July is the warmest month, with an average high temperature of . Summers range from warm to hot with occasional, sometimes severe, afternoon thunderstorms and high temperatures reaching on 38 days annually, and occasionally . December, the coldest month of the year, has an average daily high temperature of . Winters consist of periods of snow and very low temperatures alternating with periods of milder weather due to the warming effect of Chinook winds. In winter, daytime highs occasionally exceed , but they also often fail to reach during periods of cold weather. Occasionally, daytime highs can even fail to rise above due to arctic air masses. On the coldest nights of the year, lows can fall to or below. Snowfall is common throughout the late fall, winter and early spring, averaging for 1981–2010. The average window for measurable (≥) snow is October 17 through April 27; however, measurable snowfall has fallen in Denver as early as September 4 and as late as June 3. Extremes in temperature range from on January 9, 1875, up to as recently as June 28, 2018. Due to the city's high elevation and aridity, diurnal temperature variation is large throughout the year.