Summary- The basic pattern consists of high pressure continuing for the SW US and Great Basin/Rockies, with a tendency for troughing to the west of Oregon and NW Calif. Pacific into Oregon. High pressure will steer tropical cyclones NW or WNW past S Baja, and then turn westward towards Hawaii. Upper high pressure contributes hot weather for the near term (first week of Aug), followed by troughing during August 9-10th, most of which focuses in N Calif and Oregon. Beginning August 9th, we enter a succession of troughing and ridging, producing alternately cool and possibly showery periods in the mountains of N Calif/SierraNV, then followed by hot upper high pressure.
The solar eclipse on August 21st currently falls into one of the sunny and dry breaks, then is followed by a period of showers and TSTMS on the 23-27th. Tropical cyclones continue more likely to move WNW or NW, then turn westward without recurving to the N during August. Moisture for TSTMS in the SierraNV continues to be intermittent but is occasionally active thru August. Sea surface temperature anomalies (SSTA) have decreased off S Baja, while warmer than normal SSTAs remain over the region near and west of Baja. This will provide a good energy source for cyclones moving NW-WNW off S Baja, and will help to maintain warmer than normal weather in Calif and the far W US. Usually, cyclones begin to recurve N towards SOCAL bringing moisture and TSTMS into S and central Calif about 1 Sept.
A large area of warm SSTAs will continue from S Calif and N Baja WSW to Hawaii. This gives some support for redevelopment of intermittent subtropical westerlies developing in early season Oct–Nov-Dec, mostly directed into N Calif and Oregon.
El Niño, though weakly present in June and July has become quiescent. The ENSO index appears to remain neutral during the upcoming wet season 2017-18. The SSTA pattern now, if continued thru winter as suggested by NMME, focuses rain into central and N Calif with below normal rainfall in late fall-early winter for SOCAL.