What seemed like welcome relief for California last December – the rainiest month in three years – instead triggered some of the worst fires in the state’s recent history. Early winter storms set records in some areas, dropping an average of 7.3 inches of rain throughout California.

The parched state responded. Reservoirs began to fill. Cattle grazed on the verdant slopes of the Central Valley. Satellite images showed plants flourishing throughout the state.

But it was not enough. The moisture did little to hydrate trees and shrubs. But it did prompt widespread growth of wild grasses, which quickly dry out without rain.

“They set seed, they turn yellow and they are done,” said Tim Chavez, a battalion chief and fire behavior analyst with CAL FIRE. “All that does is provide kindling for the bigger fuels.”

That fuel – timber and brush – has contributed to one of the state’s worst fire seasons, including the recent Valley Fire, which charred more than 76,000 acres.

A Reveal analysis of NASA satellite imagery captured during the first half of 2015 showed a state lush with new plant growth turn brown in just a few months. What followed was a fire season that started earlier than normal with blazes spreading at rapid rates – particularly in Northern California.

“It’s real important how much rain we get, but it’s even more important when it falls,” Chavez said. “It’s almost a worst-case scenario when you get early rains but almost no rains in the February, March, April, period.”

That National Weather Service predicts a 95 percent chance that this year’s El Nino will persist through the winter and into spring, providing drought relief and revitalizing plant life. Southern California should see some effects by October, but the northern reaches of the state will stay dry through December, according to fire officials – providing little relief for this year’s fire season.

Crews responded to 1,100 fires in the first five months of the year, nearly double the number normally seen in that period. By the end of June, hundreds of new blazes were being reported each week.

The Rocky Fire began in late July – typically California’s most active month for fires – growing by thousands of acres every day and spreading into three counties north of San Francisco. It fed on grass, dry brush and timber in areas never before touched by flames.

More than 69,000 acres burned in the blaze, destroying nearly 100 buildings. Flames spread on multiple fronts, often moving much faster than the prevailing winds that normally drive fire. Officials said computer simulations could not replicate the volatile nature of the Rocky Fire.

“Since mid-July, we’ve seen fires grow at really exponential rates, in some cases … thousands of acres in just an hour,” CAL FIRE Director Ken Pimlott said. “These fires are exceeding what our models would even predict.”

A month later, the Valley Fire exploded nearby, devouring more than 40,000 acres in the first 12 hours. Four firefighters were burned within minutes of responding. Four deaths have been attributed to the fire.

At least 1,958 homes and other buildings were destroyed. Cobb and other communities were decimated. Downtown Middletown was heavily damaged.

The fire began on a Saturday afternoon, coursing through drought-stricken grassy oak woodlands exacerbated by several days of high temperatures. Winds from a cold front moving into the area fanned the flames, sending embers raining down as much as a half-mile beyond fire lines.

Grasses make up a large percentage of the plants fueling wildfires. A warm winter brought rain instead of snow to Washington, Oregon and California, priming grass for an active fire season.

California’s December storms were caused, in part, by abnormally warm ocean temperatures – the same phenomenon some scientists say may play a role in the drought. A low-pressure zone off the West Coast pulled moisture inland from the warm waters.

Water levels rose at some of the state’s largest and most critical reservoirs. Lake Shasta’s storage level increased by 18 percent of its total capacity, and Oroville Lake rose by 12 percent. But it wasn’t enough to raise soil moisture or revitalize larger plants.

Then the rain stopped.

Less than half an inch of rain fell statewide in January. In a normal year, the state sees more than 4 inches of rain in the first month. The first three months of the year combined recorded less than 4 inches of rain, about a third of what normally is expected.

“On average, we get half our annual precipitation in that window and that’s also the major time period when we form our snowpack,” said state climatologist Michael Anderson.

December may have brought rain, but warm temperatures prevented snow from falling at higher elevations, further driving growth of grasses. The snowpack, which typically lasts through summer, was at 5 percent of normal levels on April 1, a record low for California.

“The snowpack is essentially the fail-safe against that drought at the higher elevations,” said Hugh Safford, a regional ecologist with the U.S. Forest Service.

But by March, the slopes were more dirt than snow. Ski resorts canceled events and closed early. The blanket of white that normally covers the Sierra Nevada in April could be seen only at the highest elevations. By late May, the snowpack was gone.

Similar weather patterns played out throughout the Pacific Northwest. Washington, Oregon and portions of western Canada reported warm winter weather with little snowpack followed by a dry spring. Western Nevada and southern Oregon also face the same drought conditions plaguing California.

The fire season started at a time when crews would normally be training. But officials anticipated the threat and started preparing earlier. The state ordered additional aircraft and increased the budget for fighting wildfires.

By Sept. 26, officials had logged nearly 5,500 fires on state or local land for the year, which scorched more than 305,000 acres. That exceeded the normal 3,859 fires that CAL FIRE responds to by this time each year.

Safford said the explosive fire behavior normally seen in Southern California could be the new norm for the northern areas of the state.

Southern California has burned so often over the past decades that hardier plants such as chaparral and coastal sagebrush have been replaced by grasses, he said: “If you want to see what Northern California is going to look like in 10 to 15 years, just look at what’s going on in the L.A. Basin.”

Eric Sagara is a senior data reporter for Reveal. He joined Reveal following a news applications fellowship at ProPublica, where he worked on projects about pharmaceutical payments to doctors, deadly force in police agencies and the trail of guns in the United States. Prior to that, he was a reporter on The Newark Star-Ledger's data team. Sagara is originally from Arizona, where he reported on business, education, crime, wildfires and government. He is based in Reveal's Emeryville, California, office.