30-day weather outlook for October 16, 2018 – November 16, 2018
Summary- High pressure will continue over central and N California, and the eastern N Pacific from N California WSW-ward. This will continue the tendency for drier than normal conditions through the remainder of October and most of November. During Oct 31st through Nov 5th, and 11-17 we expect that the best chance for troughing will occur, within an otherwise dry regime.
Tropical systems will continue through the end of October and likely through the first week to 10 days of November. The tropical season for the eastern N Pacific has been enhanced a bit due to well above normal sea surface temperatures SW of Baja California.
Moisture from the tropical Pacific off southern Baja California may add moisture to a trough that comes through central and N California on Oct 19-20th.
Thus far, the warm equatorial sea surface temperatures associated with El Niño are focusing too far east to enhance the westerlies in the near future. The greatest effects of El Niño appear to be focusing further east in the US.
Development of the El Niño pattern is still possible and is currently predicted for 2018-19 winter season, but its effects may be delayed until late Dec or Jan.
Below normal precipitation is currently indicated for the Pacific Northwest during November and most of December, and February 2019. For California there still appears to be a tendency for modestly above normal precipitation, along with generally warmer than normal conditions through December and into January.
The MJO Cycle is still in an inactive phase for the eastern Pacific. This enhances high pressure with drier than normal conditions across the west coast and all of California. We expect a shift to a more active MJO around the last week of Oct and the first half of Nov.
In the Near Term – Oct 19 – Nov 2…Salinas Valley-San Luis Obispo Co…It will be dry and warm from Oct 19-22nd. Cooler on the 23rd. Showers or rain with high snow levels are more likely to occur about the 24-25th. Another rain is possible around the 29th – 31st, and Nov 1-2.
…S Calif Avocado Area, San Luis Obispo Co to San Diego Co…There still appears to be support for some tropical activity, with upper lows continuing to develop off Baja or W of San Diego. These are not related to tropical cyclones, but could easily entrain moisture from southern Baja. We already saw a result of an upper low on Oct 11-12-13th in SOCAL. This entrained tropical moisture. There may be another similar subtropical rain about Oct 29-30th.
Summary – Nov 3-17… In the southern California avocado growing areas, from San Luis Obispo south, it remains drier and warmer than normal from San Luis Obispo Co to Ventura Co. The best chance for rains and showers is in the southern portions of SOCAL, including San Diego, Orange, Riverside-San Bernardino Co’s and the Southern Deserts, with rains occurring about Oct 21-24th, 30-31st, Nov 4-5th, and in SOCAL and Arizona on Nov 8-9th.
Seasonal Outlook / El Niño Update... Nov 12 – Jan 15… A mostly drier than normal pattern occurs from Nov 20-30. In Dec, there is a chance for more consistent rains developing, including some possible heavy rains through Santa Barbara and Ventura Co’s, and northcentral coast areas (Sonoma –Napa Co’s). With temperatures remaining above normal in Dec, the snow levels in the Sierras will tend to remain higher than usual…around 6000-7000 ft or so.
With El Niño expected to develop to moderate intensity, there is some support for a subtropical jet into Mexico and S California. The tropical cyclone season ends in Nov for the eastern N Pacific, but we will begin to see subtropical lows developing and moving to the coast. As these come inland, they will affect all of California with mild rainy conditions, but primarily SOCAL. As we go through Dec into the first part of January 2019, snow levels will tend to remain higher than normal. Although it will be raining, this is not good news for the long term water supply, due to much smaller size of the SierraNV snowpack from the storms occurring in Dec and Jan.
For southern California, after the mid November rains, the next chances for rain appear to be around Nov 22, then again from Dec 10-15 and the 22-30. After a dry start to January, there is another chance for rains, per the climatological pattern, around Jan 10-18.
With sea surface temperatures near Baja California continuing warmer than normal, frost risk will tend to be a little lower in SOCAL than usual during this normally cold period.
...Alan Fox, Fox Weather LLC...