UK GAS-Within-day prices firm on undersupplied system
* Norwegian gas imports fall by 14 mcm/day
* Gas system undersupplied by 13 mcm/day
* Day-ahead eases on mild, windy weather outlook
* European carbon prices fall by 4 pct
Dec 11 (Reuters) - British within-day gas prices rose slightly in an undersupplied system, while prices for next Monday eased as temperatures were seen to rise, denting demand.
Gas for immediate delivery rose 0.1 pence or 0.27 percent to 36.50 pence per therm by 0900 GMT, while the day-ahead contract lost 0.05 pence or 0.14 percent to 36.30 pence/therm.
Prices for the weekend were 0.3 pence down at 36.10 pence/therm.
With (Other OTC: WWTH - news) supply flows at about 256 million cubic metres (mcm) and demand expected to be about 269 mcm, Britain's gas system was 13 mcm undersupplied, National Grid (LSE: NG.L - news) data showed.
Imports from Norway via the Langeled pipeline, Britain's main sub-sea gas import route, fell by 14 mcm to 57 mcm/day, due to unexpected outages reducing output from the Kollsnes gas plant and the Troll field.
"The short system is providing support to spot prices, though good availability of storage supply is limiting (upward) moves," a UK-based trader said. "Forecasts pointing to warmer weather and a substantial drop in carbon prices put pressure on other contracts."
Temperatures were expected to rise to a maximum 12 degrees Celsius on Saturday in the south of Britain, up from a maximum 9 degrees on Friday, and compared with average temperatures for December of around 6 degrees, UK's Met Office said.
Weather through Sunday to Tuesday is forecast to remain unsettled, mild and windy, it added.
The Hartlepool 1 nuclear reactor restart was postponed until Dec. 16 from Dec. 11, its operator EDF (Paris: FR0010242511 - news) said on Friday.
Further along the curve, the contract for gas delivery in the next quarter was at 36.20 pence/therm, 0.35 pence down.
In the Netherlands, the day-ahead gas price at the TTF hub fell 0.2 euro/MWh to 16.30 euro/MWh.
In the European carbon market, front-year allowances eased 0.34 euro or 4.07 percent to 8.02 euro a tonne.
Britain's auction to secure backup power plants for the year 2019/20 cleared below last year's price at 18 pounds per kilowatt late on Thursday, and nearly half of the capacity was awarded to gas-fired power plants, results published on Friday showed.
For the first time, operators of interconnectors to France and the Netherlands, such as National Grid, also received contracts. (Reporting by Nerijus Adomaitis in Oslo; Editing by David Holmes)