(Blog written by Donald Sutherland)
Summer 2012 Thoughts:
Recent analogs have continued to suggest that odds somewhat favor the development of an El Niño during the summer. The fresh burst of westerlies out in the Pacific that has sent the SOI to -27 offers another hint, as El Niño events are typically preceded by bursts of westerlies that damp the easterly trade winds. However, given recent SSTAs, it is likely that the transition to El Niño will probably be somewhat discontinuous, with warming SSTAs followed by some cooling and then renewed warming.
The key assumptions for my summer thoughts are:
• The onset of El Niño conditions, possibly during July or August
• Possible return of PDO+ conditions
• A continuation of general warmth in the Arctic region
Typically, such a scenario would lead one to assume that the Great Lakes region and New England and perhaps a larger portion of North America would wind up cooler than normal. The persistence of the 2009 analog (ranked #2 for my June thoughts and narrowly #1 for summer with 1991 a close second) would also argue for a lot of cool anomalies. However, that exceptional anomaly is largely offset by the others, which account for more than 60% of the overall summer anomaly.
Afterward, there is the modeling. The CFSv2 has a large area of North America forecast to be above normal. Some of the warmest anomalies on that model show up in northern Canada, the Great Lakes region, and the Plains States. Likewise, the European Model has a generally warm forecast for a large section of North America.
Summer decadal trends have much of the U.S. and eastern Canada warmer than normal. Portions of northern Canada are cooler than normal.
Then, there is the persistent warmth in the Arctic region. If the source region of cool air masses remains anomalously warm, patterns that normally would produce chilly conditions in Canada and the U.S. would wind up less cool. Hence, such patterns would overperform on the warm side.
Recent trends in the analogs and modeling (e.g., CFSv2) have been toward warmer ideas. A warmer outcome than what I expect is not out of the realm of possibility. I didn’t embrace an even warmer scenario, because I am assuming that the El Niño will develop and that the resulting pattern, especially during the latter part of summer, could be sufficient to blunt the warmth in the Great Lakes area and New England (for the 3-month averages). Nevertheless, even those areas could experience some much above normal readings, possibly during the first half of summer.
Taking into consideration all this data, my summer thoughts are as follows:
West Coast (except for the Pacific Northwest) would wind up somewhat cooler than normal. The Pacific Northwest will likely be near to somewhat warmer than normal. The Great Lakes region (U.S. States and Ontario), Northern Plains and New England would likely wind up near normal with some areas of cool anomalies. The rest of the U.S. would wind up warmer than normal. The warmest anomalies would likely extend from Texas northward into the Central Plains and then eastward into the Western Gulf States. Northern Canada and much of eastern Canada, along with central Manitoba northward and central Saskatchewan northward would likely be warmer than normal. Alaska would likely have a warm summer. The rest of Canada could be near normal.