30-Day Weather Outlook for March 12, 2018, to April 12, 2018
Summary- Active development of storms occurs during March 15-22nd, followed by return of dry upper high pressure, and a turn to very warm conditions.
Support continues in the mid-latitude Pacific sea surface temperature field, for high pressure near 150-160W, a longwave trough near 135-130W, moist flow into N and central California with significant rains through March 22. High pressure builds along and off the west coast during the 24-28th.
Warm sea surface temperature anomalies persist off to W and SW of San Diego, but are smaller than in previous weeks over the past month. This may start to decrease the available moisture for fronts and storms approaching the coast from the W and NW during late Mar and early Apr.
The El Niño Southern Oscillation (ENSO) continues in the cool (La Niña) phase. This supports a return to dry conditions in California.
In the Near Term – March 16-29… In the southern California avocado growing areas, from San Luis Obispo County to San Diego County, rainy periods on March 15-29th may be interspersed with an occasional cold night in the 30s in colder valleys. The periods of the 16th through about the 22nd have potential for unusual late season frosts and freezes, following rains. Recurrent dry cold nights occur during the 24-29th, despite the warmer days.
Summary – March 30 – April 13… In the southern California avocado growing areas, from San Luis Obispo south, a significant warmup is indicated for March 29-31 in southcentral-S California. However, nights will continue on the cold side, with occasional frosts in the coldest valleys during the first few days of Apr. During Apr 5-12th, rains appear to return to N and central California (Sierras), but may produce showers in S California as well.
Seasonal Outlook / La Niña Update...April 14 – May 31… Latest solutions suggest near or below normal rainfall is suggested by CFSv2 for April, after the 13th, with a turn to above normal temperatures after the 20th. In late April, this can mean hot days with highs approaching 90 in the coastal valleys and in S California foothills-valleys, and upper 90s in the deserts.
Going forward into May, the main issue of concern that begins to develop in late April and May is unusually warm conditions in late April, followed by a hot and dry May.
We currently expect a normal start of the wildfire season in N California by May 1.
For Southern California, after the 12th of April, SOCAL appears to turn warmer and drier than normal. Warm and dry conditions in May continue onward through most of June according to latest CFSv2 and NMME results. When June is warmer than normal, extremely hot days, hottest of the whole year, are most likely to occur in the SOCAL deserts due to high solar angle and long days.
...Alan Fox, Fox Weather LLC...