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Pennsylvania State University: "An investigation of pulse-type thunderstorms: Implications for developing a local warning strategy"

Final Report


1.1 The primary objective of this project was to identify possible precursor signals of microburst storms in WSR-88D data. The NWS provided 88D level II archive data and storm damage survey reports. Penn State University did an analysis of the radar data. Fourteen microburst storm cells were positively identified from the Storm Cell Identification and Tracking (SCIT) algorithm outputs, combining WATADS to display the storm tracks and the damage survey reports from the NWS. Software developed by Rich Grumm (NWS SOO) was then used to collect the cell properties of all these storms. A large population of null-cases was also pick for each microburst case day, for comparison between microburst producing and non-microburst producing cells. Characteristics analyzed included cell maximum reflectivity, height of maximum reflectivity, cell water mass, cell vertically integrated liquid water, volume, center of mass height and core aspect ratio. Cell characteristics were ordered relative to microburst times. For each microburst, four volumes scans before and two after were analyzed. Each case/characteristic was normalized according to the maximum value in each series, before all cases were averaged together to determine trends in characteristics through the microburst event. The strongest signals were visible in the cell volume and vertically integrated liquid, but the scatter over all the cases was large. When compared to the null cases for the day, no distinguishable features were found. Therefore, it was concluded that there are no dependable precursor signals for microbursts in the 88D data.


2.1 The student working on this project spend time working at the NWS office, and had extensive interaction with the SOO on the analysis software. Unfortunately, the 2001 season did not produce much severe weather, so the opportunities for the student to participate in damage surveys did not materialize.


3.1 The research sponsored by the COMET program formed the core of the senior thesis of Jacob Petre, a Penn State Department of Meteorology senior.

Petre, J., 2001: An Analysis of Radar Echoes of Microburst-Producing Thunderstorm Cells in Central Pennsylvania. Senior Thesis, The Pennsylvania State University.


4.1 The availability of the 88D data and the WATADS program output introduced us for the first time to the raw data on which forecasting decisions are based. These data is being included in an undergraduate senior level course on radar meteorology. Moreover, the student was exposed to operational forecasting realities, and the difficulties in identifying small-scale weather events that can cause significant loss of life. The primary difficulties experienced in the work were the actual acquisition of the data from NCDC and identifying radar cells as the microburst producing cells. Acquisition of the greater bulk of radar data were delayed for several months when our e-mail requesting the data from NCDC was misplaced at NCDC. Since the time-period for delivery of data requests from NCDC apparently can span into months, no follow-ups were done for months, and the valuable summer research months passed by before the bulk of the data arrived. The identification of the microburst-producing storm in the radar data was more challenging - but that is an old problem in radar meteorology. We used the output of the SCIT algorithm to plot storm tracks for the periods and locations of damage surveys. Unfortunately, the time of the event in the damage survey is the most unreliable piece of information. In a few cases, several radar-identified reflectivity cells passed in the immediate vicinity of the damage tracks within a relatively short period. In order not to let our bias as to what a microburst storm should look like impact the analysis, we consistently stuck with the closes match in time.

4.2 This project provided a new and detailed examination of the local database of short-lived thunderstorms that pose a warning dilemma for the office The retrieval and analysis of sounding data to examine storm-scale environmental characteristics added a new dimension to previous office research studies of this type. While a dependable precursor signal for microbursts in the radar data was not observed, the knowledge gained may still assist operational forecasters. By knowing what radar characteristics on which not to rely, better utilization of the limited time available and examination of other data when making warning decisions is possible. The radar analysis procedures developed will enhance storm analyses for current and future research studies and post event reviews. Identification of the 'time of the event' as being unreliable will hopefully lead to improved determination of event times when storm surveys are conducted in the future. This will add to the cases' usefulness in any possible post analyses. A below average pulse-type storm season in 2000 precluded the addition of a significant number of cases to the database. Unfortunately, this also prevented any collaborative storm survey missions.