Ground-based GPS water vapor observations near a tornadic supercell

NOAA's Forecast Systems Laboratory, in collaboration with other NOAA organizations and federal agencies, operates a ground-based Global Positioning System (GPS) water vapor demonstration network. GPS and surface meteorological data from approximately 50 sites are routinely processed to produce integrated precipitable water vapor (IPW) every 30 minutes under all weather conditions. On the evening of June 4, 1999, supercell thunderstorms formed along a quasi-stationary cold frontal boundary across northwestern Nebraska and south central South Dakota. These storms produced several tornadoes as they moved towards the northeast, including one at Oglala, SD which caused F1 and F2 damage to hundreds of homes on the Pine Ridge Indian Reservation. At 5:28pm MDT, a tornado was spotted approximately two miles north of the GPS-IPW observation site at Whitney, NE (WHN1).

Time series of precipitable water vapor for this severe weather event are examined for the Whitney site, as well as the Merriman, NE (MRRN) GPS-IPW site which is collocated with a NOAA Profiler Network 404 MHz Wind Profiler. Profiler data, radar imagery, surface and upper air observations are used to supplement the GPS water vapor observations in an analysis of this case.