IEM Daily Feature
Thursday, 04 July 2024

Three Hour FFG

Posted: 04 Jul 2024 05:30 AM

Flash Flood Guidance (FFG) is a product issued by NWS River Forecast Centers (RFC)s to estimate the amount of rainfall over a given interval of time to cause small stream and urban flooding. The product is very much linked to the capacity of top soil to infiltrate rain water at a given rate. Recent heavy rainfall events have near surface soils quite saturated and the featured map showing a recent three hour duration FFG for Iowa indicates where some of those areas are, by how low the values are. Some parts of the state are shown below two inches, which is very low for this time of year with efficient and slow moving thunderstorms easily able to produce such rates. So look for more Flash Flood warnings with upcoming heavy rainfall events as it will not take much.

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