Rachel's remnants will trigger flooding rain and strong winds well inland across the Desert Southwest, including cities like Las Vegas.

We'll also see heavy snow in parts of the northern Rockies and Hurricane Simon is poised to rake western Mexico.

First, Rachel

As the remnant moisture and upper-level spin from Rachel moves across the Southwest, heavy rain could bring flash flooding across the region, from Southern California to Wyoming, lingering into Tuesday for some.

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Widespread rain totals of 1 to 5 inches are expected with locally higher amounts possible.

This could lead to flash flooding of normally dry creeks, arroyos, slot canyons and urban areas, including parts of the L.A. Basin, San Diego metro, Las Vegas and Salt Lake City.

If you had plans for any of the national parks in the Southwest, we would suggest canceling those plans until Wednesday, given the threat of both flash flooding and thunderstorms.

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(MORE: What to do before, during and after a flood)

Wait – is that snow on the map?

Yes, as the moisture from Rachel meets colder air from a front moving in from the Northwest, snow could accumulate in parts of the Sierra Nevada as well as the Rocky Mountains.

Snowfall totals more than a foot have been reported across portions of Montana:
Montana City (17.7 inches), Stanford (24 inches) Buffalo (12 inches), Checkerboard (19 inches), Belgrade (12 inches).

(MORE: The West's best shot at snowpack recovery is from El Niño)

Hurricane Simon

As all this is happening, a powerhouse hurricane is taking aim on southwestern Mexico.

Hurricane Simon is brushing along Mexico's coast at Category 2 intensity.

A Hurricane warning is in effect for Las Islas Marias.

Damaging winds and flooding rain are both likely along and near the track of Simon in southwest Mexico. Up to 30 inches of rain could lead to dangerous landslides in hilly or mountainous terrain.

This could be the strongest, most damaging hurricane to affect Puerto Vallarta in three years, since Hurricane Lidia downed numerous trees, damaged roofs and triggered landslides in and around the city in October 2023.

Some of Simon's remnant moisture could stream into the central U.S., giving a boost to locally heavy rain and thunderstorms Tuesday into Wednesday.

(MORE: What a historic El Niño means for your fall and winter)

SoCal's first tropical storm watch since 2023

As Rachel was approaching the California coast, SoCal was issued its first tropical storm watch since the remnant of former Hurricane Hilary moved into the state in 2023. (Note: While a Southern California tropical storm watch was issued in 2023, Hilary was not a tropical storm when its remnant moved over Southern California, according to a National Hurricane Center post-storm analysis.)

Caitlin Kaiser graduated from the Georgia Institute of Technology with both an undergraduate and graduate degree in Earth and Atmospheric Sciences before starting her career as a digital meteorologist with weather.com.