NE aspect 3/10 mi.(500 m) due S of test pit location likely during a cross loading wind event on Tuesday. One maybe sympathetically released the others, hmmm? No evidence of any slab development immediately adjacent. From afar with a monocular I couldn't ascertain with certainty the bed surface. My bet would be the top rc surface.

Thursday skies were a bit obscured once again with lows in the low teens and the winds calm. Mt. Howard saw about a 1" (2.5 cm) new snow event overnight. Flurries and squalls carried on all day and at times the sun poked out but nothing of consequence for accumulation up high.
 
 Summary: Snowpack totals this week on average from observations (depths will vary)
7500' = 6" new  total depth 12" (2300 m 15cm new total depth 30cm)
8400' = 8" new  total depth 19" (2550 m 20cm new total depth 48cm)
 
This weekly condition summary is the end of our October web test session. This particular summary is a little heavy on technical jargon, on purpose, for future reference. Beginning next week the summaries will be somewhat less technical for those using our site with a bit less experience and avalanche education. We welcome comment at info@wallowaavalanchecenter.org on which summary you prefer as the season moves on.
Regards, and be safe out there. - Your Director

Current Regional Weather Synopsis:

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
243 PM PDT THU OCT 29 2009

.SHORT TERM...TONIGHT THROUGH SATURDAY NIGHT...THE WARM FRONT THAT
HAS BEEN MOVING THROUGH THE REGION TODAY WILL CONTINUE TO LIFT
NORTHEAST AND EAST OUT OF THE REGION THIS EVENING. AS A RESULT WILL
SEE STEADY PRECIP CONTINUE ALONG AND NEAR THE CASCADES...OVER THE
BLUE MOUNTAINS AND ACROSS UNION AND WALLOWA COUNTIES THIS EVENING.
THE PRECIP SHOULD THEN DECREASE AND BECOME MORE SHOWERY OVERNIGHT.
THE BEST CHANCES OF PRECIP WILL BE NEAR THE CASCADE CREST AND ALONG
UPSLOPE FAVORED AREAS LIKE THE BLUE AND WALLOWA MOUNTAINS OVERNIGHT.
AT THE SAME...TIME WILL SEE THE SNOW LEVELS CONTINUE TO RISE THROUGH
THE EVENING AND DURING THE OVERNIGHT PERIOD. THUS SNOW ACCUMULATIONS
WILL BE LIMITED TO THE HIGHER MOUNTAINS BY EARLY FRIDAY MORNING. LOW
TEMPS IN SOME AREAS WILL OCCUR IN THE EVENING THEN RISE OVERNIGHT.
CENTRAL OREGON WILL SEE TEMPS DROP OVERNIGHT AS USUAL THOUGH AS
THERE SHOULD BE SOME BRIEF CLEARING OF SKIES. THE REGION WILL BE
WITHIN THE WARM SECTOR OF THE SYSTEM FRIDAY. AS SUCH SHOULD SEE SOME
BREEZY WINDS...MILDER HIGH TEMPS AND LIMITED PRECIP. THE COLD FRONT
WITH THIS SYSTEM WILL MOVE ACROSS THE REGION BETWEEN MIDNIGHT AND
NOON SATURDAY. THUS EXPECT CHANCES OF PRECIP TO RISE DURING THIS
PERIOD. SNOW WILL BE VERY LIMITED AS THE COOLER AIR WILL ARRIVE LATE
SATURDAY AFTERNOON AND SATURDAY NIGHT...AND THE PRECIP THREAT WILL
DECREASE TO LINGERING MOUNTAIN SHOWERS DURING THAT TIME. 90

.LONG TERM...SUNDAY THROUGH THURSDAY...MODELS START OUT IN GOOD
AGREEMENT WITH HIGH PRESSURE OFFSHORE GRADUALLY TRANSITIONING TO A
MORE ZONAL WESTERLY FLOW. EXPECT MOST OF SUNDAY, SUNDAY NIGHT, AND
MONDAY TO BE DRY ACROSS THE REGION. LATE MONDAY AFTERNOON AND
EVENING, A WEAK WAVE WILL MAINLY AFFECT THE WASHINGTON CASCADES
BRINGING RAIN ALONG WITH A BIT OF SNOW MIXED IN ABOVE MOST PASS
LEVELS. THIS IS WHERE REASONABLE CONFIDENCE IN THE FORECAST ENDS.

TUESDAY THROUGH THURSDAY, THE GFS AND IT`S ATTENDING ENSEMBLE
MEMBERS HOLD ON TO A MORE ZONAL PATTERN BUT STILL HIGHLY VARIABLE IN
THE NUMBER OF POSSIBLE SOLUTIONS. THE OPERATIONAL ECMWF STARTS
DIGGING A LARGE UPPER LOW OFFSHORE MAINLY BETWEEN 130W AND 140W. PER
HPC DISCUSSIONS, THE ECMWF ENSEMBLES ARE INDICATING SOME FORM OF A
LOW OFFSHORE BUT ARE ALSO BRING A HIGH NUMBER OF POSSIBLE OUTCOMES.
HPC PREFERS DISCOUNTING THE OPERATIONAL ECMWF AND LEANING MORE ON
THE ZONAL GFS CONCEPT.

BOTTOM LINE IS, HAVE DECIDED TO FORECAST SOME SORT OF COMPROMISE BY
GENERALLY FOLLOWING THE GFS ENSEMBLE MEAN POPS AND TEMPERATURES BUT
WITH LITTLE CONFIDENCE IN ANY PARTICULAR VALUE MUCH BEYOND MONDAY.
/JBONK