Extended Abstract (808K)4.11
A climatological study of nighttime rapidly developing low cloud ceilings in a stable environment
William H. Bauman III, ENSCO, Inc., Cocoa Beach, FL; and J. H. Barrett, III, J. L. Case, M. M. Wheeler, and G. W. Baggett
Forecasters at the Space Meteorology Group (SMG) issue 30 to 90 minute forecasts for low cloud ceilings at the Space Shuttle Landing Facility (TTS) to support Space Shuttle landings. Mission verification statistics have shown ceilings to be the number one forecast challenge for SMG. More specifically, forecasters at SMG are concerned with any rapidly developing clouds/ceilings below 8000 ft in a stable, capped thermodynamic environment. Therefore, the Applied Meteorology Unit (AMU) was tasked to examine archived events of rapid stable cloud formation resulting in ceilings below 8000 ft, and document the atmospheric regimes favoring this type of cloud development.
In the first phase of this project, the AMU examined the cool season months of November to March during the years of 1993 - 2003 for days that had low-level (below 8000 ft) temperature inversions and rapid, stable low cloud formation that resulted in ceilings violating the Space Shuttle Flight Rules. The AMU identified low-level inversions from the morning Cape Canaveral, FL rawinsonde (XMR) during the cool season and output pertinent sounding information. They then parsed all days with cloud ceilings below 8000 ft at TTS, forming a database of possible rapidly-developing low ceiling events. An event is defined as a low cloud ceiling developing suddenly (an hour or less) in a stable environment. A non-event is a low cloud ceiling in a stable environment, occurring either as a result of the advection of low clouds or widespread cloudiness for much of the day. Days with precipitation or noticeable fog burn-off situations were excluded from the database. In the first phase of this work, only the daytime hours were examined for possible ceiling development events since low clouds are easier to diagnose with visible satellite imagery. For the daytime cases, the distinguishing factor between the event and non-event days appears to be the vertical wind profile in the XMR sounding. Eighty-five percent of the event days had a clockwise turning of the winds with height in the lower to middle troposphere whereas 83% of the non-events had a counter-clockwise turning of the winds with height or negligible vertical wind shear. Phase II of this work is underway to expand the database to include nighttime cases.
For the nighttime cases, the AMU will analyze both the morning and evening soundings for the presence of inversions below 8000 ft. Unlike the daytime study, days without a low-level inversion will be retained, creating a larger nighttime database. Similar to the daytime study, the AMU will use archived satellite imagery to determine whether low ceilings are due to cloud development or the advection of low clouds. Since the higher-resolution visible imagery are not available, special IR enhancements will be employed to visualize the nocturnal low clouds. The authors will summarize the work from the nighttime cases and describe representative sample cases from this data set.
Session 4, Prediction (Use of Climate Statistics in Forecasting)
Wednesday, 17 January 2007, 8:30 AM-11:45 AM, 206A
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