30-day weather outlook for May 20, 2018 – June 10, 2018

  • May 16, 2018

Summary — High pressure is to the west, with mostly dry westerly flow into California. Weak troughing is indicated for N and northcentral California.

Troughing occurs over N and central California, but is weak, and airmasses arriving from the west are dry, because they pass over a cooler than normal areas of sea surface temperatures.

Support continues in the midlatitude Pacific sea surface temperature field, for a trough near 135-125W, 33-37N, and another trough near the coast of Oregon. high pressure predominates over Washington – British Columbia west portions.

Cool sea surface temperatures off N California continue to contribute a dry and cool airmass on frequent occasions, with cold mornings in the valleys in NW California.

Warmer than normal sea surface off S Mexico and west to south of Baja California contribute an environment favorable.

In the Near Term  — May 17 – 31… Salinas Valley-San Luis Obispo Co….It is dry and breezy in the coastal valleys and foothills, while showers focus east in the SierraNV. The cold sea surface temperature anomaly off N California may contribute to an increased risk of cold nights during a few nights within this period.

In the Near Term  — May 17 - 31…S Calif Avocado Area, San Luis Obispo Co to San Diego Co ...

Showers are unlikely. The cold sea surface temperature anomaly off N California may increase risk of cold nights in the normally coldest valleys up through mid May, during clear periods between dry cold fronts and troughing. Troughs could occasionally destabilize the airmass, resulting in breaks in the normal marine layer cloudiness, and colder than normal nights.

Summary – June 1 – 15… S Calif Avocado area... San Luis Obispo… Breezy and dry conditions predominate for Ventura Co north to San Luis Obispo. Marine low clouds and local drizzle will tend to focus moistly in the San Diego Co and N Baja California areas.

Seasonal Outdate La Ninã Update June 15 – Aug 15…

During June 16-22nd , CFSv2 is showing a tendency for upper troughs near the central California coast and dry W flow aloft. The TSTMS we saw in May and the first few days of June will be less likely to recur in mid June. Above normal rainfall is unlikely during this period due to the abnormally cold sea surface and greater atmospheric stability. This type of pattern opposes the normal monsoonal SE-ESE flow in midsummer, resulting in dry conditions for N California.

For S California, Jun 15-Aug 15... SOCAL appears to be warmer and drier than normal inland during this period. However the hot conditions inland may tend to increase onshore flow into the coastal valleys, resulting in mild conditions near the coast.

June normally continues as a foggy month In SOCAL. It is the season for fog and stratus into coast and valley areas in nights – mornings. The usual fog/stratus regime will be sometimes occasionally interrupted by a warm or hot day, with minimal fogs at the coast, and shallow marine inversion.

Warm and dry conditions in mid June Occur during 8-18th per CFSDailyAI.

Warmer than normal sea surface off S Baja California should enhance the tropical cyclone activity off S Baja. This tends to cause hot conditions inland in SOCAL, and shallow or interrupted marine layer at immediate coast.

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

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