April 22, 2021 – Dry and warm weather through the end of the week. Widespread rain and significant snow return by Sunday into early next week with mountain travel impacts possible.
Discussion
High pressure will continue over the area through Friday. Moderate flow through the Delta and upvalley flow will continue through Friday. A slight cooling trend each day with a little more cooling expected over the northern areas on Friday due to more high clouds moving over that part of the region.
A weak wave will move through the region Friday night 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 shower chances expanding southward throughout the night.
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 Friday night and persist through most of Sunday but should top 50 mph at times.
This is a decent late season storm for this time of the year and valley rain currently looks to range between a quarter of an inch to close to an inch of rain. Foothill and mountain liquid equivalent totals look to range between 1 and 2.5 inches. Snow levels during the day on Sunday will generally range between 4500 and 5500 feet but lower to 3500 to 4000 feet Sunday night. Locally some snow may fall around 3000 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.
Extended discussion (Monday through Thursday)
Showers are expected to linger on Monday. Both the European and GFS models indicate a more progressive pattern with the trough moving over Nevada while cluster analysis has the trough centered further west over California.
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.
By Tuesday a ridge will be building over the region and temperatures will be returning closer to normal. The ridge will flatten on Wednesday as another storm moves into British Columbia and the Pacific Northwest but temperatures are expected to warm to near seasonal normals.