# Presentation: 792563

## An Assessment of Using the Mean Field Bias Correction to Improve Precipitation Estimates

**An Assessment of Using the Mean Field Bias Correction to Improve ****Precipitation Estimates**

**Ken Cook and Maggie Schoonover**
**NOAA/National Weather Service Office**
**2142 South Tyler Road**
**Wichita, KS 67209**
**Phone: (316) 942-8483   Fax: (316) 945-9553**
**Email: **_[kenneth.cook@noaa.gov](mailto:kenneth.cook@noaa.gov)_

## Outline

- Introduction
- Prompted Use
- Methodology of Analysis
- Assessment
- Examination Results
- Case Studies
- Challenges
- Advantages

*Ken Cook – SOO NWS Wichita, KS (ICT)*

## What is the Mean Field Bias?

- A statistical analysis between the gauge observations and the radar bin that matches that gauge (NPair)
- Performed hourly
- Uses a minimum of 10 NPairs
- If 10 cannot be ascertained during the current hour, then looks back in time until 10 is reached
- User adaptable parameter
- Applies this statistical analysis (one number) to the entire coverage area
- Software part of Multi-sensor Precipitation Estimator (MPE)

## Why Use It?

- June 8th, 2005 case
- 2-3X observed precipitation
- Latest in a number of cases where precipitation estimates were less than desirable
- Saw media partners using this bad data
- Needed to improve forecasters confidence in radar estimated precipitation
- Improve service/warning meteorology

## Once Implemented

- Results were instantly improved
- Noticed some underestimation during various events
- How much have we improved?
- How can we make the system better?
- Local training/learning
- National science sharing/improve development

## Methodology

- Radar Data (ICT)
- 12Z STP level III data from NCDC
- Nexrad Exporter (create shapefiles)
- ArcGIS 9, create rasters
- Observation Data
- Gathered 12Z Rain Gauge (Tipping Buckets/COOP) reports
- Imported into Microsoft Access
- Loaded then added XY Data in ArcGIS 9
- Compared Datasets for the period March through June 2006
- Resulted in ~ 400 G-R Observation Cases
- Gauge data assigned a “bin” value
- .45 gauge value assigned to the .3 to .6 radar “bin”

## Results

- Slight underestimation evident

## Results

## Results

## Results

- There seems to be a clear signal of slight underestimation
- More noticeable as
- Event grows in size
- Amount of precipitation increases

## Case Studies

- 32 Gauge Observations
- Light Rain Event
- Average Gauge Observation .14 inches
- Highest Gauge Observation .22 inches
- Estimates were outstanding
- Hourly MFB Calculations Very Consistent

## Case Studies

- 43 Gauge Observations
- Moderate Rain Event
- Average Gauge Observation 1.10 inches
- Highest Gauge Observation 2.85 inches
- Poorest estimation of the cases
- Largest number of observations for one case (largest coverage)
- Highest average precipitation
- Hourly MFB Calculations somewhat less stable

## Challenges - How to Improve the MFB

- Use proper overlays in MPE to inspect suspect gauges
- Inspect gauge table in MPE
- Take out bad gauges from MPE ingest filter
- Inspect MPE Local Bias for areas that may be over/underestimating as compared to Mean Field Bias

## Advantages - Using the MFB

- Better Precipitation Estimations
- No change to Z/R relationship necessary

- Updated hourly
- Reacts to a warm rain process with no interaction
- Improved credibility & customer service

## Future

- Continued assessment
- Alter adaptable parameters?
- Alter npairs?
- Science sharing with developers other users
- Incorporate differences from second/third runs of bias?
- Assume 1:1 bias after no precipitation?
- Goal:  Improve performance
- Thank you – Questions??

## Resources

- Cook, Kenneth (SOO – ICT), 2006: WFO Wichita Science and Training Intranet Page (_[http://204.194.227.45/soo/soopage.htm](http://204.194.227.45/soo/soopage.htm)__)_
- Training Materials Also Available
- Hunter, S. M., 1996: WSR-88D rainfall estimation: Capabilities, limitations, and potential improvements. *National Weather Digest* 20 (4), 26-38
- WHFS Field Support Group Web Site (_[http://www.nws.noaa.gov/om/whfs](http://www.nws.noaa.gov/om/whfs)__)_