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Downscaling in Climate Prediction: Enhancing Forecast Accuracy

Learn about downscaling, transforming large-scale forecasts into site-specific predictions for improved accuracy and reliability. Understand the probability of exceedance, data sources, error handling, trend adjustments, and more.

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Downscaling in Climate Prediction: Enhancing Forecast Accuracy

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  1. WFO Site Specific Seasonal Outlook Product Victor Murphy Southern Region Climate Service Program Manager Nicole Kempf Climate Services Focal Point WFO Tulsa

  2. Outline • What is Downscaling anyway? • Probability of Exceedance (POE) • Data Used • Error • Trend Adjustment • Webpage • Time commitment and current status

  3. What is downscaling? • Downscaling is the transformation from a large-scale feature to a small-scale one, not necessarily of the same kind. • A downscaled forecast is one that has been defined in more detail for a particular location from a forecast for a larger area.

  4. What is downscaling…cont. • In this case, we are downscaling the Climate Prediction Center (CPC) forecast for a mega climate division (CD) to a specific station within a CWA. • Therefore, we are only ‘tweaking’ the CPC forecast…not making a brand new forecast • Method developed at CPC by Barnston, Unger, and He

  5. What is downscaling…cont. • Initially, this can be required for LCD sites • Additional sites can be added at the WFO discretion • Can be done for any station in the country that has monthly data from 1971-2000 (not just Southern Region)

  6. Probability of Exceedance • The probability that a certain value of interest would be exceeded given a forecast shift in a distribution. • Or in other words, the probability that the actual temperature will exceed a particular temperature • http://www.cpc.ncep.noaa.gov/products/predictions/long_range/lead01/poe_index.html

  7. Probability of Exceedance…cont.

  8. Probability of Exceedance…cont. • CPC already downscales for 65 select cities http://www.cpc.ncep.noaa.gov/pacdir/NFORdir/citydir/citydict.txt http://www.cpc.ncep.noaa.gov/pacdir/NFORdir/citydir/explanation_ctydf.html

  9. Data • 1971-2000 • CPC used 1951-1997 when downscaling for the select cities • Need data for both the mega CD and the station • CD data retrieved from CPC website • Station data retrieved from NCDC

  10. Data…cont. • Seasonal AverageMean Temperature • Season – consecutive 3 month periods (i.e. JFM, FMA, MAM, AMJ, MJJ, etc) • Mean – the daily mean temperature average for a month (found on F-6) • Average – must apply weight to each month • Ex. JFM: (Tjan * 31 + Tfeb * 29 + Tmar * 31)/91

  11. Data…cont. • CPC also makes POE forecasts for precipitation and degree days (heating and cooling) • CPC only makes downscaled temperature and degree day (heating and cooling) forecasts for the select cities • WFOs will only be downscaling for temperature in the immediate future

  12. Tulsa CPC Mega Climate Divisions (CD)

  13. Mega Climate Divisions

  14. Mega CD vs. Station • Develop a regression equation between the mega CD and the station • Plot the seasonal average mean temp from 1971-2000 • x-axis = CD temp • y-axis = Station temp

  15. Mega CD vs. Station…cont.

  16. Summer: R2 = 0.296 Meso- /storm-scale systems WHY? Winter: R2 = 0.76 Synoptic-scale systems

  17. Error • At least as great as the CPC POE forecast error • Uncertainty increases as correlation between the mega CD and station decreases • A lot of uncertainty with precipitation

  18. Trend Adjustment • Weights the slope and intercept of the regression equation to the last decade • Past 10 years = CPC Optimal Climate Normal • Cold decades followed by warm decades can create a bias • This is more pronounced between dry and wet decades • A way of adjusting for urbanization

  19. Trend Adjustment…cont. Tstation – Tcd (ºF)

  20. Webpage • http://www.srh.noaa.gov/tulsa/climate/downscale/climfcst.php • Uses .php to create webpage • Each office up-loads graphics and a text file (per downscaled station) to the regional server and webpage is created by user input

  21. Time Commitment • Downscaling to be done by the Climate Services Focal Point (CSFP) • An assistant CSFP and/or another person should also be trained • Takes about ½ hour or less per station (once proficient) for the data • Another ½ hour or less per station to beautify the charts for the webpage

  22. Time Commitment…cont. • CSFP will be given a template and step-by-step instructions • Will be completed for the selected stations once per month, within 7 days of the issuance of the CPC product • CPC product issued on the 3rd Thursday of each month at 8:30 am • May need to do verification/analysis to see how well it works

  23. Current Status • Experimental product with a Product Description Document (PDD) is available on the WFO TSA webpage. • Still seeking feedback from experts in this field for tweaks to the templates and method. • Trying to identify our customers. • Trying to create/package a product that can be easily used and understood by our customers.

  24. Current Status…cont. • Awaiting feedback on current experimental product from CPC, NWSH CSD, other Regions, customers. • Will provide training to other SR CSFP as needed. • NWSH timeline is for local climate products to be downscaled from CPC forecast products by the end of FY05.

  25. Sample of Current Product

  26. Sample of Current Product

  27. Any questions or comments?

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