For much of February, Northern Californians have been basking in the sun wondering what became of El Niño. Monday in Lakeport, temperatures peaked at 78 degrees, 21 above the norm for that date. Yesterday thermometers hovered in the mid-70s.
The unseasonably warm weather has a number of causes, explained meteorologist Larry Smith of the National Weather Service. For one, it’s been clear and sunny. Without the cloud cover, the lower atmosphere warms up. Also, offshore winds are blowing from east to west, cutting off the ocean’s cooling influence. As those winds descend from the Sierras, they compress and warm the air below.
But temperatures should fall today, with highs in the 50s as a storm system moves in. Rainfall is likely to begin this afternoon, according to Accuweather. The storm is expected to be a modest one, however, bringing half an inch of precipitation. Light showers are expected Thursday, with a third of an inch falling in Lake County. A stronger belt of rain returns for a final dose on Friday — another half inch expected — before the sun breaks through on Saturday.
Despite all the high hopes brought on by El Niño, February has turned out to be a much drier month than many had anticipated. Even so, forecasters said there remains a good chance that seasonal averages for rain will yet be reached.
“There’s still a strong El Niño happening,” said National Weather Service forecaster Steve Anderson. Sea surface temperatures along the equator are about 2.5 degrees above normal, half a degree higher than the El Niño threshold.
So far this month, only .08 of an inch of precipitation has been measured in Lakeport. Normal for the month is 6.12, so El Niño has a lot of catching up to do.
The season began impressively, however. In December, 7.48 inches soaked Lakeport, well above the 4.81 norm, according to Accuweather. Cobb was drenched with just over 10 inches. Last month, another 7.75 inches fell on Lakeport and 12 on Cobb.
On Dec. 1, Clear Lake measured just below 0.50 on the Rumsey Gauge. The steady rains through the end of January increased the level to 4.66, as of Tuesday afternoon. The lake is considered full at 7.56 Rumsey and it typically rises 4 inches for every inch of precipitation once the ground is saturated.
Meteorologists consider non-drought year averages reachable, particularly in the Bay Area, despite of the recent dry spell.
In San Jose, just under 8.5 inches of rain have fallen since Oct. 1; the 9 inches that constitute normal “certainly are doable,” Anderson said. Likewise, he noted that San Francisco’s 14 inches during the same period is within shooting distance of the 16-inch average, while Oakland’s 10.5 inches isn’t far from the average of 13 inches.
Still, weeks of warmer than average weather have put the brakes on a promising weather pattern. The snowpack in California has dipped back down below average for this time of year.
The Department of Water Resources estimate Tuesday put the snowpack in the Northern Sierra/Trinity region — which feeds Lake Oroville, Shasta Lake and Trinity Lake — at 97 percent of average for Feb. 16.
It was the best of the three regions DWR monitors, with the Central Sierra at 91 percent of average and the Southern Sierra at 86 percent. The statewide figure is 92 percent of average for this time of year.
Dave Faries contributed to this report
