The Relationship Between 2011 METAR and TAF Data at Chicago-Midway and Seattle-Tacoma Airports

Abstract

This study examined the relationship between expected meteorological conditions as specified by TAF reports and actual ground conditions as specified by hourly METAR reports for Chicago-Midway (MDW) and Seattle-Tacoma (SEA) airports for the period September–December 2011. MDW and SEA were targeted because they had the highest and lowest percentage of delays, respectively, for 2011. The rationale was to determine if one of the contributing factors for the difference in percentage delays was because of the relationship between TAF and METAR reports. The primary hypothesis was that the relationship between the forecasts and actual ground conditions at MDW would be weaker than the corresponding relationship at SEA. TAF and METAR data were acquired from the respective TAF and METAR products pages at “Aviation Weather Charts Archive†(2012). Descriptive statistics revealed that MDW had less total departures than SEA (86,834 vs. 100,133) for all of 2011, but it also had nearly five times as many weather-related departure delays than SEA. Chi square analyses indicated that although the relationship between TAF and METAR at each airport was statistically significant, the corresponding Kappa agreement coefficients showed that this relationship was nearly twice as strong at MDW (.60) than at SEA (.35). Plausible explanations include that 70% of the weather conditions at MDW were VFR as opposed to only 56% at SEA, MDW had one-third the number of special METARS than SEA (374 vs. 917), and MDW had approximately one-fifth the number of LIFR conditions than SEA (70 vs. 337). The analysis also revealed that SEA had difficulty correctly forecasting IFR and LIFR conditions, especially under rapidly changing conditions. Based on the study’s findings, it appears that the relationship between TAF and METAR was not a contributing factor to departure delays at both MDW and SEA during the September– December 2011 period.