30-Day Weather Outlook for August 14, 2017, to September 14, 2017

  • Aug 15, 2017

Summary- High pressure continues for S Oregon and N Calif west-southwestward. Because there is abundant moisture in this storm track, significant rains are possible in Washington State and British Columbia. Upper low pressure near S Calif and N Baja gives more support for rain and TSTMS in central Calif and the Sierra and SOCAL-Arizona. However the pattern evolves to a dry SW flow pattern into central Calif/SierraNV, SOCAL and Arizona after August 23rd while weak troughing lingers over Calif. Tropical cyclones should continue more active now, as we are near the peak of the season. Warmer than normal sea surface remains over the region near and west of Baja. This will provide a good energy source for developing tropical cyclones that move past S Baja. The warm sea surface will tend to support stronger tropical cyclone energies as they continue to the NW. This will help to maintain warmer than normal conditions as we head into fall.

In the Near Term – Aug. 17-31… In the southern California avocado growing areas from Santa Barbara County to San Diego County, it continues to be hot inland with persistently warm conditions, but with the usual night and morning low clouds or marine influence near the coast/coastal valleys. Recurrent coastal eddy conditions are indicated, with some low clouds and drizzle at times especially from August 20-24th.

Summary – Sept. 1-15… In the southern California avocado growing areas, from San Luis Obispo south, TSTMS focus in Arizona, and the S and E Deserts are warmer than normal for most of Sept. Marine layer and low clouds appear to remain about normal during the first part of Sept.

Seasonal Outlook / El Niño Update...September 15 – November 30, 2017… It currently appears quiet, rain-wise for Sept across Calif, except for a little wetter than normal in the SierraNV. Wetter than normal conditions develop in Oct in NORCAL, followed by a dry Nov.

A La Niña pattern has appeared, and this supports a shift to drier than normal conditions in central and S Calif, and a turn to wetter than normal in Oct for NW Calif.

It appears that, at least in the current set of forecasts from CFS, there is support for cutoff lows, and this throws inconsistency into the pattern. There are some indications of cutoff low activity over Arizona, which would favor dry N wind events in SOCAL, and dry conditions in central Calif thru Fall.

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

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