© 1992-2014 OneRain Incorporated
Advantages of using GARR During Extreme Rain Events
Charles Yost Meteorologist – Rainfall Analyst
Importance of Understanding Rainfall
• Saving lives and property – Flash floods, dam failures
• Engineering • Hydrologic modeling • Stormwater management
Outline
Advantages of using Gauge-Adjusted Radar Rainfall (GARR)
during Extreme Rain Events
• What is Gauge-Adjusted Radar Rainfall? • Why adjust it? • What are some advantages of using it during extreme events?
– Evaluation of the validity of rain gauge reports – Understanding rainfall patterns in non-gauged areas – Basin average intensities
Outline
Advantages of using Gauge-Adjusted Radar Rainfall (GARR)
during Extreme Rain Events
• What is Gauge-Adjusted Radar Rainfall? • Why adjust it? • What are some advantages of using it during extreme events?
– Evaluation of the validity of rain gauge reports – Understanding rainfall patterns in non-gauged areas – Basin average intensities
Outline
Advantages of using Gauge-Adjusted Radar Rainfall (GARR)
during Extreme Rain Events
• What is Gauge-Adjusted Radar Rainfall? • Why adjust it? • What are some advantages of using it during extreme events?
– Evaluation of the validity of rain gauge reports – Understanding rainfall patterns in non-gauged areas – Basin average intensities
Outline
Advantages of using Gauge-Adjusted Radar Rainfall (GARR)
during Extreme Rain Events
• What is Gauge-Adjusted Radar Rainfall? • Why adjust it? • What are some advantages of using it during extreme events?
– Evaluation of the validity of rain gauge reports – Understanding rainfall patterns in non-gauged areas – Basin average intensities
Outline
Advantages of using Gauge-Adjusted Radar Rainfall (GARR)
during Extreme Rain Events
• What is Gauge-Adjusted Radar Rainfall? • Why adjust it? • What are some advantages of using it during extreme events?
– Evaluation of the validity of rain gauge reports – Understanding rainfall patterns in non-gauged areas – Basin average intensities
Extreme Rain Event Example
2013 Colorado Flood event • 9 fatalities • 14 counties declared States of Emergencies
– 19+ counties impacted
• $2 - $3 Billion in damages
Extreme Rain Event Example
2013 Colorado Flood event • Roughly 9/9/2013 to 9/15/2013 • Over 191 gauges between UDFCD and Boulder County • Foothills west of urban corridor • Some antecedent conditions • Rain after the event
Rain “ingredients” present for long time…
Reminder: Ingredients for Rain
1. Moisture
2. Lift
3. Instability
1. Moisture
• Tropical-Like in nature • Extremely moist atmosphere • More moisture than 99.9% of
days in CO
2. Lift
Courtesy: EIU
• This is what triggers the rain • Thus, WHERE the rain will
occur • Upslope flow (pic) • Mountains don’t move…so • Localize enhancement
1.
2.
3. Instability
Overview of Storm Sept 9, 2013
• Upper Low over Las Vegas pumping S/SW moisture
• Storms start forming that afternoon
• 9 pm LST cold front moves down
Boulder County
Larimer County
Denver County
Overview of Storm Sept 10, 2013
• Upper Low remains over SW US
• Feature moves north along foothills
• Second following behind it Boulder
County
Larimer County
Denver County
Overview of Storm Sept 11, 2013
• Low still north of Las Vegas
• Wave headed north from New Mexico into CO
• Several disturbances move through NE CO
Boulder County
Larimer County
Denver County
Overview of Storm Sept 12, 2013
• Low still north of Las Vegas
• Low-level moisture
Boulder County
Larimer County
Denver County
Overview of Storm Sept 13, 2013
• Low moving into WY • Winds almost westerly
means less moisture • Rains continue through
most of Friday • Low ejects out
Saturday
Boulder County
Larimer County
Denver County
Overview of Storm
Outline
Advantages of using Gauge-Adjusted Radar Rainfall (GARR)
during Extreme Rain Events
• What is Gauge-Adjusted Radar Rainfall? • Why adjust it? • What are some advantages of using it during extreme events?
