Discussion (Today through Sunday)
Latest water vapor and model analysis showed a negatively tilted shortwave trough moving toward the Pacific northwest overnight with some moisture streaming through northern California. As a result, a band of showers developed on radar and moved through the area overnight with some brief heavy downpours.
Latest high resolution short term model guidance shows some instability and showery type precipitation continuing through the morning hours as the main line ahead of the upper trough moves into the Sierra. Lingering chances for mountain showers will continue through the afternoon north of I-80.
Another small disturbance off the coast will bring some more chances for precipitation Friday, mainly for the mountain. Some instability will be present, but confidence is not high enough to put thunder in the forecast. Between the two systems today through Friday, snow accumulations for the mountains will range between 1 and 2 inches with Lassen Park receiving up to 5 inches. Impacts from precipitation are expected to be minimal.
A shortwave ridge will develop Saturday providing mostly dry conditions across the forecast area, but a deepening trough will bring a return of some light precipitation to interior northern California Sunday. Temperatures through the period will be right around normal for March.
Extended discussion (Monday through Thursday)
Some model uncertainty to begin the extended period on Monday. ECMWF rebuilds ridging over the area in wake of Sunday’s shortwave while GFS brings another wave through, continuing showers across the area. For now have hedged toward GFS for consistency’s sake with going forecast. Amounts should be light if this solution does materialize. Snow levels generally look above pass levels so minimal impacts expected at this point.
Past Monday, looks like a wet and active rest of the week. Several systems progged to move through the area, bringing widespread precipitation and colder air. Right now, it looks like a system Tuesday, followed closely by another Wednesday, and possibly a third by the end of the work week. Specific details remain unclear but looks like a good chance for several periods of widespread precipitation across the area. Snow levels will start around 6000 feet Tuesday, dropping through the week down to around 4000 feet. Stay tuned as details become better resolved as there likely will be impacts to mountain travel!