The image shows the white, cloudy tops of several thunderstorm cells from the vantage of the GOES satellite. The TRMM orbit (dark shading) is superimposed on this cloudy background. There is a particularly intense storm cell located over western Oklahoma (left side of image). Whereas the GOES satellite shows this to be a single, isolated storm, the TRMM precipitation radar reveals that it is actually composed of three smaller precipitation cores in various stages of development. The vertical scale of the rain features has been greatly exaggerated to show details. The dark blue colors correspond to the tallest rain cells (approaching 15-16 km depth) while red colors indicated shallower rain features. This particular "multicell" storm produced damaging hail as it moved from west to east across Oklahoma. The third cell labelled "Splitting" rapidly moved off toward the northeast and merged with a separate supercell, producing a violent tornado between Joplin and Springfield, Missouri.

The Sunday, May 4 super outbreak of severe weather across the southern Plains produced 84 tornadoes, 89 reports of damaging winds (downbursts) and 275 large hail reports. The Tropical Rainfall Measurment Mission (TRMM) satellite overflew the severe weather area during the height of activity. This image shows a vertical cross section through a severe multicell hailstorm over western Oklahoma. While appearing as a single cloud in the GOES visible channel (white regions in the image background), the TRMM precipitation radar has identified three distinct precipitation cores, which have been greatly exaggerated in the vertical to show detail. Two of the more intense cells are shown here. The colors correspond to precipitation intensity. Light rain and snow (in the colder upper reaches of the cloud) are shown in blue, and the most intense rain cores are shown in red and dark maroon. The thin black lines trace contours of constant rain intensity. Like the layers of an onion, TRMM reveals that the most intense rains are contained in the lower region of the righthand cell, which towers to 16 km in height. In fact, the intensity of the precipitation is such that hail is likely mixed in with the rain near the surface.

This image shows how the TRMM precipitation radar can give clues to the severity of a thunderstorm and the nature of its precipitation. The arrows point to peculiar indentations in each of the three precipitation cores, referred to as "Bounded Weak Echo Regions" or BWERs, at about the 6 km level. These are areas of weak backscatter or energy return from the storm. These areas typically correspond to strong updrafts - fast rising columns of moist air. In the case of this severe storm, the presence of BWER regions suggests that the updrafts are strong enough to form hail. The rain and hail is ejected from each updraft core and surrounds it like a falling curtain.

These two radar images, one from the TRMM Precipitation Radar (PR, left panel) and one from the NEXRAD Doppler radar at Tulsa, Oklahoma (right panel), sampled the same severe hail-producing multicell over western Oklahoma at exactly the same time (2116 UTC). The Tulsa radar image is a composite which shows the maximum reflectivity (dBZ) measured in its sampling volume. The TRMM scan provides complementary vertical structure information and reflectivity is shown here at five horizontal levels cutting through the storm (at 1, 3, 6, 9 and 12 km). While the TRMM radar view lacks the finer horizontal resolution of the NEXRAD (4.3 km for the PR vs. a few hundred meters for the NEXRAD), the comparison shows excellent agreement in terms of overall storm morphology, with both radars capturing the three individual precipitation cells in low levels of the storm. Both radars also indicate maximum reflectivities between 55-60 dBZ. Because TRMM is not sensitive to reflectivities less than about 16-18 dBZ, the NEXRAD scan indicates more light rainfall is being blown downwind in the upper level westerly jetstream. The PR shows that the rightmost cell (Cell 3) is not as deep as the middle mature cell (Cell 2) but it contains the highest reflectivity values, and this cell will soon rapidly split off to the northeast to merge with a supercell to its north.