Christy's colleague Roy Spencer produced a chart of TMax using the same weather stations as NOAA. (globalwarming.org)
So Christy uses TMax data to estimate trends in hot weather anomalies. (globalwarming.org)
TMin for the 30 long range (roughly since 1880), rural, monthly histories I sampled, demo'ed a roughly +0.35 C trend with Tmax values in the +0.65 range. (realclimate.org)