Craig,
You don't indicate 'where' in Canada you're located, but my first thought is that your plugs frosted over, although there are a myriad of things that could cause the roughness... like a bad lead. But my first guess would be fouled plugs, especially the lower ones if yours is a high-time engine, which you also don't specify. On startup, me thinks you should be warming-up the engine above 1000 RPM so that the oil pump doesn't cavitate. Try 1100 RPM and I'll bet your results will improve.
SkyKing
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