30-Day Weather Outlook for July 17, 2017, to August 17, 2017

  • Jul 18, 2017

Summary- The basic pattern consists of high pressure over the SW US and Great Basin/Rockies, with SW flow from the Pacific into Oregon. Troughing occurs most likely during July 19-20, and 24-26th. Upper high pressure rebuilds July 27-28 with S flow of moisture from Mexico into N Calif. Warm or hot S flow continuing July 28-31st and Aug 1. Moisture for TSTMS in the SierraNV continues limited but increases during July 25-28th. A pool of warmer sea surface from SW Mexico to near Hawaii will provide an environment more favorable for development of tropical cyclones. A large area of warm SSTA’s will continue to extend W from S Calif and N Baja WSW to include Hawaii. This gives some support for redevelopment of intermittent subtropical westerlies developing in Sep – Nov. Monsoonal moisture is still present, but travels northward thru mainland Mexico, Arizona-New Mexico N thru the Rockies. El Niño is currently quiescent, with no consistent trend. Some redevelopment of El Niño is possible in midwinter 2018, with the latest NMME suggesting a wet January 2018.

In the Near Term – July 22 – July 31… 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 becomes thin or interrupted. TSTMS become more of a daily occurrence in the mountains – deserts.

Summary – Aug. 1 – 15… In the southern California avocado growing areas, from San Luis Obispo south, watch for an increase in TSTMS in the mountains and deserts of S Calif.

Seasonal Outlook / El Niño Update...August 15 – Fall 2017… As normally occurs, there will be some monsoonal SE flow episodes with TSTMS in the mountains and deserts of SOCAL, and some early rains from cutoff lows occurring in central coast and central Calif during Oct and Nov.

El Niño continues subdued thru mid or late Fall. However, sea surface temperature anomalies in the mid-latitude Pacific favor development of a WSW-ENE storm track oriented toward central and N Calif, producing a wet Oct and Nov. El Niño, if it redevelops, will have too much competition from other factors to encourage above normal rainfall in SOCAL. Wetter than normal conditions are more likely for central Calif and the central and N SierraNV, in mainly Oct – Nov.

For the late Fall to early winter, i.e. Nov – Feb… we start with a wet and mild pattern in Nov, near normal rainfall in Dec, but wetter than normal for most or all of Calif in Jan, and followed by a dry and warm Feb, per the NMME guidance. CFSv2 guidance shows drier than normal for Dec-Jan, but we place more confidence in the ensemble (NMME) guidance at this time.

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

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