Dynamical Model Atmospheric River Occurrence Forecasts

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

Weeks 1-2: Shading indicates the odds of AR occurrence 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 occurrence in each model’s hindcast record for the week-3 verification period; the bottom row shows the departure of the AR occurrence forecast for that same verification period (top panel forecast minus middle panel climatology). For this row, blue and green values represent higher than average AR activity predicted during week-3; yellow and orange 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 occurrence anomaly with respect to climatology. These regions can be interpreted as having higher confidence in their prediction of week-3 AR occurrence. The hindcast skill assessment associated with the NCEP, ECMWF, and ECCC hindcast systems is described in DeFlorio et al. 2019b.

Forecast Model:  

Week 1
Week 2
Week 3