* Third Kollsnes outage in two weeks cuts gas supplies
* But facility revamped Friday morning
* Storm over northern UK causes outages (Updates prices, notes MACD signal cross)
LONDON, Dec 9 (Reuters) - British prompt gas and power prices rose on Friday after another Norwegian gas processing plant outage and stormy weather in northern Britain cut supplies.
By Friday afternoon the market began to ease as the weather calmed and Norwegian gas supplies increased.
Norwegian gas processing plant Kollsnes, which can process 143 million cubic metres (mcm) of gas per day, was ramping up production on Friday morning after shutting down overnight for the third time in less than two weeks, North Sea infrastructure operator Gassco said on Friday.
As a result of the outage, gas flows into the UK's Easington terminal dropped from over 90 mcm on Thursday evening to 40 mcm between midnight and 0600 GMT on Friday morning before flows returned to normal by 0845 GMT, according to National Grid data.
The outage pushed prompt gas prices up.
Within-day gas prices were trading around 59.60 pence per therm at 1600 GMT, up from 57.75 pence on Thursday afternoon.
Following a heavy storm across northern Britain overnight that damaged the power infrastructure and caused some power outages, prompt wholesale power prices also rose on Friday morning.
Day-ahead baseload (24 hours) power prices were trading at 43.60 pounds per megawatt-hour (MWh) on Friday, up 30 pence on the previous afternoon.
The return of EDF Energy 640-megawatt Torness 2 nuclear reactor to the grid on Thursday evening was largely offset by Hunterston B-4's 460 MW reactor, also operated by EDF Energy, being taken off the grid on the same evening.
EDF did not say why the unit was taken off the grid or when it would reconnect.
Following Thursday's storm that saw wind speeds well above 100 miles per hour, the UK Met Office said winds were easing on Friday morning, but it warned of icy weather in the North of Britain.
"Warnings of icy roads are in force across much of Scotland, Northern Ireland, and parts of northern England as a result of temperatures dropping overnight," the Met Office said.
Temperatures were expected to remain below 5 degrees Celsius throughout the UK on Friday and over the weekend, with wet and windy conditions dominating.
DEMAND & SUPPLY
Although daily UK gas demand was seen to be above the seasonal norm of 31 mcm a day, Britain's gas system was well supplied on Friday morning, following the return of flows into Easington.
Forecast demand was at 318.7 mcm while flows stood at 312.9 mcm, according to National Grid.
This returned to the pattern seen much of the week, which largely saw demand outstrip supplies, meaning that suppliers had to rely on imports from continental Europe and storage withdrawals.
As a result, NBP gas storage levels in the UK fell from over 96 percent late last week to around 93.5 percent on Thursday, according to Gas Infrastructure Europe data.
Further out on the curve, UK summer 2012 NBP technicals improved further on Friday.
The contract was rising for the third straight session and stood 58.70 pence per therm on Friday afternoon, up from around 56 pence on Monday.
The relative strength index (RSI) rose back above 30 points mid-week and is now sending out neutral price signals.
Moving average convergence-divergence (MACD) signals remain at close to a 2011 low but have now crossed, implying a more bullish sentiment.
However, the contract remains in a clear downtrend that began in late August, and the product is still down over 15 percent since then and has erased all gains made on the back of Fukushima and the Arab spring.
Its 50 exponential daily moving average (DMA) value remains lower than both its longer-termed 100 and 200 DMAs.
GAS-Please click on the following for information about UK and Belgian prices, field maintenance and field start-ups.
UK natural gas prices <0#NBPGAS-RTR>
Belgian natural gas prices <0#ZEEGAS-RTR>
North Sea field start-ups
North Sea field maintenance
UK: baseload prices <0#ELBUK-RTR>, outages
FRANCE: baseload prices <0#ELBFR-RTR>, peak <0#ELPFR-RTR>
market report, Powernext,
Spectron baseload <0#FRBSLD-SPC>, off peak
<0#FROFPK-SPC>, peak <0#FRPEAK-SPC>
nuclear outages: report, offline
percentage EL-FROUTAGE-PC, offline capacity (MW)
GERMANY: baseload prices <0#ELBDE-RTR>, peak <0#ELPDE-RTR>
SWITZERLAND: outages, reservoir levels
EU CARBON PRICES SPEEDGUIDE: