Development of a Rapid-Update Real-Time Mesoscale Analysis of Ceiling and Visibility

A Rapid-Update (RU) Real-Time Mesoscale Analysis (RTMA) system is developed specifically to provide near-real time sub-hourly [every 15 minute] update of surface visibility and ceiling height (C and V) for the Helicopter Emergency Medical Services (HEMS) tool running at the Aviation Weather Center.  Advances in three relevant fields enable the development of RU-RTMA: a high resolution numerical weather forecast model with sophisticated cloud prediction scheme, a reliable network and timely collection of observations and the RTMA surface analysis, particularly including C and V. In this presentation we cover the challenges and efforts to develop the RU-RTMA.   

A preeminent challenge is the computer runtime.  Intense effort has been applied to the computing efficiency in order to deliver RU-RTMA within 15 minutes.  With the emphasis on C and V, a few simplifications in analysis have been considered.  Because this is the first time EMC’s Gridpoint Statistical Interpolation (GSI) is being applied at a sub-hour temporal resolution a wide range of changes in code and scripts have been required involving the preparation of first guess fields, the sub-hourly preparation of observations, the setup of GSI analysis, and the post-processing.  

The selection of observations within GSI is a new issue being addressed for RU-RTMA.  Most C and V observations are from METAR sites, which are normally reported hourly but when the atmospheric conditions change, then sub-hourly reports are generated.  These sub-hourly special observations (SPECIs) are especially important.  Though SPECI reports are not particularly numerous, they are extremely important for RU-RTMA to reflect the current weather conditions.  Therefore, a modified observation selection algorithm has been established for RU-RTMA.  The standard RTMA GSI selection includes all observations within the dump window roughly +/- 25 minutes around each hour.  In RU-RTMA only one observation per site is selected and that is the one whose observation time is closest to the analysis time.  This ensures the SPECIs get the strongest weight in the analysis.  

The ubiquitous issue of observation quality control is also being examined especially with respect to the new mesonet visibility data.  These and the progress/results of the aspects listed above will be presented.

The assessment and validation of the final product will be studied with cooperation from the FAA and other NOAA agencies.  The vision for further development of RU-RTMA will be described.