A line of thunderstorms produced strong winds, tornadoes, and flash flooding from the ArkLaTex region into the Ohio River Valley during the afternoon and evening of 24 February 2018. These storms developed in response to a progressive, negatively-tilted shortwave trough (Fig 1) and associated deepening surface low advancing into the great lakes region and trailing cold front. Organized convection in an atmosphere characterized by anomalously high TPW over already saturated soils meant flash flooding would be a key threat with this event. WPC had issued a high risk for excessive rainfall.
The Blended TPW product indicated values in excess of 1.4″ spreading over the region during the day (Fig 2). Blended TPW, generated at NESDIS, combines information from polar-orbiting satellites, GPS, and GOES satellites. These values were over 200% of normal (Fig 3), based on a weekly climatology.
The blended Layer PW product, generated by CIRA, showed locally high amounts of moisture extending vertically through the whole atmosphere over a large region (Figure 4).
The GOES-16 Rainfall Rate product utilizes ABI IR imagery and Microwave-derived rainfall rates (which serve as calibration targets for the algorithm) to identify areas of rainfall and retrieve an instantaneous rainfall rate. Microwave-derived rainfall rates are the more accurate estimates from satellite, but are not available on a continuous basis. The GOES-16 ABI product updates every 15 minutes over the full disk at a spatial resolution of 2 km. While rain gauges and radar estimates are the primary datasets used by forecasters to monitor rainfall during heavy rain events, satellite rainfall estimates can be useful in remote areas. During this event, the GOES-16 rainfall rate product captured the heaviest-rainfall-producing storms as they moves across the southeast. In figure 4, the 15-min rainfall rate product (interpolated) is overlaid with NWS Flash Flood Warnings.
Bill Line, NWS