2008: Monterey only had a high of 52° F.
2001: A heat wave started on 5.7 and ended on 5.9.
Temperatures hit 109° F at Palm Springs, Thermal, and Borrego Springs, 103° F at Hemet, and 102° F at San Bernardino.
1977: The great Mother's Day storm produced heavy rain after three years of severe drought.
Some areas received more than 3" of rain. Local flooding resulted.
3.69" of precipitation fell in Palomar Mountain, 2.47" in Idyllwild, 1.99" in Big Bear Lake, 1.49" in San Diego, and 1.06" in Victorville, each the greatest daily amount on record for May.
1.5" of rain fell in San Diego starting on 5.8 (1.49") and ending on this day (0.01"), the wettest 24-hour period on record for May.
On this day the Padres' home game against the Montreal Expos was rained out at (then) San Diego Stadium.
1964: It was 18° in Big Bear Lake, the lowest temperature on record for May.
This also occurred on 5.1.1967.
1953: 8" of snow fell at Cedarville (Surprise Valley), its all-time record one-day total for May.
1928: Wettest calendar day ever in May in Bakersfield, 0.95" of rain fell.
Source: NWS San Francisco/Monterey, Hanford, Reno, & San Diego