National Weather Service United States Department of Commerce


Assessment of Ceiling and Visibility Climatology During Observed Snowfall

Kenneth R. Cook and Bria Gruenbacher
National Weather Service, Wichita Kansas

November 01, 2006

1.0 Introduction

Forecasts of ceiling and visibility are very difficult, especially during winter weather events. Cursory analysis of the number of Terminal Aerodrome Forecast (TAF) amendments by month, used as a proxy for difficulty, shows the bulk of amendments, nearly double, occurs during these winter months (Caruso, 2007). To improve forecasts, it is imperative to develop an understanding of the climatological bounds and averages. This assessment will attempt to fulfill this by determining climatological averages and bounds of observed ceiling height and visibility during snow events at the five TAF sites in the National Weather Service's (NWS) Wichita's are of responsibility.

2.0 Methodology

Thirty years worth of hourly surface observations were gathered from the National Climatological Data Center for each of the 5 TAF sites. Only observations where snow was the only observed current precipitation element were considered. There were a significant number of observations that remained, ranging from approximately 1500 to 2500 occurrences per TAF site. Next, data were stratified by the visibility amendment criteria (NWS, 2005).

Once data were stratified, ceiling data were compiled into a box and whiskers plot for each category. Upper and Lower Quartile as well as the mean were calculated for each TAF site.

3.0 Results and Discussion

See this link for a full page view of the results of this study. The results have shown a greater skill in predicting ceiling heights and visibilities for the NWS Wichita TAF sites. We recorded the best verification scores ever during the winter season. Some of those results are likely due to the results and utilization of this study.

4.0 References

Caruso, Jim: Discussion of TAF Amendments, Personal Communication

NWS Directives: 10-813: