30-Day Weather Outlook for March 5, 2018, to April 5, 2018
Summary- The MJO Cycle that was in an inactive phase on March 5-9th heads into a more active phase during the 12-20. This will tend to encourage development of storms during the 11-23.
Support continues in the mid-latitude Pacific sea surface temperature field for high pressure near 170W, a longwave trough near 135-140W and moist flow into N and central California with significant rains.
Warm sea surface temperature anomalies persist off to W and SW of San Diego, but are smaller than in previous few weeks. This may start to decrease the available moisture for fronts and storms approaching the coast from the W and NW after mid-March.
The El Niño Southern Oscillation (ENSO) continues in the cool (La Niña) phase. There is a slow transition occurring towards El Niño-type conditions as warm sea surface temperatures anomalies (SSTAs) develop westward along the equator, extending out to 110W. This may start to energize the subtropical westerlies a little during this late season (March) before rains cease in April.
In the Near Term – March 8-22… In the southern California avocado growing areas, from San Luis Obispo County to San Diego County, rainy periods on Mach 10-22nd may be interspersed with an occasional cold night in the 30s in colder valleys. The periods of March 16th and about the 24th have the potential to be cold with a frost or two, between or following rains.
Summary – March 23 – April 6… 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, frost/freezes are suggested in our CFSDailyAI guidance for San Luis Obispo coastal valleys/Edna around the 24th, 28th and 29th of March. Interestingly, April 1-6 appears to have frost risks for Ventura and Santa Barbara Co’s as well as San Luis Obispo/Monterey Co’s interspersed between a couple of showery periods.
Seasonal Outlook / La Niña Update...April 6 – May 31… Latest solutions suggest near or below normal rainfall is suggested by CFSv2 for April after the 7th, with a turn to above normal temperatures. In 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 S California, after the first week 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 the 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...