Recent temperatures in capital go to extremes

Sacramento’s weather has had a split personality over the past month: spring by day and winter by night.

Daytime temperatures have been 10 to 15 degrees above normal. But nighttime lows have sunk below temperatures typically found at this time of year.

The wide range of temperatures – as much as a 30-degree difference between the daily low and high – has not gone unnoticed.

Ultra runner Diane Forrest has found she has to dress in layers for her five-hour weekend workouts this winter. “In the morning, I would wear what would be typical for January. I will have the gloves, the long sleeves, and the light vest on, with the head warmer,” said Forrest, 52, of Sacramento. “But if I’m wearing all that in the afternoon, I would overheat. With this weather and these temperatures – around 58 degrees – I would be in shorts and short-sleeved shirt. So it’s a big temperature difference.”

The reason for the thermometer’s wide swings: clear skies. Stefanie Henry, forecast meteorologist with the National Weather Service in Sacramento, said the lack of a cloud blanket to hold the heat in means the ground chills more rapidly in the evening.

“The heat escapes the ground overnight, and when we don’t have clouds or fog, it releases quicker,” she said.

So while no clouds and no rain have made the daytime temperatures warmer than normal, the same conditions also have produced chillier nights.

“We’re slightly colder by a few degrees throughout the (Sacramento) valley,” said Henry. “When we get rain, that makes the overnight temperatures more mild.”

Since Dec. 11, the daytime highs in Sacramento have been 10 to 15 degrees above normal, which is 53 degrees for this time of year. In December, the highs have ranged from 58 degrees on Dec. 11 to 68 degrees on Dec. 28.

The normal low for December is 40 degrees. But during the warm spell last month (Dec. 11-31), the lows ranged from 30 degrees on Dec. 11 to 39 degrees on Dec. 31. Only two days –Dec. 18 and 19 – saw above-normal overnight temperatures of 42 degrees. The coldest morning last month was Dec. 9, when the mercury dropped to 25 degrees.

On Jan. 1, the high of 65 matched the record set in 1887, but the low was 35 degrees. The next day, which saw the mercury rise to 66 degrees, broke the record of 65 degrees set in 1940, but the morning began with 37 degrees.

Forrest said she has adapted to the changeable weather by wearing a T-shirt, arm warmers, a vest, gloves, capri pants and a headband when she starts out in the morning. Once she gets going and it starts to warm up, the gloves, the vest and the headband get packed away, and the arm warmers are rolled down.

“I have to layer big time, and take things off as I go,” she said. “The temperature is fluctuating so much – I can’t run in all that gear.”