How long before the trees "bud out"?

[Packerfan]

How many nights ABOVE freezing does it take? It looks like we could have as many as seven here in S Wis. 8O 8O 8O

[mountainvan]

most years I have several streches of warm days and nights and the trees always bud around the middle of april here. now down in the flatlands they already have flowers and leaves then.