30-day weather outlook for June 26, 2018 – July 26, 2018

  • Jun 27, 2018

Summary- High pressure is to the west of northern California and Oregon 140-150W, with recurrent troughing over California.

Showers are indicated for the SierraNV near Yosemite during July, and central and N SierraNV in late June, but for the most part there continues a noticeable lack of monsoonal thunderstorms (TSTMS) in the SierraNV and NE Plateau region.

High pressure will be building over the interior SW U.S. while moisture comes from the zone of above normal sea surface temperatures S and E of Baja into W Mexico and the SW US…Arizona/New Mexico/Colorado.

In the Near Term – June 30 – July 15…Salinas Valley-San Luis Obispo Co…Seasonably warm or hot days during June 30th – July 2. Then cooler and breezy conditions July 2-5. Predominantly cooler and dry downslope winds occur at times. TSTM activity is somewhat limited through July 15.

…S Calif Avocado Area, San Luis Obispo Co to San Diego Co…Periods of night and morning coastal low clouds and fog, otherwise mostly fair days and nights.

Summary – July 16-30… In the southern California avocado growing areas, from San Luis Obispo south, dry early to mid-summer conditions prevail. Monsoonal TSTMS increase after July 15 through N Arizona, and into SE SierraNV, and the resulting dry TSTMS will become possible for the E California deserts. TSTMS with rain are most likely in the southern and eastern Deserts, and possibly the mountains of east San Bernardino-Riverside Co’s during this period.

Seasonal Outlook / El Niño Update...July 31 – September… During July and August, the CFSv2 long term forecast model continues to show a tendency for TSTMS in the central SierraNV Yosemite to Tahoe. This would be most likely associated with monsoonal moisture and upper lows and troughs near the coast of California.

July and August are the most active parts of the tropical cyclone season near and off the coast of SW Mexico and S Baja. Normally in July, these cyclones head westward, then gradually start to head NW near the coast of S Baja.  There appears to be less support in the sea surface temperature field for significant tropical cyclone-associated rains than shown earlier in the season (early June).

SOCAL appears to be warmer than normal overall in July-August and September. There appears to be an increased risk for lightning in SOCAL mountain areas. Most of the tropical moisture will be heading into Arizona. It appears that there is still a chance for about normal rainfall in SOCAL during Sept.

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

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