Lightning Forecasts and Communicating Lightning Threats for Central North Carolina

Lightning is recognized as a significant weather threat to life and property, responsible for multiple deaths and injuries as well as billions of dollars in damage per year. Given these potential dangers, accurate predictions of lightning activity, particularly excessive cloud-to-ground (CG) lightning events, would be of great benefit to the general public and other affected groups such as the aviation, forestry, and recreation communities.

In 2007, the National Weather Service Forecast Office (NWSFO) in Raleigh began development of a method for lightning prediction. Applying both established and ongoing research into the meteorological factors favoring lightning generation, as well as the results of a local lightning climatology and studies of near-storm environmental conditions during lightning events, the first iteration of the lightning forecast process involved a simple checklist intended to guide the forecaster through an assessment of environmental and storm-based factors which, when evaluated together, would help the forecaster determine that day's risk of lightning activity. Components of this checklist included the expected moisture flux and convective available potential energy, particularly in the mixed-phase region widely thought to be the core of lightning production, and automated output from the Weather Research and Forecasting (WRF) model, the Short-Range Ensemble Forecast (SREF) model, and the North American model (NAM). Incorporation of model-based output from a few different sources as well as subjective forecaster evaluation and judgment allows for a consensus-type lightning forecast that is less reliant on a single model, which may or may not be correct. Preliminary results indicate that these lightning forecasts are skillful at discerning highly active lightning cases from less-active cases.

Since its inception, the lightning forecast process has evolved to a more streamlined checklist with additional components. NWSFO Raleigh recently partnered with North Carolina State University (NCSU) to study past lightning events in North Carolina, with a focus on prolific lightning-producing convection. Using a thorough climatology of cloud-to-ground (CG) lightning in central North Carolina, surface and upper-air synoptic patterns for prolific lightning events were identified and categorized, and composites of soundings, upper-air analyses, and surface analyses were created for each category. These patterns were compared to those for “ordinary” lower-density lightning events, to highlight features unique to prolific lightning cases. These composite patterns for highly active lightning days are being added to the NWSFO Raleigh lightning forecast process.

Another new addition to the forecast methodology is the inclusion of suggested lightning-threat action statements, which a forecaster may choose to incorporate into the daily Hazardous Weather Outlook. Such wording may include the expected frequency of lightning that a person may experience with any convection that occurs, as well as specific actions recommended for our customer groups and the public, with the goal of helping to protect life and property. Conveyance of this lightning forecast information and suggested actions must be tailored for various user groups, to ensure appropriate response. Options for communicating lightning threats, including the use of graphics, and suggested responses by the public and other groups will be discussed.