Climate Zones Guide

If you’re a gardener, you’re probably familiar with climate zones in relation to the USDA plant hardiness zone map which helps determine the plants that are successful for your area. But gardeners landscapers aren’t the only people who should be aware of these zones. Understanding your local climate can help you make energy efficient home updates or inform your construction practices. These are the eight zones as established by the Pacific Northwest National Laboratory in its report for the Department of Energy.

Marine Zone

Living on the coast doesn't necessarily mean you live in the Marine Zone. Several criteria must be met to determine whether or not an area has a marine climate. This includes:

Average temps between 27°F and 65°F in the coldest month of the year,

Less than 72°F average temp during the warmest months,

Four months of average temperatures greater than 50°F,

Typically dry summers, and

Heaviest precipitation of the month during winter is at least three times as much as the one month in which the least precipitation was observed.

These requirements mean that the hurricane prone Gulf states and the east coast are not considered Marine Zones despite their location along the Gulf of Mexico and Atlantic. The only Marine Zones in the US occur in the Pacific Northwest as well as most of the California Coast.

Hot-Humid Zone

States bordering the Gulf of Mexico, like the southeastern portion of Texas, and the entire states of Louisiana and Florida fall into this category. While many cities can get the occasional hot and humid day, to define your location as a hot-humid climate zone, you must have:

Greater than 20 inches of rain per year,

Sizzling hot temperatures during the six hottest months of the year. These temps soar, making a 95 degree day with 50 percent relative humidity feel more like you're jumping into the devil's mouth with a "feels like" temp of 105 degrees Fahrenheit, and

3000 or more hours of 67 degrees Fahrenheit or higher, or 1500 or more hours of 73 degree temps or higher during the warmer months.

If you live here, you're familiar with hurricane season. Are you ready?

Mixed-Humid Zone

Similar to the hot-humid climate zones, is the mixed-humid climate zone. They get hot, too, but their criteria consist of:

More than 20 inches of annual precipitation,

Temps during the warm season at least 65 degrees for about 5,400 heating degree days (heating degree days=the given base temp for a building space subtracted from the average outdoor temp during 24-hour period.)

Mixed humid zones maintain an average outdoor temp below 45 degrees in the winter. Areas in this zone include much of “tornado alley” in the Midwest and the Carolinas on the east coast.

Hot-Dry Zone

This region is characterized by desert landscapes and tough as nails flora and fauna that can withstand its brutality. Here you'll find scorching heat so intense you can fry an egg outside. It occurs where: yearly precipitation is less than 20 inches, and monthly average outdoor temperature is consistently over 45 degrees Fahrenheit. Much of the Southwest lies in this zone. Gardening is a challenge here, but still possible with xeriscaping and creative hardscapes.

Mixed-Dry Zone

Locations that receive less than 20 inches of precipitation per year, along with about 5,400 heating degree days (using 65°F base temp) fall into this category. Here, outdoor temps will average below 45°F in the winter months. It follows a narrow swath bordering the Hot-Dry Zone that includes a portion of the Texas panhandle, central New Mexico, and a portion of central Arizona. Also included are areas on the eastern and northern part of California.

Cold Zone

Defining a cold climate might be easy enough to identify (if you need a jacket, must be cold, right?) But following the criteria set down by the Pacific Northwest National Laboratory, this region gets between 5,400 and 9,000 heating degree days (using 65°F as the base temp.) Much of the northern half of the United States is located here.

Very-Cold Zone

You might not be able to feel the difference when you're standing out in a Cold vs. Very-Cold zone, but we don't recommend standing outside when it's that cold anyway. Better to hunker down with a hot chocolate or a buttered rum. We do know that areas that fall between 9,000 and 12,600 heating degree days (65°F base temp) are identified as Very-Cold Climate Zones. These include sections of the extreme northern states that border Canada like sections of North Dakota, Minnesota, and Maine. Also included are the mountain ranges in Colorado and Wyoming.

Subarctic Zone

Alaska is the only state that lies in this zone. It is defined by receiving 12,600 heating degree days or more. Brrr! Living here requires serious grit and determination, and the rest of the world is in complete awe of you.

Keep these zones in mind for your future renovations or new builds.