30-Day Weather Outlook for February 5, 2018, to March 5, 2018
Summary- The MJO Cycle is near maximum during early to mid Feb. There is the expected increase in the number of frontal passages, but the activity is either north occurring in Washington State about Feb 20-28th, or in Nevada-Arizona, and SE California deserts about Feb 10-15th.
Support continues in the mid-latitude sea surface temperature anomaly (SSTA) field W of California to anchor the troughing into the Pacific Northwest (Oregon-Washington and Idaho-Montana, while persistent ridging continues at 120-135W and 85 to 100W in the central US and Rockies.
The El Niño Southern Oscillation (ENSO) continues in the cool (La Niña) phase. This leads to decreased energy in the subtropical westerlies east of 140W, and results in only weak disturbances or lows near central and S California and between Mexico and Hawaii in a classic, mostly unbroken dry pattern.
It will continue to be difficult to realize a good increase in snowpack with this pattern, as sparse precipitation continues with the current pattern. La Niña, coupled with the tendency for troughing in the mid Pacific at 150-160W and 85-100W supports ridging that is remarkably resilient.
In the Near Term – Feb. 9-28… In the southern California avocado growing areas, from San Luis Obispo County to San Diego County, mainly unbroken dry conditions occur through Feb 8th. A good chance for showers occurs on the 9-10-early 11th, in SOCAL, with heaviest rains occurring in higher terrain, in San Bernardino Co to San Diego Co, but minimal rain in Ventura Co. The next chance for rains in SOCAL would be about the 24-26th from a weak system that may become poorly defined as it moves ENE into the SOCAL coast.
Frost occurrence will continue mitigated somewhat by unusually warm sea surface temperatures near the coast of central and S California.
Summary – March 1 – March 13… In the southern California avocado growing areas, from San Luis Obispo south, this period appears to have the best chance for showers overall in SOCAL.
Heavy rains are unlikely for the coastal hills of Santa Barbara and Ventura Co’s, although some showers are possible, including for the City of Ventura and Montecito areas.
Seasonal Outlook / La Niña Update...March 15 – May 1… Latest solutions suggest near or a little above normal rainfall for the remainder of March as a whole, in central and N California. Rains may have a better chance to develop in March with some heavy amounts possible in NW and central California coastal mountains, and N and central SierraNV. Moderate snow may still occur in the central SierraNV and near Tahoe during March, although guidance appears less optimistic in the latest model solutions.
Showery and cold conditions possibly reach into Ventura and Santa Barbara Co’s during March. A near normal occurrence of frosts/freezes is suggested in the numerical guidance for March and early April in NW California coastal valleys and Russian/Napa Watersheds. However, as mentioned previously, unusually warm sea surface temperatures have been inhibiting the usual occurrence of cold nights this midwinter, and the trend may continue into the spring frost season for the vineyard regions. The other issue starting to develop in the long range guidance (CFSv2) is possible occurrence of unusually warm conditions in mid to late April, followed by a hot first part of May.
In central California, the SierraNV has a better than even chance for near normal rain and snow across the central SierraNV in March. There is a chance for some frosts in the first week or so of April in coastal valleys, (Salinas/Pajaro/San Benito Valleys, Edna Valley, followed by a shift to warmer and drier than normal during April 11-25th.
For S California, the ensemble (NMME) model suggests showers at times in the first half of March 2018 for southern California. In late Mar – first of April, watch for a frost. After the first few days of April, SOCAL appears to turn warmer and drier than normal.
...Alan Fox, Fox Weather LLC...