An active jet stream moving in from the Pacific Ocean on Tuesday is bringing heavy rain and storms with it.

Strong to severe storms are possible from the Dakotas to Missouri today. The biggest threat will be damaging winds and hail, but we can’t rule out a tornado or two.

On Wednesday, there is a higher threat for severe weather for parts of the Mississippi Valley from Illinois to Missouri, including St. Louis. The biggest threat tomorrow will be damaging winds, hail and a few isolated tornadoes.

Another storm system moves into the Northwest and the northern Rockies on Wednesday delivering more rain and stormy weather.

Heavy rain will fall in the Northwest and Northern Plains from two separate systems on Wednesday.(ABC News) Heavy rain will fall in the Northwest and Northern Plains from two separate systems on Wednesday.

The western storm will bring heavy rain to already-flooded Montana all the way to the Great Lakes by Friday and Saturday. The worst flooding in 37 years is forecast in parts of Montana.

More flooding is possible from the Rockies into the Northern Plains.

Heavy rain will be falling from the Rockies to the Great Lakes across the northern U.S. on Friday and Saturday.(ABC News) Heavy rain will be falling from the Rockies to the Great Lakes across the northern U.S. on Friday and Saturday.

Widespread totals of 2 to 3 inches are expected with some areas getting more than 3 inches.

Rainfall totals will be 2 to 3 inches across a wide swath of the country.(ABC News) Rainfall totals will be 2 to 3 inches across a wide swath of the country.

Heat continues in Southwest

Triple-digit heat continues for the Southwest on Tuesday -- and it's only going to get hotter.

An excessive heat watch has been issued for parts of Arizona and California as temperatures reach 105 to 110 degrees.

Excessive heat watches have been issued for parts of Southern California and Arizona.(ABC News) Excessive heat watches have been issued for parts of Southern California and Arizona.

Las Vegas could reach 100 degrees for the first time this year today.