30-Day Weather Outlook for January 29, 2018, to March 1, 2018
Summary- The MJO Cycle is becoming more active. As this occurs, there should be a more normal increase in number of frontal passages through California and more typical February rainfall/snowfall for Feb 15-25.
Support continues in the mid-latitude sea surface temperature anomaly (SSTA) field W of California to anchor the troughing at 140-150W, and a persistent ridge at 120-130W, then another trough at 80-95W in central US.
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 S California and between Mexico and Hawaii in a classic dry pattern.
The second half of Feb appears fairly wet, although on the mild side, with relatively high snow levels. It is difficult to realize good increase in snowpack with this pattern, and the high snow levels lead to a smaller areal size of snowpack in the SierraNV.
In the Near Term – Feb. 2-21… In the southern California avocado growing areas, from San Luis Obispo County to San Diego County, it is dry and unseasonably warm with predominant offshore flow and some hot days for Feb 2-12th, and mild nights in the foothills. It turns cooler and rainy at times during Feb 15th - 21st.
Frost occurrence will continue to be mitigated somewhat due to unusually warm sea surface temperatures near the coast of central and S California. Rains, possibly similar to the heavy rains that were seen on Jan 8-9, are possible in S California around Feb 17-19 and a few light showers around the 23rd.
Summary – Feb. 22 – March 5… In the southern California avocado growing areas, from San Luis Obispo south, other than the period from Feb 16-19, this period appears to have the best chance for showers overall in SOCAL. Although locally heavy rains are possible in the coastal hills of Santa Barbara and Ventura Co’s, including Ventura and Montecito fire-burned areas, excessive rainfall is unlikely.
Seasonal Outlook / La Niña Update...March 6 – 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. Heavy snow may still occur in the central SierraNV and near Tahoe during March, although guidance appears less optimistic in the latest model solutions.
Rainy 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 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.
In central California, the SierraNV has a better than even chance for above 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 8-25th.
For S California, the ensemble (NMME) model suggests showers at times in the first half of March 2018 for southern California. In late Mar – early 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...