Heat in California, July 21 to 27, 2006

Strong high pressure centered over the southwest United States and monsoon moisture during the last half of July led to numerous daily high minimum and high maximum temperature records, some of which were all time records. The strong subsidence over Southern California caused an unprecedented heat wave and widespread surface dewpoint temperatures from the upper 60s to the mid 70s resulted in record warm overnight temperatures and abnormally high humidity levels. Sea surface water temperatures along the coast remained in the mid and upper 70s during much of July and even exceeded 80 degrees by late July near Del Mar, Huntington Beach, and several miles off La Jolla. It has been speculated that this is possibly the first time 80+ degree water temperatures have been observed along the Southern California coast. Note that because of a lack of detailed historical observations concerning coastal water temperatures, the Storm Data preparer cannot confirm this claim. The heat wave reached its peak on the 22nd. Several all time record highs were tied or broken that day, including 109 at La Mesa, 112 at Escondido, 113 at El Cajon, and 114 at Wild Animal Park. Elsewhere, the temperature rose to 105 in the mountain town of Julian, 114 at Ontario, 120 at Indio and Thermal, and 121 at Palm Springs. San Diego Lindbergh Field reached 99 degrees, becoming the hottest day since September 25, 1989 and the second hottest day ever observed during the month of July. That same morning, numerous high minimum temperature records were broken, including 74 at San Diego, 78 at Alpine, 79 at Escondido, 88 at Thermal, 93 at Palm Springs, and 94 at Borrego Desert Park. Many monthly records were also broken. For example, both Palm Springs and Borrego Desert Park broke records for all time highest average temperature for any month, all time highest average minimum for any month, and all time highest average maximum temperature for the month of July. Palm Springs experienced 10 consecutive days with a minimum temperature of 85 degrees or greater, shattering the old record of 5 consecutive days set in 1917. At San Diego Lindbergh Field, not only was July 2006 the second warmest July on record, but the low temperature never dropped below 70 degrees from the 13th through the 31st. Even more remarkable, Lindbergh Field observed a minimum temperature of 78 degrees on the morning of the 28th. This would have tied the all time warmest minimum temperature on record, however the temperature eventually fell to 76 shortly before midnight, becoming the 3rd warmest minimum on record. Also remarkable for areas near the coast was the time of the year for this extreme heat. Normally onshore flow with a cool marine layer dominates the weather near the coast and record highs in July are much lower than in late summer and early fall when Santa Ana conditions are the cause of such extreme heat. The heat was particularly hard on the elderly and those without air conditioning. Power outages made for an even more dangerous situation. While high temperatures near the end of the month did not exceed excessive heat criteria, low temperatures remained at record warm levels. This was particularly problematic for residents who do not have air conditioning and were unable to cool their homes at night. There were 16 heat related deaths reported during the heat wave, however it is worth mentioning that 2 of these deaths may have occurred outside the San Diego CWA. Also worth mentioning, the number of people treated for heat related illnesses was pulled from various media reports and is likely an underestimate of the total value.