False Alarm Ratio Precip Verification
Compute observed false alarms/(hits+false alarms), not false-positive rate over observed nonevents; no-event forecasts leave ratio undefined.
Description
False alarm ratio is the fraction of forecast event cases that did not occur.
False alarm ratio is the fraction of forecast event cases that did not occur. Its denominator is forecast events, which differs from the denominator of false-positive rate.1
Compute observed false alarms/(hits+false alarms), not false-positive rate over observed nonevents; no-event forecasts leave ratio undefined.
When to use False Alarm Ratio Precip Verification
Use this tool to compute observed false alarms/(hits+false alarms), not false-positive rate over observed nonevents; no-event forecasts leave ratio undefined.
Prepare the observed sounding, cloud records or forecast verification data. Check pressure and height coordinates, wind conventions and the stated units.
How to use False Alarm Ratio Precip Verification and understand its results
- Prepare the observed sounding, cloud records or forecast verification data. Check pressure and height coordinates, wind conventions and the stated units.
- Enter hits, misses, falseAlarms, correctNegatives using the field table and calculation rules, then run the tool.
- Read falseAlarmRatio, observedForecastEventCount. The explanation below defines the units, signs, ordering and any flags or placeholder values.
- If the tool reports an input issue, correct the values and run it again. Apply the stated assumptions when interpreting a successfully returned result.
| Input field | Meaning | Value type; see rules below | Requirement |
|---|---|---|---|
| hits | Hits | integer | Required |
| misses | Misses | integer | Required |
| falseAlarms | False alarms | integer | Required |
| correctNegatives | Correct negatives | integer | Required |
Enter nonnegative integer hits, misses, false alarms and correct negatives. Validate a positive table total and require at least one forecast event; return the ratio and forecast-event count.
false alarm ratio = false alarms/(hits + false alarms) Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.
| Output field | Meaning | Value type |
|---|---|---|
| falseAlarmRatio | False alarm ratio | number |
| observedForecastEventCount | Observed forecast event count | number |
{
"input": {
"hits": 30,
"misses": 10,
"falseAlarms": 20,
"correctNegatives": 40
},
"output": {
"falseAlarmRatio": 0.4,
"observedForecastEventCount": 50
}
}Limitations and assumptions
No forecast events leaves this ratio undefined and is rejected. The result does not measure missed events or probability calibration.
Numeric inputs and returned numeric values must be finite; an unrepresentable returned value produces an error. Missing required fields, extra fields, wrong value types and violations of the calculation rules are input errors.
Alternative or Complementary methods
Use Equitable Threat Score ETS: Compute observed binary ETS after marginal random-hit correction, retaining possible negative skill; unlike raw CSI or HSS, correct negatives change chance hits but not event union directly. For a complementary task, use Bias Score Frequency Hit: Compute forecast/observed event frequency bias from explicit binary table; overforecast bias is not hit accuracy or probability calibration.
References
-
False Alarm Ratio Precip Verification — tool.io
Similar or alternative tools
- Equitable Threat Score ETS
Compute observed binary ETS after marginal random-hit correction, retaining possible negative skill; unlike raw CSI or HSS, correct negatives change chance hits but not event union directly.
- Bias Score Frequency Hit
Compute forecast/observed event frequency bias from explicit binary table; overforecast bias is not hit accuracy or probability calibration.