The same weather conditions that have been propping up summer temperatures across much of the United States — a La Nina event off the western coast of South America, a relatively cold north Pacific and record warm North Atlantic — will also help produce relatively warm temperatures through November, WSI forecasters said Monday.

WSI’s seasonal forecast calls for warmer-than-normal temperatures to dominate the country, with the exception of the Pacific Coast states. WSI issued a similar forecast in July (see Daily GPI, July 20).

“For the September-November period as a whole, we are forecasting 901 gas-weighted heating degree days, 3% less than last year and 9% less than the 1971-2000 mean,” according to WSI Chief Meteorologist Todd Crawford.

But the historically persistent negative phase of the North Atlantic Oscillation, which often acts to keep temperatures down in much of the East, is still a source of forecast uncertainty, Crawford said.

WSI predicts temperatures to average warmer than normal across all of the United States in September, except coast California and the Northwest, which is expected to be cooler than normal.

“Warmer-than-normal temperatures in September will extend the summer season dynamics well into the month,” Energy Security Analysis Inc. (ESAI) Director of Power and Gas Paul Flemming said in a statement issued in conjunction with WSI’s outlook. “Any load effects on price due to a seasonal decline in late summer temperatures will be offset somewhat by the start of the planned generator maintenance season. Northeast power prices should remain firm and gas demand above-normal through the end of summer.

“Natural gas prices should be supported with stronger-than-average demand in September, but we do not expect much upside without a hurricane disruption.”

WSI’s temperature forecast map will stay much the same into October, with the only changes coming in the Northeast and North Central regions, which are expected to see much-warmer-than-normal temperatures.

“Power demand in most regions will reflect shoulder-season temperatures and warmer-than-normal temperatures will have less impact on load,” Flemming said. “Generator maintenance will be in full swing during October and will have a greater relative impact on power prices than variations in temperature. A reduction in early season gas demand for heating could be offset by marginally increased demand from the power sector.”

Cooler-than-normal temperatures will move into the Southeast in November, but all of the rest of the country, with the exception of coastal California, will average warmer-than-normal through the month, WSI said.

“Warmer weather in November will delay heating-related demand for gas and power and this will be slightly bearish for natural gas prices,” Flemming said. “Power demand will be reflective of shoulder-season temperatures through November and the peak of generator maintenance will be seen in the first half of November, providing support for power prices in most regions.”

WSI is scheduled to issue its next seasonal outlook on Sept. 21.

In separate forecast also issued Monday, the Commodity Weather Group (CWG) said it expects the core heating season (Dec.-Feb.) to be 29% warmer than the same period last year and the warmest since 2006-07. Energy demand should run lower than normal for key population centers on the East Coast, through the Southern production region, and even into many of the Midwest consuming areas, due primarily to the developing La Nina event, CWG said.

“While the Midwest and Northeast have seen cold winters during strong La Nina events, the confluence of many factors appears to argue against this,” said CWG meteorologist Matt Rogers. La Nina is an unusual cooling of ocean surface temperatures off the western coast of South America. Chief Long Range Forecaster Joe Bastardi has also said he expects La Nina to influence weather across the United States this winter, though he expects it to produce significantly colder-than-normal temperatures in portions of the western United States (see Daily GPI, Aug. 4).

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