Some Practical Considerations Regarding Horizontal Resolution in the First Generation of Operational Convection-Allowing NWP

Abstract

During the 2005 NOAA Hazardous Weather Testbed Spring Experiment two different high-resolution configurations of the Weather Research and Forecasting-Advanced Research WRF (WRF-ARW) model were used to produce 30-h forecasts 5 days a week for a total of 7 weeks. These configurations used the same physical parameterizations and the same input dataset for the initial and boundary conditions, differing primarily in their spatial resolution. The first set of runs used 4-km horizontal grid spacing with 35 vertical levels while the second used 2-km grid spacing and 51 vertical levels.Output from these daily forecasts is analyzed to assess the numerical forecast sensitivity to spatial resolution in the upper end of the convection-allowing range of grid spacing. The focus is on the central United States and the time period 18-30 h after model initialization. The analysis is based on a combination of visual comparison, systematic subjective verification conducted during the Spring Experiment, and objective metrics based largely on the mean diurnal cycle of the simulated reflectivity and precipitation fields. Additional insight is gained by examining the size distributions of the individual reflectivity and precipitation entities, and by comparing forecasts of mesocyclone occurrence in the two sets of forecasts.In general, the 2-km forecasts provide more detailed presentations of convective activity, but there appears to be little, if any, forecast skill on the scales where the added details emerge. On the scales where both model configurations show higher levels of skill-the scale of mesoscale convective features-the numerical forecasts appear to provide comparable utility as guidance for severe weather forecasters. These results suggest that, for the geographical, phenomenological, and temporal parameters of this study, any added value provided by decreasing the grid increment from 4 to 2 km (with commensurate adjustments to the vertical resolution) may not be worth the considerable increases in computational expense.

High‐resolution simulation over central Europe: assimilation experiments during COPS IOP 9c

“…Vegetation and land-use classifications, are provided by the new IGBP-MODIS dataset containing 20 different land-use categories with a resolution of 30 . Although we operate the model with a horizontal resolution of 3.6 km, we did not use a convection parametrization, since a resolution of ∼4 km was shown to reasonably represent precipitation patterns without a convection scheme (Kain et al, 2008;Weisman et al, 2008;Clark et al, 2009).…”

“…In recent years several studies have been performed with emphasis on spatial and temporal development of precipitation with different NWP models and resolutions (Grams et al, 2006;Richard et al, 2007;Rotunno and Houze, 2007;Kain et al, 2008). Whereas the forecasts of temperature and wind have clearly improved over time, large deficits remain in the prediction of the spatial and temporal distribution as well as the intensity of precipitation (Ebert et al, 2003).…”

Predictive skill of a subset of models participating in D‐PHASE in the COPS region

“…The application of a convection scheme, necessary for grid sizes larger than 4 km (Kain et al, 2008), is associated with typical systematic model errors. This is the so-called windward/lee effect with overestimated precipitation on the windward side and underestimated precipitation on the lee of mountain ranges.…”

Transforming the sensing and numerical prediction of high-impact local weather through dynamic adaptation

“…Real-time application of LEAD to severe weather prediction (a ) Static deterministic and ensemble forecasts For more than a decade, the Center for Analysis and Prediction of Storms (CAPS) at the University of Oklahoma has collaborated with the National Oceanic and Atmospheric Administration (NOAA) Storm Prediction Center (SPC) and National Severe Storms Laboratory to study fine-scale atmospheric predictability via real-time forecasts performed during the US spring severe weather season. During spring 2005, this work involved using the WRF model to create 2 km grid spacing forecasts over two-thirds of the continental USA, with initial conditions specified by the National Centers for Environmental Prediction (NCEP) operational model analysis (Kain et al 2005(Kain et al , 2008. The forecasts provided dramatic evidence that the predictability of organized deep convection is, in some cases, an order of magnitude longer (1 day) than suggested by prevailing theories of atmospheric predictability (e.g.…”

“…An important aspect of the Spring Experiment was that the daily forecasts were evaluated not only by operational forecasters in the NOAA SPC, but by dozens of faculty staff and researchers who visited the Hazardous Weather Test Bed in Norman, Oklahoma during the 7 week period. A formal procedure is employed by the SPC to evaluate the daily forecasts, and additional details may be found in Kain et al (2008).…”