To pull off that feat of cooling, he explains, September through December would have to rank among the 20 coldest final four months on record – highly unlikely given the historical record as well as seasonal forecasts for the final four months of 2012.
Most of the continental US – from the Southwest up into the Rockies and eastward into Maine – is forecast to see warmer-than-normal temperatures throughout this final period, notes Huug van den Dool, with the National Oceanic and Atmospheric Administration's Climate Prediction Center in College Park, Md.
One key reason is the apparent shift in conditions from two consecutive years of La Niña to a weak El Niño this coming winter. La Niña and El Niño represent opposite states in sea-surface temperatures and wind patterns along the equatorial Pacific. Both can affect atmospheric circulation patterns well beyond the tropics.
For the US, La Niña tends to push average storm tracks across the continent farther north than usual, while El Niño tends to drive them farther south. The onset of El Niño is expected to bring welcome rainfall to the Southeast and mid-Atlantic states. But the more southerly path for storms could lead to a dearth of precipitation farther north in sections of the country already hit hard by drought.
As a result, forecasters are calling for drought to continue through the end of the year for much of the western two-thirds of the US, with drought conditions likely to extend into the Pacific Northwest.