* Low temperatures, overnight frost forecast this week
* Nuclear plant outages lift gas burn in thermal plants
* Yemen LNG takes forward maintenance after pipeline explosion
* Wylfa nuclear units trip, restart due this week
LONDON, Oct 17 (Reuters) - British prompt gas prices surged to a seven-week high on Monday as colder weather is expected to drive up gas demand this week and nuclear plant outages increased gas burn in thermal power plants.
British day-ahead gas rose to the highest level since late August on Monday, trading up to 60.20 pence per therm at 0920 GMT, 3.25 pence above last week's closing price.
"We see colder weather on the front for this week, but today is mild still and the system remains well supplied with LNG (liquefied natural gas) and storage," one UK gas trader at a utility said.
Weather forecasts for the latter half of the week predicted low temperatures, likely overnight frost and potential snowfall in higher grounds in the north, according to Britain's Met Office.
Cold weather is expected to lift gas used in heating systems and increase exports to Belgium.
Traders also said the high number of nuclear power plant outages encourages higher gas burn in thermal power plants to compensate for the loss in nearly 5 gigawatts (GW) of generating capacity.
Gas-fired power plants covered more than 44 percent of power production on Monday morning, National Grid data showed.
Monday gas also traded higher at 60.00 pence per therm, gaining value late in the morning as the system fell around 5 million cubic metres short, despite rising supply from LNG terminals and healthy gas storage levels.
November gas tracked gains on the prompt, rising 0.50 pence compared with the previous session to 65.50 pence.
Short-term LNG supply looked healthy with at least three more cargoes expected over the coming five days.
Yemen's LNG terminal took forward an annual maintenance outage after an explosion on the gas pipeline which feeds the terminal.
The terminal still loaded a cargo heading for India on Sunday with gas stored on site before the explosion, the operator said.
Rebounding oil prices drove curve gas contracts on Monday, with the benchmark front-season contract rising 0.25 pence to 64.10 pence per therm.
Brent futures rose close to $114 per barrel on hopes that European policymakers could reach an agreement at the G20 meeting on how to tackle the euro zone debt crisis.
Spot power prices mirrored gains in the gas market and also rose on the back of tight supply margins after a number of nuclear plant outages over the weekend.
Two units at the Welsh Wylfa nuclear power plant stopped unexpectedly on Sunday, while EDF Energy stopped a Hinkley Point reactor for a planned outage on Friday.
Baseload day-ahead power rose 60 pence to 48.60 pounds per megawatt-hour (MWh) on Monday, but trading further out was thin.
GAS-Please click on the following for information about UK and Belgian prices, field maintenance and field start-ups.
