Colder and wetter system moving through fairly quickly

April 11, 2018 – A colder and wetter weather system moves through today and Thursday. Dry weather returns later in the week, but more rain is expected Sunday.

Discussion

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Yesterday’s weak system has shifted east, but high clouds are already increasing across interior NorCal ahead of the next approaching frontal system. Current temperatures are much cooler across much of the area compared to 24 hours ago and generally range from the mid 30s to mid 40s in the mountains to the mid 40s to mid 50s in the valley.

The next system continues to dig southeastward from the Gulf of Alaska and will push another cold front through the region tonight and early Thursday. Some light warm-advection precipitation will be possible ahead of the front across the northern mountains by this afternoon, but the bulk of precipitation will occur tonight as the cold front moves through.

Snow levels, which have already fallen behind Tuesday’s front, will come “crashing down” tonight before lowering to around 2-3K feet on Thursday when the precipitation has ended. The colder air will result in higher snow to liquid ratios of at least 12:1, if not higher over the higher elevations, quite high for this time of year indicative of the cold airmass associated with this system.

4-8 inches of snow will be possible across the mountains above 4K feet with up to a foot or more over the peaks through Thursday. Impacts to travel over the higher passes will likely develop by this evening and a winter weather advisory has been issued.

Temperatures will head down further today, but Thursday will be a cold spring day in NorCal with maxes in the upper 50s to low 60s in the Valley, some 9 to 15 degrees or so below average, and as much as 20 deg below normal in some mountain areas. Much warmer and drier wx is forecast for Friday into Saturday as the Pacific ridge rebuilds over the region. Max temps will warm back up to around average for mid-April, in the low 70s in the Valley, and 50s-60s in the mountains.

Extended discussion (Sunday through Wednesday)

Pacific front moves across Interior NorCal Sunday into Sunday night followed by associated upper trough Monday. Light to moderate precipitation expected with this system with snow levels lowering to 3000 to 4000 feet Monday. Drier weather returns Tuesday into Wednesday under short wave upper ridging.