Rare Glimpse into Arizona Haboob
At a Glance
- For much of the nation, it's typically the hottest time of the year.
- Some years, tropical storms or hurricanes affect parts of the Southeast or Gulf coasts.
- Desert Southwest thunderstorm season kicks into gear.
- Large clusters of thunderstorms rumble across the Plains and Midwest.
- It's also the peak month for severe weather in the Northeast.
The jet stream and cold fronts are both weaker in July, but that doesn't mean the month's weather is any less interesting or impactful.
Here are five things we typically see in July's weather, from the Northeast and Gulf Coast to the nation's heartland and Desert Southwest.
1. Tropics Tick Up a Bit
July still lands in the quieter early-third of the Atlantic hurricane season.
The typical area of tropical development expands a bit farther eastward in July, compared to June, fanning out into the southwestern Atlantic Ocean to areas near the Lesser Antilles.
But "quieter" doesn't mean devoid of activity.
Since 2000, an average of one to two named storms formed each July, and these storms weren't always open-ocean storms adding to the seasonal tally.
In 2018, Beryl became a hurricane unusually far east for July, and unusually far south for any hurricane, triggering flooding as a remnant in the eastern Caribbean.
We've had several July hurricane landfalls with U.S. impact this decade, including 2014's Arthur over the Fourth of July holiday along the East Coast and 2010's Alex, which flooded the Texas Rio Grande Valley and parts of northern Mexico.
2. The Hottest Time of Year
July is the hottest month, on average, for an expansive part of the U.S. from the Great Basin to the central Rockies, central Plains, Midwest and East.
While the sun is highest in the sky, delivering its most direct radiation over the Northern Hemisphere at the summer solstice in late June, it takes days or weeks to warm up the Earth's surface and then the air above it. Thus, a seasonal lag typically exists between the solstice and the hottest day of the year.
3. Northeast Severe Thunderstorm Peak
While the number of tornadoes in the U.S. is cut in half from June to July, parts of the country typically have their most severe thunderstorms in July.
(MORE: July's Tornado Risk)
According to a study by NOAA's Storm Prediction Center, July averaged the highest number of severe thunderstorm reports of any month in the Northeast, from New England to the mid-Atlantic states, including areas around Boston, New York City, Philadelphia and Washington D.C.
The July severe weather peak also holds in parts of the Great Lakes, northern Plains and northern Rockies.
The jet stream migrates to the northern tier of states by July. While this summer jet is weaker than its winter counterpart, its overlap with hot, humid air typically sets off severe thunderstorms in July from the northern Plains to the Northeast.
These often take the form of squall lines with damaging straight-line wind gusts.
As we wrote about in an earlier piece, almost 3,000 reports of severe thunderstorm winds are typical for July in the U.S..
4. Summer's Thunderstorm Clusters
Any national radar loop on a July morning will probably show at least one cluster of thunderstorms known as mesoscale convective systems.
Their appearance in satellite imagery is particularly dramatic, often resembling a sunny-side-up egg covering parts of one or more states.
A 2019 study found July is one of the two peak months for these batches of thunderstorms, which often rumble through the Plains and Midwest.
When fast-moving, they can produce widespread damaging winds known as a derecho. If they stall, flooding rainfall is often the result.
Either way, they're usually prolific lightning producers, sometimes at the rate of several thousand strikes per hour.
5. Southwest Thunderstorms Return
While not nearly as pronounced as its Asian counterpart, the Desert Southwest monsoon usually switches into its wet phase by July.
When a dome of high pressure aloft builds over the southern Rockies or adjacent Plains, moisture flows northward from the Gulf of California and Eastern Pacific Ocean and also westward from the Gulf of Mexico.
This kicks off what can be a daily ritual of mainly afternoon and evening thunderstorms over the higher terrain of the Desert Southwest.
Near the beginning of the monsoon's wet phase in July, when moisture isn't as plentiful, these thunderstorms may produce more wind than rain, whipping up an intense dust storm known as a haboob.
Later in the summer, particularly when accompanied by a remnant of an Eastern Pacific tropical storm or hurricane, heavy rain and flooding can occur in the desert.
The hottest time of year in the Desert Southwest is usually in May and June, before summer's thunderstorms kick into gear. These thunderstorms shave several degrees off this extreme heat in July.
However, the added humidity can take away the common "dry heat" cliché.