30-Day Weather Outlook for June 12, 2017, to July 12, 2017

  • Jun 13, 2017

Summary- The occurrence of active westerlies will decrease, and strong warm upper high pressure will build from the Pacific into most of Calif. A pool of unusually cold water has retreated further west of Calif, and its influence is diminished. A pool of unusually cold water remains in the tropical region S thru WSW of southern Baja Calif. This will discourage development and intensification of tropical cyclones during the first part of summer 2017, continuing into early July. It also contributes below normal moisture into Baja Calif, resulting in drier than normal conditions in Baja and W Mexico during late June thru most of July. El Niño has become weak, as it usual does, in our summer. Some redevelopment in El Niño may occur during Dec – Feb 2018, to produce above normal rainfall in Central and S Calif.

In the Near Term – June 16 – July 6…  In the southern California avocado growing areas from Santa Barbara County to San Diego County, it turns hot for June 17-23rd, with a shallow but persistent marine layer S of Pt Conception. Inland valleys will have some L90s possible (Ramona), and a few m90s in the warmest inland valleys (Temecula-Riverside, and u90s Hemet). A cooler pattern follows with a deeper marine layer on June 24-27th, and persistent low clouds with morning drizzle on the 28-30th, and July 1. A return to hot conditions develops on July 2-5.

Summary – July 7-21… In the southern California avocado growing areas, from San Luis Obispo south, a marine layer of normal depth is expected, with morning low clouds and sunny afternoons at the coast and seasonably very warm or hot inland. With sea surface temperatures below normal off S Baja and SW Mexico, tropical cyclone activity will tend to remain weak or below normal for July.

Seasonal Outlook / El Niño Update...July 6 – September 6, 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 off the coast of Calif.  This may actually promote a warmer than normal July and August, with the trough off the coast and high pressure aloft over central and S Calif and the southern Rockies area. There currently is no evidence in the CFSv2 for unusual rainfall anomalies, although the monsoonal region of western Mexico appears unusually dry, coinciding with the summer hot season. Normally summer is less hot in W Mexico due to monsoonal rains, but if the rains are lacking, then July and August can be hot.

For the fall months, there is support for more rain in W Mexico in Sept, but cont’d dry conditions for central Calif. A return of showery conditions is currently indicated for October, and possibly a wet November in S Calif.  However, latest maps from CFSv2 and NMME both suggest a significant dry anomaly developing in N and central Calif during Nov and Dec.  The projected sea surface temperature anomaly (SSTA) pattern for the fall months supports troughing to the west of N and north-central Calif, but with the center of activity too far to the west to support significant rains in Calif.

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

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