Subseasonal to Seasonal (S2S) Experimental Forecasts

A multi-institutional collaboration sponsored by California DWR

Subseasonal Outlooks (Weeks 1-6)

Dynamical Model Atmospheric River Activity Forecasts

A multi-model experimental forecast for AR activity (defined as the # of AR days per week) at week-1, 2, and 3 lead time is shown below for the NCEP dynamical model.

This product was developed in collaboration with NASA’s Jet Propulsion Laboratory.

Weeks 1-2: Shading indicates the odds of AR activity for each day. ARs are defined using the Guan and Waliser (2015) algorithm and probability is calculated by the number of ensemble members predicting an AR at each grid point at 00 UTC on the given forecast day. Click on a panel to open in a new tab, click on title to open seven day panel plot.

Week 3: The top row shows the forecast number of AR days during week-3; the middle row shows the climatological values of AR activity in each model’s hindcast record for the week-3 verification period; the bottom row shows the departure of the AR activity forecast for that same verification period (top panel forecast minus middle panel climatology). For this row, blue values represent higher than average AR activity predicted during week-3; red values represent lower than average AR activity predicted during week-3. Grey rectangles surround grid cells where >75% of forecast ensemble members agree on the sign of the AR activity anomaly with respect to climatology. These regions can be interpreted as having higher confidence in their prediction of week-3 AR activity. The hindcast skill assessment associated with the NCEP, ECMWF, and ECCC hindcast systems is described in DeFlorio et al. 2019b.

Week 1
Week 2
Week 3

Seasonal Outlooks (Beyond week 6)

The seasonal precipitation forecast suggests dry fall and winter over California, particularly in the south, as well as for the desert Southwest. Skill is confined to this region in January-March, while the October-November forecast is largely similar but not skillful. Overall, the forecast anomaly pattern is consistent with La Niña, which is also anticipated ( though not yet prominent in the September SST anomaly field on which our forecast is based. Our forecast seems to be tethered to the warm western tropical Pacific (an inkling of La Niña) and north Pacific SST anomalies.

For additional products and more information visit the Odds of Reaching 100% of Normal Water Year Precipitation webpage.

All products displayed on this page are considered experimental.