WFO Site Specific Seasonal Outlook Product Victor Murphy Southern Region Climate Service Program Manager Nicole Kempf Climate Services Focal Point WFO Tulsa
Outline • What is Downscaling anyway? • Probability of Exceedance (POE) • Data Used • Error • Trend Adjustment • Webpage • Time commitment and current status
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.
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
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)
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
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
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
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
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
Tulsa CPC Mega Climate Divisions (CD)
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
Summer: R2 = 0.296 Meso- /storm-scale systems WHY? Winter: R2 = 0.76 Synoptic-scale systems
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
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
Trend Adjustment…cont. Tstation – Tcd (ºF)
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
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
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
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.
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.