Winter temperatures fluctuate dramatically at high elevations in northern Arizona. During the winter months, the thermometer often varies daily by 30 or more degrees. Daytime temperatures are often in the 40 s and 50 s, while nighttime typically drops well below freezing. During the winter, the surface cells in plants warm up in above-freezing daytime temperatures. Then nighttime chills plunging significantly below 32 degrees may freeze young tissues.
Young tissue is especially prone to damage from alternating freezing and thawing.
Sunscald may occur in late winter or early spring when the temperature of bark in direct sunlight may be higher than the surrounding air. After sunset, plummeting temperatures may quickly refreeze the water in the cells, splitting the bark and causing large wounds. During extended periods of intense cold, frost can penetrate into bark and deeper wood cells. Repeated freezing and thawing of the soil can cause heaving of soil and plant roots. This exposes roots to desiccation and freezing.