Spring and fall can bring variable weather including high pressure ridging that sends temperatures surging above and cold fronts that plunge daytime temperatures into the 40s °F (4–9 °C). However, lengthy stretches of overcast days beginning in mid fall and continuing into mid spring are most common. Rain often falls as a light drizzle for several consecutive days at a time, contributing to 155 days on average with measurable (≥) precipitation annually. Temperatures have reached as early as April 30 and as late as October 5, while has been reached as early as April 1 and as late as October 21. Severe weather, such as thunder and lightning, is uncommon and tornadoes are exceptionally rare, although not impossible.