Wind gusts have the ability to impact surface transportation considerably. Across the Northern Plains in the winter months with freshly fallen snow, strong winds gusts pick up loose snow and can reduce visibility to near zero. Also, strong wind gusts perpendicular to the travel path of high-profile vehicles and those pulling trailers can cause additional hazards. The effects of strong, gusty winds are major concerns of forecasters within the Advanced Transportation Weather Information System (ATWIS), a federally-funded, operational program that provides travelers in North and South Dakota with enroute weather forecasts and road information.
To facilitate wind gust forecasting, an operational calculation of the planetary boundary layer (PBL) Reynolds number is used, derived from model output determination of the atmospheric surface kinematic viscosity. The Reynolds number, if above a critical value, indicates where turbulence will occur, thus indicating where gusty winds can be expected. Additionally, static stability in the lower atmosphere is examined. The lapse rates in the 1000, 950, 900, 850, 800, 750, and 700 hPa layers are calculated and compared with the standard dry adiabatic lapse rate following the method of Lee and Giordo. These results are used to estimate the PBL depth and the level from which higher momentum air will be transported to the surface, thus providing the predicted magnitude of wind gusts.
These products, used operationally, result in more accurate wind gust forecasting for the ATWIS coverage area, assisting road maintenance planning, as well as the public's travel planning. The benefits are safer surface transportation and greater efficiency in maintenance planning.