Eta Simulations of Three Extreme Precipitation Events: Sensitivity to Resolution and Convective Parameterization

Abstract

A versatile workstation version of the NCEP Eta Model is used to simulate three excessive precipitation episodes in the central United States. These events all resulted in damaging flash flooding and include 16-17 June 1996 in the upper Midwest, 17 July 1996 in western Iowa, and 27 May 1997 in Texas. The episodes reflect a wide range of meteorological situations: (i) a warm core cyclone in June 1996 generated a meso-β-scale region of excessive rainfall from echo training in its warm sector while producing excessive overrunning rainfall to the north of its warm front, (ii) a mesoscale convective complex in July 1996 produced excessive rainfall, and (iii) tornadic thunderstorms in May 1997 resulted in small-scale excessive rains. Model sensitivity to horizontal resolution is investigated using a range of horizontal resolutions comparable to those used in operational and quasi-operational forecasting models. Sensitivity tests are also performed using both the Betts-Miller-Janjic convective scheme (operational at NCEP in 1998) and the Kain-Fritsch scheme. Variations in predicted peak precipitation as resolution is refined are found to be highly case dependent, suggesting forecaster interpretation of increasingly higher resolution model quantitative precipitation forecast (QPF) information will not be straightforward. In addition, precipitation forecasts and QPF response to changing resolution are both found to vary significantly with choice of convective parameterization. ABSTRACT A versatile workstation version of the NCEP Eta Model is used to simulate three excessive precipitation episodes in the central United States. These events all resulted in damaging flash flooding and include 16-17 June 1996 in the upper Midwest, 17 July 1996 in western Iowa, and 27 May 1997 in Texas. The episodes reflect a wide range of meteorological situations: (i) a warm core cyclone in June 1996 generated a meso-␤-scale region of excessive rainfall from echo training in its warm sector while producing excessive overrunning rainfall to the north of its warm front, (ii) a mesoscale convective complex in July 1996 produced excessive rainfall, and (iii) tornadic thunderstorms in May 1997 resulted in small-scale excessive rains.Model sensitivity to horizontal resolution is investigated using a range of horizontal resolutions comparable to those used in operational and quasi-operational forecasting models. Sensitivity tests are also performed using both the Betts-Miller-Janjic convective scheme (operational at NCEP in 1998) and the Kain-Fritsch scheme. Variations in predicted peak precipitation as resolution is refined are found to be highly case dependent, suggesting forecaster interpretation of increasingly higher resolution model quantitative precipitation forecast (QPF) information will not be straightforward. In addition, precipitation forecasts and QPF response to changing resolution are both found to vary significantly with choice of convective parameterization.

Assessment of the Weather Research and Forecasting (WRF) model for simulation of extreme rainfall events in the upper Ganga Basin

“…This result is consistent with previously conducted studies (Gallus, 1999;Fonseca et al, 2015;Pieri et al, 2015). For PLin MP, it is noted that considering YSU PBL along with KF CU scheme has a synergistic effect, leading to the maximum amount of rainfall over the region.…”

Evaluation of Optimized WRF Precipitation Forecast over a Complex Topography Region during Flood Season

“…Although the rainstorm centers located in the GJ and HSH sub-basins are well captured at any horizontal resolution, the rainstorm center over the QLJ sub-basin is missed unless the horizontal resolution is increased to 10 km. However, the improvement of forecast accuracy by increasing the horizontal resolution is limited; such a result is similar to those of Bresch et al [37] and Gallus [38]. The appearance of discontinuous rainbands and the intensity of forecast precipitation far exceed the observation when the grid resolution is beyond 10 km, which indicates that high horizontal resolution may explicitly resolve mesoscale features.…”

Sensitivity of Forecast Rainfall in a Texas Convective System to Soil Moisture and Convective Parameterization

“…The current domain configuration reduces any problems from lateral boundaries. Gallus (1999) found that maximum storm precipitation in the Eta Model for this event when the BMJ scheme was used was extremely sensitive to the horizontal grid resolution. The general shape of the rainfall region was relatively unchanged as resolution varied from 78 to 12 km, but finer details of the field were resolved at higher resolutions.…”