The colors on a Gulf Of Mexico Radar map represent echo intensities (reflectivity) measured in dBZ (decibels of Z). Reflectivity measures the amount of transmitted power returned to the radar receiver. Because reflectivity (Z) ranges from very weak to very strong signals, a logarithmic scale (dBZ) is used for easier calculation and comparison.
Higher dBZ values indicate stronger signals returned to the radar. Each radar image uses one of two color scales. The clear air mode scale (pictured above) shows dBZ values from -28 to +28. The precipitation mode scale represents dBZ values from 5 to 75. Importantly, the color for each dBZ value remains consistent across both modes; only the numerical values change. The specific dBZ value depends on the radar’s mode when the image was generated.
dBZ values correlate with rainfall intensity. Generally, light rain corresponds to a dBZ value of 20. Higher dBZ values indicate heavier rainfall. Forecasters use established rainrate estimates associated with specific dBZ values, varying by weather type and location.
These rainrate estimates, measured in inches per hour, are updated with each radar volume scan and accumulated over time. Hail, a strong reflector of energy, produces very high dBZ values. However, because hail can inflate rainfall estimates, adjustments are made to prevent these high dBZ readings from being directly converted to rainfall amounts. Understanding dBZ values and their relationship to rainfall intensity is crucial for interpreting Gulf of Mexico radar data and predicting precipitation.
