Definition
An area of missing or unreliable weather radar data caused by the radar beam being blocked, overshooting, or failing to detect precipitation in a particular region. On a base reflectivity display, null coverage appears as gaps or empty areas where no radar return is shown, even if weather may actually be present.
Plain English
A spot on the radar picture where the radar isn't seeing anything — either because something is blocking its view, the beam is passing over the top of the weather, or there's just no signal coming back. It doesn't necessarily mean the weather there is clear; it means the radar can't tell.
Context Anchor
Seen on multi-function display weather pages when viewing base reflectivity, especially in areas where ground radar data is missing, blocked, or not received.
Derivation
Null' comes from the Latin nullus, meaning 'none' or 'nothing.' In radar terms, a null is a place where the signal returns nothing — not because the area is empty, but because the radar gets no usable information from it.
Why Pilots Care
Absence of color on the display does not confirm clear skies; storms may exist inside null-coverage zones.
Analogy
It is like a missing piece on a weather map. The blank piece does not tell you the weather is good; it tells you the map has no information there.
Grounding Statement
Null coverage means unknown weather information in that area, not known clear weather.
Intuition Check
Do not read “null coverage” as “nothing is there.” Read it as “the display has no usable weather data for that area.”
Example Sentence 1
The pilot noticed null coverage over the mountain range and checked PIREPs before continuing, knowing the radar couldn't see what was on the other side.
Example Sentence 2
Before takeoff the pilot noted null coverage over the destination and elected to carry extra fuel in case weather was hidden there.