Wind chill refers to the effect of wind on cold. For example, if the temperature is 35 degrees and the wind is blowing 10 mph, the temperature will feel like 27 degrees. Bull!
So what is cold time? This is the number you need to know if you want to buy fruit trees. Fruit trees (apples, pears, plums, peaches, nectarines, etc.) require temperatures of 32-45 degrees Celsius for many hours during winter. Most areas of Marin receive about 800 to 1,000 hours of cold weather, but of course the number depends on whether you are inland from the coast, protected or exposed.
If you live in a temperate microclimate, you should choose “less cold” fruit tree varieties.
For a list of cold-tolerant fruit tree varieties, see UC’s California Backyard Orchards web page at homeorchard.ucanr.edu/Fruits_&_Nuts.
— Katie Martin, UC Marin Master Gardener