The features of interest are known locally as the "Denver Cyclone" and the "Longmont Anticyclone," and both have been well-documented at conferences and in the literature, through observational studies and numerical modeling using various research models. Both features are induced by the interaction of the synoptic flow with terrain in northeastern Colorado. The resultant weather that can arise in association with these features ranges from dramatic variation in the wind field to mesoscale distribution of precipitation and localized occurrence of severe (winter and convective season) weather. Clearly there is high interest in trying to make operational forecasts of these features, which before the advent of finer grid resolution models were done by generally using forecasts of the synoptic flow and an understanding of the potential mesoscale features that could develop. The potential to forecast these features directly with numerical models gives the possibility for more accurate predictions of the occurrence of these important phenomena.
Although local models have been running at FSL (and made available to the Boulder WFO) for a number of years, there has not been any consistent verification effort aimed at these two flow features. Also, a recent change of the local model to a version of the MM5, with somewhat better resolution of the lower levels, has improved the overall ability to forecast the circulations. Meanwhile, the reduction of the grid resolution of the operational Eta to 22 km has resulted in better forecasts of both features with this model, and an initial look at forecasts from the new version of the RUC, at 20-km grid resolution, has also shown good predictability. In this paper we will look at all three models, examining individual predictions as well as the potential value in an ensemble approach in a subjective examination of the predictions offered by the various models for occurrence of the Denver Cyclone and Longmont Anticylone. Comparison will be made with sensible weather using detailed observations (METAR and local mesonet) and radar data, coupled with the LAPS analysis for the verification times.
Supplementary URL: http://laps.fsl.noaa.gov/szoke/mesoconf/cases_homepage.html