April 23, 2021 – Dry weather will change over to widespread rain and significant mountain snow by Sunday persisting into Monday with mountain travel impacts possible.
Discussion
High pressure will continue over the area today with moderate flow through the Delta and upvalley flow. Some low clouds already starting to form in the valley will become more significant by morning.
Slight cooling most areas with temperatures around Sacramento similar to yesterdays highs. High clouds will be moving over the region during the day to help continue the cooling trend for most areas.
A weak wave will move through the region tonight which may bring some mainly light showers over the northern areas from around Plumas County northward.
Continued overrunning of some light precipitation may occur on Saturday and Saturday night with increased shower chances expanding southward throughout the night. There are some hints that some showers may pop up a far south as Sacramento early on Saturday as the first wave moves through.
The main part of the system is currently looking like it will arrive early Sunday morning with some steady valley rain looking probable during the morning and into the afternoon before changing over to showers. The western slopes should see steady rain and snow throughout most of the day and evening before changing over the showers from north to south Sunday night.
Conditions look to be breezy over the weekend with the strongest gusts Sunday morning for the valley with gusts to 35 mph possible over the north and around 25 mph in the south. Winds over the crest will become windy starting late tonight and persist into Sunday morning that should top 50 mph at times.
Post frontal in the valley Sunday afternoon there is starting to look like there may be enough instability for some thunderstorms to form over the Sacramento valley. Strong vertical shear also exist so some funnel clouds may be possible as well. Any thunderstorms that do form should be capable of producing heavy rainfall.
This is a decent late season storm for this time of the year and valley rain currently looks to range between a 0.15 in the San Joaquin valley to close to an inch of rain for the eastside of the valley around Butte county.
Foothill and mountain liquid equivalent totals look to range between 0.75 and 2.5 inches. Snow levels during the day on Sunday will generally range between 4500 and 5500 feet but lower 4000 feet Sunday night.
Locally some snow may fall around 3500 feet. This will allow for some significant snowfall totals to occur above 5000 feet generally between 1 to 2 feet. Significant cooldown is also anticipated over the weekend with temperatures becoming the coldest on Sunday.
Temperatures Sunday are expected to be 15 to 20 degrees colder than seasonal normals in the valley and 20 to 25 degrees colder for the foothills and mountains.
Showers are expected to linger on Monday. Temperatures will warm over Sundays highs but still remain seasonably cold 10 to 15 degrees below seasonal normals for the valley and 15 to 20 degrees for the foothills and mountains.
Extended discussion (Tuesday through Friday)
By Tuesday a ridge will be building over the region and temperatures will be returning to normal along with dry weather. The ridge will continue to build Wednesday and Thursday with temperatures warming to near 80 degrees in the valley Wednesday and mid 80s for Thursday.