Rock Creek: Warming, Isolated Wind Transport, Depth Hoar

SNOWPACK OBSERVATION
Submission Info
Forecaster
Tuesday, March 27, 2018 - 12:30pm
Red Flags: 
Rapid warming
37° 26' 39.3036" N, 118° 43' 32.8548" W
Snowpit Observations
More detailed information about the snowpack: 

Toured up the Tamarack moraine on the E side of Rock Creek canyon to the N shoulder of Mt. Morgan S to track the warming trend, look for any wind slab development, and get some baseline information about the snowpack and the potential for deep faceted layers in the area. Back down the same way.

Very isolated areas of light to moderate blowing snow off of individual peaks in the morning between 830am and noon (see green circle photo). By noon there was no more visible blowing snow. Seemed like the wind up high had either died or had exhausted what little was left for transport in fetches.

3 sets of field weather to quantify the warming trend (warming was rapid today and widespread). Site 1 at 9000' on an E aspect taken at 9am: Sky=Clear, Wind=Calm, HS=60cm, Ski pen= 10, Boot pen=15cm, Tair=-0.5 deg C, Tsurf=-7.5 deg C, T-20=-2.5 deg C, Surface=dry MFcr with dry NSF on top. Site 2 at 9800' on a small E facing rollover on an otherwise W facing slope taken at 1015am: Sky=Clear, Wind=Calm, gusting Light from the NE, HS=85cm, Ski pen= 10, Boot pen=45cm, Tair=2 deg C, Tsurf=-1 deg C, T-20=-8 deg C, Surface=moistening NSF. Site 3 at 11,000' on an ENE aspect taken at 1220pm: Sky=Few clouds, Wind=Calm, HS=95cm, Ski pen= 10, Boot pen=35cm, Tair=6 deg C, Tsurf=0 deg C, T-20=-6.5 deg C, Surface=Moistening NSFs. Most surfaces in Rock Creek, except E and S, were about 30cm deep of NSF. E aspects were warming appriciably by 10am, SE aspects warmed through all the way to 11,200' by noon. E facing test slopes at 1pm at about 9000' were touchy for loose wet slides (easy to skier trigger). Otherwise snow surfaces were variable between previously deposited wind drifts from SW winds on the lee of rollovers, rocks, and vegetation; plenty of deep surface facets (recycled pow on N aspects), and melt-freeze crusts on low elevation S and E aspects and where trees could re-radiate the suns heat in the past day or so.

Snow pit dug at 10,600' on an ENE aspect where I had confirmed the deep facet layer with my probe. The depth hoar was still dry, loose and sugary, and was large and very well developed (striated, 3mm, see magnifier crystal card photo). Test results indicate that it is still reactive in the area, but I suspect that it would need a very big trigger because of the depth and the firmness of the snow over it. See attached profile.

Snowpit or crown profile photo or graph: 
Snowpack photos: 
Weather Observations
Blowing Snow: 
Air temperature: 
Wind Speed: 
Precipitation: 
Air temperature trend: 
Wind Direction: 
Accumulation rate: 
More detailed information about the weather: 
-- placeholder --

ESAC receives significant financial support from ...