R2O: Development of NWS Snow Squall Warnings

Throughout the 20th century, physical understanding of snow squalls was based around a limited number of case studies and empirical forecast techniques. While lake effect snowfall garnered considerable attention via observational and modeling studies, other types of convective snowfall - such as snow squalls along cold fronts - did not. Roadway accidents and highway pileups - a result of the danger posed by snow squalls to motorists from sudden whiteout conditions and gusty winds - was not sufficiently mitigated. The insufficient societal mitigation occurred from a combination of factors: (1) a lack of forecast precision, (2) inadequate means to communicate the message, and (3) the limited scientific understanding.

Recent research approached the snow squall forecast problem through composite analysis of dozens of events, development of conceptual models, and development of diagnostics suitable for the operational forecast environment. Importantly, the research stressed viewing snow squalls as mesoscale convective systems, providing linkage to features with which most forecasters are already familiar. Long-lived snow squall events are typically strongly forced through well-defined synoptic and frontogenetic forcing near cold fronts, in moist environments containing low CAPE (usually < 100 J kg^-1), strong background gradient flow, and vertical temperature profiles cold enough to produce snow. Other meteorological (e.g., “flash freeze” with rapidly falling temperatures) and non-meteorological (e.g., traffic volume) factors were also identified in modulating societal impacts.

An increased scientific understanding of snow squalls provided a platform from which the National Weather Service embarked on a demonstration project of short-fused, Snow Squall Warnings (SQWs) at six Weather Forecast Offices during winter 2017-18. The SQW capability is being expanded nationwide for winter 2018-19. The higher visibility of the SQW (versus a Special Weather Statement), allows for messaging via the full array of dissemination systems, including activation of variable message boards along interstates. The primary goal of the SQW is to raise situational awareness of drivers, and encourage action in terms of slower traffic speeds and driving safely to conditions in vicinity of snow squalls.

This presentation will highlight the research-to-operations cycle, starting with forecast problem identification, performing the research, training operational forecasters on the science of snow squalls, through to delivery of enhanced products and services. Evaluations will be shown, from which additional iterations of the R2O cycle can be made. A vision for future road-centric warnings will also be described centered on three potential advancements: (1) advent of probabilistic short-term warnings, (2) increased integration of cell-based and satellite-based internet connectivity in vehicles, and (3) interaction of autonomous vehicles with rapidly changing winter road conditions.