A Preliminary Evaluation of Paired Regional/Convection-Allowing Model-Forecast Vertical Profiles in Warm-Season, Thunderstorm-Supporting Environments

Storm Prediction Center (SPC) forecasters extensively use model-derived vertical profiles of temperature, moisture, and wind to help predict when, where, and whether thunderstorms will develop and, if thunderstorms develop, their potential severity and hazards (e.g., tornadoes, hail, and wind). Historically, output from regional models such as the North American Mesoscale (NAM) and Rapid Refresh (RAP) has been used to derive these forecast vertical profiles. Though these models are unable to explicitly represent thunderstorms, historically, their higher resolution relative to global models and timeliness relative to convection-allowing models has fostered their extensive use in operations starting in the 1990s.

In the last decade, convection-allowing models have proven capable of providing reliable forecasts of convective mode and potential storm severity in the Day 1 forecast period. The added detail that their finer horizontal grid spacing permits is a double-edged sword, however: they also can crudely predict horizontal convective roll circulations within the daytime planetary boundary layer. Observations indicate that boundary layer thermodynamic profiles have significant variation across a roll circulation. Thus, the local thermodynamic profile variability resolved by convection-allowing models may not be representative of the mesoscale environment of particular interest to SPC forecasters.

To date, no research has been conducted to isolate the influence of horizontal grid spacing (and accompanying shift from parameterized to explicit representation of deep, moist convection) on short-range (0-24 h) model forecast skill for vertical temperature, moisture, and wind profiles in warm-season, thunderstorm-supporting environments. The outcome of such research has great potential to impact SPC operations, particularly as NOAA moves toward model system unification with FV³: the need for separate regional model configurations is obviated if convection-allowing models are capable of short-range predictions of vertical temperature, moisture, and wind profiles with an identical or greater level of skill. This motivates our investigation of vertical profiles from two sets of paired regional/convection-allowing models: the NAM/NAM-Nest and RAP/HRRR pairs. Preliminary results from an evaluation of model-forecast vertical profiles during the 2017 Hazardous Weather Testbed Spring Forecasting Experiment will be presented.