Flash Flood Warning Performance Improvement
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Transcript of Flash Flood Warning Performance Improvement
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Flash Flood Warning Performance Improvement
Michael L. Jurewicz, Sr.NOAA/NWS, Binghamton, NY
ER Flash Flood Workshop, Wilkes-Barre, PAJune 3, 2010
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Motivation Methodology / Data Results Conclusions / Future Work
Outline
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Flash Flood Warning Performance Improvement
Motivation
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ER FFW Statistics (2000-Present)
* Courtesy of NWS “Stats on Demand” Site
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ER FFW Statistics (2000-Present)
* Courtesy of NWS “Stats on Demand” Site
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ER FFW Stats: POD, FAR, and CSI
2000-01 2001-02 2002-03 2003-04 2004-05 2005-06 2006-07 2007-08 2008-09 2009-100
0.1
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PODFARCSI
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ER FFW Stats: Lead-Time Numbers
LT (Minutes): 2000 - Present
Percentage of Zero LT Warnings: 2000 - Present
2000
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2001
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Lead Time
Lead Time
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% Zero LT
% Zero LT
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Although overall trends in LT have been good through the last 10 years:◦ Zero LT Warnings are still running around 15%
About 1 out of every 6 FFW’s Simply in “reactive mode”
POD has remained exemplary, however: FAR’s have steadily increased
As a result, CSI’s have lowered over time
What to do ?
Things to Consider
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Flash Flood Warning Performance Improvement
Methodology / Data
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Significant flash flood vs. “nuisance” runoff event◦ Pre-storm assessments◦ Warning operations
An established “tool of the trade” for warning decision making◦ Flash Flood Guidance (FFG) vs. radar estimated /
observed rainfall FFG improvements over time (county-wide values
down to gridded basin specific) What else can we look at ?
Can We Better Differentiate ?
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Previous research by Davis (2000) and Kelsch (2001)◦ Frequency of short-duration bursts vs. FFG /
cumulative rainfall ratios Main suggestion: Monitoring instantaneous rate
trends may be at least as important as using FFG (especially in fast responding watersheds)
Utilized archived data (WES / NCDC) to test this idea◦ Can the results help us gain skill in flash flood
situations ?
Looking Back to Go Forward
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Selected 10 major flash flood events from NY / PA since 2002◦ Combined costs:
11 fatalities At least hundreds of millions of dollars in damages
◦ Other numbers: Warm season cases:
Averaged 6-7” rainfall / 3 hours Maximum: 10+” on 6/19/07 (Colchester, NY)
Cool season cases (2): Averaged 2-3” rainfall / 2 hours
Database
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For our selected events, we evaluated the following data:◦ KBGM WSR 88-D
0.5 Degree Base / Composite reflectivity 1-hour estimated instantaneous rates 1-hour, 3-hour, and storm total estimated rainfall
◦ 1-hour and 3-hour FFG (MARFC) Unavailable for one of the cases
Graphically compared the following◦ Instantaneous rates over time◦ Ratios of accumulated rainfall to FFG
Testing the Hypothesis
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Rainfall Rates and FFMP
Threat Basin Table Basin Trend Graphs
Rainfall rates tracked every volume scan, basin by basin
Instantaneous hourly rates, accumulated rainfall, and FFG can all be displayed graphically
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Flash Flood Warning Performance Improvement
Results
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In the majority of cases (8 / 10), initial reports of major flooding coincided with the third burst of high intensity rainfall◦ Specific rainfall rates were relative (air mass /
season dependent)
Heavy Rain Bursts
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Rates vs. Times Examples
June 19, 2007 January 25, 2010
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January 2010 (Broome/Susq FF):
Rate vs. Time
Rate
2036
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2143
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Colchester: Rate vs. Time
Rates
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FFW vs. Actual Flooding
June 19, 2007 January 25, 2010
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January 2010 (Broome/Susq FF):
Rate vs. Time
Rate
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Colchester: Rate vs. Time
Rates
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3
Black = Major FloodingGreen = FFW Issuance
Black = Major FloodingGreen = FFW Issuance
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FFW vs. Actual Flooding (LT Issues)
June 19, 2007 January 25, 2010
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January 2010 (Broome/Susq FF):
Rate vs. Time
Rate
2036
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Colchester: Rate vs. Time
Rates
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3
Opportunity for more LT ?
Opportunity for more LT ?
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At times when major flooding was reported / observed, mean accumulated rainfall to FFG ratios were:◦ Warm season
1-hour: 1.45; 3-hour: 1.95 Significant flooding normally occurred well after FFG
values were exceeded◦ Cool season
1-hour: 0.75; 3-hour: 0.9 Significant flooding occurred prior to FFG values
being reached Impervious / frozen surface ?
Rainfall to FFG Ratios
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Warm Season Case
22z, 13 June – 03z, 14 June 2003 (Rate vs. Time)
22z, 13 June – 03z, 14 June 2003 (Rainfall / FFG Ratio vs. Time)
2200
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4.5Broome FF: Rate vs.
Time
Rate
Major Flooding
Major Flooding
Rainfall first reaches FFG values
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Cool Season Case
11z – 17z, 25 January 2010 (Rate vs. Time)
11z – 17z, 25 January 2010 (Rainfall / FFG Ratio vs. Time)
1116
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January 2010 (Broome/Susq FF):
Rate vs. Time
Rate
3
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1 Hr FFG3 Hr FFG
Major Flooding
Major Flooding
Rainfall not yet at FFG values
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Flash Flood Warning Performance Improvement
Conclusions / Future Work
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Timing bursts of high intensity rainfall show promise as a flash flood predictor◦ At least for higher-end events
Opportunities to combine this kind of diagnosis with analyses of FFG
Sooner recognition of major flooding / better LT ? Rainfall amounts tend to “rocket” past FFG
values for significant warm season flash floods ◦ Possible assistance in warning decision making◦ Lower FAR’s / better CSI’s ?
Summary
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Assessing flash flood potential can be especially difficult in rapidly changing situations◦ Severe threat evolving to a flash flood threat
Can be tough to switch gears on the fly Precipitable water (PWAT) can be a fickle
parameter◦ Values can change substantially / quickly as NWP
model CPS’s trigger Another way to view this field ?
Pre-Storm Interrogation
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Maximum potential PWAT (Arnott, 2007) may provide a useful way to assess flash flood potential ahead of time, especially given the expectation of training / repeat cells◦ Calculates PWAT, assuming a saturated profile
along the wet-bulb temperature May have the advantage of being a more stable
value Needs an automated application to run and
the utility itself also has to be tested◦ Plan to address these issues in the coming
months
Future Work
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BUFKIT Comparisons
Standard Profile Max Potential PWAT (saturated along WB temp (light blue trace))
As storms develop/CPS trigger, then depart, model moisture profiles tend to modify quickly * PWAT could change significantly, hour to hour
Max Potential PWAT values should be less subject to wild fluctuations in time / space
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Arnott, J., 2007: Maximum potential precipitable water development and application for forecasting flash flood potential. <http://www.erh.noaa.gov/bgm/research.shtml>.
Davis, R. S., 2000: Detecting flash flood on small urban
watersheds. Preprints, 15th Conference on Hydrology, Amer. Meteor. Soc., 233-236.
Kelsch, M., 2001: The relationship between intense, short-duration precipitation and flash floods. Preprints, Symposium on Precipitation Extremes: Prediction, Impacts, and Responses, Amer. Meteor. Soc., 124-128.
References
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The End !!
Questions ??