30-Day Weather Outlook for February 12, 2018, to March 12, 2018
Summary- The MJO Cycle has passed maximum as of 12th. The expected increase in in number of frontal passages has occurred, but rain amounts have remained small.
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 current pattern of troughing in California and high pressure off the coast differs from what we have expected from the sea surface temperature anomaly pattern. Although the pattern may persist for about 10 days, eventually we expect a return of the upper high and drier conditions in California about Feb 26-28th – Mar 3. Until the transition is complete, we should expect some inconsistency in the extended range forecasts.
The El Niño Southern Oscillation (ENSO) continues in the cool (La Nina) phase. This continues to support decreased energy in the subtropical westerlies from about 140W in the Pacific to S California. Mainly weak disturbances or lows near central and S California and between Mexico and Hawaii are most likely.
We are seeing some more snow in the SierraNV, which is lucky in this current pattern. There will continue a lack of moisture to produce the usual February-late winter-type snow amounts. Upper lows continue to develop off central and S Baja, which is logical for late winter and the current active phase of the MJO cycle.
In the Near Term – Feb. 16 – March 3… In the southern California avocado growing areas, from San Luis Obispo County to San Diego County, after a dry and warmer period, Feb 16-17th, the next chance for rains in SOCAL would be about the 21-23rd from another upper low that develops from a cold frontal remnant.
Frost occurrence will continue mitigated somewhat by unusually warm sea surface temperatures near the coast of central and S California. Our CFSDaily system is showing a possibly significant rain about March 5.
Summary – March 5-20… 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.
Moderate rains are possible on March 5-6th in an apparently well-defined front. Other rains are indicated for the 10-13th. Heaviest rains occur Mar 12th, and affect both Ventura Co (fire burned areas of Ventura City and foothills), and SE Santa Barbara Co mountains.
Seasonal Outlook / La Niña Update...March 21 – May 15… Latest solutions suggest another rain in California, including both N and S portions of the state about the 19-20th. Otherwise, near or a little below normal rainfall is suggested by consensus of cFSv2 and NMME for the last week of March. April turns sharply warmer and drier per both NMME and CFSv2 solutions.
As mentioned in last week’s report, unusually warm sea surface temperatures west of central and S California have been inhibiting the usual occurrence of cold and frosty nights this midwinter, and this trend may continue into the spring frost season for the vineyard regions of NW California. The main issue of concern, that begins to develop in the long range guidance (CFSv2) is unusually warm conditions in mid to late April, followed by a hot first part of May.
In central California, there is a chance for some frosts in the first week or so of April in coastal valleys, including Salinas, Pajaro, San Benito Valleys, and Edna Valley. A shift to warmer and drier than normal is suggested during April 11-25.
For S California, the ensemble (NMME) model suggests showers some cold nights in SOCAL during late March – April 1. After the first few days of April, SOCAL appears to turn warmer and drier than normal.
...Alan Fox, Fox Weather LLC...