Summary- The basic pattern consists of the tendency for troughing near and over northcentral and N Calif. A pool of unusually cold water off the coast of central and N Calif, while warmer than normal sea surface temperatures are W and SW of SOCAL. The sea surface temperature anomaly (SSTA) pattern in the central N Pacific is strong and persistent enough to continue the tendency for WSW flow towards N Calif and troughing near or just W of Oregon into early June. El Niño has developed, and is already interrupting the transition to the warm season. A typical moderate to strong El Niño anomaly pattern is expected to develop per the current SSTA pattern and the NMME (North American Multi-Model Ensemble): time frame- later in the summer and autumn.
In the Near Term – May 19- June 2… In the southern California avocado growing areas from Santa Barbara County to San Diego County, it is warm and dry from May 19-24th, then cooler in general from the 25th -31st. Cold mornings are still an issue from May 23-26th. Rain is unlikely, but deep marine layer and drizzle is possible.
Summary – June 3-17… In the southern California avocado growing areas, from San Luis Obispo south, there is risk of a continuation of cool and showery conditions across central and S Calif during the first half of June. This currently appears most likely about June 1-3 and 5-17th. Temperatures average a little cooler than normal in SOCAL overall due to recurrent troughing and recurrent deep marine layer. The rainy or showery periods will most likely be cooler than normal, while the intervening dry and warm periods, if they occur, would be much warmer than normal though brief.
Seasonal Outlook / El Niño Update...June 18 – August 1, 2017… Troughing is still possible to some extent, with some drizzly mornings in early to mid-June.
El Niño continues to strengthen during the early to mid-summer. In addition, the SSTA pattern in the mid-latitude NE Pacific will continue to support troughing near the coast of Calif in early June. Troughing near the Calif coast N of the Bay Area will tend to encourage showers and TSTMS to develop in the Siskiyou’s, NW Calif mountains, and in the N SierraNV. Troughing off N Calif may start to come into phase with the summer monsoonal SE flow from Mexico during the first part of July. This would tend to encourage TSTMS in Yosemite and central SierraNV areas.
For the hurricane season west of Mexico, warmer than normal sea surface temperatures will add fuel for developing tropical cyclones off S Mexico, but there lacks the warm sea surface for these to maintain intensity west of S Baja during the first part of summer, i.e. late June thru July. Cyclones that develop will tend to move into Jalisco/Colima/Michoacan during June. It will most likely be early Aug before cyclones maintain intensity when moving WNW past southern Baja.
A few preliminary comments are in order regarding the next wet season: Nov 2017-Mar 2018. For rainy season (winter) 2017-18, there is an active El Niño coupled with the residual SSTA pattern left over from the troughing and storms of this late winter and spring. The bottom line is that with both El Niño (ENSO warm phase) and the mid-latitude SSTA pattern working together, after opposing each other in the previous two years, we may have a better chance for an upcoming wet winter in 2017-18 for all Calif.
...Alan Fox, Fox Weather LLC...