30-Day Weather Outlook for March 26, 2018, to April 26, 2018
Summary- Mostly dry and somewhat inactive period through April 3, with a minor cold front on the 27th. Unusually warm and dry.
Support continues in the mid-latitude Pacific sea surface temperature field, for high pressure near 145-160W 37-43N, a longwave trough near 135-128W with active westerlies into the N and central California coast, moist and recurrent WSW-SW flow into N and central California with significant rains returning during April 3-14.
Warm sea surface temperature anomalies persist off to the W and SW of San Diego. This will tend to provide abundant moisture for upper lows, troughs, and fronts that develop or move into California from the W.
The El Niño Southern Oscillation (ENSO) continues in the cool (La Niña) phase. This supports drier than normal conditions in California during March 26 – April 2, and again after about April 14.
In the Near Term – March 29 - April 12… In the southern California avocado growing areas, from San Luis Obispo County to San Diego County, drier than normal conditions and warmer days occur through March 30th. Chances for showers return about April 4-6 and 7th, then again about the 10-11th. The best chance for rains will remain north of the Thomas Fire burned areas (Santa Barbara Co).
The cold sea surface temperature anomaly off N California may increase risk of cold nights in the normally coldest valleys in early to mid-April, during clear periods between fronts and rains.
Rains are possible about April 4-7th, and 10-11th from San Luis Obispo Co north, but unlikely further south.
Summary – April 13-27… In the southern California avocado growing areas, from San Luis Obispo south, the best chance for cold nights occurs during April 13-23rd. Precipitation turns below normal.
Seasonal Outlook / La Niña Update...April 23 – June 10… Below normal rainfall is suggested by CFSv2 for April after the 20th, with a turn to above normal temperatures after the 22nd. In late April, this can mean warm days with highs approaching the mid-80s in the coastal valleys and S California foothills-valleys, and upper-90s in the deserts.
Going forward, the main issue of concern is unusually warm conditions around the end of April followed by a hot and dry May.
For Southern California it appears to be warmer and drier than normal during this period. May is the season for fog and stratus in coast and valley areas. The usual fog/stratus regime will be occasionally interrupted by a warm or hot day, with minimal fogs at the coast, and shallow marine inversion.
Warm and dry conditions in May are followed, according to CFSv2, by some possible troughing during the first week or so of June. This troughing would tend to support TSTMS in N California, but a deeper marine layer and seasonally cool drizzly coastal marine layer conditions in SOCAL coast and valleys.
Looking out further into the summer, NMME (ensemble) guidance is suggesting conditions that support an unusually hot summer. If warmer than normal conditions develop in mid to late June, some of the hottest days of the year can occur in the SOCAL deserts. These are supported by a high solar angle, and long periods of daytime heating during high sun, together with the highest probability of possible sunshine.
...Alan Fox, Fox Weather LLC...