Frontal passages can be seen on radar even when no precipitation is present. The primary mechanisms responsible for this are insects and other particulate being concentrated due to convergence and turbulence along the front, and some degree of beam-bending due to density gradients along the boundary. Warm and cold fronts, drylines, outflow from thunderstorm downdrafts, and sea and lake breezes can all show up on radar when precipitation is not immediately nearby.

Most fronts and boundaries that lack precipitation have the following characteristics on radar:

• A very thin line of low reflectivity (<=15 dBZ), which is often called a "fine line." The line may appear as a narrow strip of enhanced reflectivity if the surroundings are significantly cluttered.
• An arc-shape to the fine line, which moves away from a recent thunderstorm in the case of outflow boundaries
• A distinct difference in wind direction behind and ahead of the front, if enough scatterers are present on both sides

Fronts often serve as lifting mechanisms and produce precipitation or thunderstorms later in the day, provided there is enough moisture ahead of the front. This is especially true if multiple boundaries intersect each other. These regions may also produce turbulent motions that should be monitored for aircraft concerns.

In this example, we can see a fine line of enhanced reflectivity when the loop begins in clear air mode. Thunderstorms begin to develop rapidly along this dryline and forecasters switch to precipitation mode accordingly.