Here’s why Modesto area has been foggy lately. It will give way to a chance of rain
The Modesto area’s long stretch of foggy days could give way to light rain this week.
The National Weather Service forecast up to 0.10 inches of rain Monday night, followed by up to a quarter-inch Wednesday and Thursday.
The past few weeks have brought plenty of the tule fog that can settle on the Central Valley from November to March. It has not been dense enough to cause major traffic accidents, but drivers should take care.
The current spell resulted from the heavy rain in late October, said Noah Hughes, professor of earth sciences at Modesto Junior College, in an email Monday. “The damp soil provides the moisture to the lower atmosphere that can form tule fog on long autumn nights. (Contrast this with last November, when we had record dry soil moisture levels),” he wrote. “In addition to the moisture, we have also had very light winds.”
The October rain and snow kicked off the storm season and raised cautious hopes that the state would not have a third straight year of drought.
But little has fallen since then, leaving the central Sierra Nevada watershed at only 15% of average for Dec. 6, the California Department of Water Resources said. It is the main source for Modesto-area farms and cities. The storm season runs mostly though March.
The Weather Service forecast a return to patchy fog Tuesday night and Wednesday morning. Drivers should reduce their speed in dense conditions, use low-beam headlights and watch for nearby vehicles.
Hughes noted another ill effect of the fog: “The lack of mixing winds allows an inversion (a layer of colder air near the surface) to develop. That is why the foggy weather is also associated with elevated air pollution readings. This stagnant pattern has also led to nightly fireplace burning bans almost every night this month.”
