Extreme weather across US puts 150 million Americans at risk this week

At least 150 million Americans are at risk for severe weather as a triple threat of extreme events stretches across the country.

While there are more than 100 fires burning throughout the United States -- including the Dixie Fire, which has become the 2nd largest in California history -- other severe weather is also on its way.

A tornado outbreak hit the Midwest with more storms headed to the area, record temperatures are possible in both the Northeast and Northwest, and a tropical system is likely to become Tropical Storm Fred later Tuesday.

Tornadoes in the Midwest

After a tornado outbreak on Monday in the Midwest, several more rounds of severe weather are expected in that region through at least Thursday.

There were 16 reported tornadoes in the Midwest, with 14 of them happening in Illinois alone.

The severe weather will pick up again Tuesday from Kansas to Michigan, including parts of already hard-hit Illinois and Wisconsin. While brief tornadoes will be possible, widespread damaging winds are the main concern.

Summer heat waves

The severe weather is being fueled in part by extreme heat. A heat wave is already developing across the Mississippi River valley with temperatures that will feel like over 100 degrees Fahrenheit from Texas to Illinois. The heat index may reach over 105 degrees in cities like Little Rock, Arkansas, and Memphis, Tennessee.

Record high temperatures will be challenged in both the Northwest and Northeast later this week.

In the Northwest, temperatures will exceed 100 degrees Fahrenheit in parts of Oregon, Idaho and Northern California. Portland, Oregon, could see temperatures top 107 degrees by Thursday

In the Northeast, temperatures are soaring into the 90s from Washington, D.C., to Boston. Of particular concern will be parts of New Jersey, where the heat index may reach 110 degrees on Thursday.

Tropical system in Caribbean

A tropical system is brewing in the Atlantic and is currently affecting the Caribbean; the current forecast shows that it could begin affecting Florida as soon as this weekend.

This system will likely become Tropical Storm Fred sometime Tuesday. Tropical storm alerts have been issued for parts of the Caribbean, including Puerto Rico and the U.S. Virgin Islands.

The system will likely weaken a little bit over the Dominican Republic, and while it's too early to determine the magnitude and location of exact impacts, ABC News' forecast models in the last 24 hours have seemed to indicate that a restrengthening tropical system may head toward Florida by the end of this week.

This system could continue to be a nuisance -- particularly to the southeast U.S. -- through early next week.