Fast moving weather system arrives tomorrow to Thursday with gusty winds

Today's cooler temperatures will continue into next week. A fast-moving weather system may bring light mountain showers and gusty valley winds on Wednesday and Thursday. Another weather system could move into the region early next week.

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Temperatures will vary across interior Northern California, with some areas 2 to 5 degrees cooler and the northern Sacramento Valley 3 to 6 degrees warmer. The current synoptic pattern is a broad zonal flow with offshore troughs, and highs are expected to drop as a Pacific Northwest trough moves into the region today. The falling highs will help lower today's afternoon temperatures, and with the enhanced onshore flow, humidity levels will also rise to the highs of 15 to lows of 30 during the day, helping to ease fire weather concerns. Afternoon highs will range from 27 to 35 degrees, with warmer temperatures in the northern Sacramento Valley.

On Wednesday, a closed low pressure system will form north of our area and work its way southeast, following a synoptic pattern near an interior slider. The low pressure system will bring precipitation and thunderstorm chances, primarily for far north and northeast Shasta and Lassen counties Wednesday morning into the evening. The National Blend of Models (NBM) indicates about a 5-15% chance of precipitation for the above areas, exceeding 0.10 inches. Therefore, any precipitation will be light with little to no accumulation. Thunderstorm chances increased slightly this morning for far north and northeast Shasta County, with about a 10-15% chance for Wednesday morning and afternoon. As the low pressure system continues to work its way forward and into the Great Basin area, enhanced westerly flows and northerly winds will develop in the Delta. The NBM is forecasting about a 50-90% chance of wind gusts up to 30 mph for Wednesday, with the higher probabilities occurring along the I-5 corridor and in western areas of the Sacramento Valley/Delta.

On Thursday, the low pressure system will move further out of the area, and interior Northern California will be on the back side, so northerly winds will develop across most of the area. The strongest winds are expected in the wind-prone areas of the Valley, namely along the I-5 corridor and the western Sacramento Valley. The strongest winds are expected in the morning hours, with the NBM forecasting a 20–60% chance of wind gusts of at least 30 mph, with a greater 40–90% chance of northerly wind gusts of 25 mph. Temperatures will continue to be in the 80s to 90s F throughout the Valley through Thursday. Things will warm up a bit again Friday, as weak ridges to the north and weak troughs to the south will bring highs a bit higher, with temperatures in the 80s to 90s F, the highest temperatures in the northern Sacramento Valley.

Extended discussion (Saturday to Tuesday)

Highs trend downward over the weekend into early next week as several shortwave troughs transition into a longwave trough that settles along the West Coast. Models differ on the timing of the waves, creating some uncertainty in forecasts regarding POPs and degree of cooling. NBM forecasts increasing precipitation potential north of I-80 Sunday night, spreading across the entire CWA on Monday. Decreasing POPs on Tuesday before another shortwave increases precipitation potential midweek. The shortwave troughs will be accompanied by gusty winds at times. Highs will drop from the highs of 80 to below 95 degrees Fahrenheit in the Central Valley on Saturday and to above 77 degrees Fahrenheit early next week.