National Weather Service United States Department of Commerce

Mississippi Valley Summer Heat Wave; Severe Thunderstorms and Flooding Possible to the North

A dangerous summer heat wave will continue much of the Plains, Mid/Lower Mississippi Valley, Southeast U.S. today and Thursday. Areas of severe thunderstorms may occur today and again on Thursday from parts of the northern/central Rockies and High Plains into the Ohio Valley and Carolinas. Excessive rainfall over similar areas may bring flash flooding today and Thursday. Read More >

Gridded Flash Flood Guidance (GFFG) provides a general indication of the amount of rainfall necessary to cause small streams to overflow their natural banks. During heavy rainfall, usage of this guidance must involve combination of rainfall that has already occurred plus any additional rainfall that is expected to fall over the same location, not to exceed the guidance duration (example: 1-hr or 3-hr). It should be noted that these GFFG values are based upon estimates of average soil moisture and stream flow conditions over 4km x 4km grids. GFFG values also assume that the rainfall event will be evenly distributed over the guidance duration. Flooding may occur with less rainfall than indicated in areas of very high rainfall intensities, impervious surfaces (urban areas), or steep slopes.

The 1, 3, and 6 Hourly Gridded Flash Flood Guidance is also viewable on NOAAs GIS Integrated Dissemination Program (IDP) web services. Metadata and additional information on the gridded flash flood guidance and other GIS Web Services can be found at the National Weather Service Data as OGC Web Services site .  Flash flood guidance on a national scale, can be found here.