30-Day Weather Outlook for July 3, 2017, to August 3, 2017

  • Jul 05, 2017

Summary- The basic pattern consists of high pressure over the southwestern US and Great Basin/Rockies, with SW flow to the west of Oregon. This upper high is helping tropical cyclones to develop off SW Mexico and south of Baja Calif. Troughing still occurs in the westerlies, but the westerlies are displaced well to the north now during the early to mid-summer period. Moisture for TSTMS in the SierraNV continues somewhat limited. A pool of cooler than normal sea surface remains in the tropical region S thru WSW of southern Baja Calif. This will discourage intensification of tropical cyclones during July. It also contributes below normal moisture into Baja Calif, resulting in drier than normal conditions in Baja, NW Mexico, and S Calif during July. Monsoonal moisture is still present, but travels northward thru mainland Mexico, and into New Mexico, east Arizona, and the southern Great Plains. El Niño continues, but is subdued as is typical in mid-summer. Some redevelopment of El Niño is possible in mid-winter 2018, but forecasted results are inconclusive.

In the Near Term – July 7 – July 21… In the southern California avocado growing areas from Santa Barbara County to San Diego County, it continues to be unusually hot inland, while typical summertime coastal fog pattern continues. The marine layer will be predominantly shallow. Monsoonal moisture and TSTMS return about on schedule, settling in on July 17-20th.

Summary – July 22 – Aug. 4… In the southern California avocado growing areas, from San Luis Obispo south, a marine layer of normal depth is expected, with morning low overcast in coast thru coastal valleys, with troughing again inducing a fairly deep marine layer for July 25th – Aug 3. Low clouds focus in the mornings along the coast and into the valleys, with sunny afternoons, and seasonably warm or occasionally hot inland. Seasonable occurrence of TSTMS is suggested in the guidance for the SierraNV.

Seasonal Outlook / El Niño Update...August 6 – Fall 2017… The summer currently appears quiet, with regard to tropical cyclones. However, support for troughing will tend to continue off central and N Calif during the summer period, with dry SW flow into southcentral and S Calif. As normally occurs, there will be a few monsoonal SE flow episodes.

El Niño continues subdued thru summer, but has a chance to intensify in the mid-fall. In addition, the SSTA pattern in the mid-latitude NE Pacific will continue to support troughing off the coast, centered about 130-140W. Also Supported is a band of westerlies across the mid-Pacific that is further south than normal.

For California, this supports a near normal seasonal trend in the late summer and early fall, without significant precipitation anomalies.

For the late Fall, and December, as we enter winter in Dec above normal rainfall focuses into W Mexico, while a drier than normal pattern focuses in the Pacific Northwest and south thru Calif.

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

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