The National Weather Service has released new experimental web pages showing short and medium range ensemble river forecasts based on ensemble precpitation forecasts. The largest source of uncertainty in river forecasts is the uncertainty in precipitation forecasts. In order to show this uncertainty, precipitation forecast models are run as ensembles. Basically, the intial conditions of each run are changed slightly. The spread between the amounts of precipitation of each forecast run shows the uncertainty of the forecast. If the spread is small, the uncertainty is low, but is the spread is high, the uncertainty is also high.
The three forecast ensembles used are the GEFS (Global Ensemble Forecast System), the SREF (Short Range Ensemble Forecasts), and the NAEFS (North American Ensemble Forecast System). The SREF is the best for the one to three day range, and NAEFS is the best for the three to seven day range. The SREF and NAEFS pages are linked to every AHPS forecast point web page under the "Additonal Information" section. Here is an example of short and medium pages for McAlpine Lower. The ensemble forecast web pages are also collected under a Google Map style interface where all three model ensembles can be viewed at this link.
At this time, since there is little forecast of precipitation in the near furture, these pages show no uncertainly at most locations. This will change as we move closer to winter.
The National Weather Service is asking for comments on these new pages. If you have any suggestions or comments please send them to this link. We hope that the information on these pages is useful for those with river interests.