June 14, 2018 – Dry weather through Friday with a gradual cooling trend. A few mountain showers and thunderstorms possible this weekend with additional cooling. A slight warm up early next week with continued mountain shower threat.
A weak upper trough over the Pacific Northwest and NorCal will bring a little cooling today although daytime highs will remain several degrees above normal. At this time it appears only a moderate delta breeze has developed and marine layer remains at only around 1000 feet deep so the delta and Sacramento regions should remain relatively warm today as well.
The upper trough over the Pacific Northwest digs a bit southward over NorCal on Friday bringing a little more airmass cooling and still slightly cooler temperatures but any precipitation should remain north of the forecast area. A continued moderate delta breeze should help to drop Sacramento temperatures down to close to season normals.
A small low dropping into the west coast trough and into NorCal on Saturday will bring a slight threat of showers or thunderstorms to the northern mountains of Shasta county and the southern Cascades. This inside slider type system will likely not bring any precipitation west of the Sierra foothills with most of the CWA remaining dry.
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Daytime temperatures should continued to fall however with most locations seeing high temperatures near or below normals. The upper low moves into the central Great Basin on Sunday generating a continued threat of mountain showers or thunderstorms over the Sierra Cascade range on Sunday while keeping daytime highs on the cool side for mid June.
Extended discussion (Monday through Thursday)
Longer range models continue to trend toward a more unsettled weather pattern next week. It is becoming more likely that a closed upper low dropping south from the PacNW will remain quasi-stationary over the region into the middle of next week. Where precisely this sets up is uncertain at this stage, but there appears to be enough dynamics for a chance of showers and thunderstorms over higher terrain. Temperatures forecast to be close to average.