A fairly violent thunderstorm passed through Utah County, starting at the south end and progressing northward. Scattered clouds began about 13:30 as evidenced by the variations in the solar irradiance, with heavy overcast moving at 15:25 with the sky completely obscured by 16:00 (it was very dark by then). The rainfall began at 16:10 with a peak rate of about 4.5"/hour for roughly 20 minutes. The temperature fell 15°F in about 10 minutes and the humidity rose by about 60% over the period from 16:05 to 16:10. After the rain stopped, about 19:00, the temperature dropped another 7°F or so. There is also a slow drop in the station pressure (absolute atmospheric pressure) until 16:00 when there is an abrupt rise due to the downdrafts in the thunderstorm. Peak winds were 47 mph at about 16:10, just before the rain started.
The conditions at BYU around this time: