The Operational Use and Assessment of a Layered Precipitable Water Product for Weather Forecasting

Operational forecasters have a variety of new research products and tools to interrogate precipitation systems for different environments and precipitation regimes. One such product is satellite-derived, column-total precipitable water retrieved in discrete layers as an experimental product developed by the Cooperative Institute for Research in the Atmosphere (CIRA), and transitioned by the National Aeronautics and Space Administration's Short-term Prediction, Research, and Transition Center to numerous weather forecast offices (WFOs) to address specific forecast issues. In 2013 the CIRA layered precipitable water (LPW) product was formally assessed by National Weather Service WFOs in Alaska, the West Coast of the United States, and San Juan, Puerto Rico. Forecasters used LPW to address forecast challenges associated with atmospheric rivers, convective storms, and other types of precipitation events across diverse forecasting domains ranging from marine zones to complex topography. This paper describes the use of LPW by operational forecasters at their WFOs and shows the impact LPW had on precipitation forecasting, as determined by assessment results. During 72 formal user feedback submissions and multiple assessment periods, 62.5% of forecasters had high confidence in LPW. Fifty percent stated that LPW had a "large" impact on their decision process, and another 22.2% said LPW had "some" impact. For 76.4% of the events surveyed, forecasters stated that LPW had "large" to "very large" value over traditional total precipitable water products. Individual case examples will provide a context for forecasters' evaluation of the product in their county warning area.