Improvements to the Localized Aviation MOS Program (LAMP) statistical guidance for ceiling height and sky cover

Skillful short-term forecasts of ceiling height and sky cover are important for both aviation and public interests. The Meteorological Development Laboratory (MDL) of the National Weather Service (NWS) disseminates Localized Aviation MOS Program (LAMP) guidance forecasts of ceiling height and sky cover. The LAMP guidance is generated every hour of the day with one hour forecasts out to 25 hours and serves as an update to the Global Forecast System (GFS) Model Output Statistics (MOS) guidance. Potential predictors available for the LAMP regres-sion equations include the GFS MOS guidance, the most current observations, advection model output, and geoclimatic variables.

In 2005, the NWS refined its definition of sky cover from an assumption of 100 percent cloud opacity for all sky cover observations (total sky cover) to a definition where sky cover is depend-ent on cloud opacity (opaque sky cover). Both the GFS MOS and LAMP guidance had previ-ously defined the sky cover element as total sky cover. In response to the refinement of the NWS sky cover definition, the GFS MOS sky cover guidance was redeveloped. In 2007, MDL began public dissemination of the new GFS MOS opaque sky cover guidance. In addition, the GFS MOS ceiling height guidance is currently being redeveloped. In response to the redevelopment of the GFS MOS ceiling height and sky cover guidance, MDL is currently redeveloping the LAMP ceiling height and sky cover guidance. The LAMP ceiling height and sky cover categori-cal definitions remain the same.

The primary objective of this LAMP redevelopment is to enable the LAMP guidance to update the new GFS MOS guidance. Another objective is to improve forecast skill. Four factors in-volved in increasing the skill of the guidance include separating the development of the ceiling height and opaque sky cover guidance, utilizing single station equations (opaque sky cover only), offering a more meteorologically representative sky cover observation predictor, and including a new set of ceiling height and opaque sky cover MOS probabilities as predictors. The first two factors were used in the new GFS MOS guidance. In this paper, we investigate the changes in LAMP guidance skill based on these four factors. We illustrate the contribution of each factor to the improvement in forecast skill. We also compare the skill of the LAMP and GFS MOS cate-gorical forecasts, and persistence. To evaluate these improvements, the Heidke skill score (a measure of overall forecast skill) and the threat score (measure of the ability to forecast a threat event) were computed. The comparison was conducted on an independent sample of data from the LAMP 1000 UTC cycle and MOS 0600 UTC cycle guidance. Initial results show the Heidke skill scores for the new LAMP opaque sky cover guidance to be substantially more skillful than the current LAMP total sky cover guidance. We also compare the Heidke skill scores for LAMP and GFS MOS sky cover. The Heidke skill scores for LAMP are higher than GFS MOS by about 10 percent for the opaque sky cover guidance, while they are only about 5 percent higher for the total sky cover guidance.