Summer 2010 forecast for North America
Summary. The summer (JJA) of 2010 is forecast to be warmer than the summer of 2009 over the eastern United States, with temperatures above the 1971-2000 average. Colder than normal temperatures are expected in the Pacific Northwest and western Canada. The temperature anomaly pattern in June is likely to be similar to that established in May, with warmer than normal temperatures in the southeastern United States and negative anomalies in the western states. The July pattern will represent a tripole, with positive anomaly centers in the Southwest and British Columbia, and a negative anomaly center in between these region. In August the highest CF for above normal temperatures are centered over the Great Lakes, that is the area that experience a very cold summer in 2009.
Discussion
The forecast temperature anomaly pattern for the summer of 2010 (Fig. 1) has not practically changed from our preliminary outlook issued on Apr 21, 2010. Positive temperature anomalies are expected over much of the eastern North America and negative anomalies in the Pacific Northwest, British Columbia and Alberta.
The summer temperature averaged over the contiguous United States is forecast to be above normal (1971-2000) and warmer than in the summer of 2009. One reason for this forecast is a positive 500-hPa height anomaly in the tropical and subtropical latitudes that is found to be related to summer temperatures in the U.S. (rule 363). This is similar to a lag relationship described by Erickson (1983). Another rule that suggests anomalously warm summer in the contiguous US involves the circum-global teleconnection (CGT) index (Ding and Wang, 2005). The index has significantly increased from summer 2009 to spring 2010 and is expected to remain positive through the forthcoming summer. Positive CGT index favors anomalously warm summer temperatures over much of the contiguous U.S., particularly in its eastern half in June and August (rule 298).
The distribution of temperature anomalies during the summer of 2010 is predicted to be almost opposite to that observed in the summer of 2009 (see the review). That summer was anomalously cold in the Great Lakes region and warm in British Columbia. This summer the pattern is likely to be reversed (Fig. 1). It appears that, as of this writing (third decade of May), this pattern is already trying to establish itself with frequent upper atmospheric troughing over the West Coast and ridging over the East Coast.
Although the majority of forecasting rules point to anomalously warm summer in the eastern half of the contiguous United States, the confidence factors for this forecast were somewhat reduced due to excessive amount of spring precipitation in this area, increased soil moisture and it possible cooling effect on summer temperatures. This makes drought-amplifying heat waves less likely.
 Fig. 2. June 2010 SAT forecast.
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 Fig. 3. July 2010 SAT forecast.
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 Fig. 4. August 2010 SAT forecast.
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Monthly forecasts for June, July and August are presented in Figs. 2-4. In June (Fig. 2), the highest CFs for above normal temperature are in the southeastern United States. In the past three years (2007-2009) June temperature in this region was well above normal. It appears that June 2010 will continue the sequence. Compared to our preliminary outlook, CFs for above normal temperatures in the Southwest are reduced. Although there is a strong warming trend in this region, the type of atmospheric circulation observed in April suggests a possible cooling in this area in June (rule 1219). At the same time, positive temperature anomalies are now appears to be more likely in the Great Lakes region.
It is interesting to note that the temperature forecast pattern for July 2010 (Fig. 3) closely resembles the observed temperature anomaly pattern observed in June 2009. Positive temperature anomalies are forecast both for the southeastern United States and British Columbia, and negative temperature anomalies in between these two regions. For British Columbia and the Pacific Northwest July will probably be the only month of the season with positive temperature anomalies. The July pattern (Fig. 3) is quite unusual from the viewpoint of teleconnections. For example, there is a strong positive correlation between July temperatures in Vancouver and Salt Lake City (r = 0.60 for the detrended values from 1897-2009). In recent years, however, there is some disagreement in temperature fluctuations in these two cities.
In August (Fig. 4) the highest CF for above normal temperatures are centered over the Great Lakes, that is the area that experienced a very cold summer in 2009. Although the latest data (April through mid-May) confirmed our preliminary outlook, there are still a few rules suggesting that the temperature increase from the last summer would not be enough to bring temperatures in this area above their 1971-2000 average level. In the Southeast, the CFs (and hence, probably, the magnitude of temperature anomalies) are smaller than in June and July. Negative temperature anomalies are still more likely in the Pacific Northwest and western Canada.
The official CPC forecast indicates that the chances of below normal temperatures are elevated over their climatological probability for much of the Great Plains and Great Lakes regions. Above normal temperatures are favored for central and southern sections of the interior west, the Gulf Coast, and sections of the Southeast. This is similar to the IRI multi-model probability forecast. The latest CFS forecast shows anomalously cold summer over much of the contiguous US. In contrast, the UK Met Office forecasts above normal temperatures almost everywhere in North America.
