* Within-day gas price hits premium this year
* Gas stockpiles depleting, withdrawals ease
LONDON, Feb 22 (Reuters) - British gas prices rose on Friday morning as bitterly cold weather boosted demand for heating to above average levels, while strong withdrawals from storage facilities struggled to plug gaps in supply.
Gas for Monday delivery rose 0.20 pence to 69.70 pence per therm as the system was undersupplied by about 4 million cubic metres (mcm) owing to higher-than-expected demand.
Steep gains on gas for immediate delivery made it the highest priced contract in the current gas year at 70.5 pence, up 1.75 pence, prompting traders to pull more gas out of storage in a bid to balance supply and demand.
Withdrawals from storage fell below Thursday levels, however, to 99 mcm from 114 mcm as stockpiles at Rough, the UK's biggest storage site, and other mid-range facilities fell below last year levels.
"We see a need for continued high withdrawals until mid next week, and lower withdrawals as we approach March due to the lower consumption," analysts at Thomson Reuters Point Carbon.
Because of the ongoing cold, Britain's gas storage sites are emptying fast.
Gas demand was expected to be at 365 mcm on Friday, 20 percent above the seasonal average, data from National Grid (LSE: NG.L - news) showed.
"The wind chill factor makes it feel colder than it actually is and overnight it's still going to be below freezing...that's the real driver of demand right now," one UK gas trader said.
"The cold and relatively drier spell of weather will continue during next week, with brisk winds in the south and southeast making it feel very raw here," Britain's MetOffice said in its fortnightly forecast.
The benchmark summer 2013 gas contract rose 0.30 pence to 64 pence, supported by stronger crude oil prices and bullishness on prompt gas markets.
Baseload power for 24-hour delivery on Monday rose to 53.1 pounds per megawatt hour, up 1.85 pounds compared with Thursday levels, tracking bullish sentiment on gas markets. (Reporting by Oleg Vukmanovic; Editing by Alison Birrane)
