30-day weather outlook for July 31, 2018 – August 31, 2018
Summary- Strong upper high pressure will continue over the central Great Plains WSW to central and S California.
Troughs and upper lows will tend to form off the coast of California as well as inland over the Pacific Northwest.
Upper high pressure will tend to develop south of Alaska and into the Gulf of Alaska, at 45-55N, 145-155W. This recurrent feature will tend to encourage troughing into the northern Rockies and Idaho and troughing to the west of California.
A warmer than normal sea surface and strong high pressure in the SW U.S. will tend to support tropical cyclone formation during this most active part of the season.
Anomalously hot periods with unusually high risk of wildland fires will continue into the early fall.
As troughs develop further south in late Aug and Sept, there appears to be an above normal risk of tropical cyclone moisture coming north into California and Arizona.
The El Niño (warmer than normal sea surface) along the equatorial central and east Pacific, continues to show some development through the fall, as suggested by the latest NMME and CFSv2 forecast models.
In the Near Term – Aug 4 – Aug. 18…Salinas Valley-San Luis Obispo Co…A cool period occurs between Aug 4-7th, with a deeper marine layer and drizzle. Low clouds extend inland through the Salinas Valley for a few days. Hot weather returns to inland areas on Aug 10-16th with a shallower marine layer.
…S Calif Avocado Area, San Luis Obispo Co to San Diego Co…A cooler period with a little deeper marine layer occurs for a few days during Aug 6-9th. During the 10-18, hot weather returns with a shallow marine layer and hottest conditions into the Riverside Valley and interior San Diego Co on the 16th and 18-19th, as well as the S Deserts.
Summary – Aug. 18 – Sept 2… In the southern California avocado growing areas, from San Luis Obispo south, fairly uneventful conditions are suggested from Aug 19th through the end of the month. However, there is suggestion of cool drizzly mornings on Aug 27-31st. This is followed by a hot spell from Sept 2-5.
Seasonal Outlook / El Niño Update...Sept 2 – Nov 15… Warming of equatorial temperatures in the NMME Model forecast through the fall confirms an El Niño pattern expected to develop. However, with warmer than normal sea surface in most of the eastern N Pacific and Gulf of Alaska, the mid-latitude Pacific SSTA (sea surface temperature anomaly) pattern does not yet add support for a wet El Niño season.
For southern California, occasional surges of monsoonal moisture are possible, especially as troughs dig further south to tap tropical moisture left by tropical cyclones near Baja in Sept – early Oct. Because of proximity to tropical cyclones, SOCAL may see some rains in early to mid Sept as troughs deepen southward off the coast. Near or perhaps a little above normal rainfall for Sept may occur in SOCAL, followed by a continuation of showery conditions for a few days in early Oct. During late Oct, we are more likely to see Santa Anas.
Latest updates of the CFSv2 are suggesting a warm and dry Nov (offshore flow events and Santa Anas).
...Alan Fox, Fox Weather LLC...