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Rachel L. Miller, Conrad L. Ziegler, and Michael I. Biggerstaff

Abstract

This case study analyzes a nocturnal mesoscale convective system (MCS) that was observed on 25–26 June 2015 in northeastern Kansas during the Plains Elevated Convection At Night (PECAN) project. Over the course of the observational period, a broken line of elevated nocturnal convective cells initiated around 0230 UTC on the cool side of a stationary front and subsequently merged to form a quasi-linear MCS that later developed strong, surface-based outflow and a trailing stratiform region. This study combines radar observations with mobile and fixed mesonet and sounding data taken during PECAN to analyze the kinematics and thermodynamics of the MCS from 0300 to 0630 UTC. This study is unique in that 38 consecutive multi-Doppler wind analyses are examined over the 3.5 h observation period, facilitating a long-duration analysis of the kinematic evolution of the nocturnal MCS. Radar analyses reveal that the initial convective cells and linear MCS are elevated and sustained by an elevated residual layer formed via weak ascent over the stationary front. During upscale growth, individual convective cells develop storm-scale cold pools due to pockets of descending rear-to-front flow that are measured by mobile mesonets. By 0500 UTC, kinematic analysis and mesonet observations show that the MCS has a surface-based cold pool and that convective line updrafts are ingesting parcels from below the stable layer. In this environment, the elevated system has become surface based since the cold pool lifting is sufficient for surface-based parcels to overcome the CIN associated with the frontal stable layer.

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Matthew D. Parker, Brett S. Borchardt, Rachel L. Miller, and Conrad L. Ziegler

Abstract

The 25–26 June 2015 nocturnal mesoscale convective system (MCS) from the Plains Elevated Convection at Night (PECAN) field project produced severe winds within an environment that might customarily be associated with elevated convection. This work incorporates both a full-physics real-world simulation and an idealized single-sounding simulation to explore the MCS’s evolution. Initially, the simulated convective systems were elevated, being maintained by wavelike disturbances and lacking surface cold pools. As the systems matured, surface outflows began to appear, particularly where heavy precipitation was occurring, with air in the surface cold pools originating from up to 4–5 km AGL. Via this progression, the MCSs exhibited a degree of self-organization (i.e., structures that are dependent upon an MCS’s particular history). The cold pools eventually became 1.5–3.5 km deep, by which point passive tracers revealed that the convection was at least partly surface based. Soon after becoming surface based, both simulations produced severe surface winds, the strongest of which were associated with embedded low-level mesovortices and their attendant outflow surges and bowing segments. The origin of the simulated mesovortices was likely the downward tilting of system-generated horizontal vorticity (from baroclinity, but also possibly friction) within the simulated MCSs’ outflow, as has been argued in a number of previous studies. Taken altogether, it appears that severe nocturnal MCSs may often resemble their cold pool-driven, surface-based afternoon counterparts.

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Melissa L. Finucane, Rachel Miller, L. Kati Corlew, Victoria W. Keener, Maxine Burkett, and Zena Grecni

Abstract

Understanding how climate science can be useful in decisions about the management of freshwater resources requires knowledge of decision makers, their climate-sensitive decisions, and the context in which the decisions are being made. A mixed-methods study found that people managing freshwater resources in Hawaii are highly educated and experienced in diverse professions, they perceive climate change as posing a worrisome risk, and they would like to be better informed about how to adapt to climate change. Decision makers with higher climate literacy seem to be more comfortable dealing with uncertain information. Those with lower climate literacy seem to be more trusting of climate information from familiar sources. Freshwater managers in Hawaii make a wide range of climate-sensitive decisions. These decisions can be characterized on several key dimensions including purpose (optimization and evaluation), time horizon (short term and long term), level of information uncertainty (known, uncertain, deeply uncertain, and completely unknown), and information type (quantitative and qualitative). The climate information most relevant to decision makers includes vulnerability assessments incorporating long-term projections about temperature, rainfall distribution, storms, sea level rise, and streamflow changes at an island or statewide scale. The main barriers to using available climate information include insufficient staff time to locate the information and the lack of a clear legal mandate to use the information. Overall, the results suggest that an integrated and systematic approach is needed to determine where and when uncertain climate information is useful and how a larger set of organizational and individual variables affect decision making.

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