Frankfurt Airport Train Station

On line, I buy advance rail tickets to save money & allow 3 hours to go through immigration & then get to the rail station in the other terminal by monorail.

Any purchase the day of arrival involves some risk. While three hours may appear to be plenty of time, I have taken over two and half hours to clear immigration. Granted it was only one time but still that is a possibility. Bigger problem if the original flight is cancelled. That happened to us once and we lost the on going air line ticket even thought we had planned a five hour window as we normally do and normally works well for us. And one time our flight arrived five hours late but we had nothing planning so that one didn't matter. The point is -- while infrequent delays can happen so you need to weigh the risk of missing the connection against the cost of the additional ticket if you miss.

German trains don't require reservations, you stand if there are no seats available. So buying a ticket in advance does not guarantee you a seat. But you can buy seat reservations for 4.50 EUR per 2nd class seat, and you don't even have to buy a ticket. If you don't mind spending the extra money, you could buy seat reservations on multiple trains.

The 10:52 ICE is the one you are probably looking at. It starts in Hamburg going to Munich through the most populous region of Germany on a Friday, so I can see why it is probably expected to be full.

Is it too late to get a Rail&Fly adder to your Lufthansa ticket? Then you will have prepaid for the train, at least as far as Offenburg, then it is local unreserved trains from there to Colmar. Another option is to take the Lufthansa Bus to Strasbourg, then continue on by local train to Colmar.

I guess I usually wait as what if your flight is delayed or cancelled? The train station is basically attached to the airport. Follow the signs.

Is there anyway you can delay your arrival in Colmar by one day and stay in the Frankfurt area until the next day when you can count on making a specific train with reserved seats?

A couple of years ago, I arrived at FRA and went to St Goar by regional train the first day. We spent a day in St. Goar, then used a train specific Savings Fare ticket to get to where I wanted to go in Bavaria. I had wanted to do (sometime) a Rhein cruise from Bingen to St. Goar anyway.

Other than that, I like the idea of getting Rail&Fly tickets, which are open tickets valid for any trains (including an ICE) on the day of arrival, then getting just seat-reservations-only on several trains that day. Or just get open, full fare tickets (which are also valid on any train) and multiple reservations.

Is something going on that weekend in Mannheim? Seems trains into Mannheim from any directions have that warning, and it's not just the 18th.

Look into a connecting flight from FRA to Basel (although you would have the same problem with a late flight into FRA if it were a separate ticket). Colmar is close to Basel and there don't seem to be any high traffic warnings on that route.

Given that planes sometimes land late, should we get train tickets ahead of time or after we land?

If the cost of an advanced fare is small enough that you don't mind the loss if late, then get the advanced fare. Worst case is that you wind up paying more, but you would have done that anyway if you opted to wait and purchase on arrival. The advice above about staying overnight in Frankfurt and getting the train the next day is definitely something to consider.

We will land at Frankfurt Airport at 8:35 AM

You will land (hopefully) whenever the plane gets there. There is no guaranteed landing time on a long trans-Atlantic flight, such as from Seattle. I would never buy train specific tickets that depends on the meeting a scheduled landing time.

I once booked a USAir flight from PHL to Munich. After I booked, the flight was 9 and 10 hours late getting to Munich on 2 days in the next week.

Just note that there are two railway stations at Frankfurt airport, so make sure you go to the correct one.