A record-breaking heat wave affected much of the state of California during the period from Sunday, July 16 through Wednesday, July 26, 2006. Although numerous daily maximum temperature records were set, the aspect that made this event unique was the elevated overnight minimum temperatures that easily surpassed previous daily, or even all-time, high minimum temperatures at several reporting stations. This was especially true in the southern Sacramento Valley and much of the San Joaquin Valley. Along with the intensity of this heat wave, the duration of abnormally high maximum and minimum temperatures was particularly noteworthy. This event impacted California's economy, energy supply and health. An all-time record for statewide energy consumption was reached on July 24, 2006 with 50,270 Megawatts. 131 heat-related deaths were reported. Given these impacts and the numerous temperature records set across the state, this is a significant historical event when put in perspective with other summertime heat waves. This case study entailed an analysis of the synoptic meteorological factors of the heat wave, and a comparison to climatology for the period. Particular interest was given to the peak of the event, which spanned Friday, July 21 to Monday, July 24. Also, a comparison was made to a recent heat wave event that took place August 8-16, 1996. In general, an expansion to the west and north of the 500mb semi-permanent 4- corners high brought above normal heights to the state of California. This abnormally strong upper high was only part of a northern hemispheric amplified pattern, which was slow to transition. Associated with this upper high expansion was an unseasonably warm airmass settling over the region through the duration of the event, with an influx of monsoonal moisture from lower latitudes near the Gulf of California and Baja California. Typical mid-level winds from the southwest to west shifted to the southeast to south. This allowed for maximum transport of moisture over southern and central California, and resulted in higher minimum overnight temperatures along with more humid conditions during the daytime hours not typical across California. On a more local scale, these abnormally high overnight temperatures were exacerbated in developed areas where the "urban heat island" effect was observed. In order to determine the magnitude of this event and place it properly into historical context, temperature and moisture observations from numerous stations in California were analyzed. Daytime heat index, or apparent temperature, was found not to play a substantial role in the discomfort of people living in the most affected regions. Unusually little overnight temperature recovery was found to be coupled with high dew point temperatures and calm winds. The duration of the event was unique, with dozens of locations reporting a record consecutive number of days with minimum temperatures above 75 F. Early morning dew points reached the lower 60s. The coincident high temperatures statewide occurred on a weekend, leading to increased use of residential air conditioning units. One utility provider found this to be a 1-in-50 year event for inland areas.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- 3399 General or miscellaneous