Fresno is marked by a semi-arid climate (Köppen BSh), with mild, moist winters and hot and dry summers, thus displaying Mediterranean characteristics. December and January are the coldest months, and average around 46.5 °F (8.1 °C), and there are 14 nights with freezing lows annually, with the coldest night of the year typically bottoming out below 30 °F (−1.1 °C). July is the warmest month, averaging 83.0 °F (28.3 °C); normally, there are 32 days of 100 °F (37.8 °C)+ highs and 106 days of 90 °F (32.2 °C)+ highs, and in July and August, there are only three or four days where the high does not reach 90 °F (32.2 °C). Summers provide considerable sunshine, with July peaking at 97 percent of the total possible sunlight hours; conversely, January is the lowest with only 46 percent of the daylight time in sunlight because of thick tule fog. However, the year averages 81% of possible sunshine, for a total of 3550 hours. Average annual precipitation is around 11.5 inches (292.1 mm), which, by definition, would classify the area as a semidesert. Most of the wind rose direction occurrences derive from the northwest, as winds are driven downward along the axis of the California Central Valley; in December, January and February there is an increased presence of southeastern wind directions in the wind rose statistics. Fresno meteorology was selected in a national U.S. Environmental Protection Agency study for analysis of equilibrium temperature for use of ten-year meteorological data to represent a warm, dry western United States locale.