Abstract
Straight-line winds are arguably the most challenging element considered by operational forecasters when issuing severe thunderstorm warnings. Determining the potential maximum surface wind gust prior to an observed, measured gust is very difficult. This work builds upon prior research that quantified a relationship between the observed outflow boundary speed and corresponding measured wind gusts. Whereas this prior study was limited to a 30-case dataset over eastern Colorado, the current study comprises 943 cases across the contiguous United States and encompasses all times of day, seasons, and regions while representing various convective modes and associated near-storm environments. The wind gust ratios (WGRs), or the ratio between a measured wind gust and the associated outflow boundary speed, had a nationwide median of 1.44, mean of 1.68, 25th percentile of 1.19, and 75th percentile of 1.91. WGRs varied considerably by region, season, time of day, convective mode, near-storm environment, and outflow boundary speed. WGRs tended to be higher in the plains, Intermountain West, and southern coastal regions, lower in the cool season and during the morning and overnight, and lower in linear convective modes relative to supercell and disorganized modes. Environments with stronger mean winds and low- to midlevel shear vector magnitudes tended to have lower WGRs, whereas those with steeper low-level lapse rates and other thermodynamic characteristics favorable for momentum transfer and evaporative cooling tended to have higher WGRs. As outflow boundary speed increases, WGRs—and their variability—decrease. Applying these findings may help operational meteorologists to provide more accurate severe thunderstorm warnings.
Significance Statement
Forecasting thunderstorm peak wind gusts is a challenge for operational forecasters, especially in comparison with forecasting hail. This study improves upon a method from 1988 to forecast these wind gusts, which uses the ratio of peak thunderstorm wind gust divided by thunderstorm speed. Herein, we expanded the sample from 30 to 943 cases and from eastern Colorado to across the contiguous United States, with a focus on airports where winds are especially impactful to aviation. We found considerable variability in typical ratios of wind gusts to thunderstorm motion speed based upon the time of day, season, region, and mode and environment of the thunderstorms, with an average ratio of 1.68. The results herein may help to improve the accuracy of severe thunderstorm warnings, allowing the public to more readily prepare for the associated hazards.
Mose’s current affiliation: School of Meteorology, University of Oklahoma, Norman, Oklahoma.
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