30-Day Weather Outlook for December 27, 2017, to January 27, 2018
Summary- The MJO Cycle continues active, but appears, to be transitioning to less activity. As this occurs, there will be support for more upper high pressure near the coast of California.
Support continues in the mid-latitude sea surface temperature anomaly (SSTA) field west of California for troughing near the coast of Oregon and N California.
The El Niño Southern Oscillation (ENSO) Continues in the cool (La Niña) phase. This opposes activity in the subtropics. Because of this, most active westerlies focus in the Pacific Northwest/Oregon.
There is support for troughing and cold conditions in the east-central US. There is support for near or above normal snowfall in the Great Lakes, middle Atlantic region, and NE U.S., as well as Montana – the upper Midwest states through about 20 Jan.
Primarly, support exists for intermittent rainy episodes, while snow focuses in the SierraNV.
For S California, warm sea surface temperatures are present to the southwest, but the La Niña pattern tends to discourage development of subtropical westerlies. Lows and troughs develop mostly to the E of SOCAL, producing risk of more Santa Anas, or predominant offshore flow patterns.
With colder than normal sea surface temperatures developing west of California, support for below normal temperatures will be a risk factor for spring frosts/freezes in February and March, especially in N and central California.
In the Near Term – Dec. 30 – Jan. 12… In the southern California avocado growing areas, from San Luis Obispo County to San Diego County, we still have a risk of offshore flow and crisp cold nights after mild or warm days. Watch for frosts/freezes, long nights, short daytime heating period and predominantly dry airmasses through this period.
Summary – Jan 13 – Jan 27… In the southern California avocado growing areas, from San Luis Obispo south, rains will be mostly occurring in N California and the SierraNV. However, a cutoff low is always possible in such an erratic pattern, with some showers.
Seasonal Outlook / La Niña Update...January 29 – March 25… Latest solutions show colder and return to dry conditions for the most part during Feb followed by a return to wet conditions in March.
N and Central California, of greatest concern is the chance for below normal temperatures indicated for Feb through some of N and central California, along with dry conditions. This type of configuration points to cold dry N winds in central California as well as some more Santa Anas in SOCAL during late Jan, and accompanying frequent wetbulb freeze events. Feb is about as cold, but drier, with risk of wetbulb freezes.
For S California, there is support for dry Santa Anas, and accompanying frequent wetbulb freeze events. Feb is cold in SOCAL, with risk of many wetbulb freezes. Other than a possible showery period or two, associated with upper lows, both Jan and Feb are unusually dry for S California. The ensemble (NMME) model suggests more showers in the first half of March 2018 for SOCAL, and the southern half of California.
...Alan Fox, Fox Weather LLC...