Definition
A NEXRAD weather radar product that displays the strength of returned radar energy from a single, low-elevation antenna scan, typically the lowest tilt angle (around 0.5 degrees above the horizon). The intensity of the returned signal is shown in color-coded levels (measured in dBZ) and indicates the size and concentration of precipitation particles within the scanned slice of atmosphere.
Plain English
A weather radar picture made from one sweep of the radar beam at its lowest angle, showing how heavy the precipitation is at that level. Stronger returns mean bigger or denser precipitation, like heavy rain or hail.
Context Anchor
Seen in NEXRAD weather discussions and cockpit weather displays, especially when learning why radar weather images can miss or understate some storm hazards.
Derivation
‘Base’ here means the lowest scan angle the radar uses — the foundation level of the scan sequence. ‘Reflectivity’ comes from the Latin reflectere, ‘to bend back,’ and refers to how much radar energy is bent back to the antenna by precipitation. So ‘base reflectivity’ literally means the strength of returns from the radar’s lowest sweep.
Why Pilots Care
Helps pilots assess low-level precipitation intensity important for avoiding turbulence, icing, or wind shear near the ground.
Grounding Statement
Base reflectivity is one low radar slice, not a full top-to-bottom view of the weather.
Intuition Check
“Base” does not mean the basic or most reliable weather picture here. It means the lower scan layer used to make this radar image.
Example Sentence 1
The base reflectivity image showed a line of heavy returns along our route, so we requested a deviation around the cells.
Example Sentence 2
Pilots review base reflectivity to judge surface rain intensity before deciding on an approach.