It is not uncommon for severe weather to strike the plains this time of the year. Storms systems organizing east of the Rockies in the springtime are known for delivering severe weather to the central US as was the case this past week as an upper-level trough tapped into Gulf-of-Mexico moisture to spread strong storms with hail and gusty winds from the panhandle of Texas into the Ohio valley and midatlantic region.

The Tropical Rainfall Measuring Mission or TRMM satellite uses both passive and active sensors to measure precipitation from space. The TRMM Precipitation Radar or PR, the first and only precipitation radar in space, allows TRMM to look deeper into storms than can other satellites. The first image shows an instantaneous snapshot of a storm complex that extended from northern Texas into eastern Kansas. The image was taken at 07:23 UTC on 13 May 2005 (2:23 am CDT). The left hand side shows the horizontal distribution of rain intensity as seen from above by the TRMM satellite. Rain rates in the center swath are from the PR, and rain rates in the outer swath are from the TRMM Microwave Imager (TMI). The rain rates are overlaid on infrared (IR) data from the TRMM Visible Infrared Scanner (VIRS). The center of the line of storms over Oklahoma contains a squall line, which is characterized by a linear convective leading edge having strong updrafts and heavy rain (red areas) followed by an area of stratiform rain with weaker rainrates (green and blue areas). The right hand side of the image shows a vertical cross section through the center of the squall line taken by the PR. A tall convective tower reaches up to 13 km at the front of the line containing radar reflectivites in excess of 55 dBZ (grey area embedded in the black area), indicating the likely presence of hail aloft, followed by a broad area of weaker 20 to 30 dBZ echo (light blue and green) approximately 200 km wide. Prior to this image there were reports of hail and wind damage from the central Texas panhandle northeastward up through western Oklahoma, central Kansas and into northwestarn Missouri.

The second image was taken the following morning at 06:29 UTC 14 May 2005 (1:29 am CDT) and shows a similar pattern only with a wavy looking squall-line type system in far eastern Oklahoma and more intense convective cells over north-central Texas. There were several hail reports associated with the storms over Texas and wind damage was reported with the passage of the squall line in eastern Oklahoma and western Arkansas as areas of strong winds can distort the linear features of a squall line into a wavy pattern. Overlaid on the rain rates are lightning data from the TRMM Lightning Imaging Sensor (LIS). The clusters of magenta-colored crosses indicate areas of lightning activity observed near the time of the image and include cloud-to-cloud, cloud-to-ground, and intracloud flashes.

The final image shows a 3D perspective view of the 30 dBZ isosurface associated with the squall line along the Oklahoma-Arkansas border. The surface is colored according to the height of the surface with red being the highest. The higher the surface the more intense the convection is. Echoes near this intensity that penetrate above the -10 to -20 C level are also a good indication of the potential for cloud-to-ground lightning.

TRMM is a joint mission between NASA and the Japan Aerospace Exploration Agency (JAXA).

Images produced by Hal Pierce (SSAI/NASA GSFC) and caption by Steve Lang (SSAI/NASA GSFC).