The Front Range is expecting a winter storm with temperatures expected to reach the low 20’s Fahrenheit, 3 to 5 below 0 Celsius. This event will likely cause significant bud and blossom death in fruit trees in this area, as well as to other fruits and vegetables. How much damage is determine by the specific plant (apple, peach, grape, spinach, etc) and the development stage. There are methods to limit or prevent damage, and we recommend you do some research and apply as appropriate/reasonable to your specific plants, location and resources. Mark Longstroth with Michigan State University Extension has a couple of tables with critical temperatures for tree fruits, which you can find here: http://msue.anr.msu.edu/news/freeze_damage_depends_on_tree_fruit_stage_of_development
This weather event is not expected to out right kill any apple trees on the Front Range, but local conditions and the health of individual trees vary, so it is possible. We will keep an eye on our trees around Boulder County and certainly take note of this event.