Greetings from the RFK Stadium campus, where it’s always 10 degrees cooler than the rest of the metro area. This morning’s offering: raw, windy and overcast for D.C. United’s training session. With yesterday’s rain turning the grass to mush, D.C. United opted to work out on the artificial turf field for about 90 minutes.

The team will practice in town again early Saturday before flying to Denver ahead of Sunday’s match against the MLS champion Colorado Rapids (7 p.m. ET, Galavision).

In Denver, where weather conditions this time of year are as unpredictable as Lionel Messi in possession, it’s going to be in the 70s today and tomorrow and in the 60s with a chance of rain Sunday.

Playing at altitude, the best course of action is to either arrive several days early or as late as possible.

Said captain Dax McCarty: “It’s a big factor. Maybe my first year or two, I didn’t think about it because it’s just another game, but a few more years of experience, you realize it takes a toll on your lungs. It’s not so much your legs. You find yourself out of breath a little faster. For them, it’s a tremendous home-field advantage.”

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*Midfielder Clyde Simms, nursing a calf injury that prevented him from playing last weekend at New England, worked out for a while before leaving practice early. “He looked okay and he’ll be in the mix,” Coach Ben Olsen said.

*Defender Jed Zayner, who missed the previous match with a hamstring ailment, jogged on the side and said he is progressing well but still unsure whether he will travel with the club.

*With Zayner questionable, Perry Kitchen with the U.S. under-20s and Dejan Jakovic suspended, the backline may very well look like this: Marc Burch at left back, Rodrigo Brasesco and Daniel Woolard in the middle and Chris Korb on the right.

*Goalkeeper Pat Onstad seems likely to start again Sunday, but Bill Hamid is on course to make his 2011 debut soon, perhaps Wednesday in a U.S. Open Cup qualifier against the Philadelphia Union at Maryland SoccerPlex.

“Bill is getting closer and closer,” said Onstad, the goalkeepers coach who came out of retirement to fill a void left by injuries to Hamid and Steve Cronin. “I have no input as to who is going to play. From the get-go, it’s been clear to Bill that Benny and [assistant] Chad [Ashton] will make that decision. The big thing really is to get Bill up to speed, and he is pretty darn close. He has had a game and a half [reserve matches] under his belt now. We have an Open Cup game coming up next week -- it’s a good opportunity for him — and after that I’m sure we’ll sit down and see where we are.”

Meantime, Cronin (broken wrist) is ahead of schedule and could be in the mix for playing time in a few weeks.

*Forward Josh Wolff (hamstring) trained today and should be available Sunday.

*Olsen, on rookie central defender Ethan White: “He has been good at times and he has had some youthful moments. That’s what this is about. His role for us is going to be certainly something that we are trying to develop for the future. Can he step in and do a job in a pinch this year? I think so. He’s a competitive guy who has seen some big games with the youth national team and the College Cup. I don’t think the lights are going to be too bright for him [overwhelmed by the moment]. But he has a ways to go. The technical side can get better, tactically he is not there yet. He has a lot of improvement to do before he is ready to step in and be at the level we all want him to be. He’ll get there eventually. Like most young guys, he needs to work on concentration every day, every play, and when he gets his chance in reserve games, make sure he proves to us he’s ready to go.”

*United is hoping to finalize reserve scrimmages with both the University of Maryland and University of Virginia a week from Sunday (April 10) at the RFK training grounds. Each of the three teams would play one another for 45 minutes.