Flash Flood Watch
until MON 12:00 AM MST, Northwest Plateau, Lake Havasu and Fort Mohave, Northwest Deserts, Grand Canyon Country, Coconino Plateau, Yavapai County Mountains, Little Colorado River Valley in Coconino County, Little Colorado River Valley in Navajo County, Little Colorado River Valley in Apache County, Western Mogollon Rim, Eastern Mogollon Rim, White Mountains, Northern Gila County, Lake Mead National Recreation Area, Yavapai County Valleys and Basins, Oak Creek and Sycamore Canyons, Western Pima County including Ajo/Organ Pipe Cactus National Monument, Tohono O'odham Nation including Sells, Upper Santa Cruz River and Altar Valleys including Nogales, Tucson Metro Area including Tucson/Green Valley/Marana/Vail, South Central Pinal County including Eloy/Picacho Peak State Park, Southeast Pinal County including Kearny/Mammoth/Oracle, Upper San Pedro River Valley including Sierra Vista/Benson, Eastern Cochise County below 5000 ft including Douglas/Wilcox, Upper Gila River and Aravaipa Valleys including Clifton/Safford, White Mountains of Graham and Greenlee Counties including Hannagan Meadow, Galiuro and Pinaleno Mountains including Mount Graham, Chiricahua Mountains including Chiricahua National Monument, Dragoon/Mule/Huachuca and Santa Rita Mountains including Bisbee/Canelo Hills/Madera Canyon, Santa Catalina and Rincon Mountains including Mount Lemmon/Summerhaven, Baboquivari Mountains including Kitt Peak, Aguila Valley, Northwest Valley, Tonopah Desert, Gila Bend, Buckeye/Avondale, Cave Creek/New River, Deer Valley, Central Phoenix, North Phoenix/Glendale, New River Mesa, Scottsdale/Paradise Valley, Rio Verde/Salt River, East Valley, Fountain Hills/East Mesa, South Mountain/Ahwatukee, Southeast Valley/Queen Creek, Superior, Northwest Pinal County, West Pinal County, Apache Junction/Gold Canyon, Tonto Basin, Mazatzal Mountains, Pinal/Superstition Mountains, Sonoran Desert Natl Monument, San Carlos, Dripping Springs, Globe/Miami, Southeast Gila County

WATCH: How can police tell if you are too high for the highway?

How can officers tell if drivers are too high for the highway? We all know when it comes to alcohol consumption, the more there is in your blood stream, the worse off you are. But it's not so simple when it comes to 'The Devils Lettuce'.

A new study by the AAA's Safety Foundation says some drivers can have low levels of THC in their blood streams and still be impaired behind the wheel. While others with high levels of THC may not be as dangerous or even feel the effects of it. This is because marijuana is not metabolized the same way as alcohol.

Currently six states use blood level tests to determine if a driver is impaired. Now that may not be the best way to figure out if someone is unfit to drive.

Watch video above for full story.