One more morning of valley fog and stratus expected then a strong storm will bring a pattern change. Periods of significant wet weather with moderate to high snow levels forecast this week into next weekend. High Wind Warning from 10 PM this evening to 10 AM PST Tuesday for West Slope Northern Sierra Nevada-Western Plumas County/Lassen Park. Winter Storm Warning from 10 AM Tuesday to 10 AM PST Wednesday for West Slope Northern Sierra Nevada-Western Plumas County/Lassen Park.
Discussion
We are going to see a major weather pattern change starting later Monday as deep troughing builds over the West. This will bring multiple rounds of rain and snow through the week and through the weekend. Dense fog has developed over the Valley and we should see that slowly lift into a stratus layer throughout the morning into early afternoon. This will once again hold temperatures down in lower elevations with mild temperatures in the foothills.
Light showers begin to push in during the afternoon into the evening mainly over the northern mountains and north Valley as warm air advection start to develop over the area.
Low level winds will amplify later Monday evening into Monday night as the trough digs strengthening the warm front and bring widespread moderate to heavy rain over NorCal. This system will tap into deep Pacific moisture with the Integrated Water Vapor (IVT) pushing upwards of 1000 kg/ms and PWATs 1.0-2.0″.
The cold front will then work south through NorCal Monday morning into the afternoon likely stalling out for a time over the northern San Joaquin Valley. Moderate to heavy rain can also be expected along and ahead of the front. Activity will become more showery during for a time in the afternoon except over the mountains where upslope flow will keep widespread rain/snow going.
Showers will become more widespread again during the evening and early overnight as a short wave trough axis pushes through. Mainly dry conditions will set in Wednesday morning into the afternoon as northwest flow develops.
Localized flooding will be possible with this rain as streams and creeks rise and roadway flooding of poorly drained areas will become an issue as well.
Some weak instability builds in right behind the cold front and that may bring a thunderstorm or two during late morning into the early overnight mainly from around Stockton north. CAPE looks limited and the thunderstorm threat should remain isolated.
The amplifying low level jet is going to bring strong winds to the area Monday night into Tuesday. 850 mb winds increase to 50-70 knots ahead of the cold front with 700 mb winds 60-85 knots. Winds gusts from Sacramento north will be 40-55 mph with wind gusts possibly up to 65 mph east of I-5 from north of Chico to Redding. Gusts 35-50 mph are expected over the northern San Joaquin. Gusts 50-85 mph are expected over the Mountains.
With a good stream of deep Pacific moisture we will see high snow levels with the onset of the precip with them 7500-8500 feet. Cold air will begin to build in Tuesday afternoon and we will see snow levels start to fall falling to 4500-5500 feet Wednesday. 6-24″ of snow is expected above 5500 feet with up to 35 inches over the higher peaks. Some light accumulation will be possible down to 4500 feet Wednesday morning.
QPF totals through Wednesday afternoon are looking to be 1.50-3″ in the Valley, 2.50-4.50″ in the foothills, and 4-6″ over the mountains. We are expecting a period of moderate to heavy rain but convective rain is looking limited, this should keep rain rates below burn scar thresholds.
Dry weather will not last long with rain and snow returning Wednesday night into Thursday as a short wave pushes to our north. This will bring another round of widespread precipitation.
Snow levels Wednesday night will be 3500-4500 feet but they will be rising Thursday reaching 5500-6500 feet. Moisture will remain elevated over the region and moderate rain and heavy snow can be expected at times.
Extended Discussion (Friday through Monday)
The storm train is going to keep on rolling through the extended period. We will see another round of widespread precip Thursday night into Friday as another short wave trough pushes to our north.
Moderate rain and heavy snow can be expected at times again with this wave. Another short wave will dig deeper over the Pacific Friday night into Saturday. This one will be able to pull in higher moisture levels and we will likely see a period of moderate to locally heavy rain along with heavy snow.
This trough is looking to favor southern areas with the heaviest precip expected from about I-80 south. Some of the timing and location may change with these short wave toughs but unsettle wet weather will continue.
It does look like we will see a break from rain and snow late Saturday night and throughout the day Sunday as a stronger short wave ridge builds in. Once again the break doesn’t look to last long as additional short wave trough move in early next week bringing the return of rain and snow.