During the summer, hot weather is predominant with occasional high humidity and cumulus buildups over the higher terrain surrounding the valley. Thunderstorms occasionally occur during influxes of monsoonal moisture in the summer as well as during Pacific storms in the winter. The warmest months are July and August, though summer-like temperatures can occur even in May and October. During this time, average high temperatures are in the 90s Fahrenheit (32–38 °C), but can rise to well over during heat waves. Temperatures have reached as recently as September 6, 2020. Winters are mild, with temperatures dropping below freezing occasionally on clear winter nights. Rain falls primarily from December through March; snow is rare but can fall in small quantities during the winter. Snowfall is more common in the mountains surrounding the city. Santa Clarita lies within USDA plant hardiness zone 9b, except for a small portion of southern Newhall which is in zone 10a. Santa Clarita's average temperatures are more extreme than in downtown Los Angeles but less extreme than in the Antelope Valley.