Assessing Systematic Impacts of PBL Schemes on Storm Evolution in the NOAA Warn-on-Forecast System

Abstract

The NOAA Warn-on-Forecast System (WoFS) is an experimental rapidly updating convection-allowing ensemble designed to provide probabilistic operational guidance on high-impact thunderstorm hazards. The current WoFS uses physics diversity to help maintain ensemble spread. We assess the systematic impacts of the three WoFS PBL schemes—YSU, MYJ, and MYNN—using novel, object-based methods tailored to thunderstorms. Very short forecast lead times of 0–3 h are examined, which limits phase errors and thereby facilitates comparisons of observed and model storms that occurred in the same area at the same time. This evaluation framework facilitates assessment of systematic PBL scheme impacts on storms and storm environments. Forecasts using all three PBL schemes exhibit overly narrow ranges of surface temperature, dewpoint, and wind speed. The surface biases do not generally decrease at later forecast initialization times, indicating that systematic PBL scheme errors are not well mitigated by data assimilation. The YSU scheme exhibits the least bias of the three in surface temperature and moisture and in many sounding-derived convective variables. Interscheme environmental differences are similar both near and far from storms and qualitatively resemble the differences analyzed in previous studies. The YSU environments exhibit stronger mixing, as expected of nonlocal PBL schemes; are slightly less favorable for storm intensification; and produce correspondingly weaker storms than the MYJ and MYNN environments. On the other hand, systematic interscheme differences in storm morphology and storm location forecast skill are negligible. Overall, the results suggest that calibrating forecasts to correct for systematic differences between PBL schemes may modestly improve WoFS and other convection-allowing ensemble guidance at short lead times.

Publication
Monthly Weather Review, 148(6), 2567–-2590
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Dr. Jeremy A. Gibbs
Dr. Jeremy A. Gibbs
Research Meteorologist

My name is Jeremy Gibbs. I am a Research Meteorologist at the NOAA National Severe Storms Laboratory. My research includes computational and theoretical studies of atmospheric boundary-layer flows, turbulence modeling, land-surface modeling, parameterization of boundary-layer and surface-layer interactions, and multi-scale numerical weather prediction. I am currently working on projects to improve atmospheric models in the areas of scale-aware boundary-layer physics, heterogeneous boundary layers, and other storm-scale phenomena.

Dr. Elizabeth N. Smith
Dr. Elizabeth N. Smith
Research Meteorologist

Elizabeth joined NSSL as a research meteorologist in January 2020, where she focuses on boundary-layer processes relevant to near- and pre-storm environments and convection initiation.