30-Day Weather Outlook for September 18, 2017, to October 18, 2017
Summary- Troughing will continue in the interior west US, while California and the California coast sees a return of drier and warmer than normal conditions. Santa Ana winds, or their central and northern California equivalents will occur during this period.
Support exists in the sea surface temperature anomaly (SSTA) field for a long wave trough in the central North Pacific near 155W, a robust storm track developing NNE of Hawaii to the British Columbia coast, but high pressure extending from the E North Pacific to near the Pacific Northwest coast. Cold fronts coming south from Washington State move into the SierraNV and Nevada-Arizona with a tendency for troughing, cool and gusty winds in the S California deserts and Colorado River Valley. So, expect some significant Santa Ana winds also to develop in southcentral California (Santa Barbara-San Luis Obispo Counties, and Ventura County after cool and showery during September 22-23rd.
In the Near Term – Sept. 22 - Oct. 5… In the southern California avocado growing areas, from Santa Barbara County to San Diego County, it will be cool with troughing and deep marine layer, and light showers through September 23rd, ending early 24th. Hot and dry conditions (possible Santa Anas) develop on 24-28th, followed by weak upper low pressure and deeper marine layer again about September 30th-Oct 1. Offshore flow and hot conditions with more Santa Anas return October 3-7.
Summary – Oct. 6-25… In the southern California avocado growing areas, from San Luis Obispo south, persistently dry and warm conditions are suggested for this period due to support from the sea surface temperature field, and GFS/CFS guidance. For southern California, this means Santa Anas. However, it also means a greater potential for dry, cold nights with wetbulb temperatures dipping into the 30s.
Seasonal Outlook / La Niña Update...October 26 – December 31, 2017… After a hot and dry period during mid to late October, wet conditions return to NW California and the Siskiyou’s at times from the end of Oct through most of Nov. Best chances for rains in Nov are usually during 10-20th, and again around 28-30th. A period of heavy rains and storm events often occurs during Nov 18-23rd and Dec 27-30. December appears wetter than normal for most of central and N California. Southern California rainfall currently is indicated to remain near or a little below normal for Dec.
In agreement with the current La Niña, there is suggestion of colder than normal conditions developing for California in mid to late December, and early to mid-January, 2018.
...Alan Fox, Fox Weather LLC...