The official start of autumn on Sunday 22 September marks the beginning of a season where the atmosphere is a battle between the leftovers of summer and winter trying to force its way forward.

The first frost and snow of the season often come in the fall. But hurricane season can remain active and severe weather, including tornadoes, can sometimes be a concern. The West is also introduced to several changes.

Here are five things we typically look for when the new season starts.

1. For many, the first frost of the season has arrived: The first 0 degree Celsius temperatures are usually experienced before or just before fall officially begins in the higher elevations in the west and near the Canadian border.

By late October, the first frost has typically occurred across much of the Northeast into the Midwest and even the northern parts of the South. First frost often occurs in November, from the mid-Atlantic coast to much of the Deep South.

2. The first measurable snow falls for many: In the higher mountains in the west, snow is most likely to fall in late September, or perhaps even earlier.

October typically sees the first measurable snow, defined as at least one-tenth of an inch, in the higher elevations west to the Northern Plains, northern Michigan, and northern New England.

An even larger portion of the country experiences its first measurable snowfall in late November or early December, from the Northeast to the Midwest and the southern Rockies.

(MORE: Dig deeper into when to expect the first snow)

3. Hurricane season may still be active, but the end is in sight: The Atlantic hurricane season is still in full swing as fall begins.

There are typically four more named storms that form in the Atlantic Ocean after the autumn equinox, based on the 1991-2020 average.

Since 2016, we have seen hurricanes Matthew, Nate, Michael, Delta and Zeta all make landfall in the United States in October.

October typically sees the formation zones of tropical storms and hurricanes moving westward into parts of the Caribbean Sea, the Gulf of Mexico, and the far western Atlantic Ocean as the “Cabo Verde” portion of the hurricane season – with the development of African easterlies in the eastern Atlantic – winds down.

November 30 marks the official end of hurricane season, but Atlantic storms have been rare since that date.

4. Extreme weather conditions and tornado outbreaks are possible: Like spring, fall is a season when warm, moist air from the Gulf of Mexico meets the increasingly strong cold fronts and jet streams that typically sweep across the country.

When this mix of ingredients comes together, it can create numerous severe thunderstorms that produce damaging winds, large hail, and tornadoes. That said, the average number of tornadoes in the fall is still nowhere near the level we see in the spring.

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

One of the nation’s worst tornado outbreaks occurred just days before Thanksgiving 1992, when a swarm of 105 tornadoes tore through parts of 13 states, from Texas to the Carolinas. The extreme weather claimed 26 lives and injured another 638.

5. Two changes to watch for in the West: A weather pattern that forms in the fall is a strong high pressure area over the inland west, resulting in offshore winds, including Santa Ana winds, from the northeast or east that sweep through canyons and passes in Southern California. These winds can also cause high temperatures.

Santa Ana winds are most common from September through March and can increase fire danger when combined with low humidity or persistent fires. Wildfire danger is usually greatest in the fall due to drier vegetation as California ends its dry season.

The second thing that typically happens as fall progresses is that the jet stream pushes low pressure areas further south than in summer, causing more precipitation in the west.

This also applies to Los Angeles, where average rainfall increases significantly from November onwards.

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

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