The warm, unstable airmass that arrived at the end of September remained over interior central California through the 3rd day of October. However, cooler air arrived as an upper level trough moved over the area on the 4th. The airmass remained moist and unstable until the 6th, and then began to dry out by the 8th due to high pressure over the central California interior. By the 10th, temperatures warmed to slightly above normal.
Events for the first week of this month included several incidents of roadway flooding in Kern County, and several days of thunderstorms in the San Joaquin Valley. On the 2nd, the California Highway Patrol reported of large rocks that created hazardous conditions on Highway 178 in the Kern River Canyon near Bodfish; in fact a Flash Flood Warning had been issued around 2:15 that afternoon due to slow moving thunderstorms in the area. Some strong thunderstorms developed near and west of Frazier Park around noon of October 2nd; Pine Mountain Club reported hail around one-half inch in diameter (smaller than dime size). During that evening, thunderstorms developed over Yosemite National Park, with some heavy rain over the area that caused nuisance flooding.
Showers and thunderstorms redeveloped during the afternoon and evening of the 3rd.
On the night of the 3rd, and into the early morning hours of the 4th, quite a few thunderstorms developed over the Hanford and Visalia areas, and spread northward into Fresno, Madera, and Mariposa. Lightning was quite frequent with these storms, and large hail about the size of halfdollars (1.25 inches) was reported near Mariposa around 1:00 AM on the 4th.
As for October 5th, there were quite a few showers, including snow showers in the higher elevations of the Southern Sierra Nevada, mainly above 7,500 feet. The snow accumulated up to 8 inches at Tioga Pass and 7 inches at Bishop Pass in the Southern Sierra Nevada, bringing a dangerous early season snowstorm to the popular hiking areas.
The storm that produced these showers subsequently moved into Arizona, triggering numerous thunderstorms. The storm also spawned eight tornadoes in northern Arizona, including near Flagstaff, during the early morning hours of the 6th; a new record for the most tornadoes in one day for Arizona.

Flood in KERN, CALIFORNIA
From 01-OCT-10 12:33:00 to 01-OCT-10 17:00:00 (PST-8)
Location: GRAPE VINE
Flood cause: Heavy Rain
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Law Enforcement

The Highway Patrol reported flooded lanes on I5 at Fort Tejon due to heavy rain and hail from thunderstorms.

Flood in KERN, CALIFORNIA
From 02-OCT-10 13:49:00 to 02-OCT-10 14:49:00 (PST-8)
Location: DEMOCRAT SPGS
Flood cause: Heavy Rain
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Law Enforcement

CHP reported large amount of rocks in road due to heavy rain CA HWY 178 just west of Old Kern Canyon road near Democrat Hot Springs.

Flood in MARIPOSA, CALIFORNIA
From 02-OCT-10 15:00:00 to 02-OCT-10 18:00:00 (PST-8)
Location: YOSEMITE VLG
Flood cause: Heavy Rain
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Park/Forest Service

Park official reported flooding between El Portal and Yosemite Valley. Some roads were temporarily closed due to flood debris.

Flood in MARIPOSA, CALIFORNIA
From 04-OCT-10 06:30:00 to 04-OCT-10 08:30:00 (PST-8)
Location: YOSEMITE VLG
Flood cause: Heavy Rain
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Park/Forest Service

Park official reported flooding and debris along the west side of Yosemite Valley.

Hail in MARIPOSA, CALIFORNIA
From 04-OCT-10 00:00:00 to 04-OCT-10 00:05:00 (PST-8)
Location: USONA
Magnitude: 1.25 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Large hail to the size of half dollars reported at Woodland about 10 miles southeast of Mariposa.

Thunderstorm Wind in MADERA, CALIFORNIA
From 03-OCT-10 23:15:00 to 03-OCT-10 23:20:00 (PST-8)
Location: COARSEGOLD
Magnitude: 55.00 EG
Property damage: 75.00K
Crop damage: 0.00K
Reported by: Public

Tree down and roof damage to a house in Yosemite Lakes Park.

Flash Flood in KERN, CALIFORNIA
From 02-OCT-10 13:00:00 to 02-OCT-10 16:00:00 (PST-8)
Location: MIRACLE HOT SPGS
Flood cause: Heavy Rain
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Law Enforcement

CHP reported debris and mud in roadway on Caliente Bodfish Rd just south of intersection with Saddle Springs Road.

Winter Storm in S SIERRA MTNS, CALIFORNIA
From 04-OCT-10 08:00:00 to 05-OCT-10 16:00:00 (PST-8)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Park/Forest Service

Winter Storm in TULARE CTY MTNS, CALIFORNIA
From 04-OCT-10 08:00:00 to 05-OCT-10 16:00:00 (PST-8)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Park/Forest Service