Flash-Flood Producing Mesoscale Convective

Systems: A Statistical Analysis of Precipitation Efficiency

Patrick S. MarketDept. of Atmospheric

ScienceUniversity of Missouri-

Columbia

Scott M. RochetteDept. of the Earth

SciencesSUNY, College at

Brockport

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)

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?

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

Precipitation EfficiencyRatio of Precipitation (P) to Ingested Moisture (Q)

)(

6

1 6 igi

RP

6

6

1)(

iigiPW

Q

R=6-h gridpoint rainfall

Q=gridpoint precipitable water (6-h avg)

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%

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

Analysis – PE statistics

Median

10th

25th

75th

90th

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

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

MCS – Maximum PE (2000)

12 September 2000 40% Vigorous cold front Forward propagation

Associated squall line

MCS – Minimum PE (2000)

17 August 2000 4% Elevated convection

North of warm front Scattered convection Forward propagation

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

Questions, Comments, Scorn and Contempt?

E-mail: marketp@missouri.edu rochette

@esc.brockport.edu