"tempest – A severe storm with very high winds and often rain, hail, or snow." … "From Latin tempestas, from tempus, ‘time’. The Latin word originally meant ‘period of time’, which evolved into ‘weather’ and, finally, ‘storm’."
This is very interesting, Terry! In my humble opinion, it can only be this: A digital weather station does the same as a barograph, it registers the atmospheric pressure over time. Now, for centuries seafarers have used barometers to predict the weather. But the barograph is really what interests them because e.g. a ten hectoPascal fall or rise during a period of 8 hours is a certain sign that a gale force wind is on its way. It can’t be wrong; the gradient force of a lower pressure is what generates wind.
So, how steep is the curve of the plotted pressure is what, I think, your "tempest index" mean. It is not a usual name in meteorology but, perhaps your instrument was made in China and/or translated from another language. "Tempest" is actually the French word "tempête" that the Normands took with them when they invaded England.
This is what I had found online.
Definition of tempest relating to weather:
"tempest – A severe storm with very high winds and often rain, hail, or snow." … "From Latin tempestas, from tempus, ‘time’. The Latin word originally meant ‘period of time’, which evolved into ‘weather’ and, finally, ‘storm’."
According to a user manual I found online…
http://www.lacrossetechnology.com/9020/manual.pdf
The "Tempest Index" gives you the forecast probability of tempest type of a storm occurring for that forecast period.
Just a way of warning if a storm is coming.
Perhaps it is the Total Solar Irradiance that you get at your location.
a portion of time, a season, weather, storm, akin to tempus time
a violent wind or storm
This is very interesting, Terry! In my humble opinion, it can only be this: A digital weather station does the same as a barograph, it registers the atmospheric pressure over time. Now, for centuries seafarers have used barometers to predict the weather. But the barograph is really what interests them because e.g. a ten hectoPascal fall or rise during a period of 8 hours is a certain sign that a gale force wind is on its way. It can’t be wrong; the gradient force of a lower pressure is what generates wind.
So, how steep is the curve of the plotted pressure is what, I think, your "tempest index" mean. It is not a usual name in meteorology but, perhaps your instrument was made in China and/or translated from another language. "Tempest" is actually the French word "tempête" that the Normands took with them when they invaded England.