Tropical moisture and favorable atmospheric conditions will fuel a multiday flood risk this week across seven states from California to Colorado. Severe storms are also likely, especially across Arizona.

Millions are under a flood watch as days of rain will bring a threat of debris flows and landslides, especially across burn scars.

Happening now

Severe storms are ramping up across parts of Arizona while bands of rain are also hitting parts of California and the Four Corners region. Here's the latest as the situation unfolds:

• A tornado watch has been issued across parts of central and northern Arizona until 6 p.m. MST. There have already been tornado warnings across the greater Flagstaff area Wednesday morning and early afternoon.
• A flash flood warning is in place that includes Zion National Park. The warning states that "National Park Service employees reported muddy flows across SR 9 in Springdale."

Any ongoing tornado watches and warnings as well as any flash flood warnings warnings are on the map below:

Timing out this week’s rainfall

Wednesday: The highest risk of flooding on Wednesday covers much of Arizona and New Mexico, and portions of Colorado and Utah, as well as Southern California.

There will be an abundance of moisture available to support heavy downpours and training storms. This means storms will produce heavy rain over the same areas for long periods of time. The Weather Prediction Center is forecasting rainfall rates as high as 2 inches per hour. 

Get More of Our News on Google

Set The Weather Company as a 'Preferred Source' to get quicker access to the news you value.

Some of the biggest concerns will be the possibility of mudslides over recent burn scar areas as well as slot canyons and arroyos. 

If you have plans to visit any of the national parks in the West this week, make sure you check the forecast daily and pay attention to any warnings or advisories issued.

There is also an enhanced threat of severe weather on Wednesday for portions of Arizona, southern Utah, western New Mexico and coastal southern California.
Large hail, strong wind gusts and a couple tornadoes are expected along the Mogollon Rim across parts of Arizona. Some strong wind gusts and an isolated tornado threat will also be possible along the southern and central California Coast.

Thursday: Moisture will continue to pump into the Southwest on Thursday, only enhancing the flood threat on already saturated soils. 

Some forecast models are alluding to near record levels of moisture available for October in this region, which means there’s a great concern for flooding and the possibility that rainfall amounts could end up higher than currently forecast.

While the greatest risk for flooding moves out of California, it remains for much of Arizona, Nevada, New Mexico, Colorado and Utah. This includes places like Las Vegas, Phoenix, Tucson and Albuquerque. 

Thursday also has a threat of severe weather where isolated storms could produce strong wind, hail and even a tornado across portions of the Desert Southwest and Four Corners region, with Arizona under the greatest risk yet again.

How much rain and snow is expected?

Right now, we are expecting as much as 3 inches of rain across portions of the Desert Southwest, which is more than enough for flash flooding in this region. Some isolated locations could see up to 5 inches. 

And yes, we could even squeeze some snow out of this system for some of the higher elevations. 

Parts of the Sierra and Rockies could see the first significant snow of the season. This could be a nice base for some of the ski resorts that were robbed of snow last winter. 

While widespread snowfall totals will stay under 6 inches, we could see isolated peaks pick up a foot of snow. 

Make sure you check back often, as the forecast could change. And don’t be caught off-guard if you are traveling through some of the higher elevations, as the rain could change to snow quickly.

Recap

Downtown Flagstaff reported hail the size of golfballs, or 1.75 inches in diameter, on Wednesday. There was also a gust to 72 mph at the Flagstaff Airport.

Expect this section to grow as more storms occur.