May began warm and dry. Humidities were in the teens across the mountains of Kern and Tulare Counties on May 1st through the 3rd, and as highs in the southern San Joaquin Valley climbed into the mid 90s on the 2nd, relative humidities in the south end of the Valley fell to 10 percent or lower for several hours.
An upper-level low approached central California on May 4th. The southerly flow ahead of the low funneled through the passes and canyons of the Temblors, Diablo Range and the Tehachapi Mountains. This created gusty winds along the west side of the San Joaquin Valley that persisted from the afternoon of the 4th through the evening of 5th. Winds gusted to 51 mph at Sunflower Valley, and to 50 mph at Panoche Road. A gust to 59 mph was measured at the California Highway Patrol Weigh Station at the base of the Grapevine during the late afternoon of May 5th.
Winds also gusted to 45 mph at Meadows Field, Bakersfield during this time. The gust at Meadows Field tied the highest gust on record at Bakersfield for May, last occurring on May 23rd, 1990.
The upper-level low moved to off Monterey Bay on the evening of May 5th. In addition to the gusty winds generated by the cyclonic circulation, the low also spun subtropical moisture into central California, and as a series of upper-level disturbances rotated around the low, they triggered showers and thunderstorms across the region on the 6th. One of the thunderstorms spawned a tornado that touched down at 7:10 PM on May 6th in the dry riverbed of the Kern River near the intersection of Old River Road and Stockdale Highway, not far from the California State University, Bakersfield, campus in west Bakersfield.
The low moved into San Luis Obispo County during the night of May 6th-7th, and tracked across Kern County during the morning of the 7th. Moderate showers continued across parts of the central California interior through the morning hours, and continued over the Southern Sierra Nevada into the afternoon. A few of the stronger showers caused some road flooding, including northeast of Chowchilla and northwest of Bakersfield.
As the low moved east of California on May 8th, the cyclonic flow continued to generate showers over the eastern flanks of the Southern Sierra Nevada, some of which drifted west of the crest and into the central and southern San Joaquin Valley. Showers also moved into the Tehachapi Mountains.
Thunderstorms over the Southern Sierra Nevada during the afternoon and evening of May 9th dropped small hail on the floor of Yosemite Valley. Nearly two inches of rain fell on Yosemite Valley, with 1.87 inch falling in only 30 minutes. This heavy rain caused some road flooding and ponding of water on the Yosemite Valley floor.
Further south, thunderstorms over southeastern Kern County produced little rain, but did generate gusty winds. One thunderstorm generated an outflow wind that was measured at 40 mph at the Edwards AFB North Base Auxiliary Field. Winds also gusted to 55 mph in the Indian Wells Valley.

Strong Wind in SW S.J. VALLEY, CALIFORNIA
From 04-MAY-13 16:00:00 to 05-MAY-13 01:00:00 (PST-8)
Magnitude: 45.00 MG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Mesonet

Heavy Rain in MARIPOSA, CALIFORNIA
From 09-MAY-13 15:00:00 to 09-MAY-13 15:00:00 (PST-8)
Location: YOSEMITE VLG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Park/Forest Service

Heavy Rainfall with a total of 1.85 inches, reported by the Park Service.

Flood in MARIPOSA, CALIFORNIA
From 09-MAY-13 16:00:00 to 09-MAY-13 16:00:00 (PST-8)
Location: YOSEMITE VLG
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Park/Forest Service

The National Park Service reported minor road flooding.  Heavy rainfall with total of 1.87 inches in only 30 minutes.

Tornado in KERN, CALIFORNIA
From 06-MAY-13 18:10:00 to 06-MAY-13 18:12:00 (PST-8)
Location: JASTRO
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

A tornado occurred on the west side of Bakersfield.  It was weak and short lived.  The location was near the intersection of Stockdale Hwy and Old River Rd.  No damage was reported and it was rated an EF0.