A Comparison of Iowa Flash Flood Events and Eight Common Features of Excessive Rainfall for...

Brittany Konradi1Mentors: Melinda Beerends2 and Dr.

Kristie Franz1

Iowa State University1, NWS Des Moines2

A Comparison of Iowa Flash Flood Events and Eight Common Features of Excessive Rainfall for 2006-2011

Outline Background Information Methodology Analysis and Results Conclusions Future Work

Background Flash flood occurs within 6 hours of a

causative event Flood forecasts

Flash flood guidance (FFG) software from local river forecast center (RFC)

Soil conditions, estimated precipitation, river levels, and terrain

Current variable checklist is small Improve checklist

Motivation Second-most deadly weather event in

the United States First is heat-related events

Damages and fatalities are increasing Antecedent environmental conditions

and location

Hypothesis When environmental and antecedent

conditions meet the criteria of Maddox et al. (1979), a flash flood event will occur in Iowa.  

Data Archived data

Iowa Environmental Mesonet Storm Prediction Center NCDC (National Climatic Data

Center) StormData Wunderground University of Wyoming soundings AWIPS (Advanced Weather

Interactive Processing System)

Case Selection Watches, Warnings,

and LSRs Ice jams 1. Watch and warning

issued, and flash flood reported

2. Watch issued, and no flash flood reported

3. No watch issued, and flash flood reported

2006 2007 2008 2009 2010 20110

5

10

15

20

25

30

35

Winter Events and Watches per YearExcluded Winter EventsTotal Watches

Num

ber o

f Wat

ches

CasesCase Start (UTC) End (UTC) Flood

EventWatch

1 10/14/2007 21:00

10/15/2007 8:48

Yes Yes

2 4/25/2008 2:00

4/25/2008 16:53

Yes Yes

3 5/11/2008 0:00

5/11/2008 8:57

No Yes

4 7/7/2010 8:00

7/7/2010 18:00

Yes No

5 8/9/2010 3:00

8/10/2010 15:00

Yes No

6 5/25/2011 8:00

5/26/2011 2:20

No Yes

Maddox et al. (1979) Eight criteria1. Associated with convective storms.2. Surface dew points are high.3. High moisture content is present throughout the layer4. Weak to moderate vertical wind shear throughout the

layer5. Repeatedly move over the same area6. Weak, mid-tropospheric, meso-α scale trough

Meso-α scale = 200-2000 km (squall lines, MCSs, tropical cyclones)

7. Very near the mid-tropospheric, large-scale ridge position

8. Occurs during the nighttime hours

Results: Convective (#1) and Motion (#5)

Lightning strikes and slow motion

Case 1 (10/14/2007) Case 3 (5/10/2008)

Results: Dew Point (#2) Threshold: Climatological average

0 1 2 3 4 5 60

10203040506070

Dew Point vs. Climatological Average

Avg Max Clim. Avg

Case Number

Dew

Poi

nt (˚

F)

Case Td Climate Avg (˚F)

14 Oct 2007

42.6

25 Apr 2008

41.5

10 May 2008

46.1

7 Jul 2010

64.3

9 Aug 2010

64.2

25 May 2011

52.0

Results: Moisture (#3) High moisture throughout layer

Moisture transport vectors, Θe, and precipitable water Equivalent potential temperature = total moisture and heat

Case 1 Case 3

Results: Precipitable Water (#3) Threshold: Climatological average

0 1 2 3 4 5 60

0.51

1.52

2.53

Precipitable Water vs. Clima-tological Average

Min Max Clim. Avg

Case

Prec

ipita

ble

Wat

er (i

n)

Case Pwat Climate Avg (in.)

14 Oct 2007

0.53

25 Apr 2008

0.75

10 May 2008

0.93

7 Jul 2010

1.22

9 Aug 2010

1.1

25 May 2011

1.06

Results: Shear (#4) Threshold: Weak to

Moderate shear Slower storm motion

0 1 2 3 4 5 60

102030405060

0-6 km Shear vs. Criteria0-6 km shear Criteria

Case

0-6

km sh

ear

(kts

)

Criteria Threshold

0-1 km shear

< 12 kts

0-6 km shear

< 35 kts

Effective shear

< 25 kts

Results: Shear (#4) Threshold:

Veering near surface

Uni-directional aloft

Increasing in magnitude with height

Case 1 (left) Ideal Maddox

(middle) Case 3 (right)

Results: Set-up (#6, #7) Thresholds:

Weak, mid-tropospheric, meso-α scale trough

500 mb analysis Mid-tropospheric, large-

scale ridge position

Maddox et al (1979) ideal set-up

Double jet streaks Strong moisture axis at all levels Developing cyclone

Results: Set-up Case 1

SW trough Large-scale

ridge

300 mb

500 mb

Surface

850 mb

Results: Set-up Case 3

Short-wave trough

Large-scale trough

850 mb

Surface

500 mb

300 mb

Results: Nighttime event (#8) Nighttime event

3Z to 12 Z Low-level jet

Results: Antecedent Precipitation

1

2

3

4

5

6

0% 200% 400% 600%

Monthly Percentage of Normal Precipitation

Percent of Normal

Cas

e

1

2

3

4

5

6

0% 50%

100%

150%

200%

Annual Percentage of Normal Precipitation

Percent of Normal

Cas

e

Results: Criteria ComparisonCase Flood

EventConvectiv

eDew Point

Moisture Content

1 Yes X X X2 Yes X X X3 No X    4 Yes X X X5 Yes X X X6 No X X  

Case Vertical shear

Same Area

SW Troug

h

Ridge

Night

1 X X X X2 X X   X3   X     X4 X X   X  5 X X   X X6   X      

Conclusion Moisture and

forcing Cyclone maturity

and weak to moderate shear

Flood events meet more criteria

Case Flood Event

Watch

Criteria Met

1 Yes Yes 7

2 Yes Yes 63 No Yes 34 Yes No 65 Yes No 76 No Yes 3

Future Work More cases Only spring and fall events Freezing level

Winds increase with height in radiosonde LLJ influence

References Ashley, S. T. and W. S. Ashley, 2008: Flood Fatalities in the United States. J. Appl.

Meteor. Climatol., 47, 805–818. Ashley, W. S., 2007: Spatial and Temporal Analysis of Tornado Fatalities in the United

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Forecasting, 11, 560–581. European Space Agency, cited 2009: SMOS Scientific Objectives. [Available online at

http://www.esa.int/esaLP/ESAS7C2VMOC_LPsmos_0.html.] Funk, Theodore W., 1991: Forecasting Techniques Utilized by the Forecast Branch of the

National Meteorological Center During a Major Convective Rainfall Event. Wea. Forecasting, 6, 548–564.

Junker, N. W., R. S. Schneider, and S. L. Fauver, 1999: A Study of Heavy Rainfall Events during the Great Midwest Flood of 1993. Wea. Forecasting, 14, 701–712.

Maddox, R. A., C. F. Chappell, and L. R. Hoxit, 1979: Synoptic and Meso-α Scale Aspects of Flash Flood Events1. Bull. Amer. Meteor. Soc., 60, 115–123.

Morss, Rebecca E., 2010: Interactions among Flood Predictions, Decisions, and Outcomes: Synthesis of Three Cases. Natural Hazards Review, 11, 3, 83.

WFO DMX Station Duty Manual, Vol. 1, Section 5.2, 2011. Roebber, P. J., and J. Eise, 2001: The 21 June 1997 Flood: Storm-Scale Simulations and

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Acknowledgements Mindy Beerends Kristie Franz

Questions?

Vortex Insurance Agency cited 2009. [Available online at http://www.vortexinsuranceagency.com/AboutUs/InsuranceOrDerivative.aspx.]