Large Scale Summary
- For near term conditions, the longwave pattern supports a tendency for warm upper high pressure through 29 Mar but with some cooling already starting to develop on 30th. For April 4 - 6, upper high pressure builds into most of California but with a weak trough in SOCAL and at the southern California coast. High pressure rebuilds into central to southern California from the southwest, giving warmer days and earlier burn-off of coastal low clouds and fog through the 9th. Rain reaches into the Bay Area and NORCAL from the west on 10-11th. Dry and warmer with some local NE winds on 12-13th. There is a chance for rains 14-16th in California. Troughs with rains come through California again 14-16 April.
- During April 10-15, there is less tendency for dry conditions in California and a return to more of the usual cool upper troughs and cold fronts with some light showers coming through on about April 14-16. The important factor to consider is that troughing in the subtropics will tend to affect prevailing patterns in the jet stream circulations 42N to 33N. Look for greatest variation in speed of the westerlies at 30N and 40N. Most of this variation is due to the maximum interruption to the westerlies at 30 to 40N.
- Precipitation dates with the current pattern: Dates in Apr: Central Sierras are: 1-4 and 14-16 Apr showers and cooler than average.
- Those functions that introduce increased variation in the westerlies occur at 30N and 40N for the most part as mentioned above. The increased variation is tending to inhibit consistent westerlies from moving along the usual development path. This in turn decreases the precipitation occurring in April, and at least the first part of May as well.
- In summary, the westerlies try to start up toward the end of the mid spring season. However, the favored location of troughs continues to be mid Pacific around
135-150W too far west to support troughing into California and effect more consistent rains into the near coastal areas of California.
Figures and Text: Alan Fox, Fox Weather, LLC
Copyright © 2026 Fox Weather, LLC.