Jon W. Zeitler

Predicting Supercell Motion Using a New Hodograph Technique

A physically based, shear-relative, and Galilean invariant method for predicting supercell motion using a hodograph is presented. It is founded on numerous observational and modeling studies since the 1940s, which suggest a consistent pattern to supercell motion exists. Two components are assumed to be largely responsible for supercell motion: (i) advection of the storm by a representative mean wind, and (ii) propagation away from the mean wind either toward the right or toward the left of the vertical wind shear—due to internal supercell dynamics. Using 290 supercell hodographs, this new method is shown to be statistically superior to existing methods in predicting supercell motion for both right- and left-moving storms. Other external factors such as interaction with atmospheric boundaries and orography can have a pronounced effect on supercell motion, but these are difficult to quantify prior to storm development using only a hodograph.

Application of a distributed hydrologic model to the november 17, 2004, flood of bull creek watershed, Austin, Texas

This study presents a hydrologic analysis of a flood event that took place over a small urbanizing watershed in Austin, Texas. The physically based, distributed-parameter gridded surface subsurface hydrologic analysis (GSSHA) hydrologic model was used to simulate the watershed response to a very high-intensity rain event. The hydrologic model was forced by both gauge-observed and multisensor precipitation estimator (MPE) rainfall input. Observed discharge was compared to GSSHA-generated hydrograph under various degrees of representation of the watershed physiography. In addition, simulation hydrographs by GSSHA using five different model grid sizes were compared in order to evaluate the effect of grid size on model predictions. The simulation hydrograph for the model using a 30-m grid cell generally compared well to the observed flow data once the effects of storm water detention were simulated. The comparison of simulation results from models using 30, 60, 90, 120, and 150 m grid size highlighted the los...

Comments on “Structure and Formation Mechanism on the 24 May 2000 Supercell-Like Storm Developing in a Moist Environment over the Kanto Plain, Japan”

Shimizu et al. (2008, hereinafter S08) presented an interesting case study of a rare severe nontornadic storm over the Kanto Plain in Japan—a storm that we contend was in fact a supercell. S08 labeled this as only a ‘‘supercell-like storm’’ based on perceived similarities and differences to supercells that occur across the U.S. Great Plains. The authors further suggested that midtropospheric relative humidity (RH) is an environmental factor involved in the formation of supercells, and as such somehow helped produce supercell-like characteristics in the Kanto Plain storm. The purpose of this comment is to elaborate on the storm characteristics and its environment, and to demonstrate that it indeed was a supercell by conventional definitions. Whether or not to call the Kanto Plain storm a supercell may appear to be semantics; however, to operational forecasters the proper early identification of a storm as a supercell has important implications for the warning process (e.g., Moller et al. 1994), as is discussed in more detail below. Attention also is drawn to moist supercellular environments in the United States to show they are not that different from the environment of the Kanto Plain supercell; in fact, they may be considerably more moist.

Insights into hydrometeorological factors constraining flood prediction skill during the May and October 2015 Texas Hill Country flood events

AbstractThis study evaluates the May and October 2015 flood prediction skill of a physically based model resembling the U.S. National Water Model (NWM) over the Texas Hill Country. It also investig...