The stage is set for a strong El Niño event this winter, but experts say it is unlikely to erase California’s four-year drought. While there is no single factor that will determine when the drought ends, here is a high-level look at factors the National Oceanic and Atmospheric Administration and the California Department of Water Resources will be watching for signs of improvement.

SNOWPACK California relies on gradual snowmelt from the Sierra Nevada to provide a major portion of its water supply. To make a dent in the drought, this winter’s snowpack would need to return to at least average or above — about 39 inches of snow water content on April 1.

TEMPERATURES Storms must be cold enough to support significant snowpack in the Sierra. The average winter minimum temperature in the Sierra would need to drop by 6 degrees from last year’s average — from 32.1 degrees to 26 degrees. The above-normal temperatures currently predicted for Northern California are not a good sign.

RAINFALL Based on past drought-busting years, precipitation would need to be about 120% of average — about 60 inches — in key Northern California watersheds.

RESERVOIRS Four years of drought have reduced the state’s key reservoirs to about a third of their capacity or less. Above-normal rain and runoff in Northern California would be needed for storage levels to recover this winter.

GROUNDWATER Groundwater levels are down by as much as 100 feet in some areas. Experts say recovery will be a multi-year process that depends on how basins are recharged and how much groundwater continues to be pumped.

WATER FOR FARMS AND COMMUNITIES Surface water deliveries for farms were reduced by 8.7 million acre-feet in 2015. Urban areas also have seen reduced deliveries and have been subject to mandatory conservation. Restored water deliveries and lifting of emergency conservation measures will be a sign of drought recovery.

STRENGTH AND LOCATION OF STORMS NOAA’s latest outlook does not project where and when storms may occur. Heavy rain and even flooding in Southern California — without snow in Northern California — will not be enough to end the drought.

MUDSLIDES AND DEBRIS Torrential rainfall could trigger flooding, mudslides and debris flows — even during drought. Areas affected by recent wildfires are especially susceptible to mud and debris flow, with potentially big impacts on water supply sources.

Even if El Niño brings heavy rain and snowfall this winter, drought conditions may return next year. California may be facing a “new normal” of extreme droughts and floods due to climate change.