A strong cold front pushed through Central California on December 20. While rainfall amounts in the San Joaquin Valley were generally light (a tenth of an inch or less), a cooler airmass settled into the valley behind this system. Clearing skies and light winds allowed for strong radiational cooling to take place overnight and temperatures fell into the 20's for several hours overnight. In addition, an area of dense fog formed along the center of the San Joaquin Valley impacting travel on State Route 99 in the Fresno area. On the following morning, less fog was present although some freezing fog was reported as the airmass dried and temperatures dropped even lower than on the previous morning.

Frost/Freeze in W CENTRAL S.J. VALLEY, CALIFORNIA
From 21-DEC-17 03:00:00 to 21-DEC-17 08:00:00 (PST-8)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Several locations reported minimum temperatures below 28 degrees.

Frost/Freeze in E CENTRAL S.J. VALLEY, CALIFORNIA
From 21-DEC-17 03:00:00 to 21-DEC-17 08:00:00 (PST-8)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Several locations reported minimum temperatures below 28 degrees.

Frost/Freeze in SW S.J. VALLEY, CALIFORNIA
From 21-DEC-17 03:00:00 to 21-DEC-17 08:00:00 (PST-8)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Several locations reported minimum temperatures below 28 degrees.

Frost/Freeze in SE S.J. VALLEY, CALIFORNIA
From 21-DEC-17 03:00:00 to 21-DEC-17 08:00:00 (PST-8)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Several locations reported minimum temperatures below 28 degrees.

Dense Fog in E CENTRAL S.J. VALLEY, CALIFORNIA
From 21-DEC-17 03:30:00 to 21-DEC-17 09:50:00 (PST-8)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Visibility below a quarter mile was reported in Fresno and Madera.

Dense Fog in SW S.J. VALLEY, CALIFORNIA
From 21-DEC-17 07:20:00 to 21-DEC-17 09:10:00 (PST-8)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Visibility below a quarter mile was reported in Hanford.

Frost/Freeze in W CENTRAL S.J. VALLEY, CALIFORNIA
From 22-DEC-17 01:00:00 to 22-DEC-17 09:00:00 (PST-8)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Several locations reported temperatures below 28 degrees. Frost protection measures were used at many orchards overnight.

Frost/Freeze in E CENTRAL S.J. VALLEY, CALIFORNIA
From 22-DEC-17 01:00:00 to 22-DEC-17 09:00:00 (PST-8)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Several locations reported temperatures below 28 degrees. Frost protection measures were used at many orchards overnight.

Frost/Freeze in SW S.J. VALLEY, CALIFORNIA
From 22-DEC-17 01:00:00 to 22-DEC-17 09:00:00 (PST-8)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Several locations reported temperatures below 28 degrees. Frost protection measures were used at many orchards overnight.

Frost/Freeze in SE S.J. VALLEY, CALIFORNIA
From 22-DEC-17 01:00:00 to 22-DEC-17 09:00:00 (PST-8)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Several locations reported temperatures below 28 degrees. Frost protection measures were used at many orchards overnight.