Grib to TIFF Service:
The IEM archives a lot of grib imagery, this service presents it for a given UTC date with links to download what is available.
Flash Flood Guidance @5km (FFG)
Real-time stable link: /GIS/tiff/?service=5kmffg
Failed to find any archived files.
Real-Time Mesoscale Analysis (RTMA)
Real-time stable link: /GIS/tiff/?service=rtma
rtma.t00z.awp2p5f000.grib2 As GeoTIFF, As Grib