89th American Meteorological Society Annual Meeting

Tuesday, 13 January 2009
Ensuring Consistency Between NWS National and Local 3 Month Temperature Outlooks
Hall 5 (Phoenix Convention Center)
Marina M. Timofeyeva, UCAR, Boulder, CO and NOAA/NWS, Silver Spring, MD; and A. Hollingshead and D. A. Unger
NOAA NWS introduced operational Local 3 Month Temperature Outlook (L3MTO) in January 2007. This is a forecast site-specific product that is statistically downscaled from NWS 3 Month Temperature Outlook (3MTO). In L3MTO first year operations some confusion was expressed by users because of apparent inconsistency between L3MTO and 3MTO.

To address this issue, the L3MTO developmental team has scrutinized the forecasting procedure, identified the critical factors, examined each factor impacts and adjusted the L3MTO methodology to ensure the two products consistency. The critical factors were: (a) use of homogenized data, (b) trend adjustment method, (c) technique for definition of forecasted categories, and (d) application of long-term verification filter. Adjustments were made with the goal of maintaining: (1) skill in long-term forecasts; and (2) maximum spatial consistency between L3MTO and 3MTO. Critical factors c and d were the most important to achieving these goals. As a result, the forecast categories for the downscaled locations were adjusted to be consistent with the 3MTO outlooks (effectively re-defining local climatology to be consistent with the large scale climate) and the application of the long-term verification filter was suspended.

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