UK GAS-Prices mixed on low wind and forecasts for warmer weather

June 25 (Reuters) - British prompt prices were mixed on Monday, as within-day fell on weak wind power output and low flows from Norway while day-ahead rose on forecasts for higher temperatures.

* Within-day contract was up 0.35 pence at 53.35 pence/therm at 0852 GMT.

* Day-ahead gas fell by 0.10 pence to 53.25 pence per therm.

* Forecasts for warmer weather on Tuesday reduced demand for gas and pushed day-ahead prices lower, said one gas trader, but low wind power output on Monday and low gas flows from Norway lifted within-day.

* Peak wind power generation is forecast at 0.8 gigawatts (GW) on Monday, rising to 1 GW on Tuesday, National Grid (LSE: NG.L - news) data showed. The output is very low comparing to the total capacity of Britain's wind turbines, which is 11.8 GW.

* The British gas market was slightly oversupplied, with demand forecast at 155.2 million cubic metres and flows at 156.7 mcm/day, National Grid data showed.

* Average daily temperatures in Britain are seen at about 17.9 degrees Celsius on Monday, and are expected to rise to 18.1 C on Tuesday, Thomson Reuters Eikon data showed.

* Gas supply from Norway to Britain was stable at 47 million cubic metres (mcm) per day, representing about one third of Norwegian pipeline system's maximum export capacity.

* Britain was not expecting any liquefied natural gas (LNG) vessel to arrive as of Monday

* The July contract was down 0.45 pence at 53.25 pence/therm.

* Day-ahead gas at the Dutch TTF hub fell by 0.17 euro to 21.63 euros per megawatt-hour.

* The benchmark Dec (Shanghai: 600875.SS - news) -18 EU carbon contract was down 0.02 euros at 15.10 euros a tonne. (Reporting by Lefteris Karagiannopoulos in Oslo; editing by Jason Neely)