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Verification for Summer 1998.
CAS was applied in summer 1998 and the verification results in terms of Heidke skill score are summarized in Table 3.

Table 3: Heidke Skill Score SS2 for experimental forecasts for summer 1998, based on antecedent soil moisture conditions. Element w stands for instantaneous soil moisture at the last day of the target month/season, while P and T are time averages of temperature and precip over the 30/90 days. [The smaller #s in ( ) are SS2 for official CPC forecast]

Target W T P  
June 1998 30 (NA) 14 (13) 13 (10) (data thru April 30; fcst released mid-May)
July 1998 31 (NA) 18 (17) 09 (02) (data thru May 31; fcst released mid-June)
Aug. 1998 34 (NA) 34 (15) 11 (08) (data thru June 31; fcst released mid-July)
JJA 1998 29 (NA) 28 (25) 17 (07) (data thru April 30; fcst released mid-May)

The results for Summer 1998 show that

1. Monthly forecasts for w have rather high skill (compared to say T and P, which has SS2=6.4 and 0.4 respectively, averaged over Jan95-May97). This is generally true and is helped greatly by the fact that soil moisture anomalies are, in general, much more persistent than temp and precip anomalies, thus making it an easier forecast target, even at a one, two or even four month lead.

2. Forecast skill for monthly T and especially P are high by the above-mentioned standards ( (expected is only SS2=6.4/0.4 for T/P). The scores for P are in fact record-like, certainly for summer, certainly for a short averaging period like a month, and as good as they were during the El Nino winter of 97/98.

3. On the whole the scores of this tool for summer 1998 were very good. Especially the scores on Precipitation in the summer (the most difficult target of all) SS2 ~ 9-17 are outstanding, given scores that normally hover near zero.

4. In spite of the boasting above, the scores are only modest by absolute standards (100 is perfect). The scores for T and P were much better than persistence, but the scores for w did not outperform persistence of the initial state's anomaly. This is a bit mysterious, and raises a research issue of a hybrid model, in which the physical soil model is integrated in time to produce the w forecast with the driving P and T coming from an empirical forecast like CAS.

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