A weather link to Tlachichuca is http://weather.yahoo.com/forecast/MXPA1826.html
When we were there a month ago the weather was similar to the current forecast. At the hut it was colder but no real issues as I never used my puffy. The climb was a different story. What started out as almost warm temps (high 30s) turned much colder on the glacier once the wind kicked up. I estimate it was in the single digits with 20 mph gusts on the summit. I had plastics and my puffy along. I never used the puffy, only my softshell with a wind shirt layer. You can't tell what the weather will do that high up with a lot of confidence. I've used my puffy on other trips to Orizaba and was thankful that I took it. Hope this helps. Cheers!