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Santa Ana Index
The Santa Ana (SA) Index predicts the strength of a SA wind event, which is a downslope wind common to Southern California. The methodology was produced by a team from San Diego Gas & Electric Company, combining surface pressure gradient, 825-hPa wind speed, and 825-hPa cold air advection. The SA Index is calculated below using the West-WRF ensemble output along multiple transects over Southern California.
Top left: Map showing the transect locations. Red dots indicate their start and end locations, while blue circles show the location where 825-hPa wind speed is forecasted. Yellow highlights the chosen transect.
Bottom left: Seven-day forecast of the SA Index components: Surface pressure gradient (top row), 825-hPa wind speed along the transect (middle row), 825-hPa cold air advection along the transect (bottom row). Left Column: West-WRF ensemble forecasted maximum/minimum (blue lines), 25th/75th percentiles (red lines), and ensemble mean (black line) of each SA Index component. Right Column: Shading represents the probability of each SA Index component reaching above various thresholds (as defined by colorbars).
Top right: Seven-day forecast of the SA Index from the West-WRF ensemble with maximum/minimum (blue lines), 25th/75th percentiles (red lines), and ensemble mean (black line).
Bottom right: Shading represents the probability of the SA Index along the selected transect calculated by the number of ensemble members predicting a given SA Index value at each forecast lead time.
Bottom plot: Summary of the seven-day SA Index from the West-WRF ensemble. Each row represents a transect and each column represents a forecast day. Color shading indicates the maximum SA Index forecasted by the 75th percentile of the West-WRF ensemble on the given day for the given transect.
Select a coastal and inland location below to display the SA Index for that transect.
Plot description: West-WRF Ensemble mean relative humidity shaded in percent and geopotential height contoured in decameters at 500 hPa (top row), 700 hPa, (second row), 850 hPa (third row), and 925 hPa (bottom row)
Plot description: Shading represents the probability of 12-hour accumulated precipitation to be greater than various thresholds from the West-WRF Ensemble forecast model. Probability is calculated based on the number of ensemble members predicting the variable over the chosen threshold.