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. 


Categorical
Flood Forecast Verification System  Cumulative River Forecast Center
Verification Statistics
2nd Quarter (Jan 2011  Mar2011) FY2011 


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. 



Number
Of Events
The number of events during the quarter for each flood
category. 
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 



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 




