Heavy rain and snow today, flooding continues

January 10, 2017 – Next Pacific storm picks up across the area into tonight with heavy precipitation and strong winds. Very heavy snow will continue in the mountains with severe travel impacts. The increase in precipitation will lead to renewed flood concerns through mid-week. Drier and more settled weather returns by late- week.

High Wind Warning from 10 AM this morning to midnight tonight.

Discussion

Wind and precipitation have increased across interior NorCal overnight, especially along the I-80 corridor, as the next “big” weather event for the region commences. So far, there has been some shadowing of rain across the northern two thirds of the Sacramento Valley, but areas along I-80 have already seen several hours of steady moderate to heavy precipitation. Blizzard conditions have developed overnight in the northern Sierra above 5000 feet with zero visibility in heavy snow and blowing snow resulting in the closure of I-80 across Donner Pass.

Precipitation will continue to fill in across the entire region today. Generally, 1-2 inches of rain can be expected in the valley with 3-6 inches in the foothills. After a brief respite on Monday, widespread small river and stream flooding will become more likely again by this evening.

However, strong southeast flow will lead to areas of enhanced precipitation along the west side of the Sacramento Valley where higher QPF is likely for areas such as Vacaville and Fairfield. Several hours of heavy rain with thunderstorms will also be possible this evening as the front moves inland exacerbating the flood threat for streams and urban areas.

In addition to the precipitation, gusty southerly winds will increase across the region through the day. NAM/GFS continue to show strong N-S surface pressure gradient of 12-14 mb from KSAC- KMFR developing this afternoon in response to cyclogenesis off the NW CA coast. Forecast 925 mb winds are generally in the 45-55 kts range – this would equate to surface winds of 25 to 40 mph with gusts 55 to 65 mph. But models show a corridor of higher winds, 55-60 kts, developing early this evening from KSAC-KSCK, so the high wind warning has been extended south.

Given saturated soils, there is enhanced potential for downed trees and more widespread power outages than what we’ve seen with recent events.

Another wave follows for Wednesday night and Thursday, but appears the impacts for NorCal will be much less. Drier and milder weather expected to return late-week.

Extended discussion (Saturday through Tuesday)

Drier weather is expected through the extended period as high pressure builds into California from the eastern Pacific. This will finally give area rivers and streams a chance to recede. Breezy northerly winds may be possible late this week, and it wouldn’t be surprising to see fog developing in the Valleys. This drier regime will also allow for colder overnight temperatures.

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