November to kick off with major cross-country storm bringing snow, flooding rain as it sweeps US

November is expected to begin with a bang as a powerful storm that could deliver dangerous weather to 35 states across the country. 

Starting Friday, a strong upper-level low situated near the Pacific Northwest coast will pivot a well-defined, strong Pacific jet toward the Southwest. This will allow a secondary low to develop, drawing rich Pacific moisture into the Southwest into Saturday. 

Some rain will fall in Arizona ahead of the main event, setting the stage for additional rain coming later Saturday into Sunday.

Southern California will see moderate-to-heavy soaking rains by Saturday, likely disrupting Halloween plans, especially for those in larger cities like Los Angeles and San Diego. 

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In San Diego, there have only been 9 Halloweens with measurable rain since 1850, with the most recent being in 1987.

Through Monday morning, the system will push inland across the Southwest, spreading rain eastward. This will lead to widespread 1 to 2 inches or more of rain across portions of Arizona through Monday, the FOX Forecast Center said. 

Up to 5 inches of rain could fall from Phoenix to Flagstaff through Monday. 

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So far in October, Flagstaff has recorded 5.69 inches of rain. If an additional 3 inches is recorded as forecast, significant flash flooding could occur. 

A level 2 out of 4 flash flood threat is in effect through the whole weekend. 

Up in the higher elevations, cold air will become trapped, leading to snow from the Sierra to the Rockies. 

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The southern Rockies will see the highest snow totals, between 12 and 18 inches. 

Later Monday, the storm will begin to move into the Plains and Midwest. 

Heavy rain could also increase the risk of flash flooding across the Plains. 

Nearly 40 million Americans are under a large level 1 out of 4 flash flood threat from Texas to Wisconsin on Monday. 

Ahead of the storm, a new area of low pressure across the Plains will likely form, allowing warm, moist air to stream in. 

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Said warm air will interact with an approaching cold front, which may allow severe storms to develop along it from Tuesday into Wednesday, the FOX Forecast Center said. 

The forecast remains uncertain about where severe storms will develop, as forecast models disagree on where exactly the area of low pressure will form and how strong it will become.

Regardless, the FOX Forecast Center said the atmosphere is becoming primed and energized for severe storms from Texas into parts of the Southeast by early week through midweek.

From Wednesday onward, the storms will continue moving into the East, potentially bringing heavy rain Thursday and Friday to major cities on the I-95 corridor. 

Locations from Raleigh, North Carolina, to Washington, D.C., New York City and Boston could all see rain for the first time in nearly two weeks.