"Just before" is a relative term.  If in minutes/hours before a hard freeze, the answer (see guidelines below) is wait for the hard freeze to subside to warmer temperatures ( > 40F ).  You want the water to be able to leach into the top 8"-24" of soil for most tree root systems to gain a moisture benefit.

What you want to avoid is unnecessary water runoff and ice sheeting that can mat turf grasses.

Current conditions ( 06:50 2025.01.17 ) in Boulder County call for temps well below 40F for the next week, and possibly beyond.  So watering trees is not recommended in the next week.

After a hard freeze, temps will need to be above 32F long enough for the soil to thaw, so just being above 40F is not necessarily sufficient.  You can use a garden tool to probe for proper thawing.

Here are some general guidelines:

https://extension.colostate.edu/topic-areas/yard-garden/fall-and-winter-watering-7-211/

https://planttalk.colostate.edu/topics/trees-shrubs-vines/1706-fall-winter-watering/

https://weather.com/weather/tenday/l/f70143aa9a07c14eb68e445b7b205ac02a0736b8d83e159baa9ef4d023440f91