1. Flash-Flood Producing Mesoscale Convective Systems: A Statistical Analysis of Precipitation Efficiency Patrick S. Market Dept. of Atmospheric Science University of Missouri-Columbia Scott M. Rochette Dept. of the Earth Sciences SUNY, College at Brockport

2. Support Funding: Outgrowth of a larger 2-year study with NOAA/NESDIS/ORA Precipitation Data: NCEP - Brett McDonald and Michael Baker Analysis: Stacy Allen (UMC) and Brian Pettegrew (CMC)

3. Problem Larger question For a given PW: higher PE  heavier rainfall ? Present question Do MCSs with greater PE values produce greater rainfall totals? OR… Is it necessary for an MCS to have large PE to be a flash flood producer?

4. Method Data MCS PE values of Market et al. (2002) NCDC online reports of flash flooding Over Missouri During summers: 2000, 2001 33 PE calculations 9 PE calculation periods feature flash flooding

5. Precipitation Efficiency Ratio of Precipitation (P) to Ingested Moisture (Q) R=6-h gridpoint rainfall Q=gridpoint precipitable water (6-h avg)

6. Analysis – PE statistics Flash Flood cases N = 9 Mean = 33% St. Dev = 9% Range = 22-48% Non-Flash Flood cases N = 24 Mean = 23% St. Dev = 10% Range = 4%-40%

7. Analysis – PE statistics Mann Whitney Wilcoxon rank sum test Hypothesis: Median PE of FF sample > Median PE of NFF sample p=0.0131  =0.05 p<  Reject null hypothesis (medians identical) FF PE > NFF PE at 95% confidence

8. Analysis – PE statistics Median 10 th 25 th 75 th 90 th

9. MCS Propagation and PE FF PE cases (N=9) Less than half were quasi-stationary or regenerative 4 of 9 All cases (N=32) One third were QS or REGEN 10 of 32

10. MCS Propagation and PE Therefore, 6 cases were QS or REGEN, but not associated with flash flooding Suspect MCS behavior necessitates neither large PE nor flash flooding

11. MCS – Maximum PE (2000) 12 September 2000 40% Vigorous cold front Forward propagation Associated squall line

12. MCS – Minimum PE (2000) 17 August 2000 4% Elevated convection North of warm front Scattered convection Forward propagation

13. Summary MCSs which produce Flash Flooding are more likely to be efficient precipitators Quasi-stationary or regenerative MCS motion does not require large PE or guarantee flash flooding

14. Questions, Comments, Scorn and Contempt? E-mail: marketp@missouri.edu rochette@esc.brockport.edumarketp@missouri.edu rochette@esc.brockport.edu