Guest Contributor Sheldon Kusselson provides an evaluation of the satellite view of moisture for two significant rainfall events, the event on April 17 and 18, 2016 in Houston, TX and one from April 11, 1995 that impacted southern Louisiana. The satellite product that meteorologists use to evaluate current moisture levels are the two graphics on the left. They are called the “Total Precipitable Water” product or TPW. This product provides a context of how much water is available in the atmosphere to support rainfall. The higher the TPW value, the more intense the rain can be and hence the potential for significant accumulations.
The upper left graphic shows a surge of moisture (areas shaded in yellow) into the Houston area. This constant surge refueled the storms with moisture to allow for rainfall amounts of 6 to 10 inches with isolated amounts of 16+ inches in a 24 hour period.
The graphic in the lower left is for the April 1995 Louisiana event. It shows broad areas of red, which is a TPW value of ~ 1.5 inches surging into Louisiana. While not as easy to read on the black and white contour map (our mapping abilities have improved significantly in 20 years), the graphic in the lower right shows widespread 4 to 8 inches with pockets of 13+ inches of rain in a 24 hour time frame.
To maintain heavy rainfall over a multi hour period, you need a continual feed of moisture. These satellite products are invaluable in helping forecasters identify if moisture will feed to feed into a storm and the potential for heavy rainfall and flash flooding.