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Weather Outlook

March 21, 2017

Summary- We have the wetter pattern with a broad belt of westerlies across most of Calif. The troughing pattern is bi-modal. Most troughs develop near the coast of northcentral and N Calif, but a few develop into S Calif, coming down the coast and deepening over NW Mexico and into Arizona. Forcing for troughs occurring from the N and north-central coast and WSW-ward is from the sea surface temperature anomaly (SSTA) pattern W of north-central Calif. Forcing for troughs over SE Calif, NW Mexico and Arizona and S Great Basin is related to the currently weak El Niño. The combined effect is for wet in N and north-central California, and a drier regime, punctuated by an occasional rain in southcentral and S Calif. We still could see a late season southern storm track condition, usually appearing as an upper low over SOCAL, NW Mexico, or S Arizona in April.

March 14, 2017

Summary- Strong, stationary, warm upper high pressure continued across Calif on March 13, but will weaken on the 14th. We are seeing a shift to a wetter pattern with resumption of a broad belt of westerlies across most of Calif in by March 18-19. The troughing pattern is bi-modal. Most troughs develop near the coast of northcentral and N Calif, but a few develop in the Great Basin and Rockies area. Forcing for troughs occurring from the N and Calif coast and WSW-ward is from the sea surface temperature anomaly (SSTA) pattern W of Calif. Forcing for troughs over the Great Basin is related to the currently weak El Niño. The combined effect has been wet in N and northcentral California, and drier than normal in southcentral and S Calif, however this is changing to mostly wet in N and central Calif. We still expect occasional southern storm track conditions, with showers and low snow levels in the Sierras in late Mar and Apr.

March 7, 2017

Summary- Westerlies occur across most of Calif. The troughing pattern is bi-modal, with some troughs developing just off the coast of central and N Calif, and some focusing into the Great Basin. Forcing for troughs occurring from the N and Calif coast and WSW-ward is from the sea surface temperature anomaly (SSTA) pattern W of Calif. Forcing for troughs over the Great Basin is related to the currently weak El Niño. The combined effect will be wet in N and northcentral California, and drier than normal in southcentral and S Calif. Individual troughs contain moisture but their south portions weaken upon reaching the coast. This pattern of development, related to El Niño favors development of troughs in S and SE Calif, NW Mexico, and Arizona with occasional offshore flow at the southcentral Calif coast. We still expect occasional southern storm track conditions, with showers and low snow levels in the Sierras in late March and April.