UK GAS-Prompt prices mixed on higher demand but ample supply

* Day-ahead up as colder weather boosts demand

* Within-day declines on amply supply

* Benchmark EU carbon price falls on narrowing spreads

LONDON, Jan 15 (Reuters) - British spot gas prices were mixed on Friday morning as the within-day contract declined on a well-supplied market and the day-ahead and weekend contracts rose on higher demand ahead of an expected cold snap next week.

Gas for day-ahead delivery rose by 0.40 pence from the previous settlement to 32.80 pence per therm by 0900 GMT, while gas for delivery at the weekend inched up by 0.05 pence to 32.55 p/therm.

National Grid (LSE: NG.L - news) data showed that demand was forecast to be almost 340 million cubic metres (mcm) on Friday, around 56 mcm above seasonal normal demand.

Gas-for-power generation is expected to be relatively high for the next few days at around 55 mcm/d, according to Thomson Reuters Point Carbon analysts.

That is mainly due to the blast of cold weather expected next week, which has boosted demand for gas for heating, traders said.

However, weather forecasts are now pointing towards a slightly milder than previously expected cold spell in Britain next week and the last week of January is expected to be milder than average.

Gas for immediate delivery declined by 0.15 pence to 32.35 p/therm, as flows of around 354 mcm/day were expected to amply cover the higher demand.

A fall in the benchmark European Union carbon price could also affect gas prices, traders said.

"A marked drop-off in the front carbon contract could see (gas) curve contracts come under pressure as the day continues, with oil trading lower offering longer-dated contracts downward direction," said Wingas analyst Andrew Crabtree.

In Europe's carbon market, the front-year EU Allowance price fell by 0.31 euros to 6.82 euros a tonne, having fallen as much as 6 percent at around 0900 GMT to below 6.68 euros.

The clean-dark spread - the profit from burning coal to produce electricity including the cost of buying emissions permits - has narrowed, reducing the incentive to buy carbon permits. (Reporting by Nina Chestney; Editing by Greg Mahlich)