By Paulina Duran and Jonathan Barrett

SYDNEY (Reuters) - Macquarie Group earned big profits off the winter storms sweeping across Texas and other U.S. states, with the gains from its trading operations single-handedly changing the Australian bank's outlook for the year.

The company is the second-largest gas marketer in North America behind oil major BP, and the week of big trading revenue has by itself boosted the bank's overall profit outlook for the year by 10%.

The windfall comes after nearly a week of frigid temperatures that knocked out power for millions of people in the United States, particularly in Texas, forcing many to spend several nights without heat or electricity.

Some consumers are facing exorbitant utility bills in coming months as a result of Texas's largely unregulated system. The deadly winter storm meant electricity generators had to compete for natural gas supplies, pushing up prices sharply in the deregulated market.

Real-time natural gas prices surged more than 300 times during the storms, with power prices reaching $8,800 per megawatt-hour in some parts of Texas, compared with an average of roughly $26 per MWh.

Macquarie on Monday said it expects fiscal 2021 profits to jump by as much as 10% after warning just two weeks ago that earnings would be "slightly down."

"Extreme winter weather conditions in North America have significantly increased short-term client demand for Macquarie's capabilities in maintaining critical physical supply across the commodity complex," the company said in a statement.

The company's energy business unit trades large quantities of gas to meet unexpected consumer demand, and it could boost the bank's overall profit by about A$400 million ($317 million), analysts said. Macquarie purchases natural gas and moves it along pipelines and grids, typically from areas where usage is low to high-demand markets.

"Macquarie appears to be capitalising well on volatility and financial market dislocation," Bank of America Securities analysts said in a note, as it increased its earnings forecasts for the Sydney-headquartered company.

U.S. politicians have vowed to investigate how some companies profited so handsomely from the storm even as some natural gas providers celebrated their gains. "This week is like hitting the jackpot, as some of these incredible prices," said Roland Burns, president at Comstock.

Macquarie's shares closed up 3.5% to A$147.15 on Monday, the highest level in a year, outperforming the broader market that was flat.