Did a bit more poking around. Could be a temperature inversion causing a spike (http://www.wrh.noaa.gov/slc/climate/TemperatureInversions.php http://www.wrh.noa

Did a bit more poking around. Could be a temperature inversion causing a spike (http://www.wrh.noaa.gov/slc/climate/TemperatureInversions.php http://www.wrh.noaa.gov/slc/climate/TemperatureInversions.ph...). Would be heavily dependent on the location of the sensor and surrounding topography, which all fits. If I find time, I might overlay weather data and see what it looks like.