January 19, 2018
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Warmer, drier weather is not unusual for December, local experts say

By: Katherine Minkiewicz
December 29, 2017

The past few weeks have been a bit drier and warmer than usual for Rohnert Park and for the Sonoma County region. With midday temperatures peaking around the mid 60s last week it doesn’t feel much like winter. However, local weather experts say this dry and warm spell is not unusual since the La Nina weather pattern we are in typically brings warmer temps and less rainfall to Northern and Southern California.

La Nina, an ocean-atmospheric weather phenomenon that affects the world’s weather patterns is the counterpoint of El Nino, the climate pattern that causes increased amounts of precipitation due to an increase in ocean temperature. When La Nina occurs, the temperature of the sea surface across the Pacific Ocean is cooler, leading to higher atmospheric pressure which generally creates dryer and warmer conditions.

“This is not unusual because what we are experiencing is La Nina conditions changing the temperature in the atmosphere and the jet stream. Based on NOAA (National Oceanic and Atmospheric Administration) tracking Los Angeles is experiencing drier and warmer temperatures and for Sonoma County we are experiencing less rainfall,” explained Jose J. Hernandez Ayala, a climatologist and assistant professor of geography at Sonoma State University.

And due to this La Nina pattern, we can continue to expect warmer than average temperatures for the coming winter months for Sonoma County and for the entire state of California, according to Hernandez Ayala.

However, the effects of La Nina aren’t just being noticed now during the winter when we expect to see more frigid temperatures, its effects were also seen last summer when temperatures in July in August soared higher than normal throughout Sonoma County.

“For August to September of this year, most of coastal California was above average temperatures compared to 1981 and 2001. For the first time in almost 60 years the (temperature) records broke in Santa Rosa… it was 115 in Cloverdale and 113 in Rohnert Park,” he said.

So what about rainfall — can we expect the dry conditions to continue? According to Hernandez Ayala due to the high pressure pattern that is lingering off the coast of California there is an equal chance it will continue to be dry and an equal chance that we’ll receive more rain within the next three months. Simply put, it is a 50/50 chance for either or outcome. 

Art Hayssen, who teaches meteorology and geography at the Santa Rosa Junior College said every semester he reminds his group of meteorology students that meteorology is sometimes like flipping a coin, you don’t quite know what the outcome will be. 

“Mid to long range forecasting is difficult, you can do your own forecasting or go to NOAA and I’ve students compare forecasts of different organizations, but it is difficult. The national weather service has been the most accurate,” Hayssen said.

However, Hernandez Ayala said in looking at plotting weather patterns, 2018 could be similar to 2017 in terms of precipitation. “Forecasters say to expect a weak weather event in the early months of 2018, meaning Northern California can expect cooler, wetter conditions, while Southern California can expect drier weather patterns,” Hernandez Ayala wrote in a presentation he prepared for our interview.

Yet for now, it does seem quite dry compared to last winter’s torrential amount of rain that Northern California received. Hayssen noted that according to a Windsor center that measures rainfall, we had 152.8 inches of rain.

“That is like what a tropical rainforest gets! We had record rainfall… But we’ve had spotty rain so far compared to last year,” Hayssen said.

Hernandez Ayala, who is from the tropics said when he came to Rohnert Park last February to interview for his current position at SSU, he mused if he would even see the sun again since it was so rainy, however now, it is warm and dry.

“For Ukiah the average precipitation for the water years 1894-2017 was 8.84 inches (of rain), but for the current water year, which started Sep. 1, we’ve had 5.50 inches, 62.22 percent of average,” Hernandez Ayala said. “For Santa Rosa the average precipitations for the water years 1950-2017 was 7.78 inches, but for the current water year it’s 6.27 inches, 80.59 percent of average.”

Despite seeing smaller amounts of rain so far this rainy season, we have seen a lot of dry winds, which helped fuel the gargantuan Sonoma and Southern California wildfires. Hernandez Ayala said this is also due the high pressure system that does not want to go away. The higher the pressure, the stronger winds can become.

The National Weather Service even issued a high wind advisory and red flag warning two weekends ago due to “High winds and low humidity,” according to a Nixle alert sent out by the Sonoma County Sheriff’s Office. 

When asked if we can attribute these more pervasive warmer and drier weather conditions to climate change, Hernandez Ayala said we can’t pin these weather events down to one reason.

“When we look at temperatures and patterns it is hard to tell if it’s due to one reason like La Nina or climate change. What we usually say is it’s a combination of factors, but one of the biggest factors is human induced climate change,” Hernandez Ayala said.

According to, the 10-day forecast for Rohnert Park calls for a bit chillier temperatures with highs only reaching 60 degrees and the lows dipping down into the mid 30s, with a chance of showers on the way for the first of January. So don’t put your winter coat and umbrella away just yet, you may very well may need it.