The Viability of the Froude Number as a Valuable Tool to Improve Forecast Messaging (211)

Jeremy Michael, National Weather Service, Elko, NV

Paul Frisbie, National Weather Service

Clair Ketchum, National Weather Service



Nevada's topography consists of many narrow but elongated north-south mountain ranges of 50 to 100 miles in length with some peaks exceeding 10,000 feet MSL. Nevada's terrain provides climate diversity ranging from lowland deserts to cooler low-density forests at the higher elevations. Widespread precipitation, including snowfall, is rare and more likely driven by topography. In simplified terms, precipitation falls on the windward side and downslope winds blows on the lee side but evolving high resolution models provide enhanced details of the areal extent and duration of precipitation or wind speed and direction. A common cold season weather scenario may have snow falling in close proximity to these mountains and sunshine in the open desert in relatively short distances (&lt 5-10 miles). Knowing the Froude number, a dimensionless number that describes air flow around a mountain barrier, may provide a better understanding on model interpretation and ultimately a useful forecast message for ranchers and other commercial interests that reside adjacent to these mountain ranges. Ruby and Clover valley, which is connected with Interstate 80 via highways, are prone to strong to high downslope crosswinds. By utilizing the Froude number, combined with other parameters as temperature and humidity, snowfall and wind forecasting should improve and increase situational awareness. Utilizing this information results in improved messaging on snowfall distribution and strong to high winds on the lee side of mountain ranges.