Forecasting Atmospheric Rivers During CalWater 2015

Atmospheric Rivers (ARs) are long and narrow corridors of enhanced integrated water vapor (IWV) and IWV transport (IVT) within the warm sector of extratropical cyclones that can produce heavy precipitation and flooding in regions of complex terrain, especially along the U.S. West Coast. Several field campaigns have investigated ARs under the “CalWater” program of field studies. The first field phase of CalWater during 2009–2011 increased the number of observations of precipitation and aerosols in the Sierra Nevada, Central Valley, and coastal region in California and sampled ARs in the coastal and near-coastal environment, whereas the second field phase of CalWater during 2014–2015 observed the structure and intensity of ARs in the coastal and offshore environment over the eastern North Pacific. This presentation highlights the forecasts that were prepared for the CalWater field campaign in 2015 and the development and use of an “AR portal” that was used to inform these forecasts. The AR portal contains archived and real-time forecast tools related to ARs that emphasize water vapor and water vapor flux over the eastern North Pacific, among other parameters, in a variety of formats derived from the NCEP Global Forecast System and Global Ensemble Forecast System. The tools created for the CalWater 2015 field campaign provided valuable guidance for flight planning and field activity purposes, and may prove useful in forecasting ARs and better anticipate hydrometeteorological extremes along the U.S. West Coast.