Each winter, ice storms impact large swaths of the United States, and the NOAA National Weather Service (NWS) is responsible for forecasting where freezing rain will fall, and how much ice will accumulate. 

Traditionally, forecasters rely on Automated Surface Observing System (ASOS) stations, which are sparse, point-based observations typically located at airports. However, many ASOS stations lack freezing rain sensors, leaving critical gaps in both real-time decision-making and post-event analysis.

To address this, researchers at the NOAA National Severe Storms Laboratory (NSSL) have developed an experimental new product called FRANA (Freezing Rain Accumulation National Analysis) that leverages the Multi-Radar Multi-Sensor (MRMS) system to provide a real-time analysis of freezing rain in one-kilometer spacing. By combining radar and gauge data with an ice accretion model, this tool is designed to identify both the location and accumulation of freezing rain as it happens. 

During a recent ice storm in North Dakota, the product captured widespread ice accumulations of up to one inch; coverage that ASOS alone would have missed.

FRANA has been tested with NWS offices over the past two winter seasons, with positive feedback. Forecasters have used it for both real-time nowcasting and detailed post-storm assessments. In one notable case, an NWS office submitted one such analysis to FEMA to support a request for an emergency declaration following a damaging ice storm in Oregon.

Ongoing development aims to further improve accuracy and expand the utility of this tool. Future efforts will focus on using the archived data to refine model forecasts and deepen our understanding of freezing rain climatology across the U.S.