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Unsettled weather this week as multiple systems impact interior Northern California. Rain and mountain snow are expected today. The second and more impactful system occurs Wednesday into Friday.
Areas of rain are moving through the region. Snow levels are high to start but are expected to lower to 4000 to 5000 feet over the far Northern Sierra/Lassen Park area over the next several hours while further south snow levels should lower between 5 and 8 am this morning down to around 5000 feet. Have extended the Winter Weather Advisory further northward due to moist upslope flow overnight into the early morning hours expected to produce some decent amount of snow above 5000 feet.
Models are hinting at some isolated thunderstorm activity later this morning and afternoon over the far north end of the valley and portions of the northeast foothills and adjacent mountains where we could see some convergent zones set up.
Most of the valley rain will move through by mid morning with maybe a few isolated showers persisting into the afternoon. The one exception may be the far northern part of the valley where some isolated shower and thunderstorm activity could persist into early evening.
All activity should die down by mid to late evening per current models.
The next cold front is back near 150W in the Gulf of Alaska. A lot of moisture out in front of the cold front will move over the region late today and tonight so some upslope areas may have a chance to see some precipitation ahead of the front especially over the far northern Sierra and southern Cascades.
By Wednesday morning the next front should be starting to move over the northern areas. The front will be slow to move southward so it may not be until Wednesday evening before the Sacramento area starts to see some precipitation.
Winds will increase early Wednesday over the north end of the valley and increase during the day further south. Gusty winds should persist into early Thursday before decreasing. We may need a wind advisory for portions of the Sacramento valley during this time period with the gust potential 35 to 50 mph over a good portion of the valley. The strongest winds are expected over the north end of the Sacramento valley.
The trough will deepen over the region on Thursday and portions of the Sacramento valley and adjacent mountains north of the Sacramento region may start to see some isolated thunderstorm activity in the morning.
During the afternoon is when the greatest threat over the entire region for thunderstorms will occur. Currently profiles look like they would produce heavy rain and small hail.
By Friday morning the central part of the trough moves over Nevada with the back end of the trough still over the region. Showers are expected to continue but should gradually taper during the day ending in the evening. Best chances look to be over the eastern side of the valley and adjacent foothills and mountains.
This will be a very good late season precipitation event for the region with at least 1 to 2 feet of snow over the higher elevations, a half inch to an inch and a half of rain in the valley and 1 to 3 plus inches for the foothills and mountains. Thunderstorms may end up producing locally higher amounts.
Extended Discussion (Saturday through Tuesday)
Good agreement with a ridge of high pressure building over the weekend with warmer temperatures and dry conditions. These conditions will persist through Monday. Next Tuesday a trough moving into the Pacific Northwest will start to nudge the ridge to the east. The far northern part of the state including the north end of the valley may have a chance to see a little bit of precipitation from the tail end of that trough.