NHRA factors LVMS for basically .15 that does not take into account the weather strictly the 2000' of elevation. Typically race prepped small block will loose .3 in the spring/fall and BB cars can expect to slow .2. The closer to stock you get the more you will loose.
Now if it gets hot that's out the window, you an slow another .2-3 from those numbers. For what its worth you will be lucky to see an actual barometer here of 28.00, we call anything over that "mineshaft" air here. My racing in Florida and east coast its not atypical to see actual barometer over 30.00. For instance the actual baro in Bradenton right now as I type is 30.11 and here it is mineshaft at 28.02
. Just based on those numbers I would expect a rare prepped BB to slow about 3-4 tenths.
There are some things you can do for the conditions. Adding timing is one that works well. As for jetting depends on how "racey" the engine is. For a guy coming from a place where air is typically much better than here I'd start at 5-8 thousands of jet size to start. The weather here would play a roll from there. Spring air here is typically 22-3000' DA if its typical early March weather. So expect high in the 60-70's lows in the high 30's low 40's. We have no humidity here at all so thats a plus for out DA's, But this time of year it can be quite cold. Last couple days we have struggled to get to 50 and the wind has been blowing 20-30mph. It was actually snowing at my house yesterday morning. But 4 days ago it was 77 and no wind. Its Vegas in spring can expect most anything
