Be prepared for the coming storms
The official “rainy season” for Southern California starts October 1 and continues through April 30. Rainfall events typically begin to arrive in October and continue with more frequency as we get into November and December. With above average temperatures forecast to continue into the fall, there may be a late onset of rainfall events for Southern California. Hopefully it’s not a signal of another below average rainy season. To refresh your memory, the first major storm event last season did not occur until January in Southern California. And it didn’t get any better from there. Southern California’s 2017-2018 seasonal precipitation was about 30% of normal. Below are a few of the seasonal totals from last winter.
It has been dry and hot, but a change may be on the way.
Sea surface temperatures are currently warm across a large area of the Pacific Ocean and this pattern is expected to continue into fall. There is approximately a 60% chance of El Niño in the fall, increasing to approximately a 70% during winter. The stronger temperature anomalies along the equator is consistent with the expectation of a strengthening El Niño which may peak in November and December, but we’ll have to wait to find out if it will be a typical El Niño or a Modoki El Niño. “Modoki” is a classical Japanese word which means “similar but different.” El Niño is characterized by warming in the eastern equatorial Pacific and Modoki El Niño is associated with warming in the central tropical Pacific and cooling in the eastern and western tropical Pacific. This difference has important impacts on Southern California’s winter weather. There is some evidence to suggest that a Modoki El Niño leads to an increase in hurricanes making landfall in the Atlantic. As I write this article, there are three active storms in the Atlantic with Florence setting its sights on the Carolinas.
When should we expect significant rains to arrive across Southern California and how wet will this winter be?
There is a weak correlation between the onset of a moderate to stronger El Niño and a later than average arrival of significant winter rainfall in Southern California. However, once the rain does begin, conditions tend to be wetter than normal. The current forecast indicates that the rainfall for December through January should be wet for Southern California standards and we can hope for a wetter rather than a drier winter. The three-month seasonal precipitation outlook shown below from the National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center generally favors above-average precipitation across the southern tier of the United States, including Southern California.
What to do now to prepare?
Businesses and municipalities need to implement standard rainfall contingency plans. Review your storm water pollution prevention plan, train your personnel, clean up outdoor exposed materials, perform good housekeeping practices to reduce and prevent pollution, and organize sample kits for those folks that require sampling. Now is the time to inspect your site for potential flood impacts, erosion control issues, and to perform drainage system cleaning and maintenance. With all the recent burn areas in California, these burn sites will have a higher risk for sediment and debris flows as we saw last year in the tragic mudflow event in Montecito, CA. It is important to have plans for early warning systems and ensuring that your businesses have procedures for evacuation and contingency planning for flood events if you are in one of these areas.
ALTA Environmental is a Weather-Ready Nation Ambassador (WRN) with the NOAA. As a WRN Ambassador, ALTA supports NOAA’s initiatives to inspire others to be better informed and prepared, helping to minimize or avoid the impacts of natural disasters by educating employees and the business community on workplace preparedness. More information about WRN and weather preparedness can be found at http://www.nws.noaa.gov/com/weatherreadynation/.