Fresno

Fresno, like many communities in the San Joaquin Valley, has an semi-arid climate with hot summers and mild winters.  Fresno receives about twice the average annual precipitation as Bakersfield and a little more than half of what falls on Sacramento.  The overwhelming majority of Fresno’s precipitation falls as rain from December through April. Snow flurries may happen once every few years. But measurable snowfall is extremely uncommon here.

Fresno experiences the phenomena of tule fog in the winter months.    Long cold, clear, calm winter nights between rainstorms are the catalyst for this radiation fog.  When the cold dense air settles on to the moistened valley floor that has radiated heat back into space, the low lying air cools to the dew point and condensation occurs near the surface.  

Tule fogs can be very dense with visibility falling to only a few 10s of meters. These fogs are known transportation hazards and traveling in them should be avoided. According to the California Highway Patrol (CHP), once such fog caused a 100-vehicle pileup that killed 2 people in 2007.

Rob O’Keefe