Federal forecasters place the odds of a very strong El Niño at greater than 90% for this fall and winter, with a 75% chance the event reaches historic strength.

California Governor Gavin Newsom declared a preemptive state of emergency last week, directing state agencies to stage flood-fighting supplies, protect infrastructure and prepare the California National Guard for flood response.

What does the emergency proclamation do?

Newsom's order allows state environmental and natural resources agencies to fast-track permitting for flood, landslide and debris-flow responses. The California Department of Water Resources and local water agencies can now move sandbags, pumps, snow-removal gear and traffic-control equipment into position.

"Giving local water agencies the ability to take decisive action now will help them prepare and safeguard their communities, agricultural resources and public infrastructure from potentially catastrophic flooding," said Karla Nemeth, former state DWR director and now executive director of the Association of California Water Agencies.

Cal OES Director Caroline Thomas Jacobs said the state chose not to wait for storms to arrive before mobilizing.

"Cal OES is leading California's statewide efforts by bringing state and local partners together, conducting advance planning efforts, and identifying potential needs before impacts occur," Jacobs said in a statement.

How strong is the signal so far?

The oceanic phenomenon has already reshaped Pacific weather. El Niño fueled Hurricane Polo, which made landfall in Baja California early Tuesday as a Category 2 storm and threatens heavy rain and flooding across Arizona, Utah, New Mexico and Texas later in the week.

A multiweek heat wave is forecast to push afternoon highs in California's Central Valley into the upper 90s. Record-setting ocean temperatures are sending large waves against the Southern California coastline.

University of California Agriculture and Natural Resources researcher Daniel Swain said water temperatures could exceed their averages by about 10°F. Sea level along the Southern California coast already sits about 1 foot higher than normal.

"El Niño not only warms the water … but it also decreases that storm-decapitating vertical wind shear," Swain said in a Monday webinar, adding fuel to storm systems.

When will the rain arrive?

Swain expects a warm, dry October and November across much of the West. The precipitation signal kicks in around December, peaking January through March.

"That tells us nothing about the season to come," Swain said. "When it comes in is in December, and especially January through March. … I don't expect El Niño to influence California rainfall totals until about December, or November maybe."

State climatologist Michael Anderson noted California carries the highest precipitation variability in the lower 48 states. Of the seven strongest El Niño winters on record, three ended with below-average precipitation and below-average snowpack, according to the National Integrated Drought Information System.

"We have the highest variability of the lower 48 states [in California], so we have to prepare for anything," Anderson said Monday during a NIDIS webinar.

How are growers preparing?

In the Central Valley, growers are clearing ditches and culverts, readying fields and coordinating groundwater recharge projects with local water districts.

UC ANR advisers released a cover-crop study this month showing the practice can dramatically cut runoff and erosion. In a Salinas Valley vegetable field trial funded by the California Leafy Green Research Board, sudangrass plots captured an average 92% of rainfall from atmospheric river storms, compared with 62% on bare plots. Runoff dropped 79%. Soil erosion fell 99% in covered areas versus bare ground.

Precipitation is forecast to arrive around December and peak January through March, leaving growers a tight window to finish drainage work and plant covers before storms test Central Valley infrastructure.