Gauge-Adjusted, Radar Only, Provisional: What Rainfall Labels Mean
Every Raindex reading carries a label saying how the number was made. What gauge-adjusted, radar only, provisional and no reading mean, and why there is no accuracy percentage.
Published September 29, 2026 · Raindex
Why a rainfall number needs a label
Two readings of "0.8 in" can mean very different things. One was corrected against a dozen nearby gauges; the other is a radar estimate from a beam passing high over the terrain with no gauge nearby. Most rainfall apps show both the same way. Raindex labels each reading so you can tell which you are looking at.
The labels
Labels come from what NOAA's MRMS publishes alongside the rainfall: which pass the value came from, how strongly rain gauges influenced it, and what type of precipitation was falling (Zhang et al., 2016).
- Gauge-adjusted: from the gauge-corrected pass, with strong gauge influence on that cell. The number to trust most.
- Radar only: from the gauge-corrected pass, but little gauge influence reached this cell, so it is essentially a radar estimate.
- Provisional: from an earlier pass. It will be revised as gauge data arrives, usually within a couple of hours.
- Frozen: snow or hail fell. The total is liquid equivalent and radar is weaker here, so no stronger claim is made.
- No reading: an hour is missing. It is shown as missing, never as zero, because an outage is not a dry day.
Where the line between gauge-adjusted and radar only sits
MRMS publishes a gauge-influence value for each cell but does not define a cutoff for "adjusted". Raindex draws that line itself, at a gauge influence of 0.5, and treats it as a judgement to revisit as comparisons with real gauges accumulate, not as a NOAA standard.
A window or a day is labelled by its weakest hour: one provisional hour inside a 24-hour total means the total can still move, so the whole total says so.
Revisions are shown, not hidden
When a later pass changes an hour, Raindex keeps the earlier value and says so, for example "one hour revised from 0.74 in as gauge data arrived". A number that silently changes looks like a bug; a number that tells you it was revised is the system working.
Why there is no accuracy percentage
The quality fields MRMS publishes describe radar and gauge conditions, not the probability that the figure at your property is right. Turning them into an accuracy percentage on a badge would claim something the data cannot support. The labels say what is known about how the number was made, and stop there.
See the last 24 hours for any ZIP code with the free rainfall lookup, or keep a labelled, day-by-day record for the places you care about in Raindex.
Common questions
What does gauge-adjusted rainfall mean?
A radar estimate that has been corrected toward what nearby rain gauges measured, with strong gauge influence on that particular grid cell.
What does provisional mean on a rainfall total?
At least one hour in the total comes from an earlier pass, made before most gauge reports were in, and will be revised when the gauge-corrected pass arrives, usually within a couple of hours.
Why does Raindex show a dash instead of 0.00?
A dash means no reading for that hour or window. 0.00 means it was measured and it was dry. Showing a missing hour as zero would make an outage look like a dry day.
Rain totals by city
More guides
- Why Your Rain Gauge and a Rainfall App DisagreeRadar rainfall and a backyard gauge measure different things in different places. Here is where the gap comes from, and how to compare them fairly.
- How NOAA's MRMS Rainfall Estimates WorkWhat the Multi-Radar Multi-Sensor system is, how it turns radar echoes and gauge reports into hourly rainfall on a 1 km grid, and what its passes and flags mean.
- How Much Water Is an Inch of Rain?An inch of rain on an acre is about 27,154 gallons. The same inch on a roof, a lawn or a square mile, with the arithmetic shown.