Active April weather pattern to continue after warm weekend interlude

Our track record of unusually active weather across the state of California this spring is set to continue through at least the end of the month. Warm and dry conditions have developed in the wake of the departing upper low, and these seasonably warm (and perhaps even somewhat above average) temperatures will persist into Sunday and perhaps Monday. By late in the day on Monday, however, another major pattern shift will take place. A rather strong and dynamic storm will once again move in from the Gulf of Alaska, bringing significant precipitation, gusty winds, and possible thunderstorms to much of the state.


GFS depiction of Monday/Tuesday system (NCEP)

A strong cold front (by late-April standards, anyway) will move into the region late Monday into Tuesday, bringing lowland rain, mountain snow, and regional strong winds. In the wake of the front, snow levels drop dramatically once again to the 3000-4000 foot level and the airmass becomes unstable, with very steep lapse rates and a cyclonically curved jet overhead. Widespread convective showers and isolated to scattered thunderstorms will once again affect most of the state from later Tuesday through at least late Wednesday and possibly into Thursday. More small hail and locally very heavy rainfall are likely during this period. I don’t really see any mechanism for widespread strong or severe weather, but given the time of year and the steep sun angle it’s worth keeping an eye on as the event approaches.

The models are substantially in disagreement for the Friday-Sunday period next week. An additional disturbance is expected to drop down the west side of the mean trough, but the GFS brings an inside slider-type system over Nevada while the ECMWF has a much more westerly track for the low center. This later scenario would bring continued active weather to California, with nearly daily convective chances from Tuesday through at least Saturday. We’ll just have to see which scenario winds out, though it’s worth noting that the ECMWF did better with this most recent cut-off low…