At a Glance
- August is well known for hurricane season's ramp-up, but there are several other weather factors to track.
- Tornadoes are most common in the northern tier and it's one of the wettest months in parts of the South.
- Average temperatures and the amount of daylight decrease and snow can fall in the Rockies.
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August marks the final full month of summer, and while it's known for being in the thick of hurricane season, there are other changes in the weather that help mark the slow ease toward fall.
1. Atlantic hurricane season's peak time begins. August is when a switch is flipped toward the most active portion of hurricane season, which then continues into September and October. Of course, this season we've already had three named storms prior to August, including record-breaking Hurricane Beryl.
Several factors contribute to the seasonal ramp-up.
Tropical waves are most developed and often serve as a seed for development. Intrusions of dry, dust-laden Saharan air layers also decrease. Other factors include low wind shear, widespread warm water and a more unstable atmosphere.
Given the improving atmospheric ingredients, a much larger area of the Atlantic Ocean - from near Africa to the Caribbean, Gulf of Mexico and near the East Coast - becomes supportive for tropical cyclone formation.
2. Tornado risk is highest in parts of the northern tier. August is the sixth-most tornadic month, with an average of 84 twisters each year based on data from 2003 to 2022.
While tornadoes are possible in most areas east of the Rockies, the greater risk extends from the Northern Plains to the Midwest and in parts of the Northeast and mid-Atlantic. That's because the jet stream is still located farther north toward the Canadian border where it spends much of its time in summer.
The possibility of tornadoes in the South is mostly from tropical storms and hurricanes that can spawn twisters near and inland from where they make landfall.
3. August is the wettest month in parts of the South and Alaska. The Southwest monsoon is usually in high gear in August and sometimes results in severe thunderstorms.
August is the wettest month on average for most of Arizona, New Mexico and southern Colorado because of monsoonal moisture.
Portions of the Southeast and Gulf coasts also experience their wettest month in August. Afternoon and evening thunderstorms are common there, and rainfall from tropical cyclones sometimes occurs.
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August is also the wettest month in much of Alaska.
4. Average temperatures and daylight begin their decline toward fall. Much of the country experiences the warmest time of year in July. However, August is typically the warmest month for much of the Southern Plains, lower Mississippi Valley and parts of the northern tier from North Dakota to Washington state.
The rest of the U.S. begins to slowly cool off. This translates to afternoon temperatures in the 80s and 90s for most. Meanwhile, areas from the upper Mississippi Valley into northern New England often cool into the 70s as more potent cold fronts begin to pass through the northern U.S. again, particularly later in the month.
Overnight temperatures also begin to drop. Slightly lower humidity allows for cooler lows in the 50s and 60s for much of the East, while the parts of the South and Gulf Coast remain in the upper 60 and 70s with humidity still hanging on.
The coolest air is typically found in parts of the higher elevations of the West, where lows drop into the 30s and 40s.
The length of daylight also quickly declines through August. Most cities in the northern half of the nation lose two to three minutes of daylight each day in August.
The sunset in New York City is at 8:11 p.m. on Aug. 1, but by Aug. 31, the sun dips below the horizon at 7:30 p.m. In Seattle, the sun sets at 8:43 p.m. on Aug. 1, but by Aug. 31 it will set 52 minutes earlier, at 7:51 p.m.
5. Snow chances increase in Rockies. Snow falls in the higher elevations of the Rockies occasionally during each summer month, but by late August those occurrences can become more common.
There have been multiple instances of this in recent years, including two years ago when a dusting of snow was seen at the top of Pikes Peak, Colorado.
Snow is not always confined to the highest elevations in August. Great Falls, Montana, saw its earliest snow on Aug. 22, 1992, the same year its only below-freezing temperatures were recorded in August.
In the East, Mount Washington, New Hampshire, has recorded snow in August, with an average of 0.1 inches falling during the month. The most snow measured there in August was 2.5 inches in 1965.
America's northernmost town – Utqiaġvik, Alaska, formerly known as Barrow – typically sees its first measurable snow, at least 0.1 inches, on Aug. 25, based on the latest 30-year average from 1991 to 2020. Fairbanks typically experiences its first measurable snow in late September, but has recorded snow as early as Aug. 25 in 1995.
Chris Dolce has been a senior meteorologist with weather.com for over 10 years after beginning his career with The Weather Channel in the early 2000s.
