A spotter report is a firsthand observation of a hazardous weather event submitted by a trained SKYWARN spotter or another reliable observer to a National Weather Service (NWS) forecast office in near real time.
What a good report contains
The NWS spotter guidance uses a simple checklist. A useful report tells the office who is reporting, what was observed, when it happened, and where. The what is a specific event such as a tornado on the ground, a measured hail size, a wind gust with a source, or a flooding depth. The when is the actual event time, not the time the report is called in. The where is a location referenced to a road, town, or landmark that a forecaster can find quickly.
The guidance also asks spotters to remain composed, be honest about uncertainty, and stick to what they saw. Reporting a wall cloud as a tornado, or a measured gust as an estimate, degrades everyone's picture of the event.
What forecasters do with it
Spotter reports flow into the forecast office through radio, phone, NWSChat, online report forms, and Skywarn nets. The warning forecaster overlays the report on the radar image and asks whether it is consistent with the storm's signature. When it is, the report can trigger a Local Storm Report, an upgraded warning, an extension of a polygon, or an impact-based warning tag such as tornado emergency or destructive wind.
Even routine reports are useful. A confirmed quarter-size hail report where the radar had suggested pea-size can retune how the office reads similar signatures for the rest of the day. A confirmed lack of hazard, sometimes called a null report, can also help a warning forecaster decide against extending a warning.
Where it misleads
Spotters can misidentify features, especially at night, at long range, or when scud, dust, or rain obscures the view. A shelf cloud can be reported as a wall cloud, a low-hanging piece of scud can look like a funnel, and hail size is often overestimated by observers without a reference object. Offices know this and cross-check.
Timing and location errors are also common. A report called in ten minutes late with a general town name is harder to act on than a report called in during the event with a road intersection. Following the guidance closely is what makes a spotter report useful rather than noise.
Reporting from the field
Chasers and field observers who are not part of a formal spotter net can still report through the local NWS office's online form or by phone. The same standards apply. Report what happened, not what might happen. Give the time, the location, and the observation, and be honest about what was seen and what was inferred.