There are only two radars in Utah, one on Promontory Point (KMTX) and the other on Blowhard Mountain just east of Cedar City (KICX). This makes for a huge gap in radar coverage and, on a day like today with flow from the south, difficulties tracking precipitation features from central Utah into northern Utah.
|Today's composite radar image never shows any echos over central Utah.|
The useful range of a radar is influenced by a number of factors, but most important during a situation like this is the curvature of the Earth and the tilt of the radar beam that is sent out relative to the horizon. The lowest-elevation tilt of the National Weather Service radar, plotted above, is about 0.5 degrees. That's small, but along with the curvature of the Earth, means that the height of the center of the beam relative to sea level (or in the case of the image below, Great Salt Lake level) increases as one moves away from the radar.
|Image: Wood et al. (2003)|
What this means is that eventually the beam overshoots the storm, and this is what is happening today. Precipitation features appear on the radar only after they have moved moved close enough to the radar to be intersected by the lowest-elevation radar tilt.
This makes nowcasting for northern Utah difficult, but the impediment to forecasting in central Utah where there is no coverage at all is even worse, including along the I-15 and I-70 corridors.