Introduction and Motivation
Drylines occur most frequently over the central US High Plains (i.e., western Nebraska to western Oklahoma and Texas; e.g., Fujita 1958; Rhea 1966) and mark an intersection where relatively warm, moist air originating from the Gulf of Mexico meets a relatively hot, dry air mass originating over the elevated terrain of the southwestern US and northern Mexico. Afternoon dewpoint gradients of 10K [100 km]-1 are common with drylines, and in particularly strong drylines, extreme moisture gradients up to 10K [1 km]-1 have been documented (Pietrycha and Rasmussen 2001). The strong localized convergence and abundant moisture that are often associated with drylines make them one of the most important air mass boundaries…show more content…
They established a 30-yr dryline climatology using 0000 UTC surface analyses during April ? June of 1973-2002 finding drylines on 32% of days with peak frequency occurring in mid to late May. Schultz et al. (2007) and Coffer et al. (2013) also find similar dryline frequencies over shorter time periods.
There are even fewer studies evaluating the performance of numerical weather prediction (NWP) models in predicting occurrence and location of drylines for large sets of cases. Most
model evaluation studies have focused on single cases (e.g., Ziegler et al. 1997; Hane et al. 2001). In fact, to our knowledge the only studies that have systematically diagnosed the performance of NWP models in forecasting dryline occurrence and location are Coffer et al. (2013) and Clark et al. (2015). In Coffer et al. (2013), 24 h forecasts of dryline position from a 4-km grid-spacing experimental version of the Weather Research and Forecasting (WRF) model (Skamarock et al. 2008), as well as the 12-km grid-spacing North American Mesoscale (NAM) model (Rogers et al. 2009), were evaluated for the period April ? June 2007-11. It was found that the NAM forecasts had no systematic eastward biases while the WRF forecasts had significant eastward biases. In Clark et al. (2015), the sensitivity of 24 h forecast dryline position to boundary layer parameterizations in 4-km grid-spacing WRF model simulations was examined for the cases that occurred during the 2010-12 NOAA/Hazardous Weather