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This study investigates how urban environments influence boundary layer processes during the passage of a Great Salt Lake breeze using a multi-scale modeling system, NCAR's WRF-Coupled GPU-accelerated FastEddy® (FE) model. Motivated by the need for sub-10 m scale decision support tools for uncrewed aerial systems (UAS), the FE model was used to simulate turbulent flows around urban structures at 5 m horizontal resolution with a 9 km × 9 km domain centered on the Salt Lake City International Airport. FE was one-way nested within a 1 km resolution Weather Research and Forecasting (WRF) domain spanning 400 × 400 km. Focused on the late morning lake breeze on 3 June 2022, an FE simulation was compared with WRF outputs and validated using surface and radar observations. The FE simulation revealed low sensible heat flux and cool near-surface temperatures, attributed to a relatively low specification of thermal roughness suitable for previously tested FE applications. Lake breeze characteristics were minimally affected, as FE effectively resolved interactions between the lake breeze and urban-induced turbulent eddies, providing insights into fine-scale boundary layer processes. FE's GPU acceleration ensured efficient simulations, underscoring its potential for aiding decision support in UAS operations in complex urban environments. [ABSTRACT FROM AUTHOR]

The dynamical basis of intraseasonal oscillations of the Southern Hemisphere summer and winter seasons is studied with a combination of observed diagnostics and simplified prognostic models. High-frequency oscillations, zonal mean variations, and seasonal and interannual variabilities are removed from the six-year dataset in an effort to reduce the effect of high-frequency dynamical instabilities and long-period forced fluctuations. The diagnoses focus upon those processes that have most frequently been explained in terms of Rossby-wave propagation through atmospheres with variable refractive indices. It is useful to study both winter and summer seasons simultaneously because of the large changes in the seasonally averaged state and large consequent changes in atmospheric waveguides between these seasons. A nonlinear shallow-water model slowly relaxed toward the time-averaged winter and summer observed mean fields is used to describe the characteristics of wave propagation in a horizontally varying basic state. Perturbations are introduced in four different regions corresponding to points where observed atmospheric teleconnectivities are relatively large, and the signal propagation is analyzed using averaging procedures similar to those employed for the observational study. Furthermore, differences between stationary and nonstationary patterns are also discussed. The four general regions selected for the observational study are Australia, New Zealand, South America, and the Atlantic Ocean. Differences from winter to summer are related to concomitant changes of the background latitudinal gradient of absolute vorticity. During winter and summer meridional propagation is toward the tropics. Winter wave patterns have mainly zonal paths and show a slow phase velocity on the order of 3 m [s.sup.-1], while during summer, patterns tend to be geographically fixed. During winter, regions of imaginary refractive index flank the subtropical and polar jet streams. These jet streams seem to act as waveguides for disturbances emanating from the southern Indian Ocean and western Australia, where two wave trains exist. Wave activity flux vectors suggest that these disturbances originate in the subtropical southern Indian Ocean and that equatorward propagation prevails at the exit region of the subpolar jet stream and over South America and the Atlantic Ocean. During summer, observed wave patterns tend to have a more meridional component, again in agreement with the background latitudinal gradient of absolute vorticity.

Fire management officials request spot forecasts from National Weather Service (NWS) Weather Forecast Offices to provide detailed guidance regarding atmospheric conditions in the vicinity of prescribed and wildland fires. Verifying spot forecasts represents an integral component of the forecast process and helps assess and improve the accuracy of forecasts. The verification analysis here utilizes NWS spot forecasts of mixing height, transport winds, and the Haines index (HI) from 2009-2013 issued for a location within 50 km of an upper-air sounding site and valid for the day of the fire event. Mixing height was calculated from the 0000 UTC sounding via the Stull, Holzworth, and Richardson methods. Transport wind speeds were determined by averaging the wind speed through the boundary layer as determined by the three mixing height methods from the 0000 UTC sounding. The HI was calculated at low, mid, and high elevation based on the elevation of the sounding and spot-forecast locations. Forecast statistics, including mean error and mean absolute error, were calculated for each lower-atmospheric variable by region. Mixing height forecasts exhibited large mean absolute errors and were biased toward overforecasting. Forecasts of transport wind speeds and HI outperformed mixing height forecasts with smaller errors relative to their respective means. Based on these results and the methodology, recommendations are provided to improve spot forecasts and the verification process. [ABSTRACT FROM AUTHOR]

Software has been developed to evaluate National Weather Service spot forecasts. Fire management officials request spot forecasts from National Weather Service Weather Forecast Offices to provide detailed guidance as to atmospheric conditions in the vicinity of planned prescribed burns as well as wildfires that do not have incident meteorologists on site. This open source software with online display capabilities is used to examine an extensive set of spot forecasts of maximum temperature, minimum relative humidity, and maximum wind speed from April 2009 through November 2013 nationwide. The forecast values are compared to the closest available surface observations at stations installed primarily for fire weather and aviation applications. The accuracy of the spot forecasts is compared to that available from the National Digital Forecast Database (NDFD). Spot forecasts for a selected prescribed burn are used to illustrate issues associated with the verification procedures. Cumulative statistics for National Weather Service County Warning Areas and for the nation are presented. Basic error and accuracy metrics for all available spot forecasts and the entire nation indicate that the skill of the spot forecasts is higher than that available from the NDFD, with the greatest improvement for maximum temperature and the least improvement for maximum wind speed. [ABSTRACT FROM AUTHOR]