UK GAS-Cold snap and lower Norwegian flows lift prices

LONDON, April 24 (Reuters) - British wholesale gas prices rose on Monday as colder temperatures lifted heating demand, exports to Europe remained high and imports from Britain's main supplier Norway fell. * Day-ahead gas price up by 0.80 pence to 40.90 pence per therm at 0942 GMT. * Within-day contract up by 0.30 pence to 40.50 p/therm. * Traders said weather was the key driver with UK average temperatures due to plunge to an average 5.4 degrees Celsius on Tuesday from 9.1 degrees C on Monday, according to weather data on Reuters Eikon. * Gas system is 10 million cubic metres (mcm) oversupplied on Monday, with demand forecast at 247.7 mcm and flows at 257.7 mcm/day-National Grid (LSE: NG.L - news) data shows. * Imports from top supplier Norway fell to 40 mcm/day from around 50 mcm/day last week; exports from Britain to Belgium stayed high at 40 mcm/day. * Four of Britain's 15 nuclear reactors, with a combined capacity of 2.3 gigawatts, are offline. * Just one liquefied natural gas tanker is scheduled to arrive in Britain this week, further tightening the supply outlook. * May gas contract up by 0.55 pence to 40.30 p/therm. * Day-ahead gas price at the Dutch TTF hub up by 0.15 euro to 16.73 euros per megawatt hour. * Benchmark Dec-17 EU carbon contract up by 0.14 euro to 4.71 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 Nina Chestney)