CW3E Watershed Precipitation Forecasts
Primary support by the California Atmospheric Rivers Program and U.S. Army Corps of Engineers FIRO Program
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10-day Model Precipitation Forecasts
10-day GFS/GEFS Precipitation Forecasts 10-day ECMWF/EFS Precipitation Forecast 10-day Difference Precipitation Forecast
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Methodology:
The interactive map and graphics on this page illustrate the mean areal precipiation (MAP) at different lead times from several numerical weather prediction models and NOAA/NWS forecasts. The MAP is derived by (1) identifying grid points (lat/lon pairs) that are within each of the watersheds, (2) finding the precipitation at those points using bilinear interpolation from the model grids, and (3) averaging the values across those lat/lon pairs.

Currently there are four different "scales" shown:
  • Western US Basins is the MAP forecast for USGS-designated Hydrologic Unit Code (HUC)-8 sized basins west of the Continental Divide (>500 watersheds). The geometries are obtained from the USGS and edited in QGIS (simplified/upscaled) for plotting efficiency.
  • Select California Sub-Basins is the MAP forecast for several USGS-designated HUC-10 sized basins in California, also obtained from the USGS and edited as above. This page currently only displays HUC-10 forecasts for the following HUC-8 Basins: the Russian River, the three Feather River Basins, the Upper Yuba, and the Santa Ana River.
  • AQPI Sub-Basins is the MAP forecast for several USGS-designated HUC-10 sized basins within the San Francisco Bay Region that are self-selected and designated as the "AQPI" region. AQPI is the Advanced Quantitative Precipitation Information network (more).
  • Select Reservoir Catchments is the MAP forecast for several "of interest" basins specific to the catchments for reservoirs across the western U.S. These basins are either aggregations of HUC-10 basins or otherwise unique geometries specific to the reservoir catchment (derived from USGS or the California-Nevada River Forecast Center). This page currently shows MAP forecasts for the following reservoirs: Howard Hanson, Lake Mendocino, Lake Oroville, New Bullards Bar, Englebright, Castaic Lake, Pyramid Lake, Prado, and Seven Oaks.

Data Sources:
The following is a list of the forecast data used to create the information on this page. All combined there are over 289 model forecasts!
  • National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS) Model obtained from NOAA/NCEP at 0.25-degree resolution out to 10 days via NOMADS.
  • NCEP Global Ensemble Forecast System (GEFS) obtained from NOAA/NCEP at 0.25-degree resolution out to 10 days via NOMADS.
  • NOAA/NWS National Blend of Models obtained from NOAA/NCEP at 2.5-km resolution out to 10 days via NOMADS.
  • NOAA/NWS Weather Prediction Center obtained from their website at 2.5-km resolution out to 7 days.
  • ECMWF and the ECMWF Ensemble Prediction Sytem (EPS) data are obtained from ECMWF by CW3E at 0.1 and 0.2-degrees, respectively, out to 10 days. The use of the ECMWF data are limited for research purposes and are not intended to directly support decision making operations according to our disclaimer.
  • The California-Nevada River Forecast Center (CNRFC) precipitation grids are obtained at 4-km resolutoin from their website out to 6 days.
  • The Sub-Basin analysis also illustrate precipitation forecasts by five additional CW3E in-house model forecasts by its Western Weather Research and Forecast (West-WRF) model: (1,2) A WRF model run at 9-km out to 10 days forced by the GFS and ECMWF deterministic models, (3,4) A WRF model run at 3-km out to 5 days forced by the GFS and ECMWF deterministic models, and (5) A 200-member WRF model ensemble run at 9-km out to 7 days forced by a combination of GEFS and EPS models. More on the Deterministic West-WRF model can be found here, and more on the West-WRF ensemble model can be found here.

Note that the interactive map is created using Leaflet Javascript.

Potential Limitations:
The mean areal precipitation (MAP) may not be representative of the distribution of precipitation within the watershed and may be skewed; however, it is derived from global and regional NWP models that have relatively coarse resolutions of ~2.5-25 km that are not able to resolve some of the finer resolution variability due to topography within the watersheds anyways.

Contact:
The methodology, workflow, JavaScript, visualizations, and interactivity on this page were created by Jay Cordeira (jcordeira@ucsd.edu). Please direct any questions you might have to either of them.

Acknowledgment:
The watershed forecast tools on this page were originally developed to support the California Atmospheric River (AR) Program with funding provided by the California Department of Water Resources during Phase 1 of the Program (award #4600010378) and during Phase II of the Program (award (#4600013361). Further development of these tools to expand the domain into the Pacific Northwest and added functionality focusing on watersheds involved with Forecast Informed Reservoir Operations (FIRO) has been supported by a combination of the California AR program and funding provided by the U.S. Army Corps of Enginners supporting FIRO (Phase 2) at CW3E (award W912HZ-19-2-0023).

Ongoing development of this webpage, to include all HUC-8 watersheds west of the Continental Divide was supported by projects in collaboration with the NOAA Cooperative Institute for Research to Operations in Hydrology (CIROH) and by gifted funds by the Scripps Family to the Scripps Institution of Oceanography.

Last updated 10/1/23.