Precipitable
water at Purcell, Oklahoma (PURC) as measured by GPS, radiometer and radiosonde
from 0000 UTC 22 May to 0000 UTC 26 May 1993. The small blue dots represent
radiometer measurements along the line-of-sight to GPS satellites, mapped to the
zenith. The red dots represent 30-minute averages of precipitable water (PW)
calculated from the least-squares fits of GPS wet delay. Twelve hourly
radiosonde data from Norman, OK are shown by the green dots. The vertical arrow
denotes the time of the observed surface cold front passage at Purcell. Time of
thunderstorm activity is indicated with conventional symbols.