Using the CFSv2 for Long-Range Hydrological Forecasting Including Atmospheric Rivers and Impacts

The NOAA Climate Forecast System (CFSv2) has been producing daily updates of weekly and monthly seasonal and sub-seasonal forecasts (S2S) for several years but its use for long-range weather support has been limited. One recent example is the Climate Prediction Center experimental 3 to 4 week temperature and precipitation outlooks or the typical monthly and seasonal outlooks. The challenges of forecasting beyond 2 weeks are well known but partners continue to request this type of S2S support for decision making in California. NOAA and organizations such as the California Nevada Application Program are highlighting the challenges and developed guidance to educate users on S2S forecasting.

This study will demonstrate how long lead time information from the CFS can allow for useful outlooks beyond week 2, and support information highlighting potential atmospheric rivers (and associated significant precipitation) and anomalously wet, dry, warm or cool 2 to 4 week periods or monthly outlooks. The need for these types of decision tools continues to increase but success was very limited in the record breaking El Nino wet season of 2015-16 in part due to the over dependence on ENSO analogs. This presentation will discuss examples from the 2017-18 water year when weekly and monthly CFS forecasts of precipitation had lead time of up to 4 weeks in advance.