How this works · sources
An estimate for intuition, not a forecast. Each circle is a rain cell: set how much falls, over how wide an area, and how long (a quick dump or a slow soaker). High, forested ground soaks rain up;
low desert and bare slickrock shed it to streams within ~2 mi, and it travels downstream, faster with more water, losing some to the sand.
Flows are storm runoff on top of normal river flow. Arrival is when flow passes 5 cfs.
Rain: NOAA MRMS; flows:
USGS gauges; streams:
USGS NHD;
ground: USGS 3DEP,
ESA WorldCover.