What We Typically See in the Weather in July

The weather in July can be quite interesting and impactful even though the jet stream and cold fronts are both weaker in mid-summer.

Here are five things we typically see in July's weather across the Lower 48.

1. The Hottest Time of Year for Many

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.

The sun is highest in the sky and delivers its most direct radiation over the Northern Hemisphere at the summer solstice in late June, but it takes days or weeks to warm up the Earth's surface and then the air above it. That means there's a lag between the solstice and the hottest day of the year.

Highs in July are typically in the 80s and 90s for much of the contiguous U.S., with 70s in some locations closer to the Canadian border and along the Northwest coast. Average highs in the 100s are typical in portions of the Desert Southwest in July.

(MORE: July 2020 Temperature Outlook)

2. Atlantic Hurricane Season Activity Begins to Tick Up a Bit

Tropical activity is usually still slow in July, but there is a slight uptick compared to June.

The typical area of tropical development expands a bit farther eastward in July and reaches into the southwestern Atlantic Ocean to areas near the Lesser Antilles.

An average of about one named storm develops each July and an average of one hurricane forms every two to three years, based on data from 1950-2019.

July 2019 saw one named storm, Hurricane Barry, which made landfall in Louisiana. In 2018, Beryl became a hurricane unusually far east for July and unusually far south for any hurricane. Beryl triggered flooding as a remnant low in the eastern Caribbean.

(MORE: What We're Watching in the Atlantic as July Starts)

3. Severe Thunderstorm Threat Peaks in the Northeast

The jet stream migrates to the northern tier of the U.S. by July. The jet stream in the summer is weaker than in the winter, but it overlaps with hot, humid air, which ignites severe thunderstorms from the Northern Plains to the Northeast in July.

The Northeast averages the greatest number of severe thunderstorm reports in July, according to a study by NOAA's Storm Prediction Center. This includes areas around Boston, New York City, Philadelphia and Washington D.C.

Severe thunderstorms often take the form of squall lines with damaging straight-line wind gusts in mid-summer instead of the tornadoes that dominate the spring. The number of tornadoes in the U.S. is cut almost in half from June to July, but July is still typically the fourth most active month for tornadoes.

4. Southwest Monsoon Ramps Up

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, the Eastern Pacific Ocean and 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 over the 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.

Heavy rain and flooding can occur in the desert later in the summer, particularly when moisture from a remnant of an Eastern Pacific tropical system flows into the region.

These thunderstorms shave several degrees off of extreme heat in July. The hottest time of year in the Desert Southwest is usually in May and June before the monsoon begins. However, the added humidity can take away the common "dry heat" cliché.

5. Thunderstorm Clusters Are Common

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 two peak months for these batches of thunderstorms, which often rumble through the Plains and Midwest.

When these clusters of thunderstorms are 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 a rate of several thousand strikes per hour.

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