Case study verification of RUC/MAPS fog and visibility forecasts

The operational Rapid Update Cycle (RUC) provides hourly-updated short-range forecasts of atmospheric and surface conditions as part of its ongoing hourly assimilation cycle, including evolution of soil moisture and temperature, and also snow temperature and snow depth if snow exists.

Recently performed validations of hydrological cycle components, such as precipitation, evapotranspiration and soil moisture, as well as of soil and skin temperature demonstrate the model's capability to represent surface processes with a good degree of realism. This is a prerequisite for successful application of RUC products to predict conditions that can adversely impact terminal operations, such as fog and low ceilings.

Late last year, with the availability of the new computer at the National Centers for Environmental Prediction, additional aviation impact variables became routinely available as part of RUC output. Among these is a diagnosed horizontal surface visibility product based on a modified version of the Stoelinga-Warner algorithm applied to native-grid RUC output.

In this paper we will describe examples of verification of these short-range visibility forecasts by the RUC and its developmental counterpart at FSL, the Mesoscale Analysis and Prediction System (MAPS). For selected cases having widespread fog as indicated by satellite imagery and METAR reports, we will compare areas of poor visibility as forecast by the RUC (or MAPS) with available observations and discuss performance. We will also discuss improvements anticipated with the major RUC upgrade later this year.