Campus Units

Geological and Atmospheric Sciences, Environmental Science, Human Computer Interaction

Document Type

Article

Publication Version

Published Version

Publication Date

10-1-2019

Journal or Book Title

Weather and Forecasting

Volume

34

Issue

5

First Page

1495

Last Page

1517

DOI

10.1175/WAF-D-18-0210.1

Abstract

Nocturnal mesoscale convective systems (MCSs) are important phenomena because of their contributions to warm-season precipitation and association with severe hazards. Past studies have shown that their morphology remains poorly forecast in current convection-allowing models operating at 3–4-km horizontal grid spacing. A total of 10 MCS cases occurring in weakly forced environments were simulated using the Weather Research and Forecasting (WRF) Model at 3- and 1-km horizontal grid spacings to investigate the impact of increased resolution on forecasts of convective morphology and its evolution. These simulations were conducted using four microphysics schemes to account for additional sensitivities to the microphysical parameterization. The observed and corresponding simulated systems were manually classified into detailed cellular and linear modes, and the overall morphology depiction and the forecast accuracy of each model configuration were evaluated. In agreement with past studies, WRF was found to underpredict the occurrence of linear modes and overpredict cellular modes at 3-km horizontal grid spacing with all microphysics schemes tested. When grid spacing was reduced to 1 km, the proportion of linear systems increased. However, the increase was insufficient to match observations throughout the evolution of the systems, and the accuracy scores showed no statistically significant improvement. This suggests that the additional linear modes may have occurred in the wrong subtypes, wrong systems, and/or at the wrong times. Accuracy scores were also shown to decrease with forecast length, with the primary decrease in score generally occurring during upscale growth in the early nocturnal period.

Comments

This article is published as Thielen, Jonathan E., and William A. Gallus Jr. "Influences of Horizontal Grid Spacing and Microphysics on WRF Forecasts of Convective Morphology Evolution for Nocturnal MCSs in Weakly Forced Environments." Weather and Forecasting 34, no. 5 (2019): 1495-1517. DOI: 10.1175/WAF-D-18-0210.1. Posted with permission.

Rights

Copyright 2019 AMS https://www.ametsoc.org/ams/index.cfm/publications/authors/journal-and-bams-authors/author-resources/copyright-information/copyright-policy/

Copyright Owner

American Meteorological Society

Language

en

File Format

application/pdf

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