Real-time Verification of CPC Long-Lead Forecasts Using Heidke Skill Scores from Station Data All Stations Non-EC Only % Coverage Season T 5.6 13.8 40.0 FMA 05 P 9.8 26.7 36.8 Month (LL) T -6.8 -20.0 34.2 APR 05 P -0.4 -3.8 11.1 Updated Mo. T 2.1 4.1 52.1 APR 05 P 9.0 25.0 35.9 Change T +8.9 +24.1 +17.9 (U-LL Mo.) P +9.4 +28.8 +24.8 Brief Discussion of Forecasts and Verification ---------------------------------------------- The temperature forecast for FMA 2005 had positive Heidke skill scores of 5.6 for all stations and 13.8 for non-EC only, with a fairly larger coverage of 40.0 %. These were both however slightly below the long-term averages of 9.0 for all stations and 19.1 for non-EC only. The average coverage for the entire period of record was 47.0 %. The FMA 05 seasonal forecast was based on a variety of models, including the new CFS model from NCEP, and multi-model ensembles from IRI and CDC, as well as CPC's CCA and OCN statistical tools. Since the influence of the weak central Pacific Basin El Nino was expected to be gradually fading during the season, trend-adjusted ENSO composites, which would have favored the below normal temperatures that were observed in the Southeast, were not as heavily weighted into the forecast for that area. Up to the time the forecast was issued, the Southeast had not displayed the typical El Nino signature or cooler and wetter than normal weather. It is likely that the cool conditions in the Southeast were aided by both persistently below normal SSTs in the area and the relatively wet conditions that developed during the early spring, particularly in the Florida Panhandle. With generally good agreement from both statistical and dynamical tools that the West and Alaska would have above normal temperatures, these areas were largely correctly forecast to be warmer than normal. Since there was fairly good agreement from a majority of the tools that below normal temperatures were likely to occur over the Texas area, this area was predicted to have below normal temperatures, but in fact only one station in the area forecast to be cool verified as correct, with most locations coming in as near normal. (As has often been the case, the seasonal forecast skill scores would have been better, 6.0 for all stations and 11.5 for non-EC only, if the area forecast to have below normal temperatures had been forecast to be near normal instead.) The greatest warmth relative to normal was observed between the Rockies and the western Great Lakes Region, but except for the High Plains, there were no consistent indications from the tools for anomalous warmth in that area. The precipitation forecast again this time had above average skill compared to the long-term averages, being 9.8 for all stations and 26.7 for non-EC only, with a fairly extensive coverage of 36.8 %. These forecasts were based primarily on a consensus of the models and statistical tools, which all correctly favored above median totals over the interior Southwest, while the forecast also correctly followed indications from some tools and weak El Nino composites that southern California and the southern Plains would also be wetter than usual. For the first time this cold season, dryness favored by weak El Nino composites from the central Mississippi Valley though the Ohio Valley into the Great Lakes Region actually was observed, due to the "dropping out" of the highly uncharacteristic regime of early January that produced unseasonable warmth in the Southeast and flooding rains in the Ohio Valley. Both the areas of relative dryness forecast for the Pacific Northwest and for the interior Northeast, including most of the Great Lakes Region, were largely correct. The Southeast however, which had been mostly dry until March, had a mixture of near and above median precipitation. This region was left as EC in the forecast because there was a conflict between the CFS models, which predicted dry weather, and the statistical tools and El Nino composites, which indicated wetter than normal conditions. The 0.5-month lead temperature forecast for April 2005 was rather poor, scoring -6.8 for all stations and -20.0 for non-EC only, with 34.2% coverage. Rather uncharacteristic of most monthly or seasonal forecasts made in the past few years, it had positive skill in those areas that were forecast to have below normal temperatures, and did extremely poorly in the large area of above normal that was forecast for the West, following the usual strong signals from the OCN and CCA tools, with agreement from a consensus of the dynamical models for warmth in the Pacific Northwest and part of Alaska. The area of above normal temperatures forecast in Alaska was specified almost exactly, giving Heidke skill scores of 50.0 for all stations and 88.5 for non-EC only in that state. The areas of below normal temperatures forecast for the southern Great Plains and Florida were both based on indications from the dynamical models, with support from persistently below normal SSTs in the latter area, where every station forecast to have below normal temperatures was correct. The skill of the precipitation forecast, on the other hand, was not significantly different from zero, scoring -0.4 for all stations and -3.8 for non-EC only. Only one small area centered over the upper Mississippi Valley was predicted to have above median precipitation, on the basis of a fairly consistent signal from the CFS models with hints of support from OCN, giving a modest coverage of 11.1%. Any possible residual forcing from the fading El Nino was considered to weak to be used, especially on the monthly time scale with evidence of continuing MJO activity. Alaska was left as all EC. The revised updated temperature forecast for April issued at the end of March and incorporating input from several dynamical models used for medium range forecasting resulted in a modest improvement to the temperature forecast, raising the scores to 2.1 for all stations and 4.1 for non-EC only. The models gave accurate signals that a ridge would develop over the central CONUS for the first two weeks or the month, and on this basis the area of above normal temperatures that the statistical tools indicated over the West was extended across the northern Great Plains and upper Mississippi Valley to the western Great Lakes Region. Also, indications for a trough approaching the Pacific Northwest correctly led to the removal of some of the above normal that had been forecast there on the 0.5 month lead forecast. Little change was indicated or made for the areas predicted to have below normal temperatures. Model guidance for Alaska, however, resulted in the addition of an area of basically correct forecast below normal temperatures, but led to the removal of the larger correct area of above normal temperatures. Although there was a cold period during the first part of the month, a strong ridge developing during the last few days of the month produced record high temperatures at several locations along the south coast and panhandle areas. The revisions to the precipitation forecast resulted in a considerable increase in the skill, to 9.0 for all stations and 25.0 for non-EC only, with an increased coverage of 35.9%. Short- and medium-range model forecasts favored retention of the wet area over the upper Mississippi Valley and the addition of above median forecast for coastal areas of the Pacific Northwest and most of the East Coast of the CONUS. All the increased skill came from these additional areas. No areas were forecast to have below median precipitation, and Alaska was left with a forecast of all EC. --- EOF