According to the contract rules of CX Futures Exchange L.P., TradeWeather relies on the Daily Climatological Reports (CLI) published by the National Weather Service.
While TradeWeather features separate contracts for Daily Snow and Rain and they each settle to the specific values indicated in the CLI reports for the particular station it normal to expect that these measurements may experience certain correlation.
For reference of those interested in the matter the National Oceanic and Atmospheric Administration (NOAA) has published the following Snow Measurement Guidelines.
Here is an excerpt from this document :
“• When, in your judgment, LESS THAN 50 PERCENT of the exposed ground is covered by snow, even though the covered areas have a significant depth, the snow depth should be recorded as a trace (T). Make a note of the range of depths of the remaining snow in the comments.
- When no snow or ice is on the ground in exposed areas within 100 yards (300 feet) of your normal observing location, record a “0”.
- When strong winds have blown the snow, take several measurements where the snow was least affected by drifting and average them. If exposed areas are blown free of snow while others have drifts, again try to combine visual averaging with measurements to record your representative value for snow depth. (noting that if more than half of the ground is snow-free only a trace should be reported)”
For Further information you can check the pages Understanding The Weather Measurements and The case of Trace measurement for Rain and/or Daily Snow.