UK GAS-Prompt prices edge higher on supply shortage

* Spot gas gains 0.30 pence to 35.90 p/therm

* Gas grid short of 2.4 million cubic metres

July 22 (Reuters) - British gas prices for prompt delivery rose on Friday with demand outstripping supply and lower output from wind farms could spur consumption by gas-fired power plants later in the session.

Gas for immediate delivery was up 0.30 pence at 35.90 pence per therm at 1022 GMT, while gas for day-ahead delivery was up 0.15 pence to 35.80 p/therm.

With supply flows at 178.7 mcm and demand expected to be 181.1 mcm/day, Britain's gas system was 2.4 mcm undersupplied, National Grid (LSE: NG.L - news) data showed.

Friday's demand was around 8 percent above the seasonal norm of 167 mcm, the data showed. Analysts and traders said low forecasts for output from wind farms may increase demand for gas from power generators.

Gas supply has been reduced by an unplanned outage at Centrica (LSE: CNA.L - news) 's North Morecambe gas terminal.

Flows have been cut to zero from 7.7 mcm since July 16 and the plant is not expected to resume operation until July 23.

At Britain's Teesside gas processing plant, capacity is reduced by 35 percent on Friday, potentially further tightening supply.

"The system is currently forecast to close the session 3 mcm short, which could prompt further withdrawals from medium range storage should an increase in demand widen the supply gap," Wingas UK head of trading Marcel Boonaert said.

Gas prices further along the curve also edged higher, with the August gas contract up 0.20 pence at 36.25 p/therm.

The winter 2016 gas contract fell 0.10 pence to 45.85 pence per therm.

In the Netherlands, the day-ahead price at the TTF hub fell 0.05 euro at 14.75 euros per megawatt-hour.

In Europe's carbon market, the front-year EU allowance price was up 0.01 euro at 4.67 euros per tonne. (Reporting by Oleg Vukmanovic in Milan; Editing by Ruth Pitchford)