Timing of flights

Confirming, your flight from PMO-FCO and FCO-SEA are two separate tickets? Or are they on the same reservation?

How much time do you have between flights?

If they are separate, and your first flight is delayed enough where you miss the second flight, you will have to purchase a new ticket at the last minute rate.

Sorry - not on same ticket and will have one bag checked ( the carry on international size and weights are smaller than what I carry on here at home). If plane from Sicily on time will have a little over three hours. My concern is it could be delayed.

Your concerns are valid!

You have the right concern and frankly I think this is a high-risk plan (the other way around, with the long-haul international flight first, would be less so).

You will have to pick up your luggage -- I don't think any of the airlines that fly PMO-FCO, i.e. Aeroitalia / Ryanair / ITA, will check through your bag to Alaska on a separate ticket -- and go through security again, along with outbound passport control. It looks like Alaska will likely fly out of Terminal 3, as does Aeroitalia; Ryanair and ITA operate out of Terminal 1.

Is there any way you can fly into FCO the day before?

You will need a couple of hours if all works well and three hours would be best. The big issue will be time of day and clearing immigration. AND, of course, if your first flight is on time. Second, our prior experience is that they will let you jump the line if short time.