Atmospheric river: California alerts and 7-day rain forecast

Which flood, wind and Sierra snow alerts the National Weather Service has in force in California right now, how much rain and melted snow NOAA expects across the state over the next 7 days, and what an atmospheric river and the AR1 to AR5 scale actually are.

Alerts read 18:56 UTC, 19 Oct 2026 · checked 18:56 UTC, 19 Oct 2026

Rain and melted snow, next 7 days

NOAA's Weather Prediction Center expects the most rain and melted snow at San Luis Obispo (Central Coast): at least 0.75 inches for 19 Oct to 26 Oct 2026.

Liquid amounts: snow is counted as the water it melts to, so in the Sierra 1 inch here can mean roughly a foot of snow or more. Each figure is the WPC contour band the place falls in, so "at least 1 in" means between the 1 inch contour and the next one up. The value is for the named place; totals vary a lot over short distances, especially between valleys and mountains. Issued by WPC 10:31 UTC, 19 Oct 2026.

For where flooding rain is most likely in the next few days, see WPC's Excessive Rainfall Outlook; for river forecasts, the California Nevada River Forecast Center and this site's California rivers in flood page.

What is an atmospheric river?

A long, narrow band in the atmosphere that carries water vapour out of the tropics and subtropics. NOAA says an average atmospheric river carries about as much water vapour as the average flow at the mouth of the Mississippi River, and the strongest up to 15 times that. When one runs into the coast and is pushed up over the Coast Ranges and the Sierra Nevada, that vapour comes down as heavy rain and mountain snow. The "Pineapple Express", which brings moisture from near Hawaii, is the best-known kind. Most are weak and bring the rain and snowpack California's water supply depends on; the strongest, especially when they stall or arrive one after another, bring floods, mudslides and debris flows, worst of all on recent wildfire burn scars. (NOAA)

The atmospheric river scale, AR1 to AR5

Published in 2019 by F. Martin Ralph and colleagues and used by the Center for Western Weather and Water Extremes (CW3E) at Scripps. The category comes from the strongest water vapour transport (IVT, in kilograms per metre per second, as a 3-hour average) at one place while the atmospheric river passes, then the length of time it stays:

Duration: conditions of at least 250 lasting 24 to 48 hours keep the category; under 24 hours moves it down one, over 48 hours moves it up one. So a long, moderate atmospheric river can rank higher than a brief strong one. Source: Ralph, F. M., et al., 2019: A Scale to Characterize the Strength and Impacts of Atmospheric Rivers. Bulletin of the American Meteorological Society, 100, 269–289. doi:10.1175/BAMS-D-18-0023.1.

El Niño and this California winter

On 8 October 2026 NOAA's Climate Prediction Center had an El Niño Advisory in effect and expected a strong-to-very strong El Niño through January to March 2027 (CPC ENSO discussion). NOAA describes California's El Niño signal as weaker than the Gulf Coast's and more reliable the stronger the event. An El Niño winter does not decide whether any single atmospheric river arrives.

Statewide December to February totals from NOAA NCEI Climate at a Glance.

The official outlook for this winter, state by state: California winter outlook 2026–27 · El Niño now.

Atmospheric river forecasts

CW3E at Scripps publishes daily atmospheric river forecasts, including landfall and AR scale forecasts for the West Coast, on its forecast pages. They are linked, not copied here. Your local NWS office's forecast discussion says when it expects an atmospheric river and how strong.

Questions

Is there an atmospheric river warning for California right now?

The National Weather Service does not issue a warning called an atmospheric river warning. When an atmospheric river arrives it issues flood watches and warnings, flash flood warnings, high wind warnings and, in the Sierra Nevada, winter storm warnings. No. The National Weather Service has no flood, flash flood, high wind or winter storm watches or warnings in force in California right now (checked 18:56 UTC, 19 Oct 2026).

What is an atmospheric river?

A long, narrow band in the atmosphere that carries water vapour from the tropics and subtropics toward the mid-latitudes. NOAA says an average one carries about as much water vapour as the average flow at the mouth of the Mississippi River, and the strongest up to 15 times that. When one reaches the coast and is pushed up over mountains, the vapour falls as heavy rain and mountain snow. The Pineapple Express, which brings moisture from near Hawaii to the US West Coast, is one well-known kind.

What do AR1 to AR5 mean?

They are the categories of the atmospheric river scale published by Ralph and colleagues in 2019 and used by the Center for Western Weather and Water Extremes (CW3E) at Scripps. The category comes from the strongest water vapour transport (IVT) at a place, from AR1 (250 to 500 kg per metre per second) to AR5 (1,250 or more), then moves down one if the atmospheric river lasts less than 24 hours there and up one if it lasts more than 48 hours. AR1 is described as primarily beneficial and AR5 as primarily hazardous.

Are atmospheric rivers good or bad?

Both. NOAA says most are weak and bring rain and snow that water supplies and the Sierra snowpack depend on. The strongest, especially when they stall over one watershed or follow earlier storms onto wet ground, cause floods, mudslides and debris flows, above all on recent wildfire burn scars.

Will El Niño bring more atmospheric rivers to California this winter?

Not with certainty. On 8 October 2026 NOAA's Climate Prediction Center had an El Niño Advisory in effect and expected a strong-to-very strong El Niño through January to March 2027. NOAA describes California's El Niño signal as weaker than the Gulf Coast's and more reliable the stronger the event: of the three strongest past El Niño winters, two were far wetter than normal in California and one (2015-16) was close to normal. Any single storm depends on the weather pattern that week, which a seasonal outlook cannot forecast.

Where can I see an atmospheric river forecast?

CW3E at Scripps publishes daily atmospheric river forecasts and landfall tools on its website, and your local National Weather Service office in California discusses incoming atmospheric rivers in its forecast discussion. This page links to both and shows the NOAA Weather Prediction Center's 7-day precipitation totals for ten places in California.

Related

California weather alerts · Winter storm warnings today · Winter storm outlook · US rivers in flood · Major US winter storms · Disaster history