There is a lot of talk about the winter storm about to hit our area, so before I get into today’s discussion I want to give a brief description of the weather patterns that bring snow to low elevations in our Northern California area. There are two types of weather patterns that do this:
The most common pattern is when cold air is trapped in the canyons and valleys and an incoming storm moves over the top of the trapped cold air. This is what happened last week in the Redding area and is also the weather pattern that results in heavy snows to low elevations in the north state (2 feet in Redding in Dec 1963).
The other weather pattern is much rarer and is the one we will be in today. This is where the jetstream originates over northern Canada or the Arctic drops southwestward off the Canadian coast and then hooks around a low pressure area off the California coast and over northern California. The very cold polar airmass is not over the warmer ocean long enough to modify or warm before it enters northern California. It also is not over the water long enough to pick up a lot of moisture. These storms result in snow to very low levels … the Bay Area in 1976. However, while they can bring heavy snows to the higher mountains they usually only bring trace amounts or a couple inches to the valley and sea level locations.
******
Today’s Forecast (Thursday): The cold low pressure area continues to drop slowly along the coast and will be off the Oregon and Northern California coast tonight. The map below for this afternoon shows a classic example of the second type of pattern from the discussion, above, on low snow level weather patterns. The jetstream is bringing cold air from the Yukon around the low and then over northern California. However, these systems have limited moisture with them and on today’s map you can see the jetstream is in a straight west-to-east line across our area. This lack of southerly flow in mid and lower levels of the atmosphere restricts the movement of moisture northward into the Sacramento Valley and creates a “rain shadow” effect in the north valley.
So here is what I expect to see with this system. Rain and snow will spread over the area today and tonight. Snow levels will start out at 1,000 to 1,500 feet but will lower tonight to 500 feet. Friday, skies will be partly cloudy with scattered showers over all areas except southern Lassen and Plumas counties southward, which will still be receiving moderate snow until Friday afternoon or evening. Friday, snow will be reported at very low elevations of 100 to 200 feet, but amounts will be very light (a few flakes or a trace).
Expected precipitation totals for the storm … Trinity, Siskiyou, Modoc, and northern Lassen counties: 12 to 16 inches of snow above 3,500 feet with lesser amounts at lower elevations. The coast range from Mendocino County southward will get 1 to 2 feet of snow above 2,000 to 2,500 feet, with lesser amounts from 500 to 2,000 feet. The Sacramento Valley will see less than .25 inches of precipitation … Redding will get an inch or less of snow, with 1 to 3 inches north of Redding in the Shasta Lake area. Friday, all areas of the valley could see light snow in the showers. Southern Lassen and Plumas counties will get 2 to 3 feet of snow on the west side of the crest with much lighter amounts on the east side areas (Nevada border).
Clouds will be decreasing Friday night and north winds will be increasing across the area. Areas sheltered from the north winds will see record or near-record cold temperatures Friday night. The storms will continue to move east of our area Saturday and most of northern California will be partly to mostly sunny. The exception will be a few lingering snow flurries Saturday morning over Plumas county. Sunny and warmer conditions are expected Sunday and Monday, with the northern Sacramento Valley above 60 degrees on Monday. A storm will reach the coast Tuesday with rain and snow expected across northern California Tuesday and Wednesday. Snow levels will be near 5,000 feet.
******
Weather Outlook for Redding, Shasta Lake City, Anderson, Cottonwood, and Red Bluff Today (Thursday): Cloudy with rain and snow. Snow level lowering to 500 feet. Max temps 42 to 44 this morning cooling to the 30s this afternoon. South to southwest winds 15 to 25 mph.
Tonight (Thursday): Cloudy with rain and snow showers. Snow level 500 feet. Min temps 31 to 35. Light wind. Friday: Partly cloudy with isolated snow showers. Max temps 41 to 45. Southwest to northwest wind 10 to 20 mph. Friday Night: Clear with a few clouds. Min temps 25 to 29 wind sheltered areas and 29 to 34 elsewhere. Wind northwest 8 to 14 mph.
Saturday: Sunny with a few clouds in the afternoon. Max temps 45 to 49. North wind 8 to 18 mph.
Saturday Night: Clear. Min temps 29 to 36. Light wind. Sunday: Sunny. Max temps 49 to 54. North wind 5 to 15 mph. Sunday Night: Clear. Min temps 34 to 39. Light north wind. Monday: Sunny. Max temps 58 to 63. Light north wind. Monday Night: Clear. Min temps 34 to 40. Light wind. Tuesday: Increasing clouds with rain. Max temps 51 to 56. South wind 10 to 20 mph. Tuesday Night: Cloudy with rain. Min temps 43 to 48. South wind 10 to 20 mph. Wednesday: Cloudy with rain turning to showers. Max temp 50 to 55. Light wind. Wednesday Night: Partly cloudy with showers ending. Min temps 40 to 45. Light wind.
-The Old Forecaster
Click here for latest water vapor satellite animation
Click on images below to enlarge
Chris Fontana — a.k.a. “the Old Forecaster” — started his career as a meteorologist with the National Weather Service (NWS) in Sacramento. After four years as a weather officer in the USAF he transferred to the NWS office in Redding. He was the meteorologist in charge of the Redding office from 1976 until it closed in 1996. From 1996 until his retirement in 2005, he was the meteorologist in charge of the USFS Predictive Service Unit. Chris and his wife Jane have been married over 40 years and he works as a window covering installer in her business, Westwood Window Coverings.
A News Cafe, founded in Shasta County by Redding, CA journalist Doni Greenberg, is the place for people craving local Northern California news, commentary, food, arts and entertainment. Views and opinions expressed here are not necessarily those of anewscafe.com.
