How to interpret precipitation observations

Snow is notoriously difficult to measure but using radar and webcams and being aware of temperature, humidity and wind will help when interpreting precipitation readings.

Precipitation parameters reported by stations

r1hr/r10m (mm)
One hour or 10 minute rain measured by a tipping bucket rain gauge.

SDpt (cm)
Snow depth is measured by an acoustic device pointing downward.

s1hr (cm)
A one hour snowfall rate (s1hr) estimated from the SDpt.

Pwt (mm)
The accumulated weight (wt) of precipitation. The number will occasionally be reset instantly downward but the gradual increase over time is due to precipitation whether rain or snow. The increase from hour to hour should match the P1hr value if provided.

p1hr/p10m (mm)
A one hour or 10 minute precipitation rate estimated from Pwt which may or may not be reported.

SWEQ (mm)
Snow Water EQUivalent reflects the snowpack and is reported by a 'snow pillow'. Snow accumulates on a platform and a scale records its weight, reported as if it's the depth of water in mm. Springtime temperatures will begin to melt the snow and the water will drain off once the snow can no longer hold the excess water. The instrument will return to near zero for the summer and increase again in the fall reaching a maximum in early spring.

Keep in mind the following when looking at the observations

Snow, having fallen on a tipping bucket rain gauge, can melt hours or days later to then be recorded as rain as it flows into the gauge. Did the "rain" start when the temperature rose above zero? Is the precipitation gauge (p1hr/p10m/SWEQ) showing no increase? Check the weather radar for precipitation.

Snow depth is measured from above over a small area. Drifting snow can have a big impact. Heavy or blowing snow can confuse the device and lead to erratic readings. Check the winds.

Old snow can settle as new snow falls on it so the new snow can appear to be less than what would be apparent on a hard surface such as a road.

Snow density can vary by a factor of five or more from wet snow perhaps mixed with rain and dense wind driven snow to light powder. Compare the snow depth to the water equivalent and watch the temperature. Driving conditions will suffer more from dense snow for a given snow depth.

Provincial highways webcams are great for monitoring the start of a snowfall.

There are lots of sensors available.