30-Day Weather Outlook for May 31, 2017, to June 30, 2017

  • Jun 01, 2017

Summary- The basic pattern consists of periods of active westerlies, and troughing near and west of N Calif and the Great Basin. A pool of unusually cold water remains W of Calif, and colder than normal sea surface is near and south of southern Baja Calif. The area of cold sea surface temperatures near southern Baja includes most of the region in which tropical cyclones form off the SW coast of Mexico. This argues for a weak or slow start to the tropical cyclone season off W Mexico this June and July. El Niño has developed. While El Niño’s Influence is mostly minimal during the mid-summer, the typical moderate to strong El Niño pattern is expected to continue thru the summer. As the season changes in the fall, El Niño has potential to become more important in modifying the prevailing pattern across Calif and the western U.S. for the 2017-18 winter wet Season, producing support for above normal rainfall.

In the Near Term – June 3-17…  In the southern California avocado growing areas from Santa Barbara County to San Diego County, usual deep marine layer conditions will occur during the first half of June. The warmest periods appear to be June 3-8th, then again about the 12-14th.

Summary – June 18-30… In the southern California avocado growing areas, from San Luis Obispo south, continuation of normal marine layer condition is expected.  With sea surface temperatures below normal off S Baja and SW Mexico, tropical cyclone activity will tend to remain below normal for late June and into early July.

Seasonal Outlook / El Niño Update...July 1 – August 31, 2017… The summer currently appears quiet, with regard to tropical cyclones. However, troughing will tend to continue off S and central Calif during the summer period, with dry SW flow into southcentral and S Calif.

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.  This may actually promote a warmer than normal July with the trough off the coast and high pressure aloft over central and S Calif and the southern Rockies area.  We currently see no evidence in the CFSv2 for unusual rainfall anomalies, although the monsoonal region of western Mexico appears unusually dry. This is bad news for Mexico, because the lack of rain occurs concurrently with the period of maximum surface heating and high solar angle, so evapotranspiration will be at a maximum.

Looking at the fall months, there is support for a dry September, but a return of showery conditions for October, and possibly a wet November, in Calif. including both north and south portions. This is supported both by the CFSV2 monthly outlooks and the projected sea surface temperature anomaly (SSTA) pattern for the fall months.

...Alan Fox, Fox Weather LLC...

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