30-Day Weather Outlook for October 30, 2017, to November 30, 2017
Summary- The wet (troughing) part of the MJO Cycle will dominate during Nov 3-12. Rains occur in N, central and S California during this period, and some locally heavy rains are possible. Support exists in the sea surface temperature anomaly (SSTA) field for a long wave trough in the east-central North Pacific 140-145W, and a trough around 120-105W (central and S California E through the southern Rockies), and in the east-central US. SST anomalies west of California, and between Baja California and Hawaii are expected to continue warm. This tends to support moisture for rains occurring into central and S California during this period.
The El Niño Southern Oscillation (ENSO) Pattern is giving mixed signals as we start into November. For N and central California there is support for W flow and a few frontal passages during Nov 3-4 and 8. Additional rains occur from the 11-13, 15-17th, and around 21st.
For S California, the pattern through Nov 24 will support alternation between cutoff lows with a few showers, an occasional rainy cold front, and still some offshore flow or Santa Ana wind. Significant rains for S California are more likely about Dec 3-8.
In the Near Term – Nov. 2-16… In the southern California avocado growing areas, from Santa Barbara County to San Diego County, during Nov 4-5th and again from the 6-7th, rains occur. The first system may emerge as only showers, with main rains occurring early on the 5th. The next rains occur from the 6-8th, and may develop more tropical characteristics, i.e. heavy upslope rainfall. More rains are currently suggested for the 11-13th. Drier and warmer conditions return from the 14-17th.
Summary – Nov. 17 – Dec. 8… In the southern California avocado growing areas, from San Luis Obispo south, our CFSDaily guidance suggests a possibly well-defined cold front with rains around the 21-22nd, followed by a dry break (possible Santa Ana) for the Thanksgiving holiday. This pattern is well-defined in today’s CFSDaily, but consistency in a forecast of that specificity is unlikely. A more plausible forecast is that the last week of Nov, where it is more likely to be dry with mild or warm days, and frost risk on multiple nights in the valleys. Although more rains, possibly quite heavy with high snow levels, are suggested for N and central California in the first week of Dec, there is no indication how much rain may be able to reach into S California.
Seasonal Outlook / La Niña Update...December 9 – January 31, 2018… Latest solutions show some near or a little above normal rainfall in Dec in N and north-central California, but drier than normal in S California. Jan 2018 solutions are near or slightly drier than normal from both the NMME (ensemble) and CFSv2 forecast model solutions. For S California, there is some support for light showers then frosts occurring between Santa Ana events, with upper lows that develop over Arizona and SE California during several periods in mid to late Dec through most of Jan. Be ready for a lot of frosts on multiple days in a series.
...Alan Fox, Fox Weather LLC...