Multiple polar vortices, which brought chilling cold to a large swath of the country last month and continuing cold over much of the nation, are driving the number of recorded heating degree-days (HDD) to unusual highs, according to National Oceanic and Atmospheric Administration (NOAA) data.

The United States experienced 1,045 gas home customer-weighted HDD last month, 141 more than in January 2013 and 55 more than the long-term average, according to NOAA. There were 1,258 HDD in New England (an increase on 146 from 2013 and 49 from the average), 1,283 in the Middle Atlantic (up 244 from 2013 and 128 from the average) and 1,489 in the East North Central region (up 325 from 2013 and 186 from the average). In fact, of the nine regions monitored by NOAA, only the Mountain and Pacific recorded fewer HDD in January than they did in January 2013 or in the long term average.

The historically cold temperatures brought to the United States by January’s polar vortices drove HDD totals higher despite a few relatively warmer days, according to NOAA Climate Prediction Center meteorologist Adam Allgood.

“The colder it gets, the more heating degree days you accumulate, and there were some really deep cold spells in January,” Allgood told NGI. “In the northern Plains it was consistently cold, but as far as the Northeast, where more of the core population is, the coldest days were fairly brief, they came in two- to three-day periods, so in a monthly total you’re averaging up the whole month and there were other parts of January that were actually above normal temperatures.”

Even before the polar vortex rolled south, HDD days were being recorded at an accelerated pace. The number of HDD was 19% higher in December than a year earlier, and was 10% higher in the second half of 2013 compared with 2012. The United States had 830 HDD in December 2013, compared with 695 in December 2012 and the 1971-2000 average of 817. And there were 1,743 HDD in the last six months of 2013, compared with 1,586 in July-December 2012 and an average 1,739.

And the 2013-2014 chill is far from over. The Northeast, North Central and lower Mississippi Valley can expect unusually cold temperatures to continue through most of the next three months, according to forecasters at Weather Services International (WSI) (see Daily GPI, Feb. 4). The Northeast is likely to have colder-than-normal temperatures as late as April, WSI said.

Last month’s polar vortex and predictions of continued cold have prompted some energy analysts to revise their forecasts upward for U.S. natural gas prices (see Daily GPI, Feb. 3). Analysts have said that sustained unusually cold weather could lead to storage levels around 1.2 Tcf by the start of April, possibly keeping gas prices higher through the year (see Daily GPI, Jan. 24).