dBZ
Also called: decibels of Z, decibels relative to Z
dBZ, short for decibels of Z, is the unit of radar reflectivity: a logarithmic measure of how much energy precipitation returns to the radar. The scale runs from about -35 to +85 dBZ. As a guide, 20 to 40 dBZ is light precipitation, 40 to 50 is moderate, and 50 to 65 is heavy rain or some hail.
What dBZ Values Usually Mean
| Reflectivity | Expected intensity |
|---|---|
| Above 65 dBZ | Extremely heavy precipitation, including water-coated hail |
| 50 to 65 dBZ | Heavy precipitation or some hail |
| 40 to 50 dBZ | Moderate precipitation |
| 20 to 40 dBZ | Light precipitation |
| 0 to 20 dBZ | Very light precipitation or general clutter |
| -35 to 0 dBZ | Extremely light drizzle or snow |
As a rough guide to rain rate, 30 dBZ is about 0.10 inch per hour, 40 dBZ about 0.45, and 50 dBZ about 1.90.
What It Does Not Tell You
- dBZ is not a rain gauge. The radar measures returned power, not rainfall, and the conversion to a rain rate is an estimate.
- Drop size dominates. Returned power rises with the sixth power of drop diameter, so a few large drops can return as much energy as hundreds of small ones while delivering far less rain.
- Tropical rain reads low. Hurricanes can show only 35 to 45 dBZ during torrential rain, because the drops are small and there is little or no hail.
Related Terms
Reflectivity
A measure of how much radar energy is reflected back by precipitation, measured in dBZ (decibels of Z). Higher values indicate heavier precipitation or larger particles. Values above 50 dBZ typically indicate heavy rain or hail.
Doppler Radar
Doppler radar is weather radar that measures the motion of precipitation as well as its location and intensity. It sends out pulses of radio waves and detects the shift in phase of the signal that returns, which shows whether targets are moving toward or away from the radar and how fast. That reveals wind patterns and rotation inside storms.
NEXRAD
Next-Generation Radar, a network of 159 high-resolution Doppler weather radars operated by the National Weather Service. NEXRAD detects precipitation, wind patterns, and severe weather signatures up to 250 miles from each station.
Echo Tops
The maximum height at which radar detects precipitation in a storm, indicating storm intensity and updraft strength. Higher echo tops generally correlate with stronger storms. Tops exceeding 40,000 feet suggest severe weather potential.
Hail
Balls or irregular lumps of ice produced in severe thunderstorms. Hailstones form when updrafts carry raindrops into extremely cold areas of the atmosphere where they freeze. Repeated cycles through the updraft can create hailstones larger than softballs.
Correlation Coefficient
Correlation coefficient (CC) is a dual-polarization radar product that measures how similar the horizontal and vertical radar pulses are after they hit their targets, on a scale from 0 to 1. Uniform rain or snow gives values above 0.97. Mixed precipitation and hail give lower values, and tornado debris typically falls below 0.80.
dBZ: Guides and Explainers
These explainers connect this definition to real-world forecasting and decision-making.
In-depth guide
Weather Radar Colors Explained: How to Read Radar Like a Pro
Learn what weather radar colors mean, from light green to purple. Understand reflectivity, precipitation intensity, and how to interpret radar images.
Weather Education
How to Read Weather Radar Like a Meteorologist
Master weather radar interpretation with this complete guide. Learn to identify storms, track precipitation, and understand what those colors really mean.
Helpful Tools and Hubs
Use these pages to apply the concept, compare conditions, or follow related weather workflows.
Feature
Professional Radar
Explore high-resolution radar, premium lightning, and satellite layers built for serious weather tracking.
Guide
Radar Beam Height Explained
Learn why radar can miss low-level rain, snow, and storm details depending on distance from the radar site.
Use Case
WeatherAI for Storm Chasers
See how WeatherAI supports active storm tracking with radar, severe weather context, and storm-focused workflows.
Guide
Richter vs Moment Magnitude
How moment magnitude replaced the Richter scale, and why each whole number means about 32 times more energy.
Sources
Explore Other Terms
Eye Wall
The ring of intense thunderstorms surrounding a hurricane's eye, containing the storm's strongest winds and heaviest rainfall. Eye wall replacement cycles can temporarily weaken a hurricane before it potentially re-intensifies.
Frost
Frost is a thin layer of ice crystals that forms on surfaces when they cool to 32°F (0°C) or below and water vapor in the air freezes onto them. It is the surface that has to reach freezing, not the air: frost can form while the official air temperature is still in the mid 30s.
Small Craft Advisory
A Small Craft Advisory is a National Weather Service alert for winds or seas that are hazardous to small boats in coastal and Great Lakes waters. The wind and sea thresholds are set separately for each geographic area. There is no precise definition of a small craft: any vessel that the conditions could affect counts.
Red Flag Warning
A Red Flag Warning is a National Weather Service alert that weather conditions could cause extreme fire behavior. It is issued when those conditions are occurring or expected within 24 hours. Typical criteria combine dry fuels with sustained winds of 15 mph or more and relative humidity of 25% or less, and exact thresholds vary by state and local office.
El Niño and La Niña
El Niño and La Niña are the warm and cool phases of a recurring climate pattern in the tropical Pacific called the El Niño-Southern Oscillation (ENSO). During El Niño, the trade winds weaken and the central and eastern tropical Pacific runs warmer than average. During La Niña, the trade winds strengthen and the same waters run cooler. Both shift weather patterns worldwide.
Kp Index
The Kp index is a 0 to 9 scale of global geomagnetic activity, reported in 3-hour intervals from ground-based magnetometers. A Kp of 5 or higher indicates a geomagnetic storm, and the values map onto NOAA's G-scale from G1 (Kp 5) to G5 (Kp 9). The higher the Kp, the farther from the poles the aurora can be seen.
Browse by Category
Get the WeatherAI App
WeatherAI is a weather app for iPhone, iPad, Mac, Apple Watch, and Apple Vision Pro. It is free to download.