Residents of Moreno Valley, California, look forward to the fall months. The city sits in the shadow of the San Gabriel and San Bernardino mountains on the western edge of Riverside County. Summers are hot and dry, and winters are mild and relatively wet. The month of October means the beginning of cooler days, occasional rains, and plenty of sun still enticing people to get outdoors. Mother Nature does tend to have the last word, and there have been exceptions to normal weather patterns.
Average Temperatures and Precipitation
The average maximum temperature in October is around 80 F, comfortable for most people. For most of the summer, the temperature is at or near the 100 F mark, so this is usually a welcome change. October's minimum temperatures average 51 degrees F. Moreno Valley only averages 0.37 inches of rain in October. This is a semi-arid region so it usually gets just under 10 inches of rain during an entire year. Most of that rain falls between December and March.
October of 2010
October 2010 proved to be a time of weather exceptions in Moreno Valley. The average high temperature was 81.6 degrees F, and the low temperatures averaged 49.5 degrees F for the month. The exception was the amount of rainfall. Moreno Valley saw 0.74 inches of rain by October 25, double the average amount. This was the most rain in the area since October of 2004. Scientists were mildly surprised, because it was a La Nina year.
Effects of La Nina and El Nino
Through 2011, La Nina caused the weather along the West Coast of the United States to be cooler than normal. In Moreno Valley, this means there were no major heatwaves, and temperatures failed to reach the 100s during the summer months. La Nina occurs when the Pacific Ocean temperatures run colder than normal near the equator. The National Weather Service keeps an eye on the current La Nina situation, but for September through November of 2011, temperatures and rainfall amounts were expected to be a bit below average in Southern California, including the Moreno Valley. In an El Nino year, when Pacific Ocean temperatures are warmer than normal near the equator, Moreno Valley, along with the rest of Southern California, usually experiences higher than average rainfall.
Santa Ana Winds
Beginning in the middle of October, the Santa Ana winds sometimes make an appearance in the Moreno Valley. These winds are warm to hot and come in from the desert to the northeast, replacing the remnants of the cooler offshore winds that are the norm, and only blow when the desert is comparatively cold. Because cold air is heavier than hot air, it sinks and becomes compressed and eventually warms up. The now hot, dry air flows through the mountains and into the valley floor. When traveling over a semi-arid landscape, the air picks up little if any moisture. The Santa Anas dry out plants, priming the area for brush fires. The Moreno Valley usually sees Santa Ana winds no more than 10 times between October and March.
- Moreno Valley: Average Yearly Weather for Moreno Valley
- Weather Currents; Another Week, Another Storm; October 2010
- Weather Currents; Outlook: Cool, Dry Autumn Expected; October 2010
- National Weather Service, Climate Prediction Center; El Nino/Southern Oscillation (ENSO) Diagnostic Discussion, La Nina Advisory; September 2011
- NOAA, El Nino Theme Page: What Is an El Nino?
- NOAA, El Nino Theme Page: What Is La Nina?
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