Subaru Repair: 03 Outback, spray water, outback

Question
I have an 03 Outback with about 52k miles.  The check engine light just came on.  It runs just fine when the weather is good, but when it rains, it runs really rough for the first few minutes.  Once the engine heats up, it usually runs fine again.  Any ideas on what the problem could be?

Answer
have the check engine light scanned. It is most likely a misfire. Most likely caused by a cracked coil, or bad plugs. With the engine running ok, spray water on top of the engine is see if it starts to skip, that would be an idication the coil is bad, and replace the wires also.