UK GAS-Prompt prices rally on supply shortfall

June 20 (Reuters) - UK prompt gas prices rose on Tuesday due to supply shortfalls as storage sites rebuilt stock levels and reduced flows coming from domestic terminals.

* British within-day gas price up by 0.68 pence, or 2.08 percent, to 33.43 pence/therm at 1056 GMT.

* Day-ahead gas price up 2.00 pence or 6.45 percent to 33 p/therm.

* Prices rose as storage sites were set to inject 63 million cubic metres/day (mcm) to rebuild stock levels; output from the St Fergus Mobil terminal dropped to 10 mcm from 20 mcm; send-out from the South Hook liquefied natural gas (LNG) fell to 3 mcm from 8 mcm.

* Norwegian flows to Britain rose by 30 mcm to 56 mcm after a shutdown of the Emden gas terminal in Germany forced the producer to reroute supplies.

* Gas system undersupplied by 19.9 million mcm with demand forecast at 190.1 mcm and flows at 170.2 mcm/day, National Grid (LSE: NG.L - news) data showed.

* July gas contract up by 0.45 pence to 35.53 p/therm.

* News that Britain's biggest gas storage site Rough will be permanently shut by operator Centrica (Frankfurt: A0DK6K - news) had little impact on prices.

* "Immediate impact on the market will depend on when Centrica releases the remaining gas," said Wayne Bryan, analyst at consultancy Alfa Energy.

* Day-ahead gas price at the Dutch TTF hub down by 0.03 euro to 15.35 euros per megawatt hour.

* Benchmark Dec-17 EU carbon contract up by 0.09 euro to 5.02 euros per tonne.

* Thomson Reuters (Dusseldorf: TOC.DU - news) analyst view: http://emea1.apps.cp.extranet.thomsonreuters.biz/cms/?pageid=united-kingdom-gas (Reporting by Oleg Vukmanovic; editing by David Evans)