How is "snow" measured in NWAC telemetry?

Does anyone know how the snow measurements are gathered for NWAC telemetry reports?

Is it a team of gnomes with rulers measuring snow falling on a piece of plywood in a windless area at each telemetry site?

Do the gnomes take the density or crystal structure of the snow into account? Is all snow created equal when it comes to inches of accumulation?

Is the "Total Snow" number a summation of freshly fallen and measured snow, or the actual amount sitting on the ground at the time of measurement, taking compaction, melting, etc, into account? Must be the latter, right?  Again, do gnomes with rulers measure this too?

How's this stuff I've been taking for granted work? What tools and techniques are involved?

Is it a team of gnomes with rulers measuring snow falling on a piece of plywood in a windless area at each telemetry site?

Yep. However, instead of rulers, I believe they use ultrasound . NWAC, Amar, or someone else better informed can tell you more.

The total snow measurement is empirical and usually separate from the 24 hour measurement. Watch after a storm and see it settle/compact. In the summer, you can watch it melt into beloved corn and return to the ocean and clouds from whence it came...

The very best part is that the gnomes make measurements in awful weather at 3 am and post it to the internet for our perusal.

Trumpetsailor has it right.

The 24 hour snowfall board is cleared every 24 hours, for WSDOT that happens at 0600 each day.  The Total Snow is the height, or depth, of snow on the ground.  Amar proves good details of an exceptional period of snow settlement here: www.turns-all-year.com/skiing_snowboardi...ex.php?topic=11823.0

The gnomes do take a density reading each day.  You can figure the approximate  density yourself with this formula: precipitation / snowfall = density (EX: 1.00" precipitation / 10" snow = .10 or 10%)

It is good to take into account the tendency for instrumentation in a mountain environment to suffer occasional glitches.  If the 24 hour snow suddenly increases to say 47", it is an equipment error (sorry).

"It is good to take into account the tendency for instrumentation in a mountain environment to suffer occasional glitches. If the 24 hour snow suddenly increases to say 47", it is an equipment error (sorry)."

Or Mt Baker

Stimbuck has it right but for those interested I wanted to add a bit more info about depth sensor operation:

Instead of snow gnomes or very cold grad students with rulers, the snowdepth sensors NWAC uses are acoustic depth gages (similar to sonar on board boats/ships/vessels) that send a sound wave down to the underlying snow (or water) surface. In the case of an underlying snowpack, this sound wave bounces off the snow surface (and hopefully not a snowflake somewhere in between the sensor and the surface) and returns to the sensor. The sensor, knowing the speed of sound and the total time for the round trip sound wave (and correcting this speed for the current air temperature), then runs an equation that calculates the distance between sensor and ground. Since the distance between sensor and ground is known already (NWAC or WSDOT staff measure and input this distance on installation), the depth directly under the sensor is found by subtracting the hourly measured distance between sensor and snow surface from the known sensor to ground distance. This result is the hopefully increasing snow depth (in most non split flow years).

The most common erratic depth sensor issues include:
heavy snowfall or high winds (the sound wave may bounce off snowflakes in the air),
very low density snow surface that presents little mass or an erratic surface for the sound wave to bounce off of,
off angle depth sensor (not vertically aligned),
wetness within the sensor,
or some obstruction within the 20 degree sound cone that extends from the sensor to the snow surface (like trees or ropes that encircle a snow sample area).

When the sensor does not obtain two consecutive readings that lie within an inch of each other during its up to 10 sample hourly execution interval, it effectively says "I can't find the snow surface" and outputs the "offset:. This "offset" is the aforementioned measured sensor to ground distance or sensor to plate distance (in the case of a 24-hour or storm depth sensor). Hope this information is not overly ambitious and remains helpful.

Cheers, Mark Moore--NWAC

Thanks, Mark! !