The official start of fall on Sunday, September 22, marks the beginning of a season when the atmosphere is contested between the remnants of summer and winter trying to force its way into the picture.

The first frost and snow of the season often comes in the fall. However, hurricane season may still be ongoing and severe weather, including tornadoes, may be a concern at times. Many changes are also expected in the West.

Here are five things we typically look for as the new season progresses.

1. For many, the first frost of the season is coming: The first low temperatures of -0 degrees Celsius are usually reached in the higher elevations of the West and near the Canadian border before or shortly before the official start of fall.

By the end of October, the first frost has occurred on average from much of the Northeast into the Midwest and even northern parts of the South. The first frost is common in November from the Mid-Atlantic coast to much of the Deep South.

2. For many, the first measurable snow is coming: In the higher elevations of the mountains to the west, snow is likely to fall in late September, if not earlier.

October typically sees the first measurable snowfall, at least one-tenth of an inch, in the higher elevations of the West through the northern Plains, northern Michigan, and northern New England.

In an even larger part of the country, from the Northeast to the Midwest and the southern Rocky Mountains, the first measurable snowfall occurs in late November or early December.

(MORE: Find out more about when to expect the first snow)

3. Hurricane season may still be ongoing, but its end is in sight: At the beginning of autumn, the hurricane season in the Atlantic is still in full swing.

Based on the 1991–2020 average, four more named storms typically develop in the Atlantic after the autumn equinox.

Since 2016, hurricanes Matthew, Nate, Michael, Delta and Zeta have each hit US highways in October.

By October, we typically see tropical storm and hurricane formation zones shift westward toward portions of the Caribbean Sea, Gulf of Mexico, and far western Atlantic, as the “Cape Verde” portion of the hurricane season—with the development of African easterly waves in the eastern Atlantic—winds down.

November 30th marks the official end of the hurricane season, but even after that there were still isolated storms in the Atlantic.

4. Severe weather and tornado outbreaks are possible: Like spring, fall is a turbulent season when warm, moist air from the Gulf of Mexico collides with the increasingly strong cold fronts and jet stream winds that normally sweep across the country.

When this mix of ingredients comes together, it can produce numerous severe thunderstorms that produce damaging winds, large hail, and tornadoes. However, the average number of tornadoes in the fall is nowhere near as high as in the spring.

November 2022 was a reminder of how active fall can be, with an above-average 68 tornadoes that month, most of which occurred in the South. Deadly tornadoes struck Texas and Oklahoma on November 4 and then Alabama early on November 30.

One of the worst tornado waves in the country occurred just days before Thanksgiving in 1992, when a swarm of 105 tornadoes tore through parts of 13 states from Texas to the Carolinas. The storm left 26 people dead and another 638 injured.

5. Two changes to watch out for in the West: A weather pattern that occurs in the fall is characterized by a strong high pressure system in the inland West that produces offshore winds, including Santa Ana winds, from the northeast or east that pass through canyons and passes in Southern California. These winds can also produce high temperatures.

Santa Ana winds occur most frequently from September to March and, when combined with low humidity or persistent fires, can increase fire danger. Wildfire danger is usually highest in the fall because vegetation is drier at the end of California’s dry season.

The second thing that typically happens as fall approaches is that the jet stream pushes low pressure systems further south than in summer, resulting in more precipitation in the West.

This includes Los Angeles, where average rainfall increases significantly from November onwards.

In the Pacific Northwest, precipitation amounts increase starting in October, followed by November, which is one of the three wettest months of the year in Seattle and Portland, Oregon, with averages of 5.85 inches and 5.45 inches, respectively.

Chris Dolce has been a senior meteorologist at weather.com for over 10 years after beginning his career at the Weather Channel in the early 2000s.