– Evaluation of the validity of rain gauge reports – Understanding rainfall patterns in non-gauged areas – Basin average intensities
Gauge-Adjusted Radar Rainfall
• Over 140 radars throughout country
• Send and receive pulses • Just like detecting planes,
can detect rain • But…
COMET Program - UCAR
Gauge-Adjusted Radar Rainfall
COMET Program - UCAR
• Radar detects amount of water
• Does NOT detect rain directly
• Can convert to rain rate using: Z = aRb
• Still issues
Gauge-Adjusted Radar Rainfall
• GAUGES: accurate measurements at point locations
• RADAR: coverage between gauges • Calibrate using co-location of point
measurement and radar value • Combining these data sources gives us the
best rainfall estimate available
Outline
Advantages of using Gauge-Adjusted Radar Rainfall (GARR)
during Extreme Rain Events
• What is Gauge-Adjusted Radar Rainfall? • Why adjust it? • What are some advantages of using it during extreme events?
– Evaluation of the validity of rain gauge reports – Understanding rainfall patterns in non-gauged areas – Basin average intensities
GARR Usages: Adjustment
• Use default conversion to rainfall rate • Colorado isn’t perfect
– Mountains, virga, ground clutter • This storm was tropical-like (moisture) in
nature – Different conversion – Don’t know until you’re in the event
GARR Usages: Adjustment
Adjusted GARR Raw Radar Difference _ = (Standard Conversion)
Outline
Advantages of using Gauge-Adjusted Radar Rainfall (GARR)
during Extreme Rain Events
• What is Gauge-Adjusted Radar Rainfall? • Why adjust it? • What are some advantages of using it during extreme events?
– Evaluation of the validity of rain gauge reports – Understanding rainfall patterns in non-gauged areas – Basin average intensities
GARR Usage: Evaluate Reports
Using Gauge-Adjusted Radar Rainfall to evaluate the validity of missed gauge reports
GARR Usage: Evaluate Reports
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
20:00 20:15 20:30 20:45 21:00 21:15 21:30 21:45 22:00 22:15 22:30 22:45 23:00
Surrounding Gauges + Sunset
Logan Mill
Gold Hill
Sunset
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
20:00 20:15 20:30 20:45 21:00 21:15 21:30 21:45 22:00 22:15 22:30 22:45 23:00
Surrounding Gauges
Logan Mill
Gold Hill
GARR
GARR Usage: Evaluate Reports
GARR pixel value over gauge
GARR Usage: Evaluate Reports
0
0.2
0.4
0.6
0.8
1
1.2
20:00 20:15 20:30 20:45 21:00 21:15 21:30 21:45 22:00 22:15 22:30 22:45 23:00
Sunset Gauge
Without Report
With Report
0
0.2
0.4
0.6
0.8
1
1.2
20:00 20:15 20:30 20:45 21:00 21:15 21:30 21:45 22:00 22:15 22:30 22:45 23:00
Sunset Gauge
Without Report
With Report
GARR
GARR Usage: Evaluate Reports
0
0.2
0.4
0.6
0.8
1
1.2
20:00 20:15 20:30 20:45 21:00 21:15 21:30 21:45 22:00 22:15 22:30 22:45 23:00
Rain Gauge with GARR
Sunset no report
Sunset with report
Sunset+Garr
Insert GARR for this range
GARR Usages: Evaluate Reports
0
0.2
0.4
0.6
0.8
1
1.2
20:00 20:15 20:30 20:45 21:00 21:15 21:30 21:45 22:00 22:15 22:30 22:45 23:00
Rain Gauge with GARR
Sunset no report
Sunset with report
Sunset+Garr
• Using Basin Average over Four Mile Canyon or pixel value over gauges
• Assess failed validation against: – Volume during that time – Basin-average volume
GARR Usage: Understanding Rainfall
• UDFCD and Boulder County have extensive rain gauge networks
• Still impossible to estimate rainfall over every point
• Hard to interpolate point measurements to spatial info
GARR Usages: Understanding Rainfall
15.75 in
13.12 in
17.69 in
17-18 in
GARR Usage: Basin Intensities
• Historical radar can provide context
• Compare this event to all past September storms
Conclusions
• The Colorado September 2013 flood event was a large and devastating event
• High rainfall rates for over 5 days • Radar alone did a poor job at best • Gauges alone had missing data • GARR is the best representation of rainfall
during an extreme event like this
© 1992-2014 OneRain Incorporated
Thank you!
Questions?
GARR Usages: Adjustment
Adjusted GARR Raw Radar Difference _ = (Tropical Conversion)