Flood Categories
Minor - Some public inconvenience, but minimal or no property damage likely.
Moderate - Closure of secondary roads. Transfer to higher elevation may be necessary to save property. Some evacuations may be required.
Major - Extensive inundation and property damage. Usually characterized by the evacuation of people and livestock and the closure of primary and secondary roads
Record - The highest observed River stage or discharge at a given site during the period of record keeping.
 
ABRFC Categorical Flood Forecast Verification



Average Lead Times Average Lead Time
A categorical lead time is the number of hours from the time of forecast issuance to the time of the forecast hit. A lead time is only computed when, (1) the ordinate's forecast and observation are in the same category, and (2) the previous ordinate's observation was lower than the current category. This restricts lead time calculations to instances where the stage is rising, and crossing categories.
 
Average Categorical Errors
This is the amount the forecast would have to be changed to reach the observed category. Categorical error is only computed when you have a miss.
Average Categorical Errors
Weighted Average Errors
This is an average of categorical errors, weighted toward the number of events. This accounts for the fact that there are generally a greater number of lower category events.
Weighted Average Errors
   

Number of Events
The number of missed categorical flood forecasts divided by the total number of categorical flood forecasts issued.
Minor and Moderate Major and Record Total Events
Minor and Moderate Major and Record Total Events
 
False Alarm Ratio (FAR)
The number of missed categorical flood forecasts divided by the total number of categorical flood forecasts issued.
FAR = (False Alarms / (False Alarms + Hits) ) {0.00 is best}
 
Day 1 Day 2 Day 3  
False Alarm Ratio Day 1 False Alarm Ratio Day 2 False Alarm Ratio Day 3  
 
Probability of Detection (POD)
The number of categorical flood forecast hits divided by the total number of categorical flood forecasts observed.
POD = (Hits / (Hits + Misses + No Forecast Misses) ) {1.00 is best}
Day 1 Day 2 Day 3
Probability of Detection Day 1 Probability of Detection Day 2 Probability of Detection Day 3
Total Day 1-5
POD of Minor Flooding


All NWS Southern Region RFCs


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