30-Day Weather Outlook for October 22, 2017, to November 22, 2017
Summary- Fronts will approach Washington-Oregon, but minimal rain for N, and central California. Rain is unlikely through Oct 31 for S California. There is support for troughing into SOCAL with development of cutoff upper lows. The first low appears to develop around Nov 2-3, then produces a chance for showers in the S SierraNV, and in S California around Nov 3-4. Another system, possibly with a little more rain, occurs around Nov 7-8.
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 115-100W, as well as in the east-central US. SSTA’s west of California are expected to continue warmer than normal. This will tend to make it difficult to realize rainfall in S California until mid Nov.
La Niña is present in the NMME forecasts out through this winter. La Niña favors a lack of a southern storm track, and an inactive season, rain-wise in central and S California, and above normal precipitation in The Pacific Northwest. Aggressive frosts and freezes often accompany a La Niña in central and S California.
Troughing in the east-central US teleconnects with recurrent or persistent high pressure in mostly central and S California. For N and northcentral California there is support for W flow and a few frontal passages during Nov 3-4 and 8. After a long dry spell on 10-18th, a period of significant rains occurs and is shown during Nov 14-18 and 20-26th.
For S California, the pattern through mid-November will support alternation between cutoff lows with a few showers and dry warm Santa Ana or offshore flow conditions. The period from Nov 20-28th appears to have the first series of significant rains for S California as well as in the north.
In the Near Term – Oct. 28 – Nov. 10… In the southern California avocado growing areas, from Santa Barbara County to San Diego County, it will be dry with some NE winds developing about Oct 31st through about Nov 2. During Nov 3-4 there is a chance for a shower. Another chance for showers occurs around Nov 8-9.
Summary – Nov. 11-25… In the southern California avocado growing areas, from San Luis Obispo south, a dry offshore flow appears most likely for Nov 11-13th. During Nov 15th, some periods of showers are possible as a cold front finally moves through. There appears to be another chance for showers about Nov 22-23rd as heavier rains occur in N California.
Seasonal Outlook / La Niña Update...November 26 – January 25, 2017… 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 the NMME (ensemble) and CFSv2 forecast model solutions. For S California, there is some support for a few light showers but with frosts occurring with upper lows that develop over Arizona and SE California during several periods in Dec through mid-Jan.
Consistent with La Niña conditions, watch for an active frost season in late Dec, and in Jan 2018 through central and S California.
...Alan Fox, Fox Weather LLC...