May 29, 2018 – Well above-average temperatures continue today. Afternoon and evening thunderstorms are possible over higher terrain through Thursday. A significant cool down is expected during the middle of the week followed by a warming trend for the weekend.
Discussion
Clear skies across interior NorCal early this morning. Current temperatures are milder compared to 24 hours ago and generally range from the 40s in the mountain valleys to the mid 60s to mid70s across the Central Valley.
It will be another warm/hot day across the region today as the upper ridge shifts east. North/Northeast surface gradients will reverse to onshore late in the day, but probably not early enough to make much of a difference in high temps except in the Delta. An isolated late-day storm or two may pop around Mt Lassen and in the Sierra south of Tahoe.
Next trough moves in Wednesday and Thursday and will result in dramatic cooling across the region from the combo of increased onshore flow and synoptic cooling. Temperatures Thursday are expected to be around 20 degrees cooler than those of Memorial Day.
Instability will continue to lead to a chance of showers and thunderstorms across the mountains of Shasta County and in the Sierra south of Tahoe on Wednesday, then mainly over the Shasta County mountains on Thursday.
The next warmup is scheduled to begin Friday as ridging returns to the area.
EXTENDED DISCUSSION (Saturday through Tuesday)
Upper level ridge builds this coming weekend into early next week with high temperatures warming to near to slightly above normal across northern California. The ridge will keep the active jet stream well to the north of the region and keep conditions mostly clear and dry.