February 22, 2017 – Significant flooding concerns continue as runoff from the recent rain continues to work its way downstream adding stress to waterways. Scattered showers with a few thunderstorms today, then another storm potentially late in the weekend.
Short-wave moving thru early this morning popped a few showers and one thunderstorm in the valley north of Chico while continuing numerous showers over the west slopes of the northern Sierra Nevada. Expect remaining showers will taper off this morning as the wave progresses to the east. Otherwise, partly to mostly cloudy skies cover the region and temperatures are running about 5-15 degrees cooler compared to 24 hours ago.
Next upstream vort is pivoting thru 35N/130W and will approach NorCal by this afternoon. The result is expected to be another upswing in shower and thunderstorm activity that will last into this evening. Small hail is expected to be the primary threat from any stronger storms that develop.
A few showers may linger over the mountains on Thursday, but for the most part expect dry weather to return for late-week. The airmass will be cold, and with less cloud cover nighttime temperatures will be quite chilly with some patches of frost possible in the Central Valley.
Next system approaches late Friday and slowly works its way inland on Saturday with QPF forecast to gradually increase Saturday night.
Extended discussion (Sunday through Wednesday)
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Models in fair agreement in dropping an upper low southeastward across NorCal on Sunday. At this time main frontal passage timing looks like Sunday night or early Monday and that this will be a fairly moderate system compared with recent storms.
Snow levels also look relatively low so hopefully this system will not add significantly to current flood issues. Showers continue on Monday as the trough axis shifts into the Great Basin.
Current projections put some light snow possible down into the foothills on Monday. Northerly flow develops on Tuesday so should see drying most areas but Sierra still under cyclonic flow so could see some minor continued shower activity there. Upper level ridging finally brings drying CWA wide by next Wednesday with this dry period possibly lasting for several days. Forecast highs for Wednesday come in right around normal for this time of year.