Forecast Scenarios

Sources of error and uncertainty that influence hydrologic forecasts need to be considered carefully in order to isolate the impact of one input over another. In this case study we are looking at the impact of QPF in the hydrologic model. But QPF is not the only influence. RFC forecasters routinely perform modifications within the model during the forecast process, referred to as runtime modifications, hereafter referred to as MODS.

Using IVP we will look at the performance of stage height forecasts at basin outlet points for the following scenarios:

  1. The persistence forecast which simply means that current observed stage height is the forecast for the future.
  2. Forecasts without either QPF input or MODS
  3. Forecasts with QPF input but not MODS
  4. Forecasts without QPF input but with MODS
  5. Forecasts with both QPF input and MODS

 

Forecast Scenarios: QPF Input / Forecast Modification (MODs)

Forecast Scenarios

QPF Input

Forecast Modification (MODs)

1

Persistence

2

NO

NO

3

YES

NO

4

NO

YES

5

YES

YES

The QPF input typically consists of 6-hr QPF out to 24 hours. On occasion the QPF may extend to 36, 48 or 72 hours in anticipation of widespread significant precipitation. QPF forecasts beyond 24 hours account for about 10-15% of cases.