Dry conditions through Wednesday AM before a weather system moves in midweek bringing mountain snow, widespread rain, breezy winds, and thunderstorm chances.
Discussion
Dry conditions continue today with quiet weather conditions. Afternoon highs in the Valley will be mid 60s with 50s and 40s across the foothills and mountains respectively. The pattern shifts Wednesday as a weather system brings mountain snow, widespread rain, breezy winds, and thunderstorm chances.
Precipitation begins over the mountains and Northern Sacramento Valley Wednesday morning before pushing into the Valley later that afternoon and evening.
A Winter Storm Warning has been issued for the Sierra from Wednesday 11 AM until Thursday 11 AM for periods of heavy snow and gusty winds above 5500 feet. 6 to 12 inches up to 2 feet at the highest peaks is expected with moderate travel impacts from delays, snow-covered roads, and chain controls and winds gusting as high as 45 MPH.
Probabilities show a 30-70% chance of at least 8 inches above 5500 feet. Snow levels start at 5000 to 6000 feet, then lower to 3500 to 4500 feet on Thursday.
This will be a low- end warning event but still could see impacts on the commutes that evening and morning of the next day. If you must travel, keep an extra flashlight, food, and water in your vehicle in case of an emergency!
The National Blend of Models (NBM) indicates a 40-90% chance of rain totals greater than 0.50″ from Sacramento northward in the Valley for Wednesday and Thursday with highest chances as you move north in the Valley.
Wednesday will see breezy south winds with strongest winds in the northeast foothills area.
Additionally, Wednesday and Thursday brings thunderstorm chances (10-20%) to the Valley and foothills with best chances of development north of I-80 to Redding in the afternoon and evening hours. Forecasted CAPE values aren’t impressive but there is some additional support from the upper- level divergence as the jet streak and low pressure system moves southward.
Past Thursday morning, conditions lull with lingering mountain snow showers and minor snow accumulations.
The next wave of weather will begin late Friday morning and continue into the weekend. This will be a similar weather impact storm as the Wednesday-Thursday system bringing mountain snow, widespread rain, breezy winds, and thunderstorm chances. NBM probabilities indict a 40-60% chance of snow totals exceeding 6 inches above 5000 feet Friday into early Saturday morning. Snow levels with this system will be 4000 to 5500 feet.
Additionally, the NBM shows a 50-70% chance of rain totals exceeding 0.25″ for that same time frame in the Valley.
Extended Discussion (Saturday through Tuesday)
Ensemble guidance and cluster analysis are generally in agreement for the upper level low to drop down along the western US Coastline before moving into Southern California later this weekend or early next week.
Saturday will see continued widespread light rain, moderate to heavy mountain snow, and breezy winds. Saturday will be the lighter portion of the weather system with only 3-6 inches forecasted broadly over the Sierra, heaviest south of Hwy. 50.
Rain showers will be light with Valley amounts under a quarter of an inch and an half inch in the foothills. There is a chance for isolated thunderstorms with the NBM showing a 10-25% chance, highest south of I-80. With any thunderstorm development impacts include brief heavy rain showers, lightning, gusty winds, small hail, and possible funnel clouds.
Drier conditions and northerly flow are favored by Sunday or Monday behind the passage of this system although there is a chance for some lingering light snow showers over the Sierra on Sunday